Lecture 19: O2 and CO2 TRANSPORT Flashcards
How is oxygen carried in the blood?
Dissolved in the plasma and bound to haemoglobin in RBC’s (most effective)
How much oxygen is dissolved in a litre of blood?
3mL so about 15mL in body but we need about 250mL/min
What does oxygen do?
Form an easily reversible combination with Hb to give oxyhaemoglobin
What does binding of oxygen depend on?
The partial pressure of oxygen
What is haemoglobin saturation?
The percentage of heme units containing bound oxygen at any given moment
What is the average partial pressure of oxygen of blood entering the systemic circuit?
High (95-100mmHg)
What is the average partial pressure of oxygen of blood leaving peripheral tissues (venous blood)?
Moderate (40-50mmHg)
What is the average partial pressure of oxygen in active muscle tissue?
Low (10-20mmHg)
What is the shape of the oxygen haemoglobin saturation curve?
Sigmoidal, not linear
What happens when the slope of the saturation curve is steep?
A very small change in partial pressure of oxygen in the blood will result in a large change in the amount of oxygen bound to haemoglobin or released from oxyhemoglobin. oxygen binding affinity is decreased
What happens in the flat part of the saturation curve?
Large changes in partial pressure of oxygen will result in small changes in the percentage of oxyhaemoglobin
What does the curve vary with?
Conditions to improve oxygen uptake and delivery
What shifts the curve right?
Reduced pH (Bohr’s effect), increased partial pressure of carbon dioxide and increased temperature
What shifts the curve left?
Increased pH (Bohr’s effect), decreased partial pressure of carbon dioxide and decreased temperature
How is carbon dioxide transported?
Dissolved in plasma (7%), as bicarbonate (70%) and combined with proteins as carbamino compounds (23%)
What does 70% if carbon dioxide do?
It is converted to carbonic acid by activity of enzyme carbonic anhydrase
What do the carbonic acid molecules do?
Immediately dissociate into a hydrogen ion and bicarbonate ion
What do the hydrogen ions do?
Bind to haemoglobin forming HbH+
What do the bicarbonate ions do?
Move into plasma in exchange for chloride ions (Cl-). Process called the chloride shift
What do we need to maintain?
Normal levels of oxygen and carbon dioxide for metabolic and biochemical stability
What is variable?
Oxygen usage and carbon dioxide production but despite this, oxygen and carbon dioxide are kept within close limits
What is the control centre?
Pons, medulla oblongata and other parts of the brain