CO2 Carriage Flashcards
In what three forms is CO2 carried in the blood?
- Dissolved CO2
- Carbamino compounds
- Bicarbonate ions
How much is carried as dissolved CO2?
Dissolved CO2 accounts for 10% of all CO2 carried. It is 10x more soluble than O2; the amount of CO2 reflects the PaCO2.
How much is carried as Carbamino compounds?
Carbamino compounds account for 10% of CO2 carried. They are formed by reactions of carbon dioxide with amine groups of proteins. Most abundant Carbamino compound is carbaminohaemoglobin which occurs in deoxyhaemoglobin. CO2 is carried by haemoglobin but bonds to the glob in chains rather than the haem.
What percentage is of carbon dioxide is carried as bicarbonate ions?
80% of carbon dioxide is carried as bicarbonate ions. They are formed by:
CO2 + H2O H2CO3 H+ + HCO3-
Which occurs slowly in plasma. This reaction is catalysed by carbonic anhydrase. The dissociation of carbonic acid is spontaneous,
Carbonic acid is formed in which cell? What does this contribute to?
Carbonic acid is formed the red blood cells and dissociates into bicarbonate ions and H+. The H+ stays in the cell and contributes to the Bohr effect while the bicarbonate diffuses into the plasma. Cl- moves in to the cell to balance the loss of charge.
Describe the haldane effect.
The haldane effect promotes the excretion of O2. Oxygenated haemoglobin is more acidic than deoxygenated haemoglobin. During the passage of blood through the lungs oxygen is taken up making haemoglobin more acidic. This promotes the dissociation of H+ and formation of carbon dioxide via:
H+ + HCO3- CO2 + H2O = release of CO2 into the lungs which is then expired.
What is myoglobin?
Myoglobin is an oxygen and iron binding protein found in muscle. It is structurally similar to haemoglobin. It is made up of an equivalent of one subunit of the haemoglobin molecule. It contains one globin chain and one haem group. But the globin chain it contains is different to that found in haemoglobin. It has s higher affinity for oxygen than haemoglobin. It’s dissociation curve is to the left of that of haemoglobin.
What is the function of myoglobin?
Myoglobin facilitates the diffusion of oxygen from plasma membrane to mitochondria. It keeps a continuous oxygen flow during muscle contraction. To some extent it acts as a store but doesn’t hold large amount of oxygen- enough for one or two heart beats.
Describe the carriage of nitrogen in body fluids.
Nitrogen is half as soluble as oxygen in water. It has an atmospheric pressure 4x that of oxygen.
What is caisson disease?
Caisson disease also known as the bends is common among divers. The solubility of nitrogen increases at higher pressures. There is more of it in solution and when the pressure decreases as on ascent from diving, it is released. Slower ascent allows equilibrium to occur. The smaller amounts of nitrogen released can be eliminated safely.
How is co2 removed from tissues?
It moves down its diffusion gradient from respiring tissues to blood.
