Presentation on theme: "Gas Transport in the Blood"— Presentation transcript:
1 Gas Transport in the Blood Dr Shihab KhogaliNinewells Hospital & Medical School, University of Dundee
2 See blackboard for detailed learning objectives Understand the effect of partial pressure on O2 and CO2 carriage in the bloodUnderstand the means of O2 carriage in the bloodUnderstand the oxygen-haemoglobin dissociation curve and the significance of its sigmoid shapeKnow the Bohr effect and its significance in O2 liberation at tissue levelUnderstand the means of CO2 carriage in the bloodKnow the Haldane effect and its significance in the uptake of CO2 and CO2 generated H+ at tissue level; and CO2 liberation at the lungsWhat isThisLectureAbout?See blackboard for detailed learning objectives
3 O2 Picked up by blood at the Atmospheric airO2 Picked up by blood at thelungs must be transported to the tissues for cellular useAlveoliPulmonarycirculationSystemiccirculationCO2 produced at tissues must be transported to the lungs for removal from the body
4 Oxygen Partial Pressures around the System AirGas20PulmonaryCapillaryArterialPO2 kPaDiffusion10AtmosphereTissues
5 Henry’s Law What is the Effect of Partial Pressure on Gas Solubility? This means that if the partial pressure in the gas phase is increased the concentration of the gas in the liquid phase would increase proportionallyThe partial pressure of a gas in solution is its partial pressure in the gas mixture with which it is in equilibriumWhat is the Effect of PartialPressure on Gas Solubility?Henry’s LawThe amount of a given gas dissolvein a given type and volume of liquid(e.g. blood) at a constanttemperature is:proportional to the partial pressureof the gas in equilibrium with theliquidGaseous PhaseLiquid Phase (gas in solution)
6 Dissolved OxygenThe O2 amount dissolved in blood is proportional to the partial pressure (Henry’s Law)3ml O2 per litre of blood at a PO2 of 13.3 kPaUnder Resting conditions (cardiac output 5L/min): 15 ml/min of O2 is taken to tissues as dissolved O2Even at strenuous exercise (cardiac output of 30 L/min): 90 ml/min would be taken to tissues as dissolved O2Resting O2 consumption of our body cells is about 250ml/minO2 consumption may increase up to 25 folds during strenuous exerciseClearly, another mechanism is involved in O2 transport in the blood.
7 Oxygen Transport in the Blood Most O2 in the blood is transported bound to haemoglobin in the red blood cellsNormal O2 concentration in the arterial blood is about 20 ml/100 ml (200 ml per litre) at a normal arterial PO2 of 13.3 kPa and a normal haemoglobin concentration of 15 grams/100 mlPercentage of O2 carried bound to haemoglobin = 98.5%Percentage of O2 carried in the dissolved form = 1.5%(3 ml per litre at a PO2 of 13.3 kPa )O2 is present in the blood in two forms: (1) bound to haemoglobin (2) physically dissolved (very little O2)
8 Oxygen binding to haemoglobin Haemoglobin can form a reversible combination with O2Each Hb molecule contains 4 haem groupsEach haem group reversibly binds to one O2 moleculeHaemoglobin is considered fully saturated when all the Hb present is carrying its maximum O2 loadThe PO2 is the primary factor which determine the percent saturation of haemoglobin with O2
12 Oxygen binding of haemoglobin Binding of one O2 to Hb increases the affinity of Hb for O2co-operativitySigmoidFlattens where all sites are becoming occupied
13 Significance of Sigmoid O2 concentration ml/100 ml5.313.3Blood PO2 (kPa)% Haemoglobin Saturation8.0Flat upper portions means that moderate fall in alveolar PO2 will not much affect oxygen loadingSteep lower partmeans that the peripheral tissues get a lot of oxygen for a small drop in capillary PO2
14 Bohr Effect % Hb saturation A shift of the curve to the right:- The Bohr Effect100Increased release of O2 by conditions at the tissues% Hb saturationPCO2[H+]Temperature2,3-BiphosphoglyceratePO2
15 Off-loading of O2 at Tissues Curve in arterialconditions20Curve in tissueconditionsAdditional O2 given up10O2 content (ml/10mls)Tissue O2 TensionArterial O2 Tension202.6405.3608.08010.610013.3PO2 (mm Hg, kP)
16 Means of CO2 Transport in the Blood Solution (10%)As Bicarbonate (60%)As Carbamino compounds (30%)
17 (1) CO2 in Solution Henry’s Law Carbon dioxide about 20 times more soluble than oxygenAbout 10% of carried CO2 is in solution
18 Bicarbonate: Most CO2 is transported in the blood as bicarbonate Bicarbonate is formed in the blood by:-CACarbonic AnhydraseCO2 + H2OH2CO3H+ + HCO-3Occurs in red-blood cells
20 (3) Carbamino Compounds Carbamino compounds formed by combination of CO2 with terminal amine groups in blood proteins.Especially globin of haemoglobin to give carbamino-haemoglobinRapid even without enzymeReduced Hb can bind more CO2 than HbO2
21 CO2 Dissociation Curve PO2 PO2 CO2 concentration (ml/100ml) 5.355av-PO213.3CO2 concentration (ml/100ml)a = CO2 content in arterial bloodv- = CO2 content in mixed venous blood455.36.6CO2 partial pressure (kP)
22 Removing O2 from Hb increases the ability of Hb to pick-up CO2 and The Haldane EffectRemoving O2 from Hb increasesthe ability of Hb to pick-up CO2 andCO2 generated H+The Boher effect and the haldane effect work insynchrony to facilitate:O2 liberation and uptake of CO2 & CO2 generated H+ at tissues
23 Summary of CO2 Transport in the Blood Figure 13.30: Carbon dioxide transport in the blood.Carbon dioxide (CO2) picked up at the tissue level is transported in the blood to the lungs in three ways: (1) physically dissolved, (2) bound to hemoglobin (Hb), and (3) as bicarbonate ion (HCO3−). Hemoglobin is present only in the red blood cells, as is carbonic anhydrase, the enzyme that catalyzes the production of HCO3−. The H+ generated during the production of HCO3− also binds to Hb. Bicarbonate moves by facilitated diffusion down its concentration gradient out of the red blood cell into the plasma, and chloride (Cl−) moves by means of the same passive carrier into the red blood cell down the electrical gradient created by the outward diffusion of HCO3−. The reactions that occur at the tissue level are reversed at the pulmonary level, where CO2 diffuses out of the blood to enter the alveoli.
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