Well, I have a question that might sound a little out of context. But I am quite curious about it. Just the other day I was helping my son with his EVS chapter-Air we breathe. My question is that if the air we breathe contains many other gases (apart from oxygen) then how does our body take in only oxygen. In other words, how does it filter other gases?

Simple one word answer is because of a natural chemical property of hemoglobin in red blood cells ( Erythrocytes). Although oxygen dissolves in blood, only a small amount of oxygen is transported this way. Only 1.5 percent of oxygen in the blood is dissolved directly into the blood itself. Most oxygen, 98.5 percent, is bound to a protein called hemoglobin and carried to the tissues. Now comes to the question why no other gases taken by the body.... When carbon dioxide is in the blood, it reacts with water to form bicarbonate (HCO3?) and hydrogen ions (H+). As the level of carbon dioxide in the blood increases, more H+ is produced and the pH decreases. The increase in carbon dioxide and subsequent decrease in pH reduce the affinity of hemoglobin for oxygen. So again oxygen absorption will be in the higher level by HB and the process will go on. read less

Really a good question.Actually ther are many gases in the air we breathe but we have alveoli in our lungs where exchange of gases takes place through the process of diffusion . our rbc contain a pigment called haemoglobin which reacts with very few elements and compounds. it forms a temporary compounds with oxygen and carbon dioxide and some permanent compounds with carbon monoxide. so only oxygen forms a temporary compound with haemoglobin at alveoli and again diffused at the place of each cell it should be transferred and carbon dioxide is again brought back to alveoli in the same process. so other gases dont react with haemoglobin so they are given out during exhalation. read less

Breathing Gas Swapping out the nitrogen isn’t uncommon, and sometimes necessary in certain circumstances. For instance, SCUBA divers who have to dive extremely deep will swap out the nitrogen for a helium + oxygen combo. This is due to the increased pressure divers endure when deep diving – pressures which cause nitrogen to become a narcotic when introduced into a person’s bloodstream. This phenomenon is known as “Nitrogen Narcosis“. The effects of nitrogen narcosis on the human body are very similar to that of alcohol. Unfortunately, when your 100 feet underwater and intoxicated, it’s usually a dangerous and deadly situation. Divers replace the nitrogen in their tanks with helium to remove that risk. helium nitrogenAny potential gas we would want to use as a nitrogen replacement would have to be inert or mostly inert. Being inert means it wouldn’t react or undergo chemical reactions within our body. However, even inert gases have a narcotic potential when breathed, and that potential directly corresponds to each elements mass. While hydrogen has the lowest narcotic potential, its use is limited in diving because it becomes explosive when the oxygen mixture exceeds 4%. Neon gas is also used for the same reasons as helium but is much more expensive. This relegates its use for times when a diver needs to constantly communicate as the gas does not distort a person’s voice as helium does. What About Other Inert Gasses? Noble gases like Xenon are not used because most are not sufficiently inert. Xenon gas has a strong effect on the human brain – it acts as a powerful anaesthetic. And it’s quite an effective one at that. Doctors and surgeons would love to be able to use it to keep people unconscious during surgery but thanks to the cost of production, its use in the medical field is limited. Xenon gas is also used in light bulbs, MRI machines as a contrast agent, lasers and even as propellant in cutting edge ion drives for space propulsion. Argon gas could technically be used, but since it is 2x more narcotic than nitrogen, its use is limited to industrial and scientific research. Argon is also extremely expensive. Any benefits it could provide would be outweighed pretty heavily by its disadvantages. read less

when we inhale air, we breathe in a lot more than just oxygen and gases. a lot of dust particles are also inhaled, and this means that there needs to be some sort of filtering system to keep the air we breathe clean enough to be absorbed by the body. this filter exists in the form of millions of little finger-like projections called cillia in the windpipe (which is basically rings of cartillage. every so often, the cilia send up what they filter to the oesophagus (the tube that brings down food to your stomach) and that's why you clear your throat or swallow (to get rid of that excess filtered material). this then travels down the oesophagus and into your stomach where acids will kill any external bacteria that your white blood cells haven't already picked up on. anyway, the lungs, much the same way, have a filtering system inside them called the alveoli. these tiny clusters take in only oxygen and what is useful to you and send them into capillaries. the rest of the air that you breathe in, including nitrogen and carbon dioxide, is expired (exhaled or breathed out) by you. the deeper your breathing, the more oxygen enters the lungs. but at the same time, the deeper you breathe, the more carbon dioxide gets into the lungs and the harder it is for cilia to filter out dust. that's why you cough read less

When the air comes in contact, hemoglobin reacts only with oxygen present in the air. That is the normal procedure of extracting O2 out of the air just as Mr. Monu answered... but if Carbon Monoxide is present in the air, then also CO reacts with hemoglobin.. but that can be fatal for us. Hence, oxygenated air is called fresh air and air with CO is polluted air for us... We can breathe both, so I added this info. read less