8.4 transport of oxygen and carbon dioxide in the blood Flashcards
What transports oxygen and where from/to
erythrocytes transport oxygen from the lungs to the other cells
how are erythrocytes specialised
they have a biconcave shape this gives them a large surface area and allows them to pass through narrow capillaries
they have no nucleus so more haemoglobin can fit into the cells
what’s the structure of haemoglobin like and what type of protein is it
it’s a large globular conjugated protein made of four peptide chains each with an iron containing haem prosthetic group
how many o2 molecules can each haemoglobin bind to
4
what forms when haemoglobin binds to oxygen in a reversible reaction
oxyhaemoglobin
reversible reaction of haemoglobin binding with four oxygen molecules
Hb + 4O2 forms Hb(O2)4
what does erythrocytes contain that carry’s oxygen
haemoglobin
how does oxygen enter the erythrocytes
when erythrocytes enter the capillaries in the lungs, the oxygen levels are relatively low, this makes a steep conc gradient between the inside lungs of the erythrocytes and the air in the alveoli O2 moves into the erythrocytes and binds with the Hb
what is positive cooperation
the arrangement of Hb molecules means as soon as one O2 molecule binds to a haem group the molecule changes shape making it easier for the next O2 molecule to bind
as the O2 is bound to the Hb the free O2 conc in the erythrocytes stays low so a steep diffusion gradient is maintained until all cells of the Hb is saturated with oxygen
what’s the bohr effect
as the partial pressure of carbon dioxide increases haemoglobin gives up oxygen more easily and the oxygen dissociation curve shifts to the right
what happens in the body as a result of the bohr effect
in active tissues with a high pCO2 haemoglobin gives up its oxygen more readily
in the lungs where the proportion of CO2 in the air is relatively low oxygen binds to the Hb molecules easily
why is it important that feral haemoglobin has a higher affinity for oxygen than the mothers haemoglobin
the fetus relys on the mother’s oxygenated blood that runs close to its deoxygenated blood in the placenta (they never mix) if there Hb had the same affinity for oxygen then little to no oxygen would be transferred but as fetal Hb has a higher affinity for oxygen at each point along the dissociation curve so it takes oxygen from the maternal blood as they pass each other
where is there a high partial pressure of oxygen and what does it mean for Hbs affinity for oxygen
there is a high pO2 at the lungs and sites of gas exchange and it has a higher affinity for oxygen and oxygen associates with Hb more readily and dissociates less readily
where is there a low partial pressure of oxygen and what effect does it have on Hbs affinity for oxygen
there is a low pO2 at respiring tissues and it has a lower affinity for oxygen and oxygen associates with Hb less readily and dissociates more readily
what’s on each axis for an oxygen dissociation curve
y axis % Hb saturation with O2
x axis partial pressure of oxygen
what happens to % saturation as pO2 changes
a small change in pO2 in surroundings makes a big difference in % saturation as once the first O2 molecule is attached then the change in shape means other O2 molecules are added rapidly the curve levels out at the highest pO2 as all the Haem groups are bound to O2 and can’t take any more
what does pO2 at lungs and respiring tissues mean to for loading of oxygen
the high pO2 in the lungs means the Hb is rapidly loaded with O2 but a low pO2 in respiring tissues means oxygen is released rapidly from the haemoglobin to diffuse into cells this effect is enhanced by the relatively low pH in the tissues compared to the lungs
what three ways is CO2 transported from the tissues to the lungs and what percent of CO2 is transported each way
about 5% is carried dissolved in the plasma
10-20%is combined with the amino groups in the polypeptide chains of haemoglobin from a compound called carbaminohaemoglobin
75-85% is converted into hydrogen carbonate ions in the cytoplasm of the RBC
what does carbon dioxide react slowly with water to form
carbonic acid H2CO3
what does carbonic acid dissociate to form
H+ ions and HCO3- ions
where is there high levels of the enzyme carbonic anhydrase and where are there low levels
high levels = in the cytoplasm of the RBC
low levels = in the blood plasma
what enzyme catalyses the reaction between co2 and o2 to form carbonic acid and then its dissociation to form H+ ions and HCO3- ions
carbonic anhydrase
how is it ensured that CO2 will diffuse from respiratory tissues into the erythrocytes
co2 is removed and converted into HCO3- ions
what is the concentration of CO2 like at the lung tissues
relatively low
whats the chloride shift
when the negative HCO3- ions (made from the dissociating of csrbonic acid) move out of the erythrocytes into the plama by diffusion down a concentration gradient and negatively changed Cl- ions move into the erthyrocytes which maintain the electrical balance of the cell
why does the chloride shift happen
to maintain the electrical balance of the cell
how does Hb act as a buffer by prevent changes in pH
by accepting free H+ ions in a reversible reaction to form haemoglobinic acid
