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features of erythrocytes
biconcave disc
no nucleus
contains haemoglobin
functions of erythrocytes
pass through narrow capillaries
maximise amount of haemoglobin due to no nucleus
structure of haemoglobin
globular conjugated protein
four peptide chains
each chain contain iron-containing prosthetic group
how is oxyhaemoglobin formed
oxygen bonds loose with haemoglobin
Hb + 4O2 ↔ Hb(O2)4
how is there a steep conc grad between erythrocytes and alveoli
oxygen levels relatively low in erythrocytes when enter capillaries in lungs
what happens after one oxygen molecule binds to a haem group
molecule changes shape, making it easier for the next oxygen molecules to bind
what is positive cooperativity
when oxygen molecules binding makes it easier for others to bind
what happens when blood reaches body tissues
conc of oxygen in erythrocytes higher than cytoplasm
what does an oxygen dissociation curve show
affinity of haemoglobin for oxygen
what is the shape of the oxygen dissociation curve
S shape
why is the oxygen dissociation curve that shape
increase partial pressure of oxygen
easier for other oxygen molecules for bind
levels off as haemoglobin is saturated
what happens to haemoglobin at low pO2
haem groups bound to oxygen so haemoglobin does not carry much oxygen
what happens when pO2 is increased
haem groups are bound to oxygen, making it easier for more oxygen to be picked up
what happens when the pO2 is very high
haemoglobin is saturated as all haem groups become bound
what is the bohr effect
when haemoglobin gives up oxygen more easily
why does the bohr effect happen
partial pressure of carbon dioxide rises
result of the bohr effect
in active tissues with high pCO2, haemoglobin gives up oxygen more readily
in lungs where proportion of CO2 in air relatively low, oxygen bind to haemoglobin molecules easily
what happens to the oxygen dissociation curve when the bohr effect happens
curve shifts to the right
why does fetal haemoglobin have a higher affinity for oxygen than mother
so it can remove oxygen from the maternal blood so oxygen can be transferred to the blood of the fetus
how is the fetal dissociation curve differ from normal
fetal dissociation curve is moved to the left
three ways carbon dioxide is transported from tissues to lungs
dissolved in the plasma (5%)
combined with amino groups in haemoglobin to form carbaminohaemoglobin (10-20%)
converted to hydrogen carbonate ions (75-85%)
chemical formula of hydrogen carbonate ions
HCO3-
how does CO2 enter RBC
diffusion
how does CO2 turn into H2CO3 (carbonic acid)
CO2 + H2O ↔ H2CO3 using carbonic anhydrase
what is the enzyme used to form carbonic acid
carbonic anhydrase
what does H2CO3 dissociate into
H+ and HCO3- ions
how do HCO3- ions leave RBC
diffusion into plasma
H+ ions and HbO3 (oxyhemoglobin) form what
4O2 and HHb (haemoglobinic acid)
role of HHb (haemoglobinic acid)
a pH buffer
what happens with the 4O2 produced
diffuse out into plasma
what is the chloride shift
Cl- ions diffuse into RBC to maintain neutral charge
what is the effect on RBC charge when ions diffuse out
RBC becomes positively charged until Cl- ions diffuse in
when will the HCO3- reactions reverse
when there is a relatively low concentration of carbon dioxide in the lung tissue
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