1. Gas Transport

2. Learning Objectives Covering the the transport of O 2 and CO 2 in the blood and tissue fluids. Know how O 2 and CO 2 diffuse in pulmonary capillaries, systemic capillaries and in tissues. Understand and be able to use the O 2 -hemoglobin dissociation curve. Know the quantity of O 2 and CO 2 delivered by the blood. Know what causes shifts in the O 2 -hemoglobin dissociation curve. Know how CO 2 is transported in the blood and understand the Haldane Effect.

3. Movement of Gases Gases move by diffusion, from areas of high partial pressure to areas of low partial pressure. - In the alveoli, O 2 moves from the alveoli (high P O2 ) to the pulmonary blood (low P O2 ). - In the tissues, O 2 moves from the blood (high P O2 ) to the tissues (low P O2 ). How will CO 2 diffuse?

4. Diffusion of O 2 in the Pulmonary Capillaries What is the P O2 in the arterial end? 104 mm Hg – 40 mm Hg = 64 mm Hg. What is the net direction of O 2 diffusion in the arterial end? From the alveolar space into the blood. How does the pulmonary anatomy allow the capillary blood to reach a P O2 of 104 mm Hg so quickly in the venous end? - Surface area (70 cm 2 of respiratory membrane for 60-140 mL blood). - Thin respiratory membrane. - P O2.

5. O 2 Diffusion During Exercise During exercise, the body may need 20 x more O 2. How does the exchange in the pulmonary capillaries meet this need? - Increased diffusing capacity (increased surface area and capillaries and improved V A /Q). - The blood reaches O 2 saturation quickly (see previous slide).

6. Changes in P O2 in Cardiovascular System

7. Diffusion of O 2 in the Systemic Capillaries and Tissues The P O2 in the arterial blood is ~ 95 mm Hg and P O2 in the interstitial fluid is ~ 40 mm Hg. Thus, the P O2 ~ 55 mm Hg for the diffusion of O 2 into the interstitial fluid. The P O2 in the interstitial fluid is ~ 40 mm Hg and the P O2 in the tissues ~ 23 mm Hg. Thus, the P O2 ~ 17 mm Hg for the diffusion of O 2 into the tissues.

8. Blood Flow and Interstitial P O2

9. Diffusion of CO 2 in the Systemic Capillaries and Tissues Diffuses in the opposite direction as O 2, because CO 2 accumulates in the tissues as O 2 is consumed. Note: CO 2 can diffuse ~ 20 x more rapidly than O 2 ; so less differences in partial pressures are required.

10. Diffusion of CO 2 in the Pulmonary Capillaries The P CO2 in the tissues ~ 46 mm Hg and the P CO2 in the interstitial fluid ~ 45 mm Hg. Thus, the P CO2 ~ 1 mm Hg for the diffusion of O 2 into the interstitial fluid. The P CO2 in the interstitial fluid ~ 45 mm Hg and the P CO2 in the arterial capillary blood ~ 40 mm Hg. Thus, the P CO2 ~ 5 mm Hg for the diffusion of O 2 into the blood.

11. Diffusion of CO 2 in the Pulmonary Capillaries

12. Blood Flow and the Interstitial P CO2

13. Transport of O 2 by Hemoglobin Nearly all the O 2 (~ 97%) is transported in the blood by hemoglobin. One hemoglobin molecule contains 4 heme prosthetic groups. One hemoglobin molecule can carry 4 O 2 molecules.

14. O 2 -Hemoglobin Dissociation Curve

15. Amount of O 2 Carried by Hemoglobin (Volumes) In 100 ml of blood, contains ~ 15 g of hemoglobin. Each gram of hemoglobin can carry a maximum of 1.34 ml of O 2. Thus, 100 ml of blood can carry a maximum of 20 ml of O 2 (15 x 1.34).

16. Quantity of O 2 Released to Systemic Tissues At 97% hemoglobin saturation (arterial), 100 ml of blood carries ~ 19.4 ml O 2. At 75% saturation (venous), 100 ml of blood carries ~ 14.4 ml O 2. Thus, 100 ml of blood delivers ~ 5 ml of O 2 under normal circumstances. During exercise, 100 ml of blood can deliver ~ 15 ml O 2.

17. O 2 Delivery During Exercise During exercise, 100 ml of blood can deliver ~ 15 ml of O 2 (3-fold increase from normal). What happens to cardiac output during exercise? During exercise, the cardiac output increases 6- to 7- fold. Thus, by increasing O 2 transport and cardiac output, there can be a 20-fold increase in O 2 delivery to tissues during exercise.

18. Using the O 2 -Hemoglobin Dissociation Curve The normal P O2 of the alveoli is 104 mm Hg. This results in a hemoglobin saturation of 97%. What happens to hemoglobin saturation if the alveolar P O2 drops to 60 mm Hg, while climbing a mountain? The hemoglobin saturation only drops to 89%. The venous blood P O2 only needs to drop to 35 mm Hg (from 40) for 5 ml of O 2 per 100 ml to be delivered

19. Shifts in the O 2 -Hemogobin Dissociation Curve Increases in H +, CO 2, and temperature shift the curve to the right. This enhances the release of O 2 from hemoglobin and is called the Bohr Effect. In tissues, the high CO 2 increases the [H + ] (recall blood acid/base reactions involving bicarbonate). Causing the extra release of O 2. In the lungs, the removal of CO 2 decreases the [H + ]. This increases the binding of O 2 to hemoglobin. What happens to H +, CO 2, and temperature in exercising muscle?

20. Transport of CO 2 in the Blood Under normal conditions, the blood delivers ~ 4 ml of CO 2 from the tissues to the lungs in each 100 ml of blood. Why only 4 ml of CO 2 per 100 ml if the blood delivers 5 ml of O 2 per 100 ml? For carbohydrate metabolism, 1 molecule of O 2 is formed for each CO 2 consumed. When fats are metabolized, some of the O 2 combines with H + atoms from the fat to form H 2 O.

21. Transport of CO 2 in the Blood Most of the CO 2 in RBCs reacts with H 2 O, forming carbonic acid, which dissociates to H + and bicarbonate ion.

22. Transport of Bicarbonate to the Plasma Many of the bicarbonate ions are transported out of the RBC in exchange for Cl - by the bicarbonate-chloride carrier protein.

23. CO 2 and Hemoglobin Some CO 2 combines with hemoglobin forming carbaminohemoglobin (CO 2 HbB). In the lungs, the CO 2 is released from CO 2 HbB. Hemoglobin also binds the H + released from the dissociation of carbonic acid. This helps buffer the pH of the RBC.

24. Release of bound CO 2 in the Lungs How does the CO 2 that combined with H 2 O and hemoglobin get released in the lungs? Binding of O 2 to hemoglobin tends to displace CO 2 from the blood. This is called the Haldane Effect.

25. Haldane Effect The binding of O 2 to carbaminohemoglobin promotes its conversion to hemoglobin and CO 2. The binding of O 2 to hemoglobin causes the release of a H + ion. The H + ion can then combine with bicarbonate ion to form carbonic acid, which then dissociates to CO 2 and H 2 O.

26. CO 2 and Blood pH What happens to the blood pH if CO 2 becomes elevated? - It drops, because more carbonic acid is formed. - Normally, the pH of arterial blood is 7.41 and that of venous blood is 7.37 (0.04 difference). - During exercise, the pH of venous blood can drop by 0.5 units.