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GAS TRANSPORT Lecture – 6 Dr. Zahoor Ali Shaikh 1.

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Presentation on theme: "GAS TRANSPORT Lecture – 6 Dr. Zahoor Ali Shaikh 1."— Presentation transcript:

1 GAS TRANSPORT Lecture – 6 Dr. Zahoor Ali Shaikh 1

2 Gas Transport O 2 which is taken up by the blood at the lungs is transported to the tissues for use by the cells. CO 2 produced at the cell level is transported to the lungs for elimination. 2

3 Oxygen Transport Most O 2 in the blood is transported bound to hemoglobin. Method of O2 Transport Chemically bound to Hemoglobin – 98.5% Physically Dissolved in plasma – 1.5% 3

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5 Oxygen Transport Hb is present inside red blood cells [RBC]. Hb is iron bearing protein molecule. It makes reversible combination with oxygen. When Hb combines with O 2, we call Oxyhemoglobin [HbO 2 ]. Hb + O 2 HbO 2 When O 2 not combined with Hb, we call it reduced Hemoglobin or Deoxyhemoglobin. 5

6 Oxygen Transport Cells consume 250ml of O 2 /min at rest. During exercise, it can increase 25 times. Why does Hb combine with O 2 in the lungs and release O 2 at the tissues? Because of high partial pressure of O 2 [P O 2 ] in the lungs, O 2 combines with the Hb. When this blood with high po2 reaches the tissues, P O 2 in the tissues is low, therefore, O 2 is transferred from blood to tissues. 6

7 Oxygen Transport Important Points O 2 combination with Hb [Oxyhemoglobin] does not contribute to P O 2. P O 2 is only due to dissolved O 2 in plasma which is 1.5ml. P O 2 is the primary factor determining the percent Hb saturation. 7

8 Oxygen Transport In Hb, 4 atoms of iron are present in Heme portion of Hb. Each atom can combine with O 2 molecule, so Hb molecule can carry 4 molecules of O 2. Hb is considered fully saturated when all Hb is carrying O 2. The percent Hb [% Hb] saturation can vary from 0 to 100%. 8

9 Oxygen Transport The most important factor determining the % Hb saturation is P O 2 of the blood [which refers to concentration of O 2 physically dissolved in blood ]. 9

10 Oxygen-Hemoglobin (O 2 -Hb) dissociation (saturation) curve 10

11 Oxygen-Hemoglobin (O 2 -Hb) dissociation (saturation) curve The relationship between blood P O 2 and %Hb saturation is not linear. The relationship is S – shaped for O 2 -Hb dissociation. At pressures of P O 2 60 – 100mmHg curve flattens off or plateaus i.e. within this pressure range of mmHg little more O 2 binds to Hb. 11

12 Oxygen-Hemoglobin (O 2 -Hb) dissociation (saturation) curve If the P O 2 range is mmHg, it shows small changes in P O 2 results in large change in which Hb combines with O 2 i.e. lower part is steep. IMPORTANT Upper part of curve – Plateau or Flat Lower part of curve – Steep Both parts have physiological significance. 12

13 Oxygen-Hemoglobin (O 2 -Hb) dissociation (saturation) curve Significance of Plateau Phase of O 2 -Hb curve We can see if P O 2 falls from 100mmHg to 60mmHg, there is little change in O 2 percentage saturation. Same way, if P O 2 increases to 600mmHg [by breathing pure O 2 ] there will be only little change in Hb saturation [instead of Hb 97.5% saturation, it can increase to 100% saturation]. 13

14 Oxygen-Hemoglobin (O 2 -Hb) dissociation (saturation) curve Therefore P O 2 range between 60 – 600mmHg, there is only little change in amount of O 2 being carried by Hb. It provides safety margin in O 2 carrying capacity of blood. Clinical Application In Pulmonary disease, P O 2 may decrease due to poor ventilation or gas exchange. Physiologically P O 2 may decrease at high altitude. In these circumstances, if P O 2 falls up to 60mmHg, body will be little affected, but if P O 2 falls below 60mmHg body will be affected. 14

15 Oxygen-Hemoglobin (O 2 -Hb) dissociation (saturation) curve Significance of Steep Portion of O 2 – Hb curve Steep portion of O 2 – Hb dissociation curve is from 0 – 60mmHg i.e. present at systemic capillaries when O 2 is unloaded from the Hb. At tissue level, P O 2 falls from 100mmHg to 40mmHg but % of Hb saturation is still 75% [i.e. 25% of O 2 is given to tissues]. Hb in venous blood is 75% saturated at 40mmHg. 15

16 Oxygen-Hemoglobin (O 2 -Hb) dissociation (saturation) curve If tissue cells are metabolizing more actively and need more O 2, P O 2 can drop from 40mmHg to 20mmHg in tissues, more O 2 can be given by blood and O 2 percent can drop from 75% to 30%. Therefore small drop of P O 2 can give more O 2 to tissues. 16

17 Factors At The Tissue Level Promote The Unloading Of O 2 From Hb Shifting of O 2 dissociation curve to right or more dissociation [giving] of O 2 to tissues or less affinity of O 2 for Hb. The factors are 1- Increase CO 2 2- Increase Acidity [increase H+ ion] 3- Increase Temperature 4- Increase 2,3-BPG [bisphosphoglycerate] 17

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19 BOHR EFFECT Increase CO 2 and increase H+ ion causes more release of O 2 from Hb [i.e. less affinity of O 2 with Hb]. It is known as Bohr Effect. Both CO 2 and H+ combine with Hb reversibly at sites other than O 2 binding sides and cause release of O 2. 19

20 Effect of 2,3 – BPG on O 2 -Hb Dissociation Curve 2,3 – BPG is factor inside the RBC, which affect O 2 -Hb binding. It is produced during RBC metabolism. 2,3 – BPG can bind reversibly with Hb and decreases its affinity for O 2 therefore shifts Hb-O 2 dissociation curve to right. BPG increases in RBC Examples - People living at high altitude - People suffering from respiratory disease - Anemia 2,3 – BPG, by increasing O 2 unloading helps to maintain O 2 availability to tissues. 20

21 Applied: Hb Has Higher Affinity For Carbon monoxide [CO] Than O 2 CO and O 2 compete for same binding sites on Hb, but this affinity is 240 times more for CO. Combination of CO with Hb is know asCarboxyhemoglobin [HbCO]. Even when Hb and O 2 are normal. If CO is there Hb will not be available for O 2 combination. CO poisoning occurs in coal burning. CO is odorless, colorless, tasteless and non- irritating. 21

22 CO 2 Transport CO 2 is transported in the blood by three ways: 1. Physically dissolved in Plasma – 10% 2. Bound to Hb – 30% 3. As Bicarbonate – 60% 22

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24 CO 2 Transport CO 2 combines with Hb to form Carbamino hemoglobin (HbCO 2 ). CO2 combines with globin portion of Hemoglobin [in contrast to O 2 which combines with Heme portion]. As bicarbonate – it is most important means of CO2 as 60% of CO 2 is converted into bicarbonate by the chemical reaction. CO 2 + H 2 O H 2 CO 3 H+ + HCO 3 - This reaction takes place slowly in plasma but quickly within RBC due to presence of enzyme carbonic anhydrase. 24

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26 CO 2 Transport Chloride Shift As CO 2 combines with H 2 O and HCO 3 is formed in RBC. RBC membrane has HCO 3 – Cl carrier that passively facilitates the diffusion of these ions in opposite direction across the membrane. HCO 3 is moved out of the cell and in its place Cl is moved into RBC from plasma to restore electric neutrality. This inward shift of Cl in exchange for HCO 3 [generated by CO 2 ] is known as chloride shift. 26

27 CO 2 Transport HALDANE EFFECT Removing O 2 from Hb, increases the ability of reduced Hb to pick up CO 2 and H+ ion [CO 2 generated H+ ion]. This effect is known asHaldane Effect. 27

28 IMPORTANT Remember Bohr Effect - Increase CO 2 and increase H+ ion causes more release of O 2 from Hb [i.e. less affinity of O 2 with Hb]. It is known as Bohr Effect. Haldane Effect - Removing O 2 from Hb, increases the ability of reduced Hb to pick up CO 2 and H+ ion [CO 2 generated H+ ion]. This effect is known as Haldane Effect. 28

29 What You Should Know From This Lecture How O 2 is transported in the blood ? O 2 – Hb Dissociation Curve & its Significance What factor cause the O 2 – Hb curve to shift to right ? What is Bohr Effect ? How CO 2 is transported in the blood ? What is Chloride shift ? What is Haldane Effect ? 29


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