BISC 101 Lecture Notes - Lecture 17: Gas Exchange, Countercurrent Exchange, Respiratory System

• School: Simon Fraser University
• Department: Biological Sciences
• Course: BISC 101
• Professor: Tony Williams

Document Summary

Ventilation: movement of air/water through or around gas exchange surfaces. Gas exchange occurs by diffusion as o2 and co2 move between air/water and blood at. Also occurs at tissues between blood and cells (cellular respiration) Circulatory systems transport gases throughout the body, delivering them to cells/tissues. Air and water as respiratory media drive evolution of physiology. O2 is plentiful (21% at sea level) Air is less dense and less viscous. Low efficiency (we extract only 25% of air we inhale) Much less at higher temperatures and salinities. Many small animals lack specialized gas exchange organs rely on diffusion across their body surface. Very thin body walls (1-2 cells thick) = short diffusion distance. Large surface area from long, thin or flattened body shape. Circulatory systems minimize the distance substances must diffuse to enter/leave cell. O2 from air diffuses across only 2 cell layers in lungs; at tissues, o2 again diffuses short distance from blood to cells.