Gas Exchange

[jdla]

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I don't understand how oxygen and carbon dioxide move through the body.

Can someone explain?

 

[RSAgator]

It may be a bit more helpful if you ask some more specific questions. How in depth of an answer do you want? =)

 

[tncekm]

In short, oxygen travels over large distances in the body by binding to hemoglobin, which is located in red blood cells. Oxygen can also be stored in myoglobin in the muscles, and will travel over short distances by simple diffusion.

Carbon dioxide travels in the blood largely as bicarbonate ion. Inside of the red blood cells there is an enzyme called carbonic anhydrase that catalyzes the reaction CO &#8322; + H&#8322;O <--> H&#8314; + HCO&#8323;&#8315; (and also <--> 2H&#8314; + CO&#8323;&#178;&#8315😉. Most of the carbon dioxide travels in red blood cells as bicarbonate ion. Some bicarbonate ion will stay be in the plasma, but most isn't. Some carbon dioxide can also bind to hemoglobin (not to the same sites as oxygen, however) and travel through the body bound to hemoglobin.

 

[jdla]

It may be a bit more helpful if you ask some more specific questions. How in depth of an answer do you want? =)

Okay

I understand why oxygen diffuses from the lungs to the capillaries and carbon dioxide diffuses into the alveoli. The oxygen moves from a high pressure gradient to a lower pressure gradient. Once this occurs, where does the oxygen and carbon dioxide diffuse to.

146-147 EK Bio.

 

[tncekm]

Its transported via the vascular system to tissues that are high in carbon dioxide and low in oxygen. When hemoglobin is exposed to high carbon dioxide (low pH) the oxygen dissociation curve "shifts the to the right" and oxygen is dumped off in these capillaries where it will diffuse into the cells which need it (and will be used for aerobic respiration). The carbon dioxide will diffuse into the RBC and be carried via the venous portion of the vascular system to the lungs to be expelled.

 

[RSAgator]

Okay

I understand why oxygen diffuses from the lungs to the capillaries and carbon dioxide diffuses into the alveoli. The oxygen moves from a high pressure gradient to a lower pressure gradient. Once this occurs, where does the oxygen and carbon dioxide diffuse to.

146-147 EK Bio.

Essentially carbon dioxide is a by product of metabolism. Cells produce carbon dioxide in the citric acid cycle, and the carbon dioxide has to be exported out of the cells and subsequently out of the body because we can use it for very little. The CO2 diffuses into the blood, but as a gas it is not very soluble in blood and so most of it is converted into bicarbonate, which is soluble in the blood. The bicarbonate travels in the blood to the lungs where it is converted back into CO2 and diffuses out of the lungs.

Oxygen is necessary for many cellular activities, particularly aerobic metabolism. For one thing, oxygen is used in the electron transport chain in order to produce energy from NADH/FADH2. Oxygen enters the lungs where it is bound by hemoglobin. Hemoglobin can bind 4 molecules of oxygen, which bind cooperatively. This means that after the first molecule binds to hemoglobin, it induces a conformational shift in the hemoglobin molecule (hemoglobin is a protein) which makes it easier to bind to more oxygen (at the other 3 spots). The hemoglobin (which is located in red blood cells) then moves through the rest of the body. In areas where there is a low oxygen concentration, the hemoglobin essentially unloads the oxygen into the tissue where it is generally picked up by certain molecules in the cell, usually metals such as iron cations (Fe3+). Here it will perform its designated function.

Look up the bohr shift as well, it's an important concept in circulatory gas exchange.