Human Anatomy and Physiology Respiration: Gas exchange

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

Dalton’s Law P T = P 1 + P 2 + P 3 etc. Therefore each gas has a partial pressure ( p gas) P gas = % of total mixture

Dalton’s Law Atmospheric air

Henry’s Law Gases dissolve into liquid in proportion to their partial pressure Equilibrium will be reached (e.g. gases in the lung) Gas state (lung) Liquid state (blood) (fast) (slower) (no movement)

Gas solubility Factors effecting: Temperature (not in humans) Solubility of gas Air: CO 2 > O 2 (20th) > N 2 (1/2) Would humans survive if air had more CO 2 than O 2 ?

Alveolar gases At any point in time air in alveoli contains: Less O 2, more CO 2 & H 2 O

Why is gas composition different? O 2 diffuses into blood, CO 2 in opposite direction Humid air in conductive pathway Air in alveoli a mixture of air from more than one breath How can humans alter gas composition? Increase rate and depth of breathing

Vascular circuits Systemic Coronary Pulmonary Bronchial – to lungs from heart

Gas pressure gradients

Pressure gradients Oxygen pO 2 in deoxygenated blood is 40 mmHg pO 2 in alveoli is 104 mmHg

Pressure gradients Carbon dioxide pCO 2 in alveoli is 40 mmHg pCO 2 in deoxygenated blood is 45 mmHg 5 64

Pressure gradients Relatively the same amount of O 2 and CO 2 are exchanged. Why? Answer: Solubility

Surface area Why is surface area important? Surface area in a human lung is 70m 2 Factors decreasing surface area Emphysema (volume unchanged) Tumors, mucus

Ventilation-perfusion coupling Low ventilation Well perfused High ventilation Poor perfusion Poor ventilation Poor perfusion High ventilation High perfusion vasoconstriction vasodilation

Gas transport in blood Methods of transport 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) Solution: Hb carries both O 2 and CO 2 simultaneously

Hemoglobin structure Oxy vs. deoxyhemoglobin O2O2 CO 2

Oxygen transport in blood The term percent saturation Deoxyhemoglobin: Hb is 75% saturated

Hb-O 2 affinity Decreasing affinity Decrease in pH (Bohr effect) Binding to 2,3 diphosphoglycerate Elevated temperature Increase in pCO 2 75% 55% pO 2

Oxygen transport Hypoxia: inadequate O 2 to tissues Anemic: few RBC’s Ischemic: impaired or blocked blood circulation Histotoxic: body cells unable to use O 2 even though enough delivered (cyanide) Hypoxemic: reduced arterial pO 2 (CO 2 poisoning)

CO 2 transport Ways to transport Dissolved in plasma (7 - 10%) Bound to Hb ( %) Bicarbonate ion ( %)

CO 2 transport from tissue

CO 2 transport into lungs