transport of Co2 and O2 Flashcards
what is haemoglobin
red, oxygen carrying pigment found in RBC
describe properties of haemoglobin
- globular conjugated protein made of 4 peptide chains
- contains 4 Fe haem prosthetic groups
what is meant by ‘haemoglobin has a high affinity for oxygen’?
increased tendency to combine with oxygen (1 haemoglobin can carry 4 O2 molecules)
what is the reversible reaction that forms oxyhaemoglobin
Hb + 4O2 = Hb(O2)4 (haemoglobin + 4 oxygen = oxyhaemoglobin)
how is a steep concentration gradient formed between RBC and air in alveoli
when erythrocytes enter lung capillaries, the oxygen levels in cells are relatively low
explain how oxygen binds to haemoglobin
- oxygen moves into the erythrocyte and binds to haemoglobin
- when one oxygen molecule binds to a haem group, the molecule changes shape, making it easier for the next oxygen molecule to bind
why is oxygen binding to haemoglobin known as positive cooperation
oxygen binding to a haem group increases haemoglobin’s affinity for oxygen, maintaining a steep concentration gradient until all haemoglobin is saturated
what happens when blood reaches body tissues
- concentration of oxygen in cytoplasm of body cells is lower than erythrocytes so oxygen moves out down a CG
- once the first oxygen is released, the molecule changes shape again so remaining oxygen is released more easily
what is an oxygen dissociation curve?
a graph showing the affinity of haemoglobin for oxygen
what do oxygen dissociation curves help us to understand?
how the blood carries and release oxygen
what is partial pressure of oxygen (PO2)
a measure of oxygen concentration
when is partial pressure of oxygen at its highest and why?
in the lungs as haemoglobin is rapidly loaded with oxygen
when is partial pressure of oxygen at its lowest and why?
in respiring tissues as oxygen is released rapidly from haemoglobin
what % of oxygen is released into body cells when inactive and what happens to the rest?
25% - rest acts as reservoir for when demand suddenly increases
what happens when partial pressure of Co2 increases?
haemoglobin releases oxygen more easily
how is the bohr effect represented graphically?
as the proportion of Co2 increases, the oxygen dissociation curve shifts to the right
how is fetal haemoglobin represented graphically?
the oxygen dissociation curve shifts to the left
compare the affinity for oxygen in adults with fetuses
fetal haemoglobin has a higher affinity for oxygen than the mother at the same partial pressure of oxygen
why is it important that fetal haemoglobin has a higher affinity for oxygen?
- the fetus gets oxygen from its mothers blood - one the blood has reached the placenta, its oxygen saturation has decreased
- higher affinity = it absorbs more oxygen
what 3 ways is Co2 transported to the lungs?
- 5% is dissolved in plasma
- 10-20% is combined with amine groups in polypeptide chains of haemoglobin (forms carbaminohaemoglobin)
- 75-85% is converted into hydrogen carbonate ions (HCO3-) in red blood cell cytoplasm
explain how CO2 is transported to the alveoli for expiration
- CO2 reacts with water to form carbonic acid (H2CO3-) catalysed by carbonic anhydrase
- carbonic acid dissociates into H+ ions and HCO3- ions
- H+ ion increase causes oxyhaemoglobin to unload oxygen so haemoglobin can take up H+ ions forming haemoglobinic acid (stopping H+ ions increasing cell acidity)
- HCO3- ions diffuse out of the RBC and are transported in blood plasma
- Cl- ions compensate for loss of HCO3- by diffusing into the RBC - known as chloride shift
- when blood reaches lungs, low PCo2 causes some HCO3- and H+ ions to recombine into CO2 and water
- CO2 then diffuses into alveoli and is breathed out
