Gas Transport Page 1. Introduction The blood transports oxygen and carbon dioxide between the lungs and other tissues throughout the body. These gases are carried in several different forms 1. dissolved in the plasma 2. chemically combined with hemoglobin 3. converted into a different molecule Page 2. Goals To explore how oxygen is transported in the blood. To explore how carbon dioxide is transported in the blood. To understand the effect of variables, such as PO2 and PCO2, on oxygen and carbon dioxide transport.
Page 3. Oxygen Transport Transport of oxygen during external respiration With its low solubility, only approximately 1.5 of the oxygen is transported dissolved in plasma. The remaining 98.5 diffuses into red blood cells and chemically combines with hemoglobin. Label this diagram Page 4. Hemoglobin Within each red blood cell, there are approximately 250 million hemoglobin molecules. Each hemoglobin molecule consists of 1. A globin portion composed of 4 polypeptide chains. 2. Four iron-containing pigments called heme groups. Each hemoglobin molecule can transport up to 4 oxygen molecules because each iron atom can bind one oxygen molecule. When 4 oxygen molecules are bound to hemoglobin, it is 100 saturated when there are fewer, it is partially saturated. Oxygen binding occurs in response to the high partial pressure of oxygen in the lungs. When hemoglobin binds with oxygen, it is called oxyhemoglobin. When one oxygen binds to hemoglobin, the other oxygen molecules bind more readily. This is called cooperative binding. Hemoglobins affinity for oxygen increases as its saturation increases. Label this diagram Page 5. Oxyhemoglobin and Deoxyhemoglobin The formation of oxyhemoglobin occurs as a reversible reaction, and is written as in this chemical equation In reversible reactions, the direction depends on the quantity of products and reactants present. In the lungs, where the partial pressure of oxygen is high, the reaction proceeds to the right, forming oxyhemoglobin. In organs throughout the body where the partial pressure of oxygen is low, the reaction reverses, proceeding to the left. Oxyhemoglobin releases oxygen, forming deoxyhemoglobin, which is also called reduced hemoglobin. Notice that the affinity of hemoglobin for oxygen decreases as its saturation decreases. Page 6. CO2 Transport Carbon dioxide transport Carbon dioxide is produced by cells throughout the body. It diffuses out of the cells and into the systemic capillaries, where approximately 7 is transported dissolved in plasma. The remaining carbon dioxide diffuses into the red blood cells. Within the red blood cells, approximately 23 chemically combines with hemoglobin, and 70 is converted to bicarbonate ions, which are then transported in the plasma. Fill in this diagram Page 7. CO2 Transport Carbaminohemoglobin (Tissues) Of the total carbon dioxide in the blood, 23 binds to the globin portion of the hemoglobin molecule to form carbaminohemoglobin, as written in this equation Carbaminohemoglobin forms in regions of high PCO2, as blood flows through the systemic capillaries in the tissues. Page 8. CO2 Transport Carbaminohemoglobin (Lungs) The formation of carbaminohemoglobin is reversible. In the lungs, which have a lower PCO2, carbon dioxide dissociates from carbaminohemoglobin, diffuses into the alveoli, and is exhaled. Page 9. CO2 Transport Bicarbonate Ions (Tissues) Of the total carbon dioxide in the blood, 70 is converted into bicarbonate ions within the red blood cells, in a sequence of reversible reactions. The bicarbonate ions then enter the plasma. In regions with high PCO2, carbon dioxide enters the red blood cell and combines with water to form carbonic acid. This reaction is catalyzed by the enzyme carbonic anhydrase. The same reaction occurs in the plasma, but without the enzyme it is very slow. Carbonic acid dissociates into hydrogen ions and bicarbonate...
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