PHSI 208 Lecture 39: M15 Respiratory System 2-1
Document Summary
Gas composition in the alveoli determines rate of o2 and co2 diffusion b/w alveoli and capillaries. Atm po2 = 155 mmhg, pco2 = 0. 25 mmhg. Normal ventilation: po2 = 100 mmhg, pco2 = 40 mmhg. Po2 and pco2 remain relatively constant during quiet respiration: o2 entering = o2 uptake, fresh air diluted upon entering the lungs. Ventilation and alveolar blood flow (perfusion) are matched. Bringing o2 from the atmosphere into the alveoli is only the first step of external respiration: blood flow must be high enough to pick up the available o2, wasted ventilation/perfusion. Local regional control: gravity: blood flow is highest at the base of the lung, and as you move upward there"s a reduction in blood flow. More negative intrapleural pressure due to gravity at apex means alveoli are partially open even and filled at rest, and therefore do not take much air during respiration. Very little autonomic innervation of the pulmonary arterioles.
