gas transport Flashcards
what are the primary functions of the cardiovascular system?
how do both gases move?
transport oxygen from the lungs to all tissues in the body and remove CO2 from the tissues to the lungs.
they will move by diffusion down their concentration gradients.
what 2 ways is oxygen transported in the blood?
- physically dissolved in plasma = 2%
- combined with haemoglobin = 98%
what does the amount of oxygen dissolved in the plasma depend upon?
what does Henry law state?
- the amount of oxygen dissolved in plasma depends on its solubility and partial pressure in blood (HENRYS LAW)
- henrys law states that at equilibrium for a given temperature (O2) Dis= solubility O2 x PO2
describe the solubility of oxygen at 37 degrees in plasma?
what is the partial pressure of O2 in arterial blood?
therefore how much oxygen blood can be transported at once?
why is this mechanism inadequate?
- At 37oC the solubility of O2 in plasma is poor - only 0.03ml/L/mmHg
- Partial pressure of O2 in arterial blood is ~100 mmHg
- Therefore only 3ml O2/L of blood can be transported in solution
- Equates to 15ml O2/min delivery to tissues
- BUT our bodies consume 250ml O2/min
- So this mechanism of O2 transport is completely inadequate
describe the structure of haemoglobin?
- Normal Hb (HbA) is a tetramer
- Four O2-binding heme groups each attached
to a polypeptide (globin) chain - HbA consists of 2α and 2β chains
describe the structure of haemoglobin in foetus?
In Fetal haemoglobin (HbF) the β- chains are replaced by γ-chains
what does each team group consist of?
Each haem group consists of a porphyrin ring surrounding an Fe2+ molecule
what is the way oxygen binds to the iron molecule?
what happens if the iron is oxidised?
O2 can only be bound in Fe2+ (ferrous state)
- If iron oxidised to ferric (3+) state leads to
methaemoglobin (~1.5% Hb is in this state)
– methaemoglobin reductase uses the NADPH chain to reduce metHb back to Hb
what state will Hb exist?
what are the bonds like in this tensed state?
how do you get the relaxed state?
Deoxygenated Hb exists in a tensed state (T) compared with oxygenated Hb in a relaxed state (R)
In the tensed state strong ionic bounds form between the 4 polypeptide chains – immobile and apart
As O2 binds the bonds break and the Fe moves to the plane of the porphyrin rings – relaxed state
what will B - globins also bind to?
what is the consequence of this?
β-globins also bind 2,3 DPG
- The consequence of this is that the Fe lies deeper in the pocket and cannot bind O2
why does blood change colour?
The colour of blood changes from dark blue to bright red
oxygenated = lighter
deoxygenated = darker
describe the binding of haemoglobin?
how does this happen?
Binding of one O2 molecule makes it easier for the subsequent ones to attach
- Haem-haem interaction – cooperatively. This accounts for the shape of O2-Hb dissociation curve
(the structure changes slightly allowing more oxygen to bind)
what is the colour change in blood used to measure?
The colour change is utilised clinically to measure the O2 saturation of blood using the pulse oximeter
what is O2 capacity and what does it depend on?
how much oxygen will each g of Hb carry when fully saturated?
Amount of O2/L of blood attached to Hb, at full saturation, is called O2 capacity and depends on the Hb concentration in blood
Each g of Hb, when fully saturated carries 1.35ml of O2
how can you calculate the maximal O2 bound to haemoglobin?
what will shift the curve to the left?
what is Feotal haemoglobin made from?
why does frontal haemoglobin have a higher affinity for oxygen than adult heamoglob?
MyHb and HbF shift the curve to the left
- HbF Consists of 2 α-chains and 2 γ-chains
- HbF has higher O2 affinity than HbA due to special properties of γ-chains
- May take up to 2 years to convert all HbF to HbA
what happens in pulmonary capillaries when the temperature lowers?
In pulmonary capillaries temperature is lower, Pco2 is lower and pH is higher, moves Hb to higher affinity relaxed state , so more O2 taken up by Hb
(left shift)
when CO2 increases in systemic capillaries, what happens?
In systemic capillaries increases in CO2, temperature and decrease in pH, move Hb to low affinity tensed state, so more O2 released (right shift)
what is respiratory acidosis?
what is the effect of respiratory acidosis on the oxygen dissociation?
Respiratory acidosis is a condition that occurs when the lungs can’t remove all of the CO2 produced by the body.
Bohr observed that respiratory acidosis shifted the Hb-O2 dissociation curve to right
what are the effects of temperature and pH on the O2 Hb dissociation curve?
- Temperature affects the O2 capacity of Hb, by affecting Hb structure
- Changes in pH account for most of Bohr effect causing Metabolic acidosis
why is Hb a good buffer?
- Hb good buffer for H+, as [H+] increases conformational change in Hb structure and O2 affinity reduces
what is the effect of 2,3-diphospoglycerate on the 02-Hb dislocation curve?
- RBC do not have mitochondria
– by-product of glycolysis
– decreasing PO2 of rbc’s stimulates glycolysis resulting increased levels of 2,3-DPG
- 2,3-DPG interacts with β chains destabilising interaction of O2 with Hb
(when you heave increased partial pressure of oxygen and increased conc of DPG, there will be a decrease in haemoglobin saturation causing a shift to the right)
how is CO2 transported in blood from tissues?
1- CO2 enters RBC and is converted to HCO3-
2- HCO3- is carried in plasma after being exchanged for CL-
3- H+ ions binds to haemoglobin and enhance O2 release
4- pronated haemoglobin becomes substrate for caroming formation.
describe the process of the release of CO2 from blood into the lungs?
- Partial Pressure gradients for O2 and CO2 reverse
- High PO2 causes H+ to dissociate from Hb
- H+ and HCO3- combine to form CO2 and H2O
- HCO3- reenters RBCs and combines with H+ to form H2CO3 which dissociates to release CO2 and H2O
what does the CO2 dissociation curve demostrate?
what does the carriage of CO2 depend on?
what is the relationship between PCO2 and PO2?
what is the Haldane effect?
- CO2 dissociation curves demonstrate how changes in PCO2 affect total CO2 blood content
- Carriage of CO2 in blood depends on:
– PCO2
– plasma pH
– PO2 - Near linear relationship between PCO2 and PO2 in physiological range
- Upshift of curve with decreasing PO2 – Haldane effect
what is the difference in what happens when blood enters the systemic capillaries and when blood enters the pulmonary capillaries?
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
