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GAS TRANSPORT OXYGEN(O 2 ) & CARBONDIOXIDE(CO 2 ) Lecture – 6 Dr. Zahoor Ali Shaikh 1.

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Presentation on theme: "GAS TRANSPORT OXYGEN(O 2 ) & CARBONDIOXIDE(CO 2 ) Lecture – 6 Dr. Zahoor Ali Shaikh 1."— Presentation transcript:

1 GAS TRANSPORT OXYGEN(O 2 ) & CARBONDIOXIDE(CO 2 ) 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. 6

7 Oxygen Transport  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. There is a net diffusion of oxygen from the alveoli to the blood. This occurs continuously until hemoglobin is as much saturated as possible (97.5% at P O 2 of100 mm of Hg). When this blood with high P O 2 reaches the tissues, P O 2 in the tissues is low, therefore, O 2 is transferred from blood to tissues. 7

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9 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. 9

10 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%. 10

11 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 plasma]. 11

12 Oxygen-Hemoglobin (O 2 -Hb) dissociation (saturation) curve 12

13 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. 13

14 Oxygen-Hemoglobin (O 2 -Hb) dissociation (saturation) curve IMPORTANT Upper part of curve – Plateau or Flat Lower part of curve – Steep Both parts have physiological significance. 14

15 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]. 15

16 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. 16

17 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. 17

18 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 in tissue can give more O 2 to tissues. 18

19 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] or 2,3-DPG[disphosphoglycerate] 19

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21 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’. 21

22 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. 22

23 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 as ‘Carboxyhemoglobin’ [HbCO]. Even when Hb and O 2 are normal. If CO is there Hb will not be available for O 2 combination. 23

24 Applied: Hb Has Higher Affinity For Carbon monoxide [CO] Than O 2 CO poisoning occurs in coal burning. CO a poisonous gas, liberated by burning of carbon, products, e.g. automobile gasoline, coal, wood & tobacco. CO is odorless, colorless, tasteless and non- irritating. 24

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26 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% Important – Most CO 2 is transported as bicarbonate. 26

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28 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. 28

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30 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. 30

31 CO 2 Transport  HALDANE EFFECT Removing O 2 from Hb at the tissue cells, increases the ability of reduced Hb to pick up CO 2. This effect is known as ‘Haldane Effect’. 31

32 ‘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 at tissue cells, increases the ability of reduced Hb to pick up CO 2. This effect is known as ‘Haldane Effect’. 32

33 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 ? 33

34 Thank you 34


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