8.4 transport of oxygen and carbon dioxide

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