Breathing and Exchange of Gases

Breathing is the physical process of taking in oxygen (inspiration) and releasing carbon dioxide (expiration).

Alveoli of the lungs are the primary site for gaseous exchange.

Inspiration is the process of drawing air into the lungs by expanding the thoracic cavity.

Expiration is the process of expelling air from the lungs by relaxing the thoracic cavity.

The diaphragm and external intercostal muscles assist in inspiration.

The medulla oblongata regulates breathing rhythm.

Tidal volume is the volume of air inspired or expired during normal breathing, about 500 mL in adults.

Vital capacity is the maximum amount of air a person can breathe out after a maximum inhalation.

Total lung capacity is the total volume of air the lungs can hold after maximum inspiration.

Residual volume is the amount of air remaining in the lungs after maximum expiration.

Diffusion is the movement of gases across the alveolar membrane from high concentration to low concentration.

A large alveolar surface area increases the efficiency of gas exchange.

Hemoglobin transports oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs.

About 97% of oxygen is transported bound to hemoglobin as oxyhemoglobin.

About 70% of carbon dioxide is transported as bicarbonate ions in plasma.

The Bohr effect is the decrease in hemoglobin’s oxygen-binding affinity due to increased CO₂ or decreased pH.

The Haldane effect is the increased binding of CO₂ to hemoglobin when oxygen levels are low.