L4 Physiology O2 & CO2 Transport (Respiratory System) PDF

 Transport of Gases O2 & CO2 Carriage Prof. Ahmed Abdalfattah  Exchange of O2 &CO2 CO2 O2 Airways Alveoli of lungs CO2 O2 6 CO2 exc...

 Transport of Gases O2 & CO2 Carriage Prof. Ahmed Abdalfattah  Exchange of O2 &CO2 CO2 O2 Airways Alveoli of lungs CO2 O2 6 CO2 exchange 1 Oxygen exchange at alveolar-capillary CO2 O2 at alveolar-capillary interface interface Pulmonary circulation 2 Oxygen transport 5 CO2 transport Systemic CO2 circulation O2 4 CO2 exchange 3 Oxygen exchange at cells at cells CO2 O2 Cellular Cells respiration Nutrients ATP  TRANSPORT OF OXYGEN Oxygen is transported from alveoli to the tissue by blood in two forms: 1. As simple physical solution 2. In combination with hemoglobin.  AS SIMPLE SOLUTION Oxygen dissolves in water of plasma and is transported in this physical form. Amount of oxygen transported in this way is very negligible. It is only 0.3 mL/100 mL of plasma. It forms only about 3% of total oxygen in blood. It is because of poor solubility of oxygen in water content of plasma. Still, transport of oxygen in this form becomes important during the conditions like muscular exercise to meet the excess demand of oxygen by the tissues  IN COMBINATION WITH HEMOGLOBIN Oxygen combines with hemoglobin in blood and is transported as oxyhemoglobin. Transport of oxygen in this form is important because, maximum amount (97%) of oxygen is transported by this method  Oxygenation of Hemoglobin Oxygen combines with hemoglobin only as a physical combination. It is only oxygenation and not oxidation. Oxygen combines with the iron in heme part of hemoglobin. Each molecule of hemoglobin contains 4 atoms of iron. Iron of the hemoglobin is present in ferrous form. Each iron atom combines with one molecule of oxygen. After combination, iron remains in ferrous form only. That is why the combination of oxygen with hemoglobin is called oxygenation and not oxidation  Oxygen Carrying Capacity of Hemoglobin Oxygen carrying capacity of hemoglobin is the amount of oxygen transported by 1 gram of hemoglobin. It is 1.34 mL/g  Oxygen Carrying Capacity of Blood Normal hemoglobin content in blood is 15 g%. Since oxygen carrying capacity of hemoglobin is 1.34 mL/g, blood with 15 g% of hemoglobin should carry 20.1 mL% of oxygen, i.e. 20.1 mL of oxygen in 100 mL of blood. But, blood with 15 g% of hemoglobin carries only 19 mL% of oxygen, i.e. 19 mL of oxygen is carried by 100 mL of blood. Oxygen carrying capacity of blood is only 19 mL% because the hemoglobin is not fully saturated with oxygen. It is saturated only for about 95%  Saturation of Hemoglobin with Oxygen Saturation is the state or condition when hemoglobin is unable to hold or carry any more oxygen. Saturation of hemoglobin with oxygen depends upon partial pressure of oxygen. And it is explained by oxygenhemoglobin dissociation curve  O2 transport by Blood 95-97% 3-5% In chemical combination Dissolved in plasma with Hb  O2 transport by Blood I- Oxygen in physiological solution (dissolved O2) A small amount of O2 is found in physical solution i.e. dissolved in the water of plasma and cells. In arterial blood: 0.3 ml/100ml blood. It causes a partial pressure of O2 = 100 mmHg. In venous blood: 0.13ml/100ml blood. It causes partial pressure of O2 = 40mmHg.  Importance of dissolved O2 It is responsible for O2 tension in the blood which in turn determine : Direction of O2 transport and rate of flow. Amount of O2 in chemical combination with Hb.  Percentage of saturation of Hb with O2 The % saturation of Hb with O2 is calculated as follows: O2 content X 100 O2 capacity Fig. 23-24, p. 847 Pressure difference in exchange Factors affecting diffusion of gases through the pulmonary membrane  Solubility Diffusion capacity. Of gas across the pulmonary membrane is directly proportion to the solubility of the gas. CO2 is 20 time more soluble than O2. Normal diffusion capacity of CO2 is 400 ml/min/mmHg while that for O2 is 25ml/min/mmHg  Pressure gradient For O2 is 60 (alveolar p 100 – venous blood p 40 mmHg) For CO2 is 6 (alveolar p 46-venous blood p 40 mmHg). 60X 25 =1500 ml O2 /min 6 X 400= 2400 ml CO2/min Diffusion of CO2 is more than O2  Surface area Diffusion rate is proportional to available surface area, normal surface area 70m2.  Membrane thickness Diffusion rate is inversely proportional to the thickness of the membrane this is why the walls are so thin 0.6 micron.  Factors affecting diffusion of gases through the pulmonary membrane Concentration gradient- diffusion rate is proportional to concentration gradient Most important factor- O2 and CO2 gradients will be present at lung and tissue capillaries Molecular weight of the 02 and co2 Diffusion is inversely proportional to molecular weight of the gas o2 is 32 and co2 is 40  Ventilation perfusion ratio Ventilation perfusion ratio V/Q =4 /5=0.8 4liter ventilation and 5 liter perfusion  Ventilation perfusion ratio At the apex of the lungs both V &Q decreases but the perfusion is more decreased. V/Q=3.3. At the base of the lungs both V&Q are Decrease but the perfusion is more increased V/Q= 0.6 Chemical factors enhanced the exchange of gases at the lungs  TRANSPORT OF CARBON DIOXIDE Carbon dioxide is transported by the blood from cells to the alveoli. Carbon dioxide is transported in the blood in four ways: 1. As dissolved form (7%) 2. As carbonic acid (negligible) 3. As bicarbonate (63%) 4. As carbamino compounds (30%)  AS DISSOLVED FORM Carbon dioxide diffuses into blood and dissolves in the fluid of plasma forming a simple solution. Only about 3 mL/100 mL of plasma of carbon dioxide is transported as dissolved state. It is about 7% of total carbon dioxide in the blood  AS CARBONIC ACID Transport of carbon dioxide in this form is negligible.  AS BICARBONATE About 63% of carbon dioxide is transported as bicarbonate. From plasma, carbon dioxide enters the RBCs. In the RBCs, carbon dioxide combines with water to form carbonic acid. The reaction inside RBCs is very rapid because of the presence of carbonic anhydrase. This enzyme accelerates the reaction. Carbonic anhydrase is present only inside the RBCs and not in plasma.  AS BICARBONATE That is why carbonic acid formation is at least 200 to 300 times more in RBCs than in plasma. Carbonic acid is very unstable. Almost all carbonic acid (99.9%) formed in red blood corpuscles, dissociates into bicarbonate and hydrogen ions. Concentration of bicarbonate ions in the cell increases more and more. Due to high concentration, bicarbonate ions diffuse through the cell membrane into plasma  AS CARBAMINO COMPOUNDS About 30% of carbon dioxide is transported as carbamino compounds. Carbon dioxide is transported in blood in combination with hemoglobin and plasma proteins. Carbon dioxide combines with hemoglobin to form carbamino hemoglobin or carbhemoglobin. And it combines with plasma proteins to form carbamino proteins. Carbamino hemoglobin and carbamino proteins are together called carbamino ompounds  Carbon dioxide combines with proteins or hemoglobin with a loose bond so that, carbon dioxide is easily released into alveoli, where the partial pressure of carbon dioxide is low. Thus, the combination of carbon dioxide with proteins and hemoglobin is a reversible one. Amount of carbon dioxide transported in combination with plasma proteins is very less compared to the amount transported in combination with hemoglobin. It is because the quantity of proteins in plasma is only half of the quantity of hemoglobin Transport of carbon dioxide in blood in the form of bicarbonate and chloride shift