Why does air need to be moist before reaching the lungs?
931320
So that co2 will dissolve in the most air as carbonic acid and be exhaled.
223737
When air is put under pressure it compresses, so more air fits into smaller spaces. The air at sea level is much denser than the air at 20,000 feet, which is why airplane cabins are pressurized. Humans have evolved to handle the air pressure at or near sea level, but cannot breathe the much thinner air found high up in the atmosphere.\n\nWater does not compress under pressure, so you cannot fit more water into a smaller space by exerting pressure. Therefore, as one descends into water and pressure increases due to the weight of the water above you, the force increases to levels that compress your lungs and torso, eventually stopping the expansion of your chest and crushing your ribs.
1163893
It is because the continuous flow of air can dehydrate an erode the mucosa. so the body has a mechanism to rehydrate the mucosa so it wont be damaged by the air flow\nthe way in which the body does this is by opening the blood flow through one nostril causing a normal swelling of the mucosa, this swelling prevents air from passing through there and at the same time provides water to the cells. then the same thing  happens on the other side.\nThe open side has a little less blood flow than the closed side. \nthey switch almost every 20 to 30 minutes \nbesides this the blood flow is designed to warm the air and humidify it although most of this humidification will take place in the trachea (windpipe) where there is water in vapor form.
94856
If the air is dry or cold, then when you inhale, the moisture gets taken from your lungs into the air (since hot air can hold more moisture - when the air heats in your lungs it needs moisture and takes it).  When you breathe a lot more, like when you exercise, the lungs dry out more than normal.  This drying of the lungs is normally felt as a painful burn, and it's why when people run in cold weather they normally try to breathe through their noses.  The passage through the sinuses is longer, and gives the air more time to heat up and absorb moisture on the way down to the lungs instead of in the lungs themselves.  Try to pay attention and always breathe in through your nose while exercising.  See if this helps.  If it does, and you work out at home, then you could try to get a humidifier.
29859
The tissues and cells of creatures that inhabit the deep oceans are filled with fluid and thus air space is significantly minimized . Air is subject to compression, whereby a fluid such as water cannot be compressed.\n\nWithout internal compression, the creatures have negated the potential external pressure of the depths.
1102244
I think it's harder to breath when the humidity is high. The air just feels so thick.
479744
You don't, it just doesn't evaporate like it would in non-humid conditions.  Its all about the movement of water, and if the air is already very dense with water particles (ie. humidity) then the liquid on your skin is less inclined to enter the air.  But in very dry conditions, the water on your skin evaporates quickly and this cools you down.
580853
Great answers - basically, lack of moisture in the air.\n\nFor some great pictures:\n\nhttp://www.coolantarctica.com/gallery/Antarctica_gallery_home.htm
1090299
Lung\nFrom Wikipedia, the free encyclopedia\n\nThe lungs flank the heart and great vessels in the chest cavity. (Source: Gray's Anatomy of the Human Body, 20th ed. 1918.)\n\nThe lungs flank the heart and great vessels in the chest cavity. (Source: Gray's Anatomy of the Human Body, 20th ed. 1918.)\nAir enters and leaves the lungs via a conduit of cartilaginuous passageways — the bronchi and bronchioles. In this image, lung tissue has been dissected away to reveal the bronchioles. (Source: Gray's Anatomy of the Human Body, 20th ed. 1918.)\n\nAir enters and leaves the lungs via a conduit of cartilaginuous passageways — the bronchi and bronchioles. In this image, lung tissue has been dissected away to reveal the bronchioles. (Source: Gray's Anatomy of the Human Body, 20th ed. 1918.)\n\nThe lung is the essential organ of respiration in air-breathing vertebrates. Its principal function is to transport oxygen from the atmosphere into the bloodstream, and to excrete carbon dioxide from the bloodstream into the atmosphere. This it accomplishes with the mosaic of specialized cells that form millions of tiny, exceptionally thin-walled air sacs where gas exchange takes place. Lungs also have nonrespiratory functions.\n\nMedical terms related to the lung often begin with pulmo-, from the Latin pulmonarius ("of the lungs"), cognate with the Greek pleumon ("lung").\n\nRespiratory function\n\nEnergy production from aerobic respiration often requires oxygen and produces carbon dioxide as a by-product, creating a need for an efficient means of oxygen delivery to cells and carbon dioxide excretion from cells. In smaller organisms, such as single-celled bacteria, this process of gas exchange can take place entirely by simple diffusion. In larger organisms, this is not possible; only a small proportion of cells are close enough to the surface for oxygen from the atmosphere to enter them through diffusion. Two major adaptations made it possible for organisms to attain great multicellularity: an efficient circulatory system that conveyed gases to and from the deepest tissues in the body, and a large, internalised respiratory system that centralized the task of obtaining oxygen from the atmosphere and bringing it into the body, whence it could rapidly be distributed to all tissues via the circulatory system.\n\nIn air-breathing vertebrates, respiration occurs in a series of steps. Air is brought into the animal via the airways — in reptiles, birds and mammals this often consists of the nose; the pharynx; the larynx; the trachea; the bronchi and bronchioles; and the terminal branches of the respiratory tree. The lungs of mammals are a rich lattice of alveoli, which provide an enormous surface area for gas exchange. A network of fine capillaries allows transport of blood over the surface of alveoli. Oxygen from the air inside the alveoli diffuses into the bloodstream, and carbon dioxide diffuses from the blood to the alveoli, both across thin alveolar membranes. The drawing and expulsion of air is driven by muscular action; in early tetrapods, air was driven into the lungs by the pharyngeal muscles, whereas in reptiles, birds and mammals a more complicated musculoskeletal system is used. In the mammal, a large muscle, the diaphragm (in addition to the internal intercostal muscles), drive ventilation by periodically altering the intra-thoracic volume and pressure; by increasing volume and thus decreasing pressure, air flows into the airways down a pressure gradient, and by reducing volume and increasing pressure, the reverse occurs. During normal breathing, expiration is passive and no muscles are contracted.. [\n\nNonrespiratory functions\n\nIn addition to respiratory functions such as gas exchange and regulation of hydrogen ion concentration, the lungs also:\n\n    * influence the concentration of biologically active substances and drugs used in medicine in arterial blood\n    * filter out small blood clots fo
963259
Because we have an intrinsic protective mechanism that prevents lung collapse which could cause a lot of harm and pain to ourselves.  PEEP stands for positive end expiry pressure which holds our lungs slightly open at the end of a breath.  This allows for the exchange of carbon dioxide/oxygen and prevents damage caused by lung collapse.  However, most of us can expire a lot more than we think we can.  If you breathe out and when you think you have finished your breath breathe out again you can normally get rid of a lot more!
311098
Not very much.  The water pressure on your body would prevent you from being able to bring in air that is at normal atmospheric pressure.  You need a compressor on the surface and a hose to breath from.
80795
your lil lungs keep you breathing, right.\nas you gain weight, you put pressure on them, making it harder for them to expand and help pump blood to the heart. ruining everything in your body basicslly
925762
Your lungs inflate because your chest expands (intercostal muscles flexing) and the diaphram flexes. This creates negative pressure inside the pleural cavity and causes the lungs to inflate (the actions of the chest wall and diaphragm essentially creates a vacuum and air tries to enter through the nasal or oral cavities, to reduce the vacuum)
417288
Moisture in the air. Scientific meaning? Humid conditions.\nMythical? Don't know.
441637
Are you in airconditioning all the time? That will do it, use a moisturiser on a regular basis, and drink plenty of water.
510672
It's a condition in which air leaks into the space between the lungs and the chest wall.  It is serious because it leads to lung collapse and needs to be treated.  The treatment is to insert a thin tube into that space - called "the pleural space" that is in turn attached to a device that reinflates the lungs and keeps them that way as the leak heals.  Yes, it's a bit uncomfortable, but so is dying of asphyxia!
1134763
I would venture to guess that it is because your tubes in your lungs get smaller when you are cold.  This forces whatever mucus in your lungs be more in the way of your breathing, so you have to cough.