Question

Cellular respiration requires O₂ as one reactant and creates CO₂ as one of the products.

A. Explain how partial pressure differences between the cell and the capillary result in the movement of those gases between the cell and the capillary.

B. Explain how CO₂ and O₂ are carried in the blood (i.e. where in the blood is most of the CO₂? Where in the blood is most of the O₂?)

C. Deoxygenated blood leaves the capillary on the venule end and then enters into veins> Veins ultimately lead back to the heart. Blood enters the human heart going first to right atrium, then the right ventricle, and then through the pulmonary artery to the lungs.Explain what happens to CO₂ and O₂ where the capillaries and alveoli meet in the lungs.

Answer 1

1. The simple diffusion of gases depends upon mainly 3 things

1. pressure gradient

• Partial pressure of O2 in tissues is 40mmHg and that in the capillary is 95mmHg whereas partial pressure of CO2 in tissues is 45mmHg and that of the capillary is 40mmHg.

2. solubility of the gas

3. The thickness of the membrane - tissue membrane is thicker than the capillary membrane.

• The gradient present for O2 in the opposite direction as that of CO2. The amount of solubility of O2 is 22 - 25 times much lesser than that of CO2. As the partial pressure of O2 which is returning from systemic arteries is greater than that of the cells, O2 freely diffuses into body tissues. The partial pressure of CO2 in the systemic vein is less than that of tissues thus CO2 diffuses out of the tissue.
• Thus by simple diffusion O2 can easily enter into tissues and CO2 can be removed from them.

2. As CO2 is a waste product the elimination must be done. Hence they are transported from the tissue into the blood via plasma and RBC.

• The transport through the plasma is about 10 % and mainly occurs in 3 ways.

1. Physical dissolved form - solubility factor is 0.03 about 5 - 9 % is transported in this form.

2. Bicarbonate form by undergoing hydration about 4 % transport occurs through this form. The reaction is very slow as it lacks carbonic anhydride

3. As carbiaminogroup only a negligible amount of CO2 is transported by combining with the NH group of plasma protein.

• In RBC it is by 3 forms physically dissolved form is very negligible. The second is by forming bicarbonate. And thirdly by forming carbaminoHb.
• The transport through RBC is 90%

1. In the physically dissolved form - the solubility factor is just 0.025 for 25 C. The CO2 transport through this process is negligible.

2. As carbiaminoHb about 20% are transported by this form, this complex is made by combining CO2 with Hb made by RBC, but this is very unstable.

3. By forming bicarbonate or isohydric transport about 70% are transported by this method here the hydration which resulted in bicarbonate is made faster by carbonic anhydrase enzyme

• O2
• O2 is mainly transported in 2 ways

1. In plasma

2. In RBC

• plasma- mainly in dissolved form.
• RBC - HbO2 in the RBC dissociate to form O2 and Hb and the O2 enters the tissue.
• mostly O2 found in the alveolar air of the body about a partial pressure of 104mmHg
• CO2 concentration is high in tissues with a partial pressure of 45mmHg are observed here.

3. The partial pressure of CO2 in the alveoli is about 40mmHg and that of PO2 is 104 mmHg, whereas in capillaries PO2 is 95 mmHg and PCO2 is 45 mmHg means PO2 is higher and PCO2 is lower in the alveoli that can cause dissociation of CO2 from carbiaminoHb.CO2 can get into alveoli through plasma or RBC. In plasma some is in dissolved form others by dehydration by dissociation of bicarbonate. Through RBC some can enter into a capillary as carbiamino Hb and others by dissociate=ing bicarbonate mediated by carbonic anhydrase.

O2 can easily be diffused out and can transport through dissolved in plasma and also by combining with HHb present in RBC to form HbO2.