Gas Transport Flashcards
What are the ways that oxygen can be transported in the blood?
- physically dissolved in the plasma (2%)
- combined with haemoglobin (98%)
Describe the structure of haemoglobin/foetal haemoglobin
- normal: 2a and 2B chains
- foetal: 2a and 2-gamma chains
What change in haemoglobin constitutes to sickle cell anaemia (HbS)?
glutamate at position 6 in the B-globin is replaced with a valine
Describe binding of oxygen to haemoglobin
O2 can only bind to haemoglobin in ferrous state (Fe2+)
Describe the change in haemoglobin structure with oxygenation
- deoxygenated Hb exists in a tensed state with strong ionic bonds formed between the 4 polypeptide chains
- immobile and apart
- oxygenated Hb exists in a relaxed staate
- as O2 binds, the bonds break and Fe moves to the plane of prophyrin rings forming the relaxed state
What is the consequence of 2,3 DPG binding to B-globin?
Fe of Hb lies deeper in the pocket and cannot bind O2
What is O2 capacity?
- amount of O2/L of blood attached to Hb at full saturation
- depends on Hb concentration in blood
Explain the physiological significance of the haemoglobin O2 dissociation curve
- binding of one O2 molecule makes it easier for the subsequent ones to attach
- haem-haem interaction cooperatively which is what causes the shape of the O2-Hb dissociation curve
How can you calculate how much oxygen is in the blood?
max O2 bound Hb = O2 capacity * [Hb]
How does myoglobin and foetal haemoglobin affect the O2 dissociation curve?
- MyHb and HbF shifts the curve to the left
- HbF has a higher O2 affinity than HbA due to special properties of gamma chains
- MyHb has the highest affinity for O2
What does left and right shift mean?
- left shift: high affinity
- right shift: low affinity
Factors that shift O2 curve to the left
- increase in pH
- decrease in PCO2
- decrease in temperature
- decrease in 2,3 DPG
Affinity for O2 in systemic capillaries
- higher CO2
- higher temperature
- lower in pH
- causes rightward shift
- Hb in low affinity tensed state
- more O2 released
Affinity for O2 in pulmonary capillaries
- lower temperature
- lower PCO2
- higher pH
- Hb in higher affinity relaxed state
- more O2 taken up by Hb
What are the 2 components of acidosis?
- decrease in pH
- increase in PCO2
Why is Hb a good buffer?
H+ increases conformational change in Hb structure and O2 affinity reduces
What is the effect of hypercapnia on O2-Hb dissociation curve?
- small changes in affinity to the the right
- CO2 binds with unprotonated amino groups on Hb - carbamino haemoglobin
How does 2,3 DPG increase in the blood?
- decreasing PO2 of RBC stimulates glycolysis
- increased levels of 2,3 DPG
- interacts with B-chains destabilising interaction of O2 with Hb
Describe the effect of CO on Hb affinity for O2
- CO (as well as NO and H2S) can bind to Hb and snap it into relaxed state
- CO has greater affinity for Hb than O2
- causes maximal O2 capacity falls to extent that CO binds
- also increases O2 affinity of Hb and shifts O2 dissociation curve to left
- does not release O2 when it gets to tissue
(decreases Hb O2-carrying capacity and O2 unloading)
How can CO2 be transported?
- in plasma: physically dissolved (10%), combined with plasma proteins and as bicarbonate ions
- in RBC: in physical solution, combined with Hb (20%) and as bicarbonate ions (70%)
Describe CO2 release from blood into the lungs
- partial pressure gradients for O2 and CO2 reverse
- high PO2 causes H+ to dissociate from Hb
- H+ and CO3- combine to form CO2 and H20
- HCO3- re-enters RBC and combines with H+ to form H2CO3 which dissociates to release CO2 and H20
What does transport of CO2 in the blood depend on?
- PCO2
- plasma pH
- PO2
Describe the haldane effect
- as blood enters systemic capillaries and release O2, CO2 carrying capacity rises
- as blood enters pulmonary capillaries and binds O2, CO2 carrying capacity falls and blood dumps CO2
