Gas Exchange and Transport in Lungs and Tissues PDF

LESSON 6. Gas Exchange and Transport in Lungs and Tissues 1. External and Internal Respiration 2. Oxygen Transport 1. The Relationship Between Hemoglobin and Oxygen Partial Pressure 2. Other Factors Affecting the Affinity of Hemoglobin for Oxygen 1. Ac...

LESSON 6. Gas Exchange and Transport in Lungs and Tissues 1. External and Internal Respiration 2. Oxygen Transport 1. The Relationship Between Hemoglobin and Oxygen Partial Pressure 2. Other Factors Affecting the Affinity of Hemoglobin for Oxygen 1. Acidity (pH). 2. Partial pressure of carbon dioxide. 3. Temperature. 4. 2,3-bisphosphoglycerate 1. External and Internal Respiration External respiration = pulmonary gas exchange = diffusion of O2 from air in the alveoli of the lungs to blood in pulmonary capillaries and the diffusion of CO2 in the opposite direction. External respiration in the lungs converts deoxygenated blood coming from the right side of the heart into oxygenated blood that returns to the left side of the heart. Internal respiration = systemic gas exchange = exchange of O2 and CO2 between systemic capillaries and tissue cells. As O2 leaves the bloodstream, oxygenated blood is converted into deoxygenated blood. Internal respiration occurs in tissues throughout the body. 2. Oxygen Transport Oxygen does not dissolve easily in water. 1.5% of inhaled O2 is dissolved in blood plasma. 98.5% of blood O2 is bound to hemoglobin in red blood cells. Oxygen and hemoglobin bind in an easily reversible reaction to form oxyhemoglobin. 2.1. The Relationship Between Hemoglobin and Oxygen Partial Pressure The most important factor that determines how much O2 binds to hemoglobin is the PO2. When reduced hemoglobin (Hb) is completely converted to oxyhemoglobin (Hb–O2), the hemoglobin is said to be fully saturated. When Hb consists of a mixture of Hb and Hb– O2, it is partially saturated. The percent saturation of hemoglobin expresses the average saturation of hemoglobin with oxygen. The relationship between the percent saturation of hemoglobin and PO2 is illustrated in the oxygen–hemoglobin dissociation curve. In pulmonary capillaries, where PO2 is high, a lot of O2 binds to hemoglobin. In tissue capillaries, where the PO2 is lower, hemoglobin does not hold as much O2, and the dissolved O2 is unloaded via diffusion into tissue cells. 2.2. Other Factors Affecting the Affinity of Hemoglobin for Oxygen 1. Acidity (pH). As acidity , the affinity of Hb for O2 , and O2 dissociates more readily from Hb. Increasing acidity enhances the unloading of oxygen from hemoglobin. When pH , the oxygen–Hb dissociation curve shifts to the right. Bohr effect. 2. Partial pressure of carbon dioxide. CO2 also can bind to Hb, and the effect is similar to that of H+ (shifting the curve to the right). As PCO2 rises, Hb releases O2 more readily. PCO2 and pH are related factors because low blood pH (acidity) results from high PCO2. An increased PCO2 produces a more acidic environment, which helps release O2 from hemoglobin. Decreased PCO2 (and elevated pH) shifts the saturation curve to the left. 3. Temperature. Within limits, as temperature increases, so does the amount of O2 released from hemoglobin. Heat is a byproduct of the metabolic reactions of all cells. Metabolically active cells require more O2 and liberate more acids and heat. During hypothermia cellular metabolism slows, the need for O2 is reduced, and more O2 remains bound to hemoglobin: shifts the saturation curve to the left. 4. BPG. A substance found in RBCs called 2,3-bisphosphoglycerate (BPG) decreases the affinity of Hb for O2 and thus helps unload O2 from Hb. BPG is formed in RBCs when they break down glucose to produce ATP in a process called glycolysis. Certain hormones, such as thyroxine, GH, epinephrine, norepinephrine, and testosterone, increase the formation of BPG. The level of BPG also is higher in people living at higher altitudes. 3. Carbon Dioxide Transport 1. Dissolved CO2. 7% is dissolved in blood plasma. Upon reaching the lungs, it diffuses into alveolar air and is exhaled. 2. Carbamino compounds. 23%, combines with the amino groups of amino acids and proteins in blood to form carbamino compounds. 3. Bicarbonate ions. 70% is transported in blood plasma as bicarbonate ions (HCO3-). 1. At lower partial pressures of oxygen (PPO2), the oxygen–hemoglobin dissociation curve exhibits: a. A leftward shift b. A rightward shift c. No shift d. A vertical shift 2. Which of the following factors leads to a rightward shift in the oxygen– hemoglobin dissociation curve? a. Decreased temperature b. Increased pH (alkalosis) c. Increased 2,3-diphosphoglycerate (2,3-DPG) levels d. Decreased carbon dioxide levels 3. In a leftward shift of the oxygen–hemoglobin dissociation curve, hemoglobin's affinity for oxygen is: a. Decreased b. Increased c. Unchanged d. Inversely proportional 4. The Bohr effect refers to the influence of __________ on the oxygen– hemoglobin dissociation curve. a. Temperature b. pH c. Pressure d. Hemoglobin concentration 5. Which condition is most likely to cause a leftward shift in the oxygen– hemoglobin dissociation curve? a. Increased temperature b. Decreased pH (acidosis) c. Decreased 2,3-diphosphoglycerate (2,3-DPG) levels d. Increased carbon dioxide levels