1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 42.7: Respiratory pigments bind and transport gases The metabolic demands of many organisms require that the blood transport large quantities of O 2 and CO 2 Gases diffuse down pressure gradients in the lungs and other organs Diffusion of a gas depends on differences in a quantity called partial pressure

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A gas always diffuses from a region of higher partial pressure to a region of lower partial pressure In the lungs and in the tissues, O 2 and CO 2 diffuse from where their partial pressures are higher to where they are lower

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inhaled airExhaled air 160 0.2 O2O2 CO 2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 40 45 100 40 104 40 120 27 CO 2 O2O2 Alveolar epithelial cells Pulmonary arteries Blood entering alveolar capillaries Blood leaving tissue capillaries Blood entering tissue capillaries Blood leaving alveolar capillaries CO 2 O2O2 Tissue capillaries Heart Alveolar capillaries of lung 45 Tissue cells Pulmonary veins Systemic arteries Systemic veins O2O2 CO 2 O2O2 Alveolar spaces 1 2 4 3 Figure 42.27

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Respiratory Pigments Respiratory pigments are proteins that transport oxygen – Greatly increase the amount of oxygen that blood can carry The respiratory pigment of almost all vertebrates is the protein hemoglobin, contained in the erythrocytes

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hemoglobin must reversibly bind O 2, loading O 2 in the lungs and unloading it in other parts of the body Heme group Iron atom O 2 loaded in lungs O 2 unloaded In tissues Polypeptide chain O2O2 O2O2 Figure 42.28

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Loading and unloading of O 2 depend on cooperation between the subunits of the hemoglobin molecule The binding of O 2 to one subunit induces the other subunits to bind O 2 with more affinity Cooperative O 2 binding and release is evident in the dissociation curve for hemoglobin A drop in pH lowers the affinity of hemoglobin for O 2

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings O 2 unloaded from hemoglobin during normal metabolism O 2 reserve that can be unloaded from hemoglobin to tissues with high metabolism Tissues during exercise Tissues at rest 100 80 60 40 20 0 100 80 60 40 20 0 100 80 60 40 200 100 80 60 40 200 Lungs P O 2 (mm Hg) O 2 saturation of hemoglobin (%) Bohr shift: Additional O 2 released from hemoglobin at lower pH (higher CO 2 concentration) pH 7.4 pH 7.2 (a) P O 2 and Hemoglobin Dissociation at 37°C and pH 7.4 (b) pH and Hemoglobin Dissociation Figure 42.29a, b

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Carbon Dioxide Transport Hemoglobin also helps transport CO 2 and assists in buffering Carbon from respiring cells diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 42.30 Tissue cell CO 2 Interstitial fluid CO 2 produced CO 2 transport from tissues CO 2 Blood plasma within capillary Capillary wall H2OH2O Red blood cell Hb Carbonic acid H 2 CO 3 HCO 3 – H+H+ + Bicarbonate HCO 3 – Hemoglobin picks up CO 2 and H + HCO 3 – H+H+ + H 2 CO 3 Hb Hemoglobin releases CO 2 and H + CO 2 transport to lungs H2OH2O CO 2 Alveolar space in lung 2 1 3 4 5 6 7 8 9 10 11 To lungs Carbon dioxide produced by body tissues diffuses into the interstitial fluid and the plasma. Over 90% of the CO 2 diffuses into red blood cells, leaving only 7% in the plasma as dissolved CO 2. Some CO 2 is picked up and transported by hemoglobin. However, most CO 2 reacts with water in red blood cells, forming carbonic acid (H 2 CO 3 ), a reaction catalyzed by carbonic anhydrase contained. Within red blood cells. Carbonic acid dissociates into a biocarbonate ion (HCO 3 – ) and a hydrogen ion (H + ). Hemoglobin binds most of the H + from H 2 CO 3 preventing the H + from acidifying the blood and thus preventing the Bohr shift. CO 2 diffuses into the alveolar space, from which it is expelled during exhalation. The reduction of CO 2 concentration in the plasma drives the breakdown of H 2 CO 3 Into CO 2 and water in the red blood cells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4). Most of the HCO 3 – diffuse into the plasma where it is carried in the bloodstream to the lungs. In the HCO 3 – diffuse from the plasma red blood cells, combining with H + released from hemoglobin and forming H 2 CO 3. Carbonic acid is converted back into CO 2 and water. CO 2 formed from H 2 CO 3 is unloaded from hemoglobin and diffuses into the interstitial fluid. 1 2 3 4 5 6 7 8 9 10 11