Gas transport and respiratory control Flashcards
How is oxygen transported in the blood?
Oxygen is carried in the blood in two forms, dissolved O2 and bound to haemoglobin in RBC. It dissolves poorly due to low solubility at physiological partial pressure
How does O2 combine with haemoglobin?
O2 forms an easily reversible combination with Hb to give oxyhemoglobin: O2 + Hb <ā> HbO2
Binding depends on PO2, driving force that forces oxygen to bind to haemoglobin
Oxygen absorbed by haemoglobin as soon as it gets into capillary hence partial pressure of plasma decreasing, creating a gradient for oxygen to go into and out of capillary
What is the oxygen-haemoglobin saturation curve?
Oxygen haemoglobin curve tells us the relationship between saturation of haemoglobin molecule and PO2, as PO2 increases more oxygen binds to haemoglobin molecule hence it becomes more saturated
Sigmoidal curve not linear
Key points in oxygen haemoglobin curve
Upper flat part of curve has moderate changes in PO2 around the normal value, small effect on the % of saturation and therefore amount of O2 carried by arterial blood i.e. some reserve capacity
Steep part of curve at lower PO2 helps with loading of Hb in lungs and unloading of O2 to the tissues. Small changes in PO2 result in large changes in amount of O2 bound to haemoglobin
How is the binding curve affected?
Lower plasma pH = reduced O2 affinity
Higher temperature = reduced O2 affinity (haemoglobin releases more oxygen) - more the curve shifts to the right
Increase PCO2 causes right shift hence haemoglobin releases more oxygen
If curve shifts to the right it is releasing O2 therefore saturation of haemoglobin drops
Left shift is where the haemoglobin saturation increases, holding on tightly to oxygen
Exercise causes pH to drop and temperature to rise in skeletal muscle - right shift
How is carbon dioxide transported in the blood?
CO2 is 20 times more soluble than oxygen in plasma
7% of all CO2 is dissolved in plasma, 70% is transported as bicarbonate and 23% is transported with proteins as carbamino compounds
Pathway of CO2 transport
As CO2 diffuses out of muscle/working tissue it immediately goes into Plasma and RBC, a proportion of the CO2 from RBC will bind to haemoglobin to form carbamino compound, the rest will react with water forming carbonic acid, dissociating into hydrogen ions and bicarbonate which travels down its concentration gradient out of RBC into plasma, a chloride ion moves into RBC when bicarbonate leaves to maintain neutrality
Transport of CO2 in lungs and peripheral tissue
Pressure gradient critical for CO2 to move out of solution into alveoli
By reducing amount of CO2 in plasma this causes partial pressure gradient between RBC and plasma hence CO2 can move out of RBC into plasma and into the alveoli
Now we have reduction of CO2 in capillary, which primes haemoglobin molecule to now be attracted to O2
What are central chemoreceptors?
Central chemoreceptors are located in medulla and are sensitive to PCO2 but not to PO2 of blood. CO2 diffuses out of cerebral capillaries which changes pH of cerebrospinal fluid and central chemoreceptors respond to pH change
These receptors are largely important as carbon dioxide receptors are the most important in determining respiratory activity
What are peripheral chemoreceptors?
Peripheral chemoreceptors are located in the carotid and aortic bodies and mainly respond to changes in arterial PO2 with limited response to changes in PCO2. They are rapidly responding.
Inflation/deflation and protective reflexes
As the lungs inflate or deflate, they send afferent input from stretch receptors, the brain then sends efferent output preventing them from stretching too far either way
Receptors also detect irritation. Brain sends efferent signal that triggers a sneeze or cough
