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Gas Transport in the Blood Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee.

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Presentation on theme: "Gas Transport in the Blood Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee."— Presentation transcript:

1 Gas Transport in the Blood Dr Shihab Khogali Ninewells Hospital & Medical School, University of Dundee

2 Understand the effect of partial pressure on O 2 and CO 2 carriage in the blood Understand the means of O 2 carriage in the blood Understand the oxygen- haemoglobin dissociation curve and the significance of its sigmoid shape Know the Bohr effect and its significance in O 2 liberation at tissue level Understand the means of CO 2 carriage in the blood Know the Haldane effect and its significance in the uptake of CO 2 and CO 2 generated H + at tissue level; and CO 2 liberation at the lungs What is This Lecture About? See blackboard for detailed learning objectives

3 O 2 Picked up by blood at the lungs must be transported to the tissues for cellular use CO 2 produced at tissues must be transported to the lungs for removal from the body Pulmonary circulation Systemic circulation Alveoli Atmospheric air

4 Oxygen Partial Pressures around the System 20 Atmosphere Tissues 10 Air Gas Pulmonary Capillary Diffusion Arterial P O 2 kPa

5 This means that if the partial pressure in the gas phase is increased the concentration of the gas in the liquid phase would increase proportionally The partial pressure of a gas in solution is its partial pressure in the gas mixture with which it is in equilibrium Henrys Law The amount of a given gas dissolve in a given type and volume of liquid (e.g. blood) at a constant temperature is: proportional to the partial pressure of the gas in equilibrium with the liquid Gaseous Phase Liquid Phase (gas in solution) What is the Effect of Partial Pressure on Gas Solubility?

6 Dissolved Oxygen The O 2 amount dissolved in blood is proportional to the partial pressure (Henrys Law) 3ml O 2 per litre of blood at a P O2 of 13.3 kPa Under Resting conditions (cardiac output 5L/min): 15 ml/min of O 2 is taken to tissues as dissolved O 2 Even at strenuous exercise (cardiac output of 30 L/min): 90 ml/min would be taken to tissues as dissolved O 2 Resting O 2 consumption of our body cells is about 250ml/min O 2 consumption may increase up to 25 folds during strenuous exercise –Clearly, another mechanism is involved in O 2 transport in the blood.

7 Oxygen Transport in the Blood Most O 2 in the blood is transported bound to haemoglobin in the red blood cells Normal O 2 concentration in the arterial blood is about 20 ml/100 ml (200 ml per litre) at a normal arterial P O 2 of 13.3 kPa and a normal haemoglobin concentration of 15 grams/100 ml Percentage of O 2 carried bound to haemoglobin = 98.5% Percentage of O 2 carried in the dissolved form = 1.5% (3 ml per litre at a P O 2 of 13.3 kPa ) O 2 is present in the blood in two forms: (1) bound to haemoglobin (2) physically dissolved (very little O 2 )

8 Oxygen binding to haemoglobin Haemoglobin can form a reversible combination with O 2 Each Hb molecule contains 4 haem groups Each haem group reversibly binds to one O 2 molecule Haemoglobin is considered fully saturated when all the Hb present is carrying its maximum O 2 load The P O2 is the primary factor which determine the percent saturation of haemoglobin with O 2

9 Oxygen Haemoglobin Dissociation Curve O 2 concentration ml/100 ml Blood P O 2 (kPa) % Haemoglobin Saturation 8.0

10 % Hb saturation O 2 concentration (ml/100 ml) 0 20 P O 2 (kPa) Total O 2 O 2 combined with Hb Dissolved O Oxygen Haemoglobin Dissociation Curve

11 Saturation P O 2 (kP) 0 13 O2 concentration (ml/100 ml) 0 20 % Hb saturation Hb = Hb = Hb =20

12 Oxygen binding of haemoglobin Binding of one O 2 to Hb increases the affinity of Hb for O 2 –co-operativity –Sigmoid Flattens where all sites are becoming occupied

13 Significance of Sigmoid Flat upper portions means that moderate fall in alveolar P O 2 will not much affect oxygen loading Steep lower part means that the peripheral tissues get a lot of oxygen for a small drop in capillary P O 2 O 2 concentration ml/100 ml Blood P O 2 (kPa) % Haemoglobin Saturation 8.0

14 Bohr Effect % Hb saturation PO2PO2 P CO 2 [H + ] Temperature 2,3-Biphosphoglycerate A shift of the curve to the right:- The Bohr Effect Increased release of O 2 by conditions at the tissues

15 Off-loading of O 2 at Tissues O 2 content (ml/10mls) P O 2 (mm Hg, kP) Arterial O 2 Tension Tissue O 2 Tension Curve in arterial conditions Curve in tissue conditions Additional O 2 given up

16 Means of CO 2 Transport in the Blood Solution (10%) As Bicarbonate (60%) As Carbamino compounds (30%)

17 (1)CO 2 in Solution Henrys Law Carbon dioxide about 20 times more soluble than oxygen About 10% of carried CO 2 is in solution

18 (2)Bicarbonate: Most CO 2 is transported in the blood as bicarbonate Bicarbonate is formed in the blood by:- CO 2 + H 2 O H 2 CO 3 H + + HCO - 3 CA Carbonic Anhydrase Occurs in red-blood cells

19 Bicarbonate Formation Red blood cell Capillary wall CO 2 H 2 O + H 2 CO 3 CA HCO 3 - H++H++ Cl - Chloride shift H + + Hb HbH

20 (3)Carbamino Compounds Carbamino compounds formed by combination of CO 2 with terminal amine groups in blood proteins. Especially globin of haemoglobin to give carbamino-haemoglobin Rapid even without enzyme Reduced Hb can bind more CO 2 than HbO 2

21 CO 2 Dissociation Curve CO 2 concentration (ml/100ml) CO 2 partial pressure (kP) PO2PO a v - PO2PO2 a = CO 2 content in arterial blood v - = CO 2 content in mixed venous blood

22 The Haldane Effect Removing O 2 from Hb increases the ability of Hb to pick-up CO 2 and CO 2 generated H + The Boher effect and the haldane effect work in synchrony to facilitate: O 2 liberation and uptake of CO 2 & CO 2 generated H + at tissues

23 Summary of CO 2 Transport in the Blood


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