Consider a section of capillary in which carbon dioxide (CO2) is being taken up
ID: 185600 • Letter: C
Question
Consider a section of capillary in which carbon dioxide (CO2) is being taken up from the tissues into the blood. Some of the CO2 that enters the blood is converted into bicarbonate (HCO3) through a reaction with water. In the diagram below, assume that [C02] is in mol/L, V is L/s, and CO2 is in mol/s. The dashed lines indicate the system boundary Write a mole balance equation for CO2 in the capillary. Explain what all of your terms represent. tissue CO2aiffusea blood blood [CO2larterialI -T--. [CO2]venousExplanation / Answer
Carbon dioxide diffuses out of the tissues and into the blood, where it is dissolved in the plasma. While some of the carbon dioxide remains dissolved in the plasma, most carbon dioxide diffuses into our red blood cells. In the red blood cell, some carbon dioxide binds to hemoglobin, forming what we call carbaminohemoglobin.
Most of the carbon dioxide, however, is converted into bicarbonate. Carbonic anhydrase is an enzyme in the red blood cells that quickly converts carbon dioxide and water into bicarbonate and hydrogen ions. The equation for this reaction is as follows: Carbon dioxide and water are converted to bicarbonate and hydrogen ions, where HCO3- is bicarbonate and H+ is hydrogen ion.
CO2 + H2O <- -> HCO3- + H+
While this reaction is reversible, as indicated by the double arrows, the high concentration of carbon dioxide pushes the reaction to the right. You might be thinking, 'What does this have to do with carbon dioxide transport?' Hold on for a moment; this gets interesting fast. Bicarbonate diffuses into the plasma, where it is used as a much-needed pH buffer. Yes, that's correct; the cellular waste product carbon dioxide plays a vital role in maintaining pH balance. Oh, but that's not all. Carbon dioxide does even more for us. Remember the hydrogen ion produced along with bicarbonate in the red blood cell. That hydrogen ion binds to hemoglobin, which causes the oxygen to be released from the hemoglobin. That released oxygen can then enter into the cells and be used to make the much-needed ATP.