Physiology of the Respiratory System

Mechanics of Breathing
Breathing is also known as pulmonary ventilation. In the mechanics of breathing, volume changes lead to pressure changes, which lead to the flow of gases to equalize the pressure.

Inspiration
In inspiration, air flows into the lungs and the inspiratory muscles contract. The thoracic cavity's height then increases. The diaphragm contracts and flattens out, which allows contractions and the thorax enlarges. There is a decrease in gas pressure in the lungs, which produces a partial vacuum that sucks air into lungs.

Expiration
In expiration, air leaves the lungs and inspiratory muscles relax. Lungs then recoil and volume decreases. Gases flow to equalize the pressure that exists in and out of the lungs.

Nonrespiratory Air Movements
Nonrespiratory air movements are the result of reflex activity such as coughs, laughs, sneezes, and emotions.

Respiratory Sounds
Bronchial Sounds
Bronchial sounds are produced by air rushing through large respiratory passageways.

Vascular Breathing Sounds
Vascular breathing sounds are soft, like a muffled breeze when air fills the alveoli.

External Respiration, Gas Transport, Internal Respiration
External Respiration
In external respiration, there is an exchange of gases between alveoli and the blood. There is more oxygen in alveoli than in the blood. Tissues remove oxygen and release carbon dioxide from the blood.

Gas Transport in the Blood
When gas transport occurs, it attaches hemoglobin molecules in red blood cells to form oxyhemoglobin. Carbon dioxide is transported in plasma as a bicarbonate ion.

Internal Respiration
Internal respiration is the exchange of gases that takes place between the blood and tissue cells. Carbon dioxide diffusing out of the tissue enters blood, and blood combines with water (carbonic acid) which releases bicarbonate ions to diffuse into plasma.