External respiration

 

External respiration which occurs in the lungs is the exchange of gases between blood and lungs. Alveoli are sites of gaseous exchange.

Oxygen from lung diffuses into blood and CO2 diffuses from blood into lungs.

The exchange of Respiratory gases (O2 and CO2) between the lungs and blood take place by diffusion across alveolar and capillary walls.

Partial pressure of oxygen is 104mmHg in alveoli, and PCO2 is only 40mmHg.

PO2 is 40mmHg and PCO2 is 45 mmHg in capillary wall.

PO2 in alveoli is higher than PO2 of capillary and PCO2 of alveoli is lower than PCO2 of capillary.

Alveolar Capillary Membrane

Alveolar Capillary Membrane consist of 4 layers-

1. Alveolar wall, epithelial

2. Epithelial basement membrane

3. Capillary basement membrane, epithelial

4. Capillary endothelial membrane

Factors of rate of external respiration

1. Respiratory membrane thickness, increase thickness of respiratory membrane decrease rate of diffusion that progress into pulmonary edema.

2. Diffusion coefficient

Measure how easily gas diffuses through liquid or tissue.

Breathing rate and depth, rate of airflow into and out of lungs.

Surface area of gas exchange, decrease surface area of Respiratory membrane , respiratory decreases

Partial pressure difference, difference between partial pressure of gas in alveoli and partial pressure of blood in pulmonary capillary.