Comparative Vertebrate Physiology Respiration: Gas exchange

Gas transfer systems Components: 1. Breathing 2. Respiratory diffusion 3. Bulk transport 4. Cellular diffusion

Dalton’s Law PT = P1 + P2 + P3 etc. Therefore each gas has a partial pressure (Pgas) Pgas = % of total mixture

Dalton’s Law Atmospheric air

Henry’s Law Gases dissolve into liquid in proportion to their partial pressure and their solubility [G] = Pgas x Sgas Equilibrium will be reached (e.g. gases in the lung)

Gas solubility Air: CO2 > O2(1/20th) > N2 (1/2) What if air had more CO2 than O2?

Alveolar gases Air in alveoli contains: Less O2, more CO2 & H2O

Why is gas composition different? O2 diffuses into blood, CO2 in opposite direction Humid air in conductive pathway Air in alveoli a mixture of air from more than one breath How to alter gas composition? Increase rate and depth of breathing

Pressure gradients

Pressure gradients Oxygen pO2 in deoxygenated blood is 40 mmHg pO2 in alveoli is 104 mmHg

Pressure gradients Carbon dioxide pCO2 in alveoli is 40 mmHg pCO2 in deoxygenated blood is 45 mmHg

Pressure gradients Relatively the same amount of O2 and CO2 are exchanged. Why? ANSWER: Solubility

Ventilation-perfusion coupling

Gas transport in blood Methods Dissolved in plasma (3 ml per liter) Problem: C.O. would need to be 80 l/min Bound to a respiratory pigment (Hb) (200 ml per liter) Hb carries both O2 and CO2 simultaneously

Hemoglobin structure Oxy vs. deoxyhemoglobin

Oxygen transport in blood Percent saturation Deoxyhemoglobin: Hb is 75% saturated

Oxygen transport in blood Lampreys have modified Hb (1 heme) Why the sigmoidal shape with Hb?

Hb-O2 affinity Decreasing affinity Bohr Effect: Decrease in pH or increase in PCO2

Hb-O2 affinity Decreasing affinity Binding to 2,3 DPG Elevated temperature

Carbon dioxide transport Ways to transport Dissolved in plasma (7 - 10%) Bound to Hb (20 - 30%) * Bicarbonate ion (60 - 70%) ** ** ** *