Blood gases

Question 1

Which blood gas contributes the most to blood pH

Answer 1

CO2.

There is 3x as much CO2 than O2 in arterial blood. It is more soluble than oxygen and reacts chemically with water.

Question 2

Respiratory and renal buffers in the human body

Answer 2

Respiratory: If the body produces acid, H+ reacts with HCO3- ions to form CO2. This is breathed out, restoring pH (rapid)

Renal: If pCO2 is too high kidneys excrete less HCO3-. The [HCO3} is raised restoring pH. (slow)

Question 3

Reactions of CO2 in the red cell

Answer 3

The high pCO2 in intersitial fluid drives CO2 from the tissue into the blood. A small amount is dissolved in the plasma but most diffuses into the red cell where it forms carbonic acid or carbaminohaemoglobin.

CO2 reacts with water to form carbonic acid, which dissociates into H+ and HCO3-.

H+ binds to Hb, HCO3- moves out of the cell and Cl- comes in to maintain electroneutrality.

Question 4

Haldane effect

Answer 4

Increased oxygenation of haemoglobin promotes dissociation of carbon dioxide and hydrogen ions by modifying the quaternary structure.

Question 5

Bohr effect

Answer 5

Oxygen is released more easily in the tissues where pH is more acidic and there is a higher CO2 concentration