12. Respiratory System 2

Question 1

Explain hemoglobin (5)

Answer 1

1. Most oxygen is transported combined with hemoglobin
2. The red pigment of blood (heme and a protein)
3. Protein is composed of four polypeptides each containing one heme
4. Each heme contains an iron
   atom in the ferrous state which combines loosely and reversible with one oxygen molecule
5. One hemoglobin can transport four molecules of oxygen
6. 66 times more efficient in transporting oxygen than relying on dissolved oxygen alone

Question 2

How much oxygen can be associated with each gram of hemoglobin?

Answer 2

1.34 ml of oxygen

Question 4

Explain the oxygen-hemoglobin disassociation curve (3)

Answer 4

1. Amount of oxygen associated with Hb is related to but not directly proportional to the pressure of the dissolved oxygen
2. At Po2 ~ that of arterial blood hemoglobin is approximately 97.5 % saturated with oxygen
3. At Po2 ~ that of venous blood hemoglobin is approximately 72 % saturated with oxygen

Question 5

Describe the oxygen buffering capabilities (6)

Answer 5

1. Basal requirement is ~ 5 ml of O2/100ml
2. Met by having the Po2 drop to 40 mm Hg
3. Therefore tissue Po2 cannot rise above 40mm Hg or not enough oxygen will be released by hemoglobin
4. The steep part of the disassociation
   curve allows deliver of extra large amounts of oxygen to tissues with only a small fall in Po2
5. Buffering against changes in Po2 of
   atmospheric air.
6. Alveolar oxygen may vary greatly – (60- 500) and still the partial pressure of
   oxygen for tissue does not vary more than a few millimeters

Question 6

Describe the 2 factors that cause the oxygen-hemoglobin curve to shift to the right and why? (3)

Answer 6

1. WHY: show a decreased affinity of hemoglobin for oxygen - reduced PO2
2. Increased temperature: See shift of curve to right during hyperthermia - Greater yield of oxygen to tissues at this time
3. Increased BPG: Note in some species fetal hemoglobin has a higher oxygen affinity because the fetus has a lower level of 2,3 –BPG than adults

Question 7

Describe the Bohr effect (4)

Answer 7

1. Increased H+ and/or increased CO2 shift the dissociation curve to the right
2. We see increased in both of these as we move from arterial blood to venous blood
   - Therefore at the tissue capillaries the hemoglobin has less affinity for oxygen and it is easily given up increasing the
   yield of oxygen
3. We see a decrease in both of these as blood reaches the lungs
   - This will increase the affinity of the hemoglobin for oxygen and thus facilitate the uptake of oxygen
4. Increased Pco2 from 40 to 45 mm Hg – less affinity for oxygen – more oxygen leaves hemoglobin and can diffuse into cells

Question 8

What is carboxyhemoglobin? (3)

Answer 8

1. Hemoglobin’s affinity for carbon monoxide is 200 times that for oxygen
2. CO binds to the same location as O2 and prevents oxygen from binding
3. Bright red colour

Question 9

What is methemoglobin? (5)

Answer 9

1. Oxidation of the ferrous iron of hemoglobin to the ferric state
2. Cannot combine with oxygen
3. Chocolate brown colour
4. Nitrate poisoning – causes methemoglobin to form
5. Treat by giving methyl blue – a reducing agent

Question 10

Explain the diffusion of carbon dioxide from the pulmonary blood into the alveolus (1)

Answer 10

Due to very large diffusion coefficient the blood is quickly in equilibrium with the alveolar air

Question 11

What are the 3 ways to transport carbon dioxide?

Answer 11

1. Dissolved CO2 ~ 7% of the CO2 transported
2. As bicarbonate ion (HCO-3) ~ 70%
3. Carbaminohemoglobin – carbon dioxide in combination with hemoglobin and plasma proteins ~23%

Question 12

Explain bicarbonate ion in carbon dioxide transport (6)

Answer 12

1. Carbonic anhydrase – catalyzes the reaction between water and carbon dioxide accelerating its rate 5000 fold
2. The H2CO3 is rapidly dissociated to H+ and HCO-3
3. H+ combines with hemoglobin
4. HCO-3 diffuses into plasma
5. Cl-diffuses into RBC – chloride shift
6. Osmotic pressure in cell now greater – water enters – cell swells

Question 13

Explain the haldane effect in the carbon dioxide dissociation curve (5)

Answer 13

1. Binding of oxygen with hemoglobin tends to displace carbon dioxide from the blood
2. Important in promoting CO2 transport
3. In the tissue capillaries the O2 removal from the hemoglobin increases the pickup of CO2
4. In the pulmonary capillaries the uptake of O2 increases the release of CO2 from the blood
5. Haldane effect doubles the uptake of CO2 from tissues or the release of CO2 in the lungs