The  lymph  drained from the bladder begins in a series of networks throughout the mucosal, muscular and serosal layers. These then form three sets of vessels: one set near the trigone draining the bottom of the bladder; one set draining the top of the bladder; and another set draining the outer undersurface of the bladder. The majority of these vessels drain into the  external iliac lymph nodes . [ 11 ]


The bladder receives both sensory and motor supply from  sympathetic  and the  parasympathetic nervous systems . [ 11 ]  The motor supply from both sympathetic fibers, most of which arise from the  superior  and  inferior hypogastric plexuses  and nerves, and from parasympathetic fibers, which come from the  pelvic splanchnic nerves . [ 12 ]


Sensation from the bladder, relating to distension or to irritation (such as by infection or a stone) is transmitted primarily through the parasympathetic nervous system. [ 11 ]  These travel via  sacral nerves  to  S2-4 . [ 13 ]  From here, sensation travels to the  brain  via the  dorsal columns  in the  spinal cord . [ 11 ]


When  viewed under a microscope , the bladder can be seen to have an inner lining (called  epithelium ), three layers of muscle fibres, and an outer  adventitia . [ 8 ]


The inner wall of the bladder is called  urothelium , a type of  transitional epithelium  formed by three to six layers of cells; the cells may become more cuboidal or flatter depending on whether the bladder is empty or full. [ 8 ]  Additionally, these are lined with a  mucous membrane  consisting of a surface  glycocalyx  that protects the cells beneath it from urine. [ 14 ]  The epithelium lies on a thin  basement membrane , and a  lamina propria . [ 8 ]  The mucosal lining also offers a urothelial barrier against the passing of infections. [ 15 ]


These layers are surrounded by three layers of muscle fibres arranged as an inner layer of fibres orientated longitudinally, a middle layer of circular fibres, and an outermost layer of longitudinal fibres; these form the detrusor muscle, which can be seen with the naked eye. [ 8 ]


The outside of the bladder is protected by a  serous membrane  called  adventitia . [ 8 ] [ 16 ]


In the developing  embryo , at the hind end lies a  cloaca . This, over the fourth to the seventh week, divides into a  urogenital sinus  and the beginnings of the  anal canal , with a wall forming between these two inpouchings called the  urorectal septum . [ 17 ]  The urogenital sinus divides into three parts, with the upper and largest part becoming the bladder; the middle part becoming the  urethra , and the lower part changes depending on the biological sex of the embryo. [ 17 ]


The human bladder derives from the  urogenital sinus , and it is initially continuous with the  allantois . The upper and lower parts of the bladder develop separately and join around the middle part of  development . [ 7 ]  At this time the ureters move from the  mesonephric ducts  to the trigone. [ 7 ]  In males, the base of the bladder lies between the rectum and the pubic symphysis. It is superior to the  prostate , and separated from the  rectum  by the  recto-vesical pouch . In females, the bladder sits inferior to the uterus and anterior to the vagina; thus its maximum capacity is lower than in males. It is separated from the  uterus  by the  vesico-uterine pouch . In  infants  and young children the urinary bladder is in the  abdomen  even when empty. [ 18 ]


Urine  is excreted by the  kidneys  and flows into the bladder through the  ureters , where it is stored until  urination  (micturition). [ 13 ]  Urination involves coordinated muscle changes involving a reflex based in the spine, with higher inputs from the brain. [ 13 ]  During urination, the detrusor muscle contracts, the external urinary sphincter and muscles of the  perineum  relax, and urine flows through the  urethra [ 13 ]  and exits the  penis  or  vulva  through the  urinary meatus . [ 11 ]


The urge to pass urine stems from  stretch receptors  that activate when between 300 - 400 mL urine is held within the bladder. [ 13 ]  As urine accumulates, the  rugae  flatten and the wall of the bladder thins as it stretches, allowing the bladder to store larger amounts of urine without a significant rise in internal pressure. [ 19 ]  Urination is controlled by the  pontine micturition center  in the  brainstem . [ 20 ]


Stretch receptors  in the bladder signal the  parasympathetic  nervous system to stimulate the  muscarinic receptors  in the detrusor to contract the muscle when the bladder is distended. [ 21 ]  This encourages the bladder to expel urine through the urethra. The main receptor activated is the  M3 receptor , although  M2 receptors  are also involved and whilst outnumbering the M3 receptors they are not so responsive. [ 22 ]


The main relaxant pathway is via the  adenylyl cyclase   cAMP  pathway, activated via the β3 adrenergic receptors. The  β2 adrenergic receptors  are also present in the detrusor and even outnumber β3 receptors, but they do not have as important an effect in relaxing the detrusor smooth muscle. [ 9 ] [ 23 ] [ 24 ]


Cystitis  refers to infection or inflammation of the bladder. It commonly occurs as part of a  urinary tract infection . [ 25 ]  In adults, it is more common in women than men, owing to a shorter  urethra . It is common in males during childhood, and in older men where  an enlarged prostate  may cause urinary retention. [ 25 ]  Other risk factors include other causes of blockage or narrowing, such as  prostate cancer  or the presence of  vesico-ureteric reflux ; the presence of outside structures in the urinary tract, such as  urinary catheters ; and neurologic problems that make passing urine difficult. [ 25 ]  Infections that involve the bladder can cause pain in the lower abdomen (above the  pubic symphysis , so called "suprapubic" pain), particularly before and after passing urine, and a desire to  pass urine frequently  and with little warning ( urinary urgency ). [ 25 ]  Infections are usually due to  bacteria , of which the most common is  E coli . [ 25 ]


When a urinary tract infection or cystitis is suspected, a  medical practitioner  may request a  urine sample . A  dipstick placed in the urine  may be used to see if the urine has  white blood cells , or the presence of  nitrates  which may indicate an infection. The urine specimen may be also sent for  microbial culture and sensitivity  to assess if a particular bacteria grows in the urine, and identify its  antibiotic sensitivities . [ 25 ]  Sometimes, additional investigations may be requested. These might include testing the function of the kidneys by assessing  electrolytes  and  creatinine ; investigating for blockages or narrowing of the renal tract with an  ultrasound , and testing for an enlarged prostate with a  digital rectal examination . [ 25 ]


Urinary tract infections or cystitis are treated with  antibiotics , many of which are  consumed by mouth . Serious infections may require treatment with  intravenous  antibiotics. [ 25 ]


Interstitial cystitis  refers to a condition in which the bladder is infected due to a cause that is not bacteria. [ 26 ] [ 27 ]


Frequent urination can be due to excessive urine production, small bladder capacity, irritability or incomplete emptying. Males with an  enlarged prostate  urinate more frequently. One definition of an  overactive bladder  is when a person urinates more than eight times per day. [ 28 ]  An overactive bladder can often cause  urinary incontinence . Though both urinary frequency and volumes have been shown to have a circadian rhythm, meaning day and night cycles, [ 29 ]  it is not entirely clear how these are disturbed in the overactive bladder.  Urodynamic testing  can help to explain the symptoms. An  underactive bladder  is the condition where there is a difficulty in passing urine and is the main symptom of a  neurogenic bladder . Frequent urination at night may indicate the presence of  bladder stones .


Disorders of or related to the bladder include:


Disorders of bladder function may be dealt with surgically, by redirecting the flow of urine or by replacement with an  artificial urinary bladder . The volume of the bladder may be increased by  bladder augmentation .  An obstruction of the bladder neck  may be severe enough to warrant surgery.  Ultrasound  can be used to estimate bladder volumes. [ 31 ] [ 32 ]


Cancer  of the bladder is known as  bladder cancer . It is usually due to cancer of the  urothelium , the cells that line the surface of the bladder. Bladder cancer is more common after the age of 40, and more common in men than women; [ 33 ]  other risk factors include  smoking  and exposure to  dyes  such as  aromatic amines  and  aldehydes . [ 33 ]  When cancer is present, the most common symptom in an affected person is  blood in the urine ; a physical  medical examination  may be otherwise normal, except in late disease. [ 33 ]  Bladder cancer is most often due to cancer of the cells lining the ureter, called  transitional cell carcinoma , although it can more rarely occur as a  squamous cell carcinoma  if the type of cells lining the urethra have changed due to chronic inflammation, such as due to stones or  schistosomiasis . [ 33 ]


Investigations performed usually include collecting a sample of urine for an inspection for malignant cells under a microscope, called  cytology , as well as  medical imaging  by a  CT urogram  or  ultrasound . [ 33 ]  If a concerning lesion is seen, a flexible camera may be inserted into the bladder, called  cystoscopy , in order to view the lesion and take a  biopsy , and a  CT scan  will be performed of other body parts (a  CT scan of the chest, abdomen and pelvis ) to look for additional  metastatic  lesions. [ 33 ]


Treatment depends on the cancer's  stage . Cancer present only in the bladder may be removed surgically via  cystoscopy ; an injection of the  chemotherapeutic   mitomycin C  may be performed at the same time. [ 33 ]  Cancers that are  high grade  may be treated with an injection of the  BCG vaccine  into the bladder wall, and may require surgical removal if it does not resolve. [ 33 ]  Cancer that is invading through the bladder wall may be managed by complete surgical removal of the bladder ( radical cystectomy ), with the ureters diverted into a segment of part of  ileum  connected to a  stoma bag  on the skin. [ 33 ]  Prognosis can vary markedly depending on the cancer's stage and grade, with a better prognosis associated with tumours found only in the bladder, that are low grade, that do not invade through the bladder wall, and that is  papillary  in visual appearance. [ 33 ]


A number of investigations are used to examine the bladder. The investigations that are ordered will depend on the taking of a  medical history  and an examination. The examination may involve a  medical practitioner  feeling in the suprapubic area for tenderness or fullness that might indicate an inflamed or full bladder. [ citation needed ]  Blood tests may be ordered that may indicate inflammation; for example a  full blood count  may demonstrate elevated  white blood cells , or a  C-reactive protein  may be elevated in an infection. [ citation needed ]


Some forms of  medical imaging  exist to visualise the bladder. A  bladder ultrasound  may be conducted to view how much urine is within the bladder, indicating  urinary retention . A  urinary tract ultrasound , conducted by a more trained operator, may be conducted to view whether there are stones, tumours or sites of obstruction within the bladder and urinary tract. A  CT scan  may also be ordered.


A flexible internal camera, called a  cystoscope , can be inserted to view the internal appearance of the bladder and take a  biopsy  if required.


Urodynamic testing  can help to explain the symptoms.


All species of mammal have a urinary bladder. [ 34 ]  This structure begins as an  embryonic cloaca . In the vast majority of species, it eventually becomes differentiated into a dorsal part, connected to the intestine, and a ventral part, associated with the urinogenital passage and urinary bladder. The only mammals in which this does not take place are the  platypus  and the  spiny anteater , both of which retain the cloaca into adulthood. [ 35 ]


The mammalian bladder is an organ that regularly stores a hyperosmotic concentration of urine. It therefore is relatively impermeable and has a multi-layer epithelium. The urinary bladders of  cetaceans  (whales and dolphins) are proportionally smaller than those of land-dwelling mammals. [ 36 ]


In all reptiles, the urinogenital ducts and the  rectum  both empty into the organ called the  cloaca . In some reptiles, a midventral wall in the cloaca opens into a urinary bladder. The urinary bladder exists in all species of turtle and tortoise and most species of lizard.  Monitor lizards , the  legless lizards , snakes, alligators, and crocodiles do not have urinary bladders. [ 35 ] : p. 474


Many turtles, tortoises, and lizards have proportionally very large bladders.  Charles Darwin  noted that the bladder of the  Galapagos tortoise  could store urine weighing up to 20% of the tortoise's body weight. [ 37 ]  Such adaptations are the result of environments, such as remote islands and deserts, where fresh water is very scarce. [ 38 ]  Other desert-dwelling reptiles have large bladders, which can hold long-term reserves of water for several months and aid in  osmoregulation . [ 39 ]


Turtles have two or more accessory urinary bladders, beside the neck of the urinary bladder and above the pubis, occupying much of the body cavity. [ 40 ]  Turtles' bladder is also usually divided into two lobes: the right lobe is under the liver, which prevents large stones from remaining in the lobe; the left lobe is likelier than the right to have  calculi . [ 41 ]


Most aquatic and semi-aquatic amphibians can absorb water directly through their skin. Some semi-aquatic animals also have similarly permeable bladder membranes. [ 42 ]  They tend to have high rates of urine production, to offset this high water intake; and the dissolved salts in their urine are highly dilute. The urinary bladder helps these animals to retain salts. Some aquatic amphibians, such as  Xenopus , do not reabsorb water from their urine, to prevent excessive water influx. [ 43 ]  For land-dwelling amphibians, dehydration results in reduced urine output. [ 44 ]


The amphibian bladder is usually highly distensible; among some land-dwelling species of frogs and salamanders, it may account for 20%–50% of total body weight. [ 44 ]  Urine flows from the kidneys through the ureters into the bladder and is periodically released from the bladder to the cloaca. [ 45 ]


The gills of most  teleost  fish help to eliminate ammonia from the body, and fish live surrounded by water, but most still have a distinct bladder for storing waste fluid. The urinary bladder of  teleosts  is permeable to water, though this is less true for freshwater dwelling species than saltwater species. [ 37 ] : p. 219   In freshwater fish the bladder is a key site of absorption for many major ions [ 46 ]  in marine fish urine is held in the bladder for extended periods to maximise water absorption. [ 46 ]  The urinary bladders of fish and  tetrapods  are thought to be analogous while the former's swim-bladders and latter's  lungs  are considered homologous.


Most fish also have an organ called a  swim-bladder  which is unrelated to the urinary bladder except in its membranous nature. The  loaches ,  pilchards , and  herrings  are among the few types of fish in which a urinary bladder is poorly developed. It is largest in those fish which lack an air bladder, and is situated in front of the  oviducts  and behind the  rectum . [ 47 ]


In nearly all bird species, there is no urinary bladder per se. [ 48 ]  Although all birds have kidneys, the  ureters  open directly into a  cloaca  which serves as a reservoir for urine, fecal matter, and eggs. [ 49 ]


Unlike the urinary bladder of vertebrates, the urinary bladder of  crustaceans  both stores and modifies urine. [ 50 ]  The bladder consists of two sets of lateral and central lobes. The central lobes sit near the digestive organs and the lateral lobes extend along the front and sides of the crustacean's body cavity. [ 50 ]  The tissue of the bladder is thin  epithelium . [ 50 ]


Bulbar urethral necrosis  is a problem that can occur after a pelvic fracture associated urethral distraction defect (PFUDD).


A  pelvic fracture  can cause the  urethra  to separate, leading to a variable length of scar that can severely hamper the ability to urinate normally.  The urethra is a tubular conduit that transports urine out of the bladder.  The  bulbar urethra  is a segment of the male urethra that is in between the  penile urethra  and the membrano-prostatic urethra that typically has a robust blood supply.  This blood supply includes antegrade flow from the paired bulbar arteries and circumflex arteries, and retrograde flow from the paired  dorsal arteries  of the  penis .


The treatment for PFUDDs is scar excision and primary  anastomosis , which means reconnecting the two ends of the urethra that were severed during the pelvic injury.  Most patients do well with this but occasionally, stricture of the repair recurs and the patients may require redo surgery.


Surgery involves making an incision between the  anus  and  scrotum  (perineal incision) and dissecting out the bulbar urethra and locating the scar and membranoprostatic urethra.  Dissecting the bulbar urethra destroys the antegrade blood flow.  However, this urethra still does well since in still gets retrograde blood flow from the dorsal arteries.  When patients have  erectile dysfunction , the dorsal arteries do not work well and therefore the bulbar urethra does not get a good blood supply.


Patients with erectile dysfunction (ED) and PFUDD or patients with PFUDD and traumatic disruption of the dorsal arteries are susceptible to bulbar urethral necrosis.  These patients need tubularized substitution  urethroplasty , which is replacement of the bulbar urethra with a various number of tubularized flaps ranging from scrotal skin to  sigmoid colon  (and others).


Penile color  duplex doppler  ultrasound can help with preoperative planning to minimize bulbar necrosis. [ 1 ] [ 2 ]


A  cloaca  ( / k l oʊ ˈ eɪ k ə /   ⓘ   kloh- AY -kə ),  pl. :  cloacae  ( / k l oʊ ˈ eɪ s i /   kloh- AY -see  or  / k l oʊ ˈ eɪ k i /   kloh- AY -kee ), or  vent , is the rear  orifice  that serves as the only opening for the  digestive  ( rectum ),  reproductive , and  urinary tracts  (if present) of many  vertebrate  animals. All  amphibians ,  reptiles ,  birds , and a few mammals ( monotremes ,  afrosoricids , and  marsupial moles , etc.) have this orifice, from which they excrete both  urine  and  feces ; this is in contrast to most  placental mammals , which have separate orifices for evacuation and reproduction.  Excretory  openings with analogous purpose in some  invertebrates  are also sometimes called cloacae. Mating through the cloaca is called cloacal  copulation  and cloacal kissing.


The cloacal region is also often associated with a secretory organ, the cloacal gland, which has been implicated in the scent-marking behavior of some reptiles, [ 1 ]  marsupials, [ 2 ]  amphibians, and  monotremes . [ 3 ]


The word is from the  Latin  verb  cluo , "(I) cleanse", thus the noun  cloaca , " sewer , drain". [ 4 ] [ 5 ] [ 6 ]


Birds reproduce using their cloaca; this occurs during a cloacal kiss in most birds. [ 7 ]  Birds that mate using this method touch their cloacae together, in some species for only a few seconds, sufficient time for  sperm  to be transferred from the male to the female. [ 8 ]  For  palaeognaths  and  waterfowl , the males do not use the cloaca for reproduction, but have a  phallus . [ 9 ]


One study [ 10 ]  has looked into birds that use their cloaca for cooling. [ 11 ]


Among  falconers , the word vent is also a verb meaning "to defecate".


Among fish, a true cloaca is present only in  elasmobranchs  (sharks and rays) and  lobe-finned fishes . In  lampreys  and in some  ray-finned fishes , part of the cloaca remains in the adult to receive the urinary and reproductive ducts, although the anus always opens separately. In  chimaeras  and most  teleosts , however, all three openings are entirely separated. [ 12 ]


With a few exceptions noted below, mammals have no cloaca. Even in the marsupials that have one, the cloaca is partially subdivided into separate regions for the  anus  and  urethra .


The  monotremes  (egg-laying mammals) possess a true cloaca. [ 14 ]


In  marsupials , the genital tract is separate from the anus, but a trace of the original cloaca does remain externally. [ 12 ]  This is one of the features of marsupials (and monotremes) that suggest their basal nature, as the  amniotes  from which mammals evolved had a cloaca, and probably so did the earliest  mammals .


Unlike other marsupials,  marsupial moles  have a true cloaca. [ 15 ]  This fact has been used to argue that they are not marsupials. [ 16 ] [ 17 ] [ unreliable source? ]


Most adult  placentals  have no cloaca. In the embryo, the  embryonic cloaca  divides into a posterior region that becomes part of the  anus , and an anterior region that develops depending on sex: in males, it forms the  penile urethra , while in females, it develops into the  vestibule  or  urogenital sinus  that receives the urethra and vagina. [ 12 ] [ 18 ]  However, some placentals retain a cloaca as adults: those are members of the order   Afrosoricida  (small mammals native to Africa) as well as  pikas ,  beavers , and some  shrews . [ 19 ] [ 20 ] [ 21 ] [ 22 ]


Being placental animals, humans have an embryonic cloaca which divides into separate tracts during the  development of the urinary and reproductive organs . However, a few human  congenital disorders  result in persons being born with a cloaca, including  persistent cloaca  and  sirenomelia  (mermaid syndrome).


In reptiles, the cloaca consists of the  urodeum ,  proctodeum , and  coprodeum . [ 23 ] [ 24 ]  Some species have modified cloacae for increased gas exchange (see  reptile respiration  and  reptile reproduction ). This is where reproductive activity occurs. [ 25 ]


Some  turtles , especially those specialized in diving, are highly reliant on cloacal  respiration  during dives. [ 26 ]  They accomplish this by having a pair of accessory air bladders connected to the cloaca, which can absorb oxygen from the water. [ 27 ]


Sea cucumbers  use cloacal respiration. The constant flow of water through it has allowed various  fish ,  polychaete  worms and even  crabs  to specialize to take advantage of it while living protected inside the cucumber. At night, many of these species emerge through the anus of the sea cucumber in search of food. [ 28 ]


The  cystocele , also known as a  prolapsed bladder , is a medical condition in which a woman's  bladder  bulges into her  vagina . [ 1 ] [ 5 ]  Some may have no symptoms. [ 6 ]  Others may have trouble starting urination,  urinary incontinence , or  frequent urination . [ 1 ]  Complications may include recurrent  urinary tract infections  and  urinary retention . [ 1 ] [ 7 ]  Cystocele and a  prolapsed urethra  often occur together and is called a cystourethrocele. [ 8 ]  Cystocele can negatively affect  quality of life . [ 9 ] [ 10 ]


Causes include  childbirth ,  constipation ,  chronic cough , heavy lifting,  hysterectomy ,  genetics , and being  overweight . [ 1 ] [ 2 ] [ 6 ]  The underlying mechanism involves weakening of  muscles  and  connective tissue  between the bladder and vagina. [ 1 ]  Diagnosis is often based on symptoms and examination. [ 1 ]


If the cystocele causes few symptoms, avoiding heavy lifting or straining may be all that is recommended. [ 1 ]  In those with more significant symptoms a vaginal  pessary ,  pelvic muscle exercises , or surgery may be recommended. [ 1 ]  The type of surgery typically done is known as a  colporrhaphy . [ 11 ]  The condition becomes more common with age. [ 1 ]  About a third of women over the age of 50 are affected to some degree. [ 5 ]


The symptoms of a cystocele may include:


A bladder that has dropped from its normal position and into the vagina can cause some forms of incontinence and incomplete emptying of the bladder. [ 1 ]


Complications may include  urinary retention , recurring urinary tract infections and incontinence. [ 1 ] [ 7 ]  The anterior vaginal wall may actually protrude though the vaginal introitus (opening). This can interfere with sexual activity. [ 6 ]  Recurrent urinary tract infections are common for those who have urinary retention. [ 15 ]  In addition, though cystocele can be treated, some treatments may not alleviate troubling symptoms, and further treatment may need to be performed. Cystocele may affect the quality of life, women who have cystocele tend to avoid leaving their home and avoid social situations. The resulting incontinence puts women at risk of being placed in a nursing home or long-term care facility. [ medical citation needed ]


A cystocele occurs when the muscles,  fascia ,  tendons  and  connective tissues  between a woman's bladder and vagina weaken, or detach. [ 2 ] [ 16 ]  The type of cystocele that can develop can be due to one, two or three vaginal wall attachment failures: the midline defect, the paravaginal defect, and the transverse defect. The midline defect is a cystocele caused by the overstretching of the vaginal wall; the paravaginal defect is the separation of the vaginal connective tissue at the  arcus tendineus fascia pelvis ; the transverse defect is when the  pubocervical fascia  becomes detached from the top (apex) of the vagina. [ 2 ]  There is some pelvic prolapse in 40–60% of women who have given birth. [ 17 ] [ 18 ]  Muscle injuries have been identified in women with cystocele. These injuries are more likely to occur in women who have given birth than those who have not. These muscular injuries result in less support to the anterior vaginal wall. [ 19 ]


Some women with connective tissue disorders are predisposed to developing anterior vaginal wall collapse. Up to one third of women with  Marfan syndrome  have a history of vaginal wall collapse.  Ehlers-Danlos  syndrome in women is associated with a rate of 3 out of 4. [ 6 ]


Risk factors for developing a cystocele are:


Connective tissue disorders predispose women to developing cystocele and other pelvic organ prolapse. The tissues tensile strength of the vaginal wall decreases when the structure of the collagen fibers change and become weaker. [ 6 ]


There are two types of cystocele. The first is distension. This is thought to be due to the overstretching of the vaginal wall and is most often associated with aging, menopause and vaginal delivery. It can be observed when the  rugae  are less visible or even absent. The second type is displacement. Displacement is the detachment or abnormal elongation of supportive tissue. [ 25 ]


The initial assessment of cystocele can include a  pelvic exam  to evaluate leakage of urine when the women is asked to bear down or give a strong cough ( Valsalva maneuver ), and the anterior vaginal wall measured and evaluated for the appearance of a cystocele. [ 26 ] [ 27 ]  If a woman has difficulty emptying her bladder, the clinician may measure the amount of urine left in the woman's bladder after she urinates called the postvoid residual. This is measured by  ultrasound . A  voiding cystourethrogram  is a test that involves taking x-rays of the bladder during urination. This  x-ray  shows the shape of the bladder and lets the doctor see any problems that might block the normal flow of urine. [ 1 ]  A urine culture and sensitivity test will assess the presence of a urinary tract infection that may be related to urinary retention. [ 12 ]  Other tests may be needed to find or rule out problems in other parts of the urinary system. [ 1 ]  Differential diagnosis will be improved by identifying possible inflammation of the  Skene's glands  and  Bartholin glands . [ 28 ]


A number of scales exist to grade the severity of a cystocele. [ citation needed ]


The  pelvic organ prolapse quantification  (POP-Q) assessment, developed in 1996, quantifies the descent of the cystocele into the vagina. [ 6 ] [ 13 ]  The POP-Q provides reliable description of the support of the anterior, posterior and apical vaginal wall. It uses objective and precise measurements to the reference point, the  hymen . Cystocele and prolapse of the vagina from other causes is staged using POP-Q criteria can range from good support (no descent into the vagina) reported as a POP-Q stage 0 or I to a POP-Q score of IV which includes prolapse beyond the hymen. It also used to quantifies the movement of other structures into the vaginal  lumen  and their descent. [ 6 ] [ 13 ]


The Baden–Walker Halfway Scoring System is used as the second most used system and assigns the classifications as mild (grade 1) when the bladder droops only a short way into the vagina; (grade 2) cystocele, the bladder sinks far enough to reach the opening of the vagina; and (grade 3) when the bladder bulges out through the opening of the vagina. [ 1 ] [ 29 ]


Cystocele can be further described as being apical, medial, or lateral. [ 30 ]


Apical cystocele  is located upper third of the vagina. The structures involved are the  endopelvic fascia  and  ligaments . The  cardinal ligaments  and the  uterosacral ligaments  suspend the upper vaginal-dome. The cystocele in this region of the vagina is thought to be due to a cardinal ligament defect. [ 16 ] [ 25 ]


Medial cystocele  forms in the mid-vagina and is related to a defect in the suspension provided by to a sagittal suspension system defect in the uterosacral ligaments and  pubocervical fascia . The pubocervical fascia may thin or tear and create the cystocele. An aid in diagnosis is the creation of a 'shiny' spot on the epithelium of the vagina. This defect can be assessed by  MRI . [ 16 ] [ 25 ]


Lateral cystocele  forms when both the pelviperineal muscle and its ligamentous–fascial develop a defect. The ligamentous– fascial creates a 'hammock-like' suspension and support for the lateral sides of the vagina. Defects in this lateral support system results in a lack of bladder support. Cystocele that develops laterally is associated with an anatomic imbalance between anterior vaginal wall and the  arcus tendineus fasciae  pelvis – the essential ligament structure. [ 16 ] [ 25 ]


Cystocele may be mild enough not to result in symptoms that are troubling to a woman. In this case, steps to prevent it from worsening include:


Treatment options range from no treatment for a mild cystocele to  surgery  for a more extensive cystocele. [ 1 ]  If a cystocele is not bothersome, the clinician may only recommend avoiding heavy lifting or straining that could cause the cystocele to worsen. If symptoms are moderately bothersome, the doctor may recommend a  pessary , a device placed in the vagina to hold the bladder in place and to block protrusion. [ 12 ] [ 23 ]  Treatment can consist of a combination of non-surgical and surgical management. Treatment choice is also related to age, desire to have children, severity of impairment, desire to continue sexual intercourse and other diseases that a woman may have. [ 6 ]


Cystocele is often treated by non-surgical means:


The surgery to repair the anterior vaginal wall may be combined with other procedures that will repair the other points of pelvic organ support such as anterior-posterior repair and anterior colporrhaphy. [ 12 ]  Treatment of cystocele often accompanies the more invasive hysterectomy. [ 32 ]  Since the failure rate in cystocele repair remains high, additional surgery may be needed. [ 13 ]  Women who have surgery to repair a cystocele have a 17% of needing another operation within the next ten years. [ 33 ]


The surgical treatment of cystocele will depend on the cause of the defect and whether it occurs at the top (apex), middle, or lower part of the anterior vaginal wall. The type of surgery will also depend on the type of damage that exists between supporting structures and the vaginal wall. [ 2 ]  One of the most common surgical repairs is  colporrhaphy . [ 32 ]  This surgical procedure consists of making a longitudinal folding of the vaginal tissue, suturing it into place and creating a stronger point of resistance to the intruding bladder wall.  Surgical mesh  is sometimes used to strengthen the anterior vaginal wall. [ 6 ]  It has a 10–50% failure rate. [ 34 ] [ 32 ]  In some cases a surgeon may choose to use  surgical mesh  to strengthen the repair. [ 32 ]


During surgery, the repair of the vaginal wall consists of folding over and then suturing the existing tissue between the vagina and bladder to strengthen it. [ 1 ] [ 11 ]  This tightens the layers of tissue to promote the replacement of the pelvic organs into their normal place. The surgery also provides more support for the bladder. This surgery is done by a surgeon specializing in gynecology and is performed in a hospital.  Anesthesia  varies according to the needs of each woman. Recovery may take four to six weeks. [ 1 ]  Other surgical treatment may be performed to treat cystocele. Support for the vaginal wall is accomplished with the paravaginal defect repair. This is a surgery, usually  laproscopic , that is done to the ligaments and fascia through the abdomen. The lateral ligaments and supportive structures are repaired, sometimes shortened to provide additional support to the vaginal wall. [ 32 ]


Sacrocolpopexy  is a procedure that stabilizes the vaginal vault (the uppermost portion of the vagina) and is often chosen as the treatment for cystocele, especially if previous surgeries were not successful. The procedure consists of attaching the vaginal vault to the sacrum. It has a success rate of 90%. [ 32 ]  Some women choose not to have surgery to close the vagina. This surgery, called  colpocleisis , treats cystocele by closing the vaginal opening. This can be an option for women who no longer want to have vaginal intercourse. [ 22 ]


If an  enterocele / sigmoidocele , or prolapse of the rectum/colon, is also present, the surgical treatment will take this concurrent condition into account while planning and performing the repairs. [ 2 ]  Estrogen that is administered vaginally before surgical repair can strengthen the vaginal tissue providing a more successful outcome when mesh or sutures are used for the repair. Vaginal thickness increases after estrogen therapy. [ 33 ]  Another review on the surgical management of cystocele describes a more successful treatment that more strongly attaches the ligaments and fascia to the vagina to lift and stabilize it. [ 35 ]


Post surgical complications can develop. The complications following surgical treatment of cystocele are:


After surgery, a woman is instructed to restrict her activities and monitor herself for signs of infection such as an elevated temperature, discharge with a foul odor and consistent pain. Clinicians may recommend that sneezing, coughing, and constipation are to be avoided. Splinting the abdomen while coughing provides support to an incised area and decreases pain on coughing. [ 12 ]  This is accomplished by applying gentle pressure to the surgical site for bracing during a cough. [ 36 ] [ 37 ]


Recurrent surgery on the pelvic organs may not be due to a failure of the surgery to correct the cystocele. Subsequent surgeries can be directly or indirectly relating to the primary surgery. [ 13 ]  Prolapse can occur at a different site in the vagina. Further surgery after the initial repair can be to treat complications of mesh displacement, pain, or bleeding. Further surgery may be needed to treat incontinence. [ 13 ]


One goal of surgical treatment is to restore the vagina and other pelvic organs to their anatomically normal positions. This may not be the outcome that is most important to the woman being treated who may only want relief of symptoms and an improvement in her quality of life. The International Urogynecological Association (IUGA) has recommended that the data collected regarding the success of cystocele and pelvic organ repairs include the presence or absence of symptoms, satisfaction and Quality of Life. Other measures of a successful outcome should include perioperative data, such as operative time and hospital stay.  Standardized Healthcare Quality of Life  should be part of the measure of a successful resolution of cystocele. Data regarding short- and long-term complications is included in the recommendations of the IUGA to better assess the risk–benefit ratio of each procedure. [ 13 ]  Current investigations into the superiority of using biological grafting versus native tissue or surgical mesh indicates that using grafts provides better results. [ 38 ]


A large study found a rate of 29% over the lifetime of a woman. Other studies indicate a recurrence rate as low as 3%. [ 13 ]


In the US, greater than 200,000 surgeries are performed each year for pelvic organ prolapse and 81% of these are to correct cystocele. [ 14 ] [ 11 ]  Cystocele occurs most frequently compared to the prolapse of other pelvic organs and structure. [ 13 ] [ 14 ]  Cystocele is found to be three times as common as vaginal vault prolapse and twice as often as posterior vaginal wall defects. The incidence of cystocele is around 9 per 100 women-years. The highest incidence of symptoms occurs between ages of 70 and 79 years. Based on population growth statistics, the number of women with prolapse will increase by a minimum of 46% by the year 2050 in the US. Surgery to correct prolapse after hysterectomy is 3.6 per 1,000 women-years. [ 13 ]


Notable is the mention of cystocele in many older cultures and locations. [ 39 ]  In 1500 B.C. Egyptians wrote about the "falling of the womb". In 400 B.C. a Greek physician documented his observations and treatments:


"After the patient had been tied to a ladder-like frame, she was tipped upward so that her head was toward the bottom of the frame. The frame was then moved upward and downward more or less rapidly for approximately 3–5 min. As the patient was in an inverted position, it was thought that the prolapsing organs of the genital tract would be returned to their normal position by the force of gravity and the shaking motion." [ 39 ]


Hippocrates  had his own theories regarding the cause of prolapse. He thought that recent childbirth, wet feet, 'sexual excesses', exertion, and fatigue may have contributed to the condition.  Polybus , Hippocrates's son-in-law, wrote: "a prolapsed uterus was treated by using local astringent lotions, a natural sponge packed into the vagina, or placement of half a pomegranate in the vagina." In 350 A.D., another practitioner named Soranus described his treatments which stated that the pomegranate should be dipped into vinegar before insertion. Success could be enhanced if the woman was on bed rest and reduced intake of fluid and food. If the treatment was still not successful, the woman's legs were tied together for three days. [ 39 ]


In 1521,  Berengario da Carpi  performed the first surgical treatment for prolapse. This was to tie a rope around the prolapse, tighten it for two days until it was no longer viable and cut it off. Wine, aloe, and honey were then applied to the stump. [ 39 ]


In the 1700s, a Swiss gynecologist, Peyer, published a description of a cystocele. He was able to describe and document both cystocele and uterine prolapse. In 1730, Halder associated cystocele with childbirth. During this same time, efforts began to standardize the terminology that is still familiar today. In the 1800s, the surgical advancements of anesthesia, suturing, suturing materials and acceptance of  Joseph Lister's  theories of  antisepsis  improved outcomes for women with cystocele. The first surgical techniques were practiced on female cadavers. In 1823, Geradin proposed that an incision and resection may provide treatment. In 1830, the first dissection of the vagina was performed by Dieffenbach on a living woman. In 1834, Mendé proposed that dissecting and repair of the edges of the tissues could be done. In 1859, Huguier proposed the amputation of the cervix was going to solve the problem for elongation. [ 39 ]


In 1866, a method of correcting a cystocele was proposed that resembled current procedures. Sim subsequently developed another procedure that did not require the full-thickness dissection of the vaginal wall. In 1888, another method of treating anterior vaginal wall Manchester combined an anterior vaginal wall repair with an amputation of the cervix and a perineorrhaphy. In 1909, White noted the high rate of recurrence of cystocele repair. At this time it was proposed that reattaching the vagina to support structures was more successful and resulted in less recurrence. This same proposal was proposed again in 1976 but further studies indicated that the recurrence rate was not better. [ 39 ]


In 1888, treatments were tried that entered the abdomen to make reattachments. Some did not agree with this and suggested an approach through the  inguinal canal . In 1898, further abdominal approaches were proposed. No further advances have been noted until 1961 when reattachment of the anterior vaginal wall to  Cooper's ligament  began to be used. Unfortunately, posterior vaginal wall prolapse occurred in some patients even though the anterior repair was successful. [ 39 ]


In 1955, using mesh to support pelvic structures came into use. In 1970, tissue from pigs began to be used to strengthen the anterior vaginal wall in surgery. Beginning in 1976, improvement in suturing began along with the surgical removal of the vagina being used to treat prolapse of the bladder. In 1991, assumptions about the detailed anatomy of the pelvic support structures began to be questioned regarding the existence of some pelvic structures and the non-existence of others. More recently, the use of stem cells, robot-assisted laparoscopic surgery are being used to treat cystocele. [ 39 ]


The  detrusor muscle , also  detrusor urinae muscle ,  muscularis propria of the urinary bladder  and (less precise)  muscularis propria , is  smooth muscle  found in the wall of the  bladder . The detrusor muscle remains relaxed to allow the bladder to store  urine , and contracts during  urination  to release urine. Related are the  urethral sphincter  muscles which envelop the  urethra  to control the flow of urine when they contract.


The fibers of the detrusor muscle arise from the  posterior  surface of the  body of the pubis  in both sexes (musculi pubovesicales), and in the male from the adjacent part of the  prostate . These fibers pass, in a more or less  longitudinal  manner, up the  inferior  surface of the  bladder , over its  apex , and then descend along its  fundus  to become attached to the prostate in the male, and to the front of the  vagina  in the female. At the sides of the bladder the fibers are arranged  obliquely  and intersect one another.


The three layers of muscles are arranged longitudinal-circular-longitudinal from innermost to outermost.


The detrusor muscle is innervated by the  autonomic nervous system .


During urination,  parasympathetic   pelvic splanchnic nerves  act primarily on postganglionic  M 3  receptors to cause contraction of the detrusor muscle. [ 1 ] [ 2 ] [ 3 ]


At other times, the muscle is kept relaxed via  sympathetic  branches from the  inferior hypogastric plexus  to allow the bladder to fill. [ 4 ]


In older adults over 60 years in age, the detrusor muscle may cause issues in voiding the bladder, resulting in uncomfortable  urinary retention . [ 5 ]


The bladder also contains  β 3  adrenergic receptors , and pharmacological agonists of this receptor are used to treat  overactive bladder .


The mucosa of the urinary bladder may herniate through the detrusor muscle. [ 6 ]  This is most often an acquired condition due to high pressure in the urinary bladder, damage, or existing connective tissue disorders. [ 6 ]


A  flame cell  is a specialized excretory cell found in simple  invertebrates , including   flatworms  ( Platyhelminthes ),  rotifers  and  nemerteans ; these are the simplest animals to have a dedicated  excretory system . Flame cells function like a  kidney , removing waste materials. Bundles of flame cells are called  protonephridia . [ 1 ]


The flame cell has a  nucleated  cell body, with a "cup-shaped" projection, with  flagella  covering the inner surface of the cup. The beating of these flagella resemble a flame, giving the cell its name. The cup is attached to a  tube cell , whose inner surface is also coated in  cilia , which help to move liquid through the tube cell. The tube opens externally through a  nephropore , or, in the  trematoda , into an excretory  bladder . The function of these cells is to regulate the  osmotic pressure  of the worm, and maintain its ionic balance.  Microvilli  in the tube cell may be used to reabsorb some  ions . [ 1 ]


Molecules enter the tubule in tube cells through the gap between the flame cell and tube cell for excretion. [ 2 ]


In  human anatomy , the  penis  ( / ˈ p iː n ɪ s / ;  pl. :  penises  or  penes ; from the  Latin   pēnis , initially "tail" [ 1 ] ) is an external  sex organ  ( intromittent organ ) through which males  urinate  and  ejaculate . Together with the  testes  and surrounding structures, the penis functions as part of the  male reproductive system .


The main parts of the penis are the  root ,  body , the  epithelium  of the penis including the shaft skin, and the  foreskin  covering the  glans . The body of the penis is made up of three columns of  tissue : two  corpora cavernosa  on the  dorsal side  and  corpus spongiosum  between them on the  ventral side . The  urethra  passes through the  prostate gland , where it is joined by the  ejaculatory ducts , and then through the penis. The urethra goes across the corpus spongiosum and ends at the tip of the glans as the opening, the  urinary meatus .


An  erection  is the stiffening expansion and orthogonal reorientation of the penis, which occurs during  sexual arousal . Erections can occur in non- sexual  situations; spontaneous non-sexual erections frequently occur during adolescence and sleep. In its flaccid state, the penis is smaller, gives to pressure, and the glans is covered by the foreskin. In its fully erect state, the shaft becomes rigid and the glans becomes engorged but not rigid. An erect penis may be straight or curved and may point at an upward angle, a downward angle, or straight ahead. As of 2015 [update] , the average erect human penis is 13.12 cm (5.17 in) long and has a circumference of 11.66 cm (4.59 in). [ 2 ] [ 3 ]  Neither age nor size of the flaccid penis accurately predicts erectile length. There are several common  body modifications  to the penis, including  circumcision  and  piercings .


The penis  is homologous to  the  clitoris  in females. [ 4 ]


Three main parts of the human penis include:


The human penis is made up of three columns of  erectile tissue : two  corpora cavernosa  lie next to each other (separated by a fibrous  septum ) on the  dorsal side  and one  corpus spongiosum  lies between them on the  ventral side . [ 7 ]  These columns are surrounded by a fibrous layer of connective tissue called the  tunica albuginea . The corpora cavernosa are innervated by lesser and greater  cavernous nerves  and form most of the penis containing  blood vessels  that fill with  blood  to help make an erection. [ 8 ]
The crura are the proximal parts of the corpora cavernosa. The corpus spongiosum is an erectile tissue surrounding the urethra. The proximal parts of the corpus spongiosum form the bulb and the distal ends form the glans penis. [ 5 ]


The enlarged and bulbous-shaped end of the corpus spongiosum forms the glans penis with two specific types of sinusoids, which supports the foreskin, a loose fold of skin that in adults can retract to expose the glans. [ 9 ]  The area on the underside of the glans, where the foreskin is attached, is called the  frenulum . The rounded base of the glans is called the  corona . The inner surface of the foreskin and corona is rich in  sebaceous glands  that secrete  smegma . The structure of the penis is supported by the  pelvic floor muscles .


The  urethra , which is the last part of the  urinary tract , traverses the corpus spongiosum ( spongy urethra ) and opens through the  urinary meatus  on the tip of the glans.


The  penile raphe  is the visible ridge between the  lateral  halves of the penis, found on the ventral or underside of the penis, running from the meatus and continuing as the  perineal raphe  across the  scrotum  and the  perineum  (area between scrotum and  anus ). [ 10 ]


The human penis differs from  those of most other mammals , as it has no  baculum  (or erectile bone) and instead relies entirely on engorgement with blood to reach its erect state. A distal ligament buttresses the glans penis and plays an integral role to the penile fibroskeleton, and the structure is called "os analog", a term coined by  Geng Long Hsu  in the  Encyclopedia of Reproduction . [ 11 ]  It is a remnant of the baculum that has likely evolved due to change in mating practice . [ 12 ]


The human penis cannot be withdrawn into the groin, and it is larger than average in the animal kingdom in proportion to body mass. The human penis is reciprocating from a cotton soft to a bony rigidity resulting from penile arterial flow varied between 2–3 to 60–80 mL/Min implies the most ideal milieu to apply Pascal's law in the entire human body; the overall structure is unique. [ 11 ]


Penile measurements vary, with studies that rely on self-measurement reporting a significantly higher average size than those which rely on measurements taken by health professional. A 2015 systematic review of 15,521 men in which the subjects were measured by health professionals showed that the average length of an erect human penis is 13.12 cm (5.17 inches) long, while the average circumference of an erect human penis is 11.66 cm (4.59 inches). [ 2 ] [ 3 ]


Among all primates, the human penis is the largest in girth, but is comparable to the  chimpanzee  penis and the penises of certain other primates in length. [ 13 ]  Penis size is affected by  genetics , but also by environmental factors such as  fertility medications [ 14 ] [ unreliable medical source? ]  and chemical/pollution exposure. [ 15 ] [ unreliable medical source? ] [ 16 ] [ unreliable medical source? ]


When the fetus is exposed to  testosterone , the  genital tubercle  elongates ( primordial phallus ) and develops into the glans and shaft of the penis and the  urogenital folds  fuse to become the penile raphe. [ 19 ] [ 20 ] [ 21 ]  The urethra within the penis (except within the glans) is developed from the  urogenital sinus . [ 22 ]


On entering  puberty , the penis, scrotum and  testicles  will enlarge toward maturity. During the process,  pubic hair  grows above and around the penis. A large-scale study assessing penis size in thousands of 17- to 19-year-old males found no difference in average penis size between 17-year-olds and 19-year-olds. From this, it can be concluded that penile growth is typically complete not later than age 17, and possibly earlier. [ 23 ] [ unreliable medical source? ]


Males expel  urine  from the bladder through the urethra, which passes through the  prostate  where it is joined by the  ejaculatory ducts , and then onward through the penis. At the root of the penis (the proximal end of the corpus spongiosum) lies the  external sphincter muscle . This is a small sphincter of  striated muscle tissue  and is in healthy males, under voluntary control. Relaxing the urethral sphincter allows the urine in the upper urethra to enter the penis properly and thus empty the urinary bladder.


Physiologically, urination involves coordination between the  central ,  autonomic , and  somatic nervous systems . In infants, some elderly individuals, and those with neurological injury, urination may occur as an involuntary reflex. Brain centers that regulate urination include the  pontine micturition center ,  periaqueductal gray , and the  cerebral cortex . [ 24 ] [ unreliable medical source? ]  During erection, these centers block the relaxation of the sphincter muscles, so as to act as a physiological separation of the excretory and reproductive function of the penis, and preventing urine from entering the upper portion of the urethra during ejaculation. [ 25 ] [ unreliable medical source? ]


The distal section of the urethra allows a human male to direct the stream of urine by holding the penis. This flexibility allows the male to choose the posture in which to urinate. In cultures where more than a minimum of clothing is worn, the penis allows the male to urinate while standing without removing much of the clothing. It is customary for some boys and men to urinate in seated or crouched positions. The preferred position may be influenced by cultural or religious beliefs. [ 26 ]  Research on the medical superiority of either position exists, but the data are  heterogenic . A  meta-analysis [ 27 ]  summarizing the evidence found no superior position for young, healthy males. For elderly males with  LUTS , however, the sitting position when compared to the standing position is differentiated by the following:


This  urodynamic  profile is related to a lower risk of urologic complications, such as  cystitis  and  bladder stones .


The penis incites sexual arousal when  sexually stimulated , such as from mental stimuli ( sexual fantasy ),  partnered  activity, or  masturbation , which can lead to  orgasm .


The glans and the frenulum are  erogenous zones  of the penis. [ 28 ]  The glans has a lot of  nerve endings , which makes it the most sensitive. [ 29 ] [ unreliable medical source? ]  The most effective way to stimulate the penis is through  oral  stimulation ( fellatio ), manual stimulation (a  handjob  or  manual masturbation ), or during  sexual penetration .  Frot  is mutual penile stimulation between men.


An erection is the stiffening and rising of the penis, which occurs during sexual arousal, though it can also happen in non-sexual situations. Spontaneous erections frequently occur during adolescence due to friction with clothing, a full bladder or large intestine, hormone fluctuations, nervousness, and undressing in a nonsexual situation. It is also normal for erections to occur during sleep and upon waking. (See  nocturnal penile tumescence .) The primary physiological mechanism that brings about erection is the autonomic  dilation  of  arteries  supplying blood to the penis, which allows more blood to fill the three spongy erectile tissue chambers in the penis, the corpora cavernosa and corpus spongiosum, causing it to lengthen and stiffen. After  vasocongestion , the now-engorged erectile tissue presses against and constricts the veins that carry blood away from the penis. More blood enters than leaves the penis until an equilibrium is reached where an equal volume of blood flows into the dilated arteries and out of the constricted veins; a constant erectile size is achieved at this equilibrium.


Erection facilitates sexual intercourse though it is not essential for various other  sexual activities .


Although many erect penises point upwards, it is common and normal for erect penis to curve in any direction. Many penises are curved in right, left, upwards or downwards direction depending upon the tension of the  suspensory ligament  that holds it in position.


The following table shows how common various erection angles are for a standing male, out of a sample of 81 males aged 21 through 67. In the table, zero degrees is pointing straight up against the abdomen, 90 degrees is horizontal and pointing straight forward, while 180 degrees would be pointing straight down to the feet. An upward pointing angle is most common. [ 30 ] [ unreliable medical source? ]


Ejaculation is the ejection of semen from the penis. It is usually accompanied by orgasm. A series of muscular contractions delivers semen, containing male  gametes  known as sperm cells or  spermatozoa , from the penis. Ejaculation usually happens as the result of sexual stimulation, but it can be due to  prostatic disease  in rare cases. Ejaculation may occur spontaneously during sleep (known as a  nocturnal emission ).  Anejaculation  is the condition of being unable to ejaculate.


Sperm  are produced in the  testicles  and stored in the attached  epididymides . During ejaculation, sperm are propelled up the  vasa deferentia , two ducts that pass over and behind the bladder. Fluids are added by the  seminal vesicles  and the vasa deferentia turn into the  ejaculatory ducts , which join the urethra inside the  prostate . The prostate, as well as the  bulbourethral glands , add further secretions (including  pre-ejaculate ), and the semen is expelled through the penis.


Ejaculation has two phases: emission and ejaculation proper. The emission phase of the ejaculatory reflex is under control of the  sympathetic nervous system , while the ejaculatory phase is under control of a  spinal reflex  at the level of the  spinal nerves  S2–4 via the  pudendal nerve . A refractory period succeeds the ejaculation, and sexual stimulation precedes it. [ 31 ]


The  ischiocavernosus muscle  helps to stabilize the penis during erection by compressing the crus and slowing the return of blood through the veins. The  bulbospongiosus muscle  also contributes to erection along with the expulsion of urine and semen.


The human penis has been argued to have several evolutionary adaptations that maximise  reproductive success  and minimise  sperm competition . Sperm competition is where the sperm of two males simultaneously occupy the reproductive tract of a female and they compete to fertilise the egg. [ 32 ]  If sperm competition results in the rival male's sperm fertilising the egg,  cuckoldry  could occur. This is the process whereby males unwittingly invest their resources into offspring of another male and, evolutionarily speaking, should be avoided. [ 33 ]


The most researched human penis adaptations are  penis size  and semen displacement. [ 34 ]


Evolution has caused sexually selected adaptations to occur in penis size in order to maximise reproductive success and minimise sperm competition. [ 35 ] [ unreliable medical source? ] [ 36 ] [ unreliable medical source? ]


Sperm competition has caused the human penis to evolve in length and size for sperm retention and displacement. [ 36 ]  To achieve this, the penis must be of sufficient length to reach any rival sperm and to maximally fill the  vagina . [ 36 ]  In order to ensure that the female retains the male's sperm, the adaptations in length of the human penis have occurred so that the ejaculate is placed close to the female cervix. [ 37 ] [ unreliable medical source? ]  This is achieved when complete  penetration  occurs and the penis pushes against the cervix. [ 38 ] [ unreliable medical source? ]  These adaptations have occurred in order to release and retain sperm to the highest point of the vaginal tract. As a result, this adaptation also leaves the sperm less vulnerable to sperm displacement and semen loss. Another reason for this adaptation is that, due to the nature of the human posture, gravity creates vulnerability for semen loss. Therefore, a long penis, which places the ejaculate deep in the vaginal tract, could reduce the loss of semen. [ 39 ] [ unreliable medical source? ]


Another evolutionary theory of penis size is female  mate choice  and its associations with social judgements in modern-day society. [ 36 ] [ 40 ] [ unreliable medical source? ]  A study which illustrates female mate choice as an influence on penis size presented females with life-size, rotatable, computer generated males. These varied in height, body shape and flaccid penis size, with these aspects being examples of masculinity. [ 36 ] [ unreliable medical source? ]  Female ratings of attractiveness for each male revealed that larger penises were associated with higher attractiveness ratings. [ 36 ] [ unreliable medical source? ]  These relations between penis size and attractiveness have therefore led to frequently emphasized associations between masculinity and penis size in popular media. [ 40 ] [ unreliable medical source? ]  This has led to a social bias existing around penis size with larger penises being preferred and having higher social status. This is reflected in the association between believed sexual prowess and penis size and the social judgement of penis size in relation to 'manhood'. [ 40 ] [ unreliable medical source? ]


The shape of the human penis is thought to have evolved as a result of sperm competition. [ 41 ]  Semen displacement is an adaptation of the shape of the penis to draw foreign semen away from the cervix. This means that in the event of a rival male's sperm occupying the  reproductive tract  of a female, the human penis is able to displace the rival sperm, replacing it with his own. [ 42 ]


Semen displacement has two main benefits for a male. Firstly, by displacing a rival male's sperm, the risk of the rival sperm fertilising the egg is reduced. [ 43 ]  Secondly, the male replaces the rival's sperm with his own, thereby increasing the probability of his fertilising the egg and successfully reproducing with the female. However, males have to ensure they do not displace their own sperm. It is thought that the relatively quick loss of erection after ejaculation, penile hypersensitivity following ejaculation, and the shallower, slower thrusting of the male after ejaculation prevent this from occurring. [ 42 ]


The  coronal  ridge is the part of the human penis thought to have evolved to allow for semen displacement. Research has studied how much semen is displaced by differently shaped artificial genitals. [ 43 ]  This research showed that, when combined with thrusting, the coronal ridge of the penis is able to remove the seminal fluid of a rival male from within the  female reproductive tract . It does this by forcing the semen under the  frenulum  of the coronal ridge, causing it to collect behind the coronal ridge shaft. [ 43 ]  When model penises without a coronal ridge were used, less than half the artificial sperm was displaced, compared to penises with a coronal ridge. [ 43 ]


The presence of a coronal ridge alone, however, is not sufficient for effective semen displacement. It must be combined with adequate thrusting to be successful. It has been shown that the deeper the thrusting, the larger the semen displacement. No semen displacement occurs with shallow thrusting. [ 43 ]  Some have therefore termed thrusting as a semen displacement behaviour. [ 44 ]


The behaviours associated with semen displacement, namely thrusting (number of thrusts and depth of thrusts), and duration of  sexual intercourse , [ 44 ]  have been shown to vary according to whether a male perceives the risk of partner  infidelity  to be high or not. Males and females report greater semen displacement behaviours following allegations of infidelity. In particular, following allegations of infidelity, males and females report deeper and quicker thrusting during sexual intercourse. [ 43 ]


In many cultures, referring to the penis is considered taboo or vulgar, and a variety of slang words and euphemisms are used to talk about it. In English, these include  member ,  dick ,  cock ,  prick ,  johnson ,  dork ,  peter ,  pecker ,  manhood ,  stick ,  rod ,  third/middle leg ,  dong ,  willy ,  schlong , and  todger . [ 49 ]  Many of these are used as  insults —though sometimes playfully—meaning an unpleasant or unworthy person. [ 50 ] [ 51 ]  Among these, historically, the most commonly used euphemism for penis in English literature and society was  member . [ 52 ]


The penis is sometimes pierced or decorated by other body art. Other than circumcision, genital alterations are almost universally elective and usually for the purpose of aesthetics or increased sensitivity. Piercings of the penis include the  Prince Albert ,  apadravya ,  ampallang ,  dydoe ,  deep shaft  and  frenum piercings .  Foreskin restoration  or stretching is a further form of body modification, as well as  implants  under the shaft of the penis. Another type of alteration to the penis is  genital tattooing .


Trans women  who undergo  sex reassignment surgery  have their penis surgically modified into a vagina or clitoris via  vaginoplasty  or clitoroplasty respectively. [ 53 ]   Trans men  who undergo such surgery have a  phalloplasty  or  metoidioplasty .


Other practices that alter the penis are also performed, although they are rare in Western societies without a diagnosed medical condition. Apart from  penectomy , perhaps the most radical of these is  subincision , in which the urethra is split along the underside of the penis. Subincision originated among  Australian Aborigines , although it is now done by some in the U.S. and Europe.


The most common form of body modification related to the penis is  circumcision : removal of part or all of the foreskin. It is most commonly performed as an  elective procedure  for  prophylactic ,  cultural , or  religious  reasons. [ 54 ]  For infant circumcision, modern devices such as the  Gomco clamp ,  Plastibell , and  Mogen clamp  are available. [ 55 ]  The  ethics of circumcision  in children is a source of  controversy . [ 56 ] [ 57 ]  Among the world's major medical organizations, there is a consensus that circumcision reduces heterosexual HIV infection rates in high-risk populations during penile-vaginal sex. [ 58 ] [ 59 ] [ 60 ] [ 61 ]  There are differing perspectives on the prophylactic efficacy and  cost effectiveness  of circumcision in  developed nations . [ 54 ]   Circumcision plays a significant role  in many of the world's cultures. [ 62 ]  When performed for religious reasons, it is most common among both  Jews  and  Muslims , among whom it is near-universal. [ 63 ]


There are efforts by scientists to  partially or fully regenerate the structures of the human penis . [ 64 ] [ 65 ] [ 66 ]  Patients who can benefit most from this field are those who have congenital defects, cancer, and injuries that have excised parts of their  genitalia . [ 67 ] [ 68 ] [ 69 ]  Some organizations which perform research into, or conduct regeneration procedures, include the  Wake Forest Institute for Regenerative Medicine  and the  United States Department of Defense . [ 68 ] [ 69 ]  The first successful penis  allotransplant  surgery was done in September 2005 in a military hospital in  Guangzhou , China. [ 70 ]  A man at 44 sustained an injury after an accident and his penis was severed;  urination  became difficult as his urethra was partly blocked. A recently brain-dead man, aged 23, was selected for the transplant. Despite  atrophy  of blood vessels and nerves, the  arteries ,  veins , nerves and the corpora spongiosa were successfully matched. But, on 19 September (after two weeks), the surgery was reversed because of a severe  psychological  problem (rejection) by the recipient and his wife. [ 71 ]


In 2009, researchers Chen, Eberli, Yoo and Atala have produced  bioengineered  penises and implanted them on rabbits. [ 72 ]  They were able to obtain  erection  and  copulate , with 10 of 12 rabbits achieving  ejaculation . This study shows that in the future it could be possible to produce artificial penises for replacement surgeries or  phalloplasties . In 2015, the world's first successful penis transplant took place in  Cape Town , South Africa in a nine-hour operation performed by surgeons from  Stellenbosch University  and  Tygerberg Hospital . The 21-year-old recipient, who had been sexually active, had lost his penis in a botched circumcision at 18. [ 73 ]


In  biology ,  Input [ 1 ]   and output [ 2 ]  (I&O) is the measure of  food  and fluids that enter and exit the body. Certain patients with the need are placed on I & O, and if so, their  urinary  output is measured.


With self-toileting patients on I & O, or those who are assisted to a regular toilet or portable commode, a receptacle is placed in the toilet bowl that catches all urine that is put out by the patient. This, in turn, is measured by the nursing staff and recorded prior to its disposal.


If the patient is using a bedpan, the nursing staff member who empties the bedpan measures the urine prior to its disposal.


Urinals usually contain measuring lines providing easy measurement.  Urinals  are also useful for measuring urine from other sources.


Catheters , which are frequently used when it is necessary to measure a patient's output, often have measuring lines on their bags, but these are not considered to be accurate because the bag is floppy. Urine that is emptied from a catheter must be placed in a level container (such as a urinal) in order to be measured.


This  medical treatment –related article is a  stub . You can help Wikipedia by  expanding it .


The  internal urethral sphincter  is a  urethral sphincter  muscle which constricts the  internal urethral orifice . It is located at the junction of the  urethra  with the  urinary bladder  and is continuous with the  detrusor muscle , [ 1 ] [ 2 ]  but anatomically and functionally fully independent from it. [ 3 ]  It is composed of  smooth muscle , so it is under the control of the  autonomic nervous system , specifically the  sympathetic nervous system .


This is the primary muscle for maintaining  continence  of  urine , a function shared with the  external urethral sphincter  which is under  voluntary  control. It prevents urine leakage as the muscle is tonically contracted via  sympathetic  fibers traveling through the  inferior hypogastric plexus  and  vesical nervous plexus . [ 4 ]  Specifically, it is controlled by the hypogastric nerve, predominantly via the  alpha-1 adrenergic receptor . [ 5 ]


During urination, the  preganglionic  neurons of this sympathetic pathway are inhibited via signals arising in the  pontine micturition center  and traveling through the  descending reticulospinal tracts , allowing the muscle to relax. During  ejaculation , the muscle contracts to prevent reflux of  semen  into the  urinary bladder , a phenomenon called  retrograde ejaculation . [ 6 ] [ 7 ]


Spasms of the internal urethral sphincter are associated with penile erection. [ 8 ]  Because the internal urethral sphincter is under involuntary control, it is believed to play a role in  paruresis , in which a person who perceives oneself to be under observation is unable to urinate.


This article incorporates text in the  public domain  from  page 429-431  of the 20th edition of   Gray's Anatomy   (1918)


In  male   anatomy , the  lacuna magna  (also called  Guérin's sinus ) is the largest of several recesses in the roof of the  navicular fossa of the male urethra .


The lacuna magna is a large recess in the roof of the  navicular fossa of the male urethra . [ 1 ]


The  embryological  origin of the lacuna magna is contested. [ 2 ]  However, recent evidence suggests it and the navicular fossa of the male urethra derive from infiltrating  endodermal  cells of the  urethral plate . [ 2 ]


In young males, the presence of the lacuna magna is associated with  painful   urination  ( dysuria ), bloody  urine  ( hematuria ), and bloody spotting of underwear. [ 3 ] [ 4 ]


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Michaelis–Gutmann bodies   (M-G bodies)  are concentrically layered  basophilic   inclusions  found in  Hansemann cells  in the  urinary tract . These are 2 to 10 μm in diameter, and are thought to represent remnants of  phagosomes  mineralized by  iron  and  calcium  deposits. [ citation needed ]


M-G bodies are a  pathognomonic  feature of  malakoplakia , an inflammatory condition that affects the  genitourinary  tract. They were initially discovered in 1902 by  Leonor Michaelis  and Carl Gutmann. [ citation needed ]


Michaelis-Gutmann bodies stain positive for  von kossa  (calcium),  Prussian Blue  (iron), and  PAS diastase stain .


A  natriuretic peptide  is a  hormone  molecule that plays a crucial role in the regulation of the  cardiovascular system .  These hormones were first discovered in the 1980s and were found to have very strong  diuretic ,  natriuretic , and  vasodilatory  effects. There are three main types of natriuretic peptides:  atrial natriuretic peptide (ANP) ,  brain natriuretic peptide (BNP) , and  C-type natriuretic peptide (CNP) . [ 1 ]  Two minor hormones include  urodilatin  (URO) which is processed in the  kidney  and encoded by the same gene as ANP, and  dendroaspis NP (DNP)  that was discovered through isolation of the venom from the green mamba snake. [ 2 ]  Since they are activated during  heart failure , they are important for the protection of the heart and its tissues. [ 1 ]


Additionally, there are three natriuretic peptide receptors:  natriuretic peptide receptor A  (NPR-A), Natriuretic Peptide Receptor-B (NPR-B), and Natriuretic Peptide Receptor-C (NPR-C). NPR-A and NPR-B use  cyclic guanosine monophosphate (cGMP)  as its intracellular messenger. NPR-A binds selectively to ANP and BNP while NPR-B binds selectively to CNP. [ 1 ]  Although initially thought to have no signaling activity, NPR-C is now believed to inhibit  cyclic adenosine monophosphate (cAMP)  using the  Giα subunit  along with activating  phospholipase C-β  using the  Giβγ subunit . The three natriuretic peptides ANP, BNP, and CNP can bind to NPR-C however it has a higher affinity towards ANP and CNP. Natriuretic peptides will lose their activity when degraded by the enzyme  neprilysin  which is found on the plasma membrane. [ 1 ]


The existence of natriuretic peptides was predicted over fifty years ago by key cell biological observations. Atrial cells were found to contain highly developed Golgi networks and  spherical granules , while balloon distension of the  atria  correlated with increased urination in dogs. [ 3 ]  De Bold and colleagues linked these studies and discovered the first natriuretic peptide that works by stimulating renal sodium and water secretion. Shortly after, atrial peptides with natriuretic, diuretic, and/or  smooth muscle  relaxing activity were purified and sequenced. [ 3 ]  The 1980s saw an increase in natriuretic peptide research, particularly due to the 1981 work by de Bold et al., which found that giving rats an extract of rat atrial tissue quickly reduced blood pressure and increased urination. [ 1 ]  To pinpoint the molecule causing this action, various structures that would eventually come to be known as an atrial natriuretic peptide, or ANP, were discovered. Kangawa and Matsuo determined the complete  amino acid sequence  of α-hANP using protein isolated from human atrial tissue. [ 1 ]  They were able to isolate and identify BNP and CNP from  porcine  brain in 1988 and 1990, respectively. [ 1 ]


The first of these hormones is most frequently referred to as atrial natriuretic peptide (ANP), whereas the second hormone, B-type natriuretic peptide (BNP), was formerly known as brain natriuretic peptide but is now more frequently linked to the  cardiac ventricles  of people with heart failure. [ 3 ]  C-type natriuretic peptide (CNP), the third hormone, was isolated from the swine brain and could relax smooth muscle. The three hormones share a similar structural makeup but come from different genes. [ 3 ]  These preliminary findings produced more investigation to establish the genetic makeup and regulatory mechanisms of these molecules.


Natriuretic peptides and their receptors have many different effects on the body, such as controlling  blood pressure  and helping bones grow. Each peptide has its own unique effects and interacts with specific receptors. Scientists have observed these effects by studying mice with specific natriuretic peptides or receptors removed. [ 3 ]


Natriuretic peptides have a wide range of  physiological  effects that include the regulation of blood pressure, fluid and electrolyte balance, and cardiovascular function. [ 1 ]  They are also involved in the regulation of vascular remodeling,  inflammation , and  apoptosis . One of the major clinical applications of natriuretic peptides is the diagnosing and managing of heart failure. Elevated levels of ANP and BNP are commonly found in patients with heart failure and can be used as  biomarkers  for the diagnosis and prognosis of this condition. [ 1 ]


Induction of natriuresis by inhibiting Na+, H+ exchanger in the  proximal tubule , Na+, Cl− co-transporter in the  distal tubule , and Na+ channels in the  collecting duct


Natriuretic and diuretic effects due to increased medullary blood flow


Induction of diuresis due to inhibition of  Arginine vasopressin -induced aquaporin-2 incorporation into collecting ducts' apical membrane


Natriuretic and diuretic effects


Inhibition of cardiac remodeling (hypertrophy and fibrosis)


Suppression of vascular smooth muscle  cell proliferation


Suppression of vascular  fibrosis


Reduction of pulmonary  hypertension /fibrosis


Elevation of capillary hydraulic conductivity


Decrease in cardiac preload and afterload


−  Renin–angiotensin–aldosterone axis


− Sympathetic outflow


− Arginine vasopressin


−  Endothelin


Inhibition of growth factor-mediated  hypertrophy  in  fibroblasts


C-type natriuretic peptide (CNP) primarily interacts with NPR-B, which triggers an increase in the concentration of cGMP in the cell. This process can lead to several physiological effects, such as tissue remodeling, reduction of pulmonary hypertension and fibrosis, and stimulation of long bone growth. [ 1 ]  CNP is highly concentrated in vascular endothelial cells and plays a crucial role in regulating vascular tone through its vasodilatory action. Furthermore, CNP has been shown to have anti proliferative effects on vascular smooth muscle and an inhibitory effect on the migration of human coronary artery smooth muscle cells. [ 1 ]


Studies on mice have helped researchers understand the critical role of ANP in preventing hypertension or high blood pressure. When ANP-deficient mice were studied, they showed signs of hypertension when consuming too much salt. [ 1 ]  Similarly, when NPR-A, a receptor for ANP, was knocked out in mice, they also displayed hypertension and a reduced response to diuretics. This suggests that ANP is essential in regulating blood pressure and fluid balance. [ 1 ]  Interestingly, when NPR-A was knocked out specifically in the endothelial cells lining blood vessels, mice showed increased  plasma  volume, suggesting that ANP may regulate fluid balance by increasing the permeability of blood vessels in these cells. These findings indicate that ANP and its receptor NPR-A are essential in regulating mice's blood pressure and fluid balance. [ 1 ]


Recent advances in the biology of natriuretic peptides (NPs) have led to the developing of "designer" NPs. These peptides have larger surface areas compared to smaller natural molecules, making them better suited for activating specific receptors with minimal off-target effects. [ 2 ]  While inhibiting enzymatic degradation of peptides can boost endogenous peptides, it may not be enough to achieve optimal receptor stimulation. Therefore, designer peptides with specific properties could be a new strategy to improve upon existing therapies. [ 2 ]  Three designer NPs have been bioengineered, tested in cell-based assays and animal models of heart failure, undergone pharmaceutical toxicology studies, and have received FDA approval for clinical studies. [ 2 ]


Natriuretic peptides can block the activity of the  renin-angiotensin-aldosterone system (RAAS) , which regulates blood pressure. Studies have shown that ANP can suppress  renin  secretion and  aldosterone  production. Additionally, natriuretic peptides suppress the  sympathetic nervous system (SNS) , which controls the body's "fight or flight" response. [ 1 ]  The relationship between natriuretic peptides and  vasopressin , a hormone that regulates water balance, has been found through studies that have shown that ANP can suppress vasopressin signaling. Researchers are working on having a better understanding of this relationship. Animal studies show the possibility of using a vasopressin receptor antagonist along with BNP to improve heart function and blood flow. [ 1 ]


B-type natriuretic peptide (BNP) and its pro hormone  NT-proBNP  are especially useful in diagnosing heart failure, as their levels in the blood increase along with the severity of the condition. [ 3 ]  Rapid testing of BNP and NT-proBNP can also help distinguish between shortness of breath due to heart and lung-related causes. Monitoring NT-proBNP levels over time can provide important information about an individual's risk of developing heart failure or cardiovascular disease in the future. [ 3 ]


It can be difficult to tell if someone's having trouble breathing because of heart or lung problems. However, this can often be clarified with tests like X-rays and blood work. [ 3 ]  Rapid testing of BNP and NT-proBNP can also tell if the problem is in the heart or the lungs, though, specific lung problems can also raise NP levels. Due to this, BNP levels can be high for cases other than heart failure. [ 3 ]


The human gene that makes ANP is called NPPA, and it's on chromosome 1 at location 1p36.21. The gene is about two kilobases long and has three parts called  exons  and two called  introns . The  mRNA  from this gene makes a protein called preproANP with 151 parts called amino acids. [ 3 ]  The first 25 parts are removed to create a 126-part protein called proANP which is stored in the atrial granules. When the body needs ANP, Corin (an enzyme) breaks apart proANP to make the active form of ANP, which is 28 amino acids long. [ 3 ]


BNP was first discovered in pig brain tissue but was later found more abundant in the heart (Mukoyama et al. 1991; Mukoyama et al. 1990). The human gene that encodes for BNP is called  NPPB  (GeneID 4879) and is located on chromosome 1 at 1p36.2. In mice, NPPb is found on chromosome 4. [ 3 ]  NPPB has three exons and two introns, and its preproBNP comprises 134 amino acids. This includes a 26 amino acid signal sequence followed by 108 amino acids that contain proBNP. Unlike ANP, the sequence of BNP is not similar across different species. [ 3 ]


The natriuretic peptide CNP was initially discovered in pig brain extracts. Most CNP is found in the brain, although it can also be found in  chondrocytes  and the blood vessel lining cells. The human gene for CNP (NPPC), in contrast to the genes for ANP and BNP, is located on chromosome 2 and consists of just two exons and one intron. [ 3 ]  The CNP gene is also located on chromosome 2 in mice. The 126 amino acids long protein produced by NPPC has a signal sequence of 23 amino acids and then a proCNP segment with 103 amino acids. [ 3 ]


A  penis  ( / ˈ p iː n ɪ s / ;  pl. :  penises  or  penes ) is a male  sex organ  that is used to  inseminate  female or  hermaphrodite  animals during  copulation . [ 1 ] [ 2 ]  Such organs occur in both  vertebrates  and  invertebrates , including humans, but not in all male animals.


The term  penis  applies to many  intromittent organs , but not to all. As an example, the  intromittent organ  of most  Cephalopoda  is the  hectocotylus , a specialized arm, and male spiders use their  pedipalps . Even within the  Vertebrata , there are morphological variants with specific terminology, such as  hemipenes .


The word "penis" is taken from the  Latin  word for " tail ". Some derive that from  Indo-European   *pesnis , and the Greek word πέος = "penis" from Indo-European  *pesos . Prior to the adoption of the Latin word in English, the penis was referred to as a "yard". The  Oxford English Dictionary  cites an example of the word  yard  used in this sense from 1379, [ 3 ]  and notes that in his  Physical Dictionary  of 1684,  Steven Blankaart  defined the word  penis  as "the Yard, made up of two nervous Bodies, the Channel, Nut, Skin, and Fore-skin, etc." [ 4 ]  According to  Wiktionary , this term meant (among other senses) "rod" or "bar".


As with nearly any aspect of the body involved in sexual or  excretory  functions, the penis is the subject of many  slang  words and  euphemisms  for it, a particularly common and enduring one being "cock". See  WikiSaurus:penis  for a list of alternative words for penis.


The Latin word  " phallus "  (from  Greek  φαλλος) is sometimes used to describe the penis, although "phallus" originally was used to describe  representations , pictorial or carved, of the penis. [ 5 ]


The external genital organs appeared in the  Devonian , about 410 million years ago, when  tetrapods  began to abandon the aquatic environment. [ 7 ]  In fact, the necessity to overcome the absence of a liquid phase in which to release the gametes was achieved through the transition to  internal fertilization .


Among amniotes, the development of an erectile penis occurred independently for  mammals ,  squamates  ( lizards  and  snakes ),  testudines  (turtles), and  archosaurs  ( crocodiles  and  birds ).


Over time, birds have lost this organ, with the exception of  Paleognathae  and  Anseriformes . [ 8 ]


The penis is an  intromittent organ  used to transfer  sperm  into the female  genital tract  (i.e.,  vagina  or  cloaca ) for potential  fertilization . The penises of different animal groups are not  homologous  with each other, but were created several times independently of each other in the course of evolution.


An  erection  is the stiffening and rising of the penis, which occurs during  sexual arousal , though it can also happen in non-sexual situations.
During  ejaculation , a series of muscular contractions delivers  semen , containing male  gametes  known as sperm cells or  spermatozoa , from the penis. Ejaculation is usually accompanied by  orgasm .


The last common ancestor of all living  amniotes  (mammals, birds and reptiles) likely possessed a penis. [ 9 ]


Most male birds (e.g.,  roosters  and  turkeys ) have a  cloaca  (also present on the female), but not a penis. Among bird species with a penis are  paleognaths  ( tinamous  and  ratites ) [ 11 ]  and  Anatidae  (ducks, geese and swans). [ 12 ]  The  magpie goose  in the family  Anseranatidae  also has a penis. A bird penis is different in structure from mammal penises, being an erectile expansion of the cloacal wall (in ducks) and being erected by  lymph , not blood. [ 13 ]  It is usually partially feathered and in some species features spines and brush-like filaments, and in a flaccid state, curls up inside the cloaca.


As with any other bodily attribute, the length and girth of the penis can be highly variable between  mammals  of different  species . [ 14 ] [ 15 ]  In many mammals, the penis is retracted into a  prepuce  when not erect. Mammals have either  musculocavernous  penises, which expand while erect, or  fibroelastic  penises, which become erect by straightening without expanding. [ 16 ]   Preputial glands  are present in some prepuces. In  placentals , the  urethra , which is connected to the  vasa deferentia , travels through and exits the penis, thus  both  urine  and semen are expelled from this organ. [ 17 ] [ 18 ]  The  perineum  of  testicond  mammals (mammals without a  scrotum ) separates the  anus  and the penis.


A bone called the  baculum  is present in most placentals but absent in humans, cattle and horses.


In mammals, the penis is divided into three parts: [ 19 ]


The internal structures of the penis consist mainly of cavernous,  erectile tissue , which is a collection of  blood sinusoids  separated by sheets of  connective tissue  (trabeculae).


Canine penises  have a structure at the base called the  bulbus glandis . [ 21 ] [ 22 ]  During copulation, the  spotted hyena  inserts his penis through  the female's pseudo-penis  instead of directly through the  vagina , which is blocked by the false scrotum. The  pseudo-penis  and pseudo-scrotum, which are actually a  masculinized   vulva ,  closely resemble the male hyena's genitalia, but can be distinguished from the male by the female's  greater thickness and more rounded  glans . [ 23 ]   Domestic cats  have barbed penises, with about 120–150 one millimetre long  backwards-pointing spines . [ 24 ]


Marsupials  usually have bifurcated penises [ 25 ]  that are retracted into a preputial sheath in the male's  urogenital sinus  when not erect. [ 26 ]   Monotremes  and  marsupial moles  are the only mammals in which the penis is located inside the cloaca. [ 27 ] [ 28 ]


Male  turtles  and  crocodilians  have a penis, while male specimens of the reptile order  Squamata , which are  snakes  and  lizards , have two paired organs called  hemipenes .  Tuataras  must use their cloacae for reproduction. [ 29 ]  Due to  evolutionary convergence , turtle and mammal penises have a similar structure. [ 30 ]


In some fish, the gonopodium, andropodium, and  claspers  are intromittent organs (to introduce sperm into the female) developed from modified fins. [ 31 ]


Harvestmen  are the only male  arachnids  that  have a penis .


In male  insects , the structure analogous to a penis is known as an  aedeagus . The male copulatory organ of various lower invertebrate animals is often called the  cirrus . [ 32 ]


In 2010, entomologist Charles Linehard described a new genus of  barkflies  called  Neotrogla . Species of this genus have sex-reversed genitalia: females have penis-like organs called gynosomes that are inserted into vagina-like openings of males during mating. [ 33 ]  A similar female structure has also been described in the closely related  Afrotrogla . [ 34 ]  Scientists who study these insects have occasionally called the gynosome a "female penis" [ 35 ] [ 36 ]  and insisted to drop the definition of penis as "the male copulatory organ". [ 37 ]  Motivations for using the term "female penis" include that such a term "is easier to understand and much more eye-catching" [ 38 ]  and that the gynosome have "analogous features" with male penises. [ 37 ]  Meanwhile, critics have argued that it does not fit the intromittent organ definition of "a structure that enters the female genital tract and deposits sperm". [ 39 ]


Pizzles are represented in  heraldry , where the adjective  pizzled  (or  vilené [ 40 ] ) indicates that part of an animate  charge 's anatomy, especially if coloured differently.


A  pig bladder  or  pig's bladder  is the  urinary bladder  of a  domestic pig , similar to the human urinary bladder.  Today, this  hollow organ  has various applications in  medicine , and in traditional cuisines and customs.  Historically, the pig bladder had several additional uses, all based on its properties as a lightweight, stretchable container that could be filled and tied off.


The pig bladder has several traditional ceremonial uses in Europe.  It is traditional during the festival  Fasching  in  Bad Aussee  to brandish inflated pig bladders on sticks.  Similarly, in  Xinzo de Limia , Spain, inflated pig bladders are carried during  Carnival .  See also  Clown society  and  Jester  and  Gigantes y cabezudos  and  Vejigante .


In traditional Germanic communities a public  Schlachtfest  (of a pig) is announced by hanging the pig's inflated bladder in front of the host establishment.  The bladder is used as a  casing  for several traditional food items, including the  sausages  known as  ventricina  and  sobrassada .


Historically the pig bladder was used in sports, as the airtight membrane ("bladder") inside a  football [ when defined as? ] .  In the early 19th century the inventor  William Gilbert  used pig bladders in the manufacture of  rugby balls .  Decades later,  Richard Lindon  did the same.  (See also  Mob football ,  Medieval football , and  La soule .)


For centuries before the invention of the paint tube, artists used to store their paints in pig bladders. When the artist was ready to use the paint, they would puncture a hole in the bladder and squeeze out the desired amount of paint. They would have to mend the hole when finished and the whole process was quite messy.  [ 1 ]  The  oil paint  tube was invented in 1841, as the primary packaging of paints for transport and storage. [ 2 ]


In the  bian lian  ("face changing") style of Chinese opera, painted pig bladders were used as face masks.


The  reniculate kidney  is a multilobed  kidney  found in  marine  and  aquatic mammals  such as  pinnipeds  ( seals ,  sea lions  and  walruses ) and  cetaceans  ( dolphins  and  whales ) but absent in terrestrial mammals except  bears . [ 1 ]   Kidneys of this  morphology  have increased surface area for removing toxins from the body more efficiently than a non-lobed kidney.


The reniculate structure in cetaceans and pinnipeds does not result in a greater concentrating ability. While many marine mammals can concentrate their urine beyond the concentration of sea water, [ clarification needed  -  discuss ]  only  sirenians  and  otters  can reach levels of  Na +  and  Cl −  concentrations similar to sea water, making it possible for them to consume salt water without losing fresh water. However, pinnipeds and cetaceans typically regulate their water balance by metabolism and only drink sea water occasionally to maintain salt balance. In contrast,  sea otters  and  manatees  often drink sea and fresh water. [ 1 ]


The  trigone  (also known as the  vesical trigone ) [ 1 ]   is a smooth triangular region of the internal  urinary bladder  formed by the two  ureteric orifices  and the  internal urethral orifice .


The area is very sensitive to expansion and once stretched to a certain degree, stretch receptors in the urinary bladder signal the  brain  of its need to empty. The signals become stronger as the bladder continues to fill.


Embryologically, the trigone of the bladder is derived from the caudal end of  mesonephric ducts , which is of  mesodermal  origin (the rest of the bladder is  endodermal ). In the female the mesonephric ducts regress, causing the trigone to be less prominent, but still present.


The region can be infected causing  trigonitis  to persist.


The  ureters  are tubes composed of  smooth muscle  that transport  urine  from the  kidneys  to the urinary  bladder . In an adult human, the ureters typically measure 20 to 30 centimeters in length and about 3 to 4 millimeters in diameter. They are lined with urothelial cells, a form of transitional  epithelium , and feature an extra layer of smooth muscle in the lower third to aid in  peristalsis .
The ureters can be affected by a number of diseases, including  urinary tract infections  and  kidney stone .  Stenosis  is when a ureter is narrowed, due to for example chronic inflammation.  Congenital abnormalities  that affect the ureters can include the development of two ureters on the same side or abnormally placed ureters. Additionally, reflux of urine from the bladder back up the ureters is a condition commonly seen in children.


The ureters have been identified for at least two thousand years, with the word "ureter" stemming from the stem  uro-  relating to  urinating  and seen in written records since at least the time of  Hippocrates . It is, however, only since the 1500s that the term "ureter" has been consistently used to refer to the modern structure, and only since the development of  medical imaging  in the 1900s that techniques such as  X-ray ,  CT , and  ultrasound  have been able to view the ureters. The ureters are also seen from the inside using a flexible camera, called  ureteroscopy , which was first described in 1964.


The ureters are tubular structures, approximately 20–30 cm (8–12 in) in adults, [ 1 ]  that pass from the  pelvis  of each kidney into the bladder. From the renal pelvis, they descend on top of the  psoas major  muscle to reach the  brim of the pelvis . Here, they cross in front of the  common iliac arteries . They then pass down along the sides of the pelvis and finally curve forward and enter the bladder from its left and right sides at the back of the bladder. [ 2 ]  The ureters are 1.5–6 mm (0.06–0.24 in) in diameter [ 1 ]  and surrounded by a layer of  smooth muscle  for 1–2 cm (0.4–0.8 in) near their ends just before they enter the bladder. [ 2 ]


The ureters enter the bladder from its back surface, traveling 1.5–2 cm (0.6–0.8 in) before opening into the bladder at an angle on its outer back surface at the slit-like  ureteric orifices . [ 2 ] [ 3 ]  This location is also called the vesicoureteric junction. [ 4 ]  In the contracted bladder, they are about 25 mm (1 in) apart and about the same distance from the  internal urethral orifice ; in the distended bladder, these measurements may be increased to about 50 mm (2 in). [ 2 ]


A number of structures pass by, above, and around the ureters on their path down from the kidneys to the bladder. [ 2 ]  In its upper part, the ureter travels on the  psoas major muscle  and sits just behind the  peritoneum . As it passes down the muscle, it travels over the  genitofemoral nerve . The  inferior vena cava  and the  abdominal aorta  sit to the midline of the right and left ureters, respectively. [ 2 ]  In the lower part of the abdomen, the right ureter sits behind the lower  mesentery  and the  terminal ileum , and the left ureter sits behind the  jejunum  and the  sigmoid colon . [ 2 ]  As the ureters enter the pelvis, they are surrounded by connective tissue, and travel backward and outward, passing in front of the  internal iliac arteries  and  internal iliac veins . They then travel inward and forward, crossing the  umbilical ,  inferior vesical , and  middle rectal arteries . [ 2 ]  From here, in males, they cross under the vas deferens and in front of the  seminal vesicles  to enter the bladder near the trigone. [ 2 ]  In females, the ureters pass behind the  ovaries  and then travel in the lower midline section of the  broad ligament of the uterus . For a short part, the  uterine arteries  travel on top for a short (2.5 cm (1 in)) period. They then pass by the  cervix , traveling inward towards the bladder. [ 2 ]


The arteries which supply the ureter vary along its course. The upper third of the ureter, closest to the kidney, is supplied by the  renal arteries . [ 2 ]  The middle part of the ureter is supplied by the  common iliac arteries , direct branches from the  abdominal aorta , and  gonadal arteries ; [ 1 ]  the gonadal arteries being the  testicular artery  in men and the  ovarian artery  in women. [ 2 ]  The lower third of the ureter, closest to the bladder, is supplied by branches from the  internal iliac arteries , mainly the  superior  and  inferior vesical arteries . [ 1 ]  The arterial supply can be variable, with arteries that contribute include the  middle rectal artery , branches directly from the aorta, [ 1 ]  and, in women, the uterine and vaginal arteries. [ 2 ]