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CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL
Lesson Objective:
7.1b Describe the structures of haemoglobin & itscharacteristics as respiratory pigments
7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS
Characteristics of Hb as respiratory pigmentCharacteristics of Hb as respira tory pigment
Shows high affinity for O 2 (easy to bind O 2)especially in an environment with high oxygen partial pressure ( Po 2) such as in the lungs.
Hb binds O 2 to form oxyhaemoglobin (HbO 2).HbO 2 also release O 2 easily when Po 2 such as in the tissue area.
Shows allosteric cooperativity .Binding of O 2 to 1 subunit induces the remaining subunits to change their shapes slightly so thattheir affinity for O 2 increases too.
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CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL
Lesson Objective:
7.1c Explain the transport of oxygen by haemoglobin. Show the characteristicsof oxygen dissociation curve of haemoglobin & myoglobin
7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS
Oxygen Dissociation Curve Shows the amounts of O 2 bound to Hb at different Po 2 .
At Po 2 of ~100 mmHg (typical in the lungs), Hb is about 98% saturated with O 2.
At Po 2 of 40 mmHg (common in the tissue area), Hb is only ~70% saturated.
Hb will release its reserve of O 2 to tissues that are very active metabolically (Po 2 ~10 mmHg) and only~20% saturated.
The curve is S-shaped. Cooperative oxygen binding and release is evident in the O 2 dissociation curve for Hb.
When Po 2 , the tendency of HbO 2 to release O 2 is greater.
When Po 2 , the amounts of O 2 bound to Hb (O 2 saturation of Hb) .
The steep slope in the curve shows the characteristic of Hb which releases O 2 fast when O 2 isneeded for cell respiration.
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CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL
Lesson Objective:
7.1c Explain the transport of oxygen by haemoglobin. Show the characteristicsof oxygen dissociation curve of haemoglobin & myoglobin
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CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL
7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS
Another protein that can bind O 2 ismyoglobin .
It functions as an O 2 store in the muscles.
It has a greater affinity towards O 2 (whencompared with Hb).
It remains fully saturated with O 2 even at lowPo 2 (when Hb starts to release O 2).
The O 2 dissociation curve for myoglobin issituated well to the left of the O 2 dissociation curve for Hb.
It only releases O 2 when Po 2 falls very low (asin severe muscular exertion).
Lesson Objective:
7.1c Explain the transport of oxygen by haemoglobin. Show the characteristicsof oxygen dissociation curve of haemoglobin & myoglobin
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CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL
Lesson Objective:
7.1d Compare oxygen dissociation curves of haemoglobinas in foetus & adult
7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS
Hb in fetus is slightly different from theHb of adults.
Fetal Hb has a higher affinity towardsO 2 (when compared with Hb of themother).
This ensures that the fetus will get thesupply of O 2from the mothers bloodwhen Po 2 is low in the uterus.
The O 2 dissociation curve for fetal Hb issituated to the left of the O 2 dissociation curve for the mothers Hb.
20 40 60 80 100
50
100
Partial pressure of oxygen (mm Hg)
Percentageoxyhem
oglobin
Saturation(%
)
Adult (maternal)hemoglobin
Fetal hemoglobin
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Lesson Objective:
7.1c Explain the transport of carbon dioxide byhaemoglobin.
CO 2 is transported in blood between respiring tissues and the lungs in 3 ways
1. As dissolved CO 2 in blood plasma
CO 2 diffuses into the blood plasma and moves towards the lungs as dissolved CO 2
Only about 7% as CO 2 is not so soluble in water
Carbon dioxide transport
2. As carbamino-haemoglobin
CO 2 diffuses into the blood plasma and enters the erythrocyte
Inside, the CO 2 binds to amino group of the Hb to form carbamino-haemoglobin
The carbamino-haemoglobin will be transported in the erythrocyte until it reaches the lungs area
About 23% of the CO 2 is transported this way
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CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL
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Lesson Objective:
7.1c Explain the transport of carbon dioxide byhaemoglobin.
Carbon dioxide transport3. As bicarbonate ions About 70% of the CO 2 diffuses into the blood plasma, enters the erythrocyte and reacts with water
to form carbonic acid (H2CO 3)
This is catalyzed by carbonic anhydrase
The H 2CO 3 dissociates into H + and bicarbonate ion (HCO 3-)
The H + attaches to Hb While the HCO 3- diffuses into the plasma and carried towards the lungs
When the HCO 3- diffuses out from erythrocyte, the charge in the blood cell will change
Chloride ion (Cl -) will move from the plasma into the erythrocyte to keep the charge in the cellconstant
This is the chloride shift
*All of the processes that occur in the tissue area are reversed in the lungs
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Lesson Objective:
7.1c Explain the transport of carbon dioxide byhaemoglobin.
Carbon dioxide transport
From lungs
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Lesson Objective:
7.1e Explain the Bohr effect due to partial pressure of carbon dioxide
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The CO 2 partial pressure (Pco 2) also has an effect on the O 2 dissociation curve of Hb.
Metabolically active tissues produce a lot of CO 2 which reacts with water to form carbonic acid whicheventually can form H + .
This lowers the pH (more acidic) of the blood at the active tissues.
This induces the Hb to release more O 2 to be supplied to the active tissues while the Hb picks up the H + toform haemoglobinic acid (to prevent harmful changes in blood pH).
At the same Po 2 , O 2 saturation of Hb is lowered when the pH is lowered.
This shifts the O 2 dissociation curve to the right as a drop in pH lowers the affinity of Hb towards O 2 .
This is the Bohr shift ( Bohr effect ).
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7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS
Lesson Objective:
7.1e Explain the Bohr effect due to partial pressure of carbon dioxide