8.4 - Transport of Oxygen & Carbon Dioxide in Blood

Question 1

How is oxygen binded to haemoglobins?

Answer 1

• Erythrocytes continually formed in red bone marrow - As rbcs mature, they lose their nuclei to maximise capacity for haemoglobin (limits lifespan to 120 days) Haemoglobin - red pigment that carries oxygen - 300million Hb molecules/rbc. 4O2 molecules bind to each Hb Hb + 4O2 <> Hb(O2)4

Question 2

How is oxygen carried?

Answer 2

Erythrocytes in capillaries of lungs, O2 levels are low (steep conc. gradient between air in alveoli and erythrocytes) - Oxygen diffuses into rbc and binds to a Hb POSITIVE COOPERATIVITY: 1 O2 binds to a heam group, Hb changes shape to allow the next O2 to bind - Due to O2 being bound to haemoglobin, free O2 conc. in erythrocytes stay low until all haemoglobin is saturated (maintains conc. gradient)

Question 3

How is oxygen released?

Answer 3

• As erythrocytes and blood meet body tissue, O2 conc. in somatic cell’s cytoplasm is lower –O2 moves out by diffusion, Hb molecule changes shape each time to release O2 molecule

Question 4

What is partial pressure?

Answer 4

In an ideal gas system, many gases make up a mixture, the partial pressure is the individual pressure of each gas.

Question 5

What is an oxygen dissociation curve?

Answer 5

• Graph showing relationship between O2 and Hb at different O2 partial pressures x axis - pO2, y axis - % sats of Hb w/ O2. - Represents the affinity of Hb with O2

Question 6

How are changes in pO2 represented by oxygen dissociation curves?

Answer 6

• Small rise in pO2 - Hb saturation increases at a faster rate as more O2 is available - Curve levels at high pO2 as Hb is saturated - Small drop in pO2 of surrounding (tissue), O2 is rapidly releases from Hb to diffuse into cells –effect enhanced by low pH in tissues vs. lungs (Alkaline conditions - favour for O2 binding to O2 acidic - favour for O2 dissociation

Question 7

What is the effect of CO2 on an oxygen dissociation curve?

Answer 7

As pCO2 rises, Hb dissociates O2 faster to remove the CO2, odc moves to the right, so lower Hb/O2 sat Known as the Bohr effect

Question 8

What is the importance of the Bohr effect?

Answer 8

• In active tissues with high pCO2, Hb more readily gives up O2 - In lungs where there is low pCO2, O2 binds to Hb easily.

Question 9

Describe and explain the affinity of fetal haemoglobin.

Answer 9

• Fetus developing in uterus reliant on mother for O2 - Oxygenated blood runs close to deoxygenated fetal blood from umbilical artery in placenta (site of gas exchange) - If affinity for fetal haemoglobin & adult was the same, no O2 would be transferred — fetal haemoglobin has higher affinity to attract O2

Question 10

What are the 3 ways CO2 is transported in the blood?

Answer 10

1. 5% carried dissolved in plasma 2. 10-20% combined with amino group in polypetide chani of Hb forming carbaminohaemoglobin (Hb.Co2) 3. 75-85% converted to HCO3- in erythrocyte cytpolasm – most of the CO2 diffuses that into the blood from cells is transported in the form of HCO3-

Question 11

Describe how the bulk of CO2 is transported in blood.

Answer 11

CO2 + H2O <>(carbonic anhydrase catalyses this) H2CO3 (carbonic acid) <> H+ + HCO3-

• H+ ions bind with Hb > Hb.H (haemoglobinic acid, causes the release of oxygen into respiring tissue)
• HCO3- moves into plasma, Cl- moves into the cell to maintain the ion/electrical imbalance of the cell Known as chloride shift

Question 12

How is free CO2 produced to be released in the lungs?

Answer 12

As blood nears lung tissue, where there is a low CO2 conc. - Carbonic anhydrase catalyses H2CO3<> CO2 + H2O - HCO3- diffuses back into erythrocytes to react w/ H+ to form carbonic acid.