8.4 transport of oxygen and carbon dioxide in the blood

Question 1

What transports oxygen and where from/to

Answer 1

erythrocytes transport oxygen from the lungs to the other cells

Question 2

how are erythrocytes specialised

Answer 2

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

Question 3

what’s the structure of haemoglobin like and what type of protein is it

Answer 3

it’s a large globular conjugated protein made of four peptide chains each with an iron containing haem prosthetic group

Question 4

how many o2 molecules can each haemoglobin bind to

Answer 4

4

Question 5

what forms when haemoglobin binds to oxygen in a reversible reaction

Answer 5

oxyhaemoglobin

Question 6

reversible reaction of haemoglobin binding with four oxygen molecules

Answer 6

Hb + 4O2 forms Hb(O2)4

Question 7

what does erythrocytes contain that carry’s oxygen

Answer 7

haemoglobin

Question 8

how does oxygen enter the erythrocytes

Answer 8

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

Question 9

what is positive cooperation

Answer 9

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

Question 10

what’s the bohr effect

Answer 10

as the partial pressure of carbon dioxide increases haemoglobin gives up oxygen more easily and the oxygen dissociation curve shifts to the right

Question 11

what happens in the body as a result of the bohr effect

Answer 11

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

Question 12

why is it important that feral haemoglobin has a higher affinity for oxygen than the mothers haemoglobin

Answer 12

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

Question 13

where is there a high partial pressure of oxygen and what does it mean for Hbs affinity for oxygen

Answer 13

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

Question 14

where is there a low partial pressure of oxygen and what effect does it have on Hbs affinity for oxygen

Answer 14

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

Question 15

what’s on each axis for an oxygen dissociation curve

Answer 15

y axis % Hb saturation with O2

x axis partial pressure of oxygen

Question 16

what happens to % saturation as pO2 changes

Answer 16

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

Question 17

what does pO2 at lungs and respiring tissues mean to for loading of oxygen

Answer 17

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

Question 18

what three ways is CO2 transported from the tissues to the lungs and what percent of CO2 is transported each way

Answer 18

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

Question 19

what does carbon dioxide react slowly with water to form

Answer 19

carbonic acid H2CO3

Question 20

what does carbonic acid dissociate to form

Answer 20

H+ ions and HCO3- ions

Question 21

where is there high levels of the enzyme carbonic anhydrase and where are there low levels

Answer 21

high levels = in the cytoplasm of the RBC
low levels = in the blood plasma

Question 22

what enzyme catalyses the reaction between co2 and o2 to form carbonic acid and then its dissociation to form H+ ions and HCO3- ions

Answer 22

carbonic anhydrase

Question 23

how is it ensured that CO2 will diffuse from respiratory tissues into the erythrocytes

Answer 23

co2 is removed and converted into HCO3- ions

Question 24

what is the concentration of CO2 like at the lung tissues

Answer 24

relatively low

Question 25

whats the chloride shift

Answer 25

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

Question 26

why does the chloride shift happen

Answer 26

to maintain the electrical balance of the cell

Question 27

how does Hb act as a buffer by prevent changes in pH

Answer 27

by accepting free H+ ions in a reversible reaction to form haemoglobinic acid