Internal (tissue) respiration is the exchange of gases between tissue blood capillaries and tissue cells (Figure 23.17) and results in the conversion of oxygenated blood into deoxygenated blood. At rest only 25% of the available oxygen in oxygenated blood actually enters tissue cells. During exercise, more oxygen is released. TRANSPORT OF OXYGEN AND CARBON DIOXIDE IN THE BLOOD Oxygen Transport In each 100 ml of oxygenated 1.5% of the O2 is dissolved in the plasma and 98.5% is carried with hemoglobin (Hb) inside red blood cells as oxyhemoglobin (HbO2) (Figure 23.18). Hemoglobin consists of a protein portion called globin and a pigment called heme. The heme portion contains 4 atoms of iron, each capable of combining with a molecule of oxygen. Hemoglobin and Oxygen Partial Pressure The most important factor that determines how much oxygen combines with hemoglobin is PO2. The relationship between the percent saturation of hemoglobin and PO2 is illustrated in Figure 23.19, the oxygen-hemoglobin dissociation curve. The greater the PO2, the more oxygen will combine with hemoglobin, until the available hemoglobin molecules are saturated. Other Factors Affecting Hemoglobin Affinity for Oxygen In an acid (low pH) environment, O2 splits more readily from hemoglobin (Figure 23.20). This is eferred to as the Bohr effect. Low blood pH (acidic conditions) results from high PCO2. Within limits, as temperature increases, so does the amount of oxygen released from hemoglobin (Figure 23.21). Active cells require more oxygen, and active cells (such as contracting muscle cells) liberate more acid and heat. The acid and heat, in turn, stimulate the oxyhemoglobin to release its oxygen. BPG (2, 3-biphosphoglycerate) is a substance formed in red blood cells during glycolysis. The greater the level of BPG, the more oxygen is released from hemoglobin.
Internal (tissue) respiration is the exchange of gases between tissue blood capillaries and tissue cells (Figure 23.17) and results in the conversion of oxygenated blood into deoxygenated blood. At rest only 25% of the available oxygen in oxygenated blood actually enters tissue cells. During exercise, more oxygen is released. TRANSPORT OF OXYGEN AND CARBON DIOXIDE IN THE BLOOD Oxygen Transport In each 100 ml of oxygenated 1.5% of the O2 is dissolved in the plasma and 98.5% is carried with hemoglobin (Hb) inside red blood cells as oxyhemoglobin (HbO2) (Figure 23.18). Hemoglobin consists of a protein portion called globin and a pigment called heme. The heme portion contains 4 atoms of iron, each capable of combining with a molecule of oxygen. Hemoglobin and Oxygen Partial Pressure The most important factor that determines how much oxygen combines with hemoglobin is PO2. The relationship between the percent saturation of hemoglobin and PO2 is illustrated in Figure 23.19, the oxygen-hemoglobin dissociation curve. The greater the PO2, the more oxygen will combine with hemoglobin, until the available hemoglobin molecules are saturated. Other Factors Affecting Hemoglobin Affinity for Oxygen In an acid (low pH) environment, O2 splits more readily from hemoglobin (Figure 23.20). This is eferred to as the Bohr effect. Low blood pH (acidic conditions) results from high PCO2. Within limits, as temperature increases, so does the amount of oxygen released from hemoglobin (Figure 23.21). Active cells require more oxygen, and active cells (such as contracting muscle cells) liberate more acid and heat. The acid and heat, in turn, stimulate the oxyhemoglobin to release its oxygen. BPG (2, 3-biphosphoglycerate) is a substance formed in red blood cells during glycolysis. The greater the level of BPG, the more oxygen is released from hemoglobin.
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