1. Partial Pressures of O 2 and CO 2 Normal air pressure at sea level 760 mm Hg = 1 atm = 101.3 kPa airtracheaalveoliartery vein PO2159.6149.2104.0100.0 40.0 PCO 2 000.3 040.0 46.0 PH2 O 000.0047.0 47.0 PN2600.1563.5569.0 P total 760.0 756.0706.0

2. Gas Exchange in Alveoli Alveolar Capillaries (Blood traveling from heart to lung – deoxygenated blood) diffusion of oxygen from the alveoli into the blood diffusion of carbon dioxide from the blood into the alveoli.

4. Gas Exchange in Alveoli PO 2 = 40 mm Hg relatively low because this blood has just returned from the systemic circulation & has lost much of its oxygen PCO 2 = 45 mm Hg relatively high because the blood returning from the systemic circulation has picked up carbon dioxide

5. Pressure in the Lungs

6. Gas Exchange in the Tissue Blood leaving the alveolar capillaries returns heart and is pumped into the systemic circulation. This blood travels through arteries and arterioles and finally capillaries where gas exchange with the surrounding tissue occurs.

7. Gas Exchange in the Tissue

8. Entering the systemic capillaries PO 2 = 100 mm Hg PCO 2 = 40 mm Hg Body cells (resting conditions) PO 2 = 40 mm Hg PCO 2 = 45 mm Hg

9. Gas Exchange in the Tissue Differences in partial pressures of oxygen & carbon dioxide in the systemic capillaries & the body cells cause: oxygen to diffuse from the blood & into the cells carbon dioxide to diffuse from the cells into the blood.

10. Gas Exchange in the Tissue Leaving the systemic capillaries PO2 = 40 mm Hg PCO2 = 45 mm Hg Blood leaving the systemic capillaries returns to the heart and is then pumped to the lungs to repeat the process

11. Review