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7.1 Gaseous Exchange Control in Mammals

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  • 8/8/2019 7.1 Gaseous Exchange Control in Mammals

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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

    7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS

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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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    CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL

    7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS

    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

    7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS

    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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    CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL

    7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS

    Lesson Objective:

    7.1c Explain the transport of carbon dioxide byhaemoglobin.

    Carbon dioxide transport

    From lungs

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    CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL

    Lesson Objective:

    7.1e Explain the Bohr effect due to partial pressure of carbon dioxide

    7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS7.1 GASEOUS EXCHANGE & CONTROL IN MAMMALS

    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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    CHAPTER 7 : GASEOUS EXCHANGE & ITS CONTROL

    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

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