Respiratory Organs
Lungs: The lungs’ primary function is gas exchange. Oxygen is delivered to the tissue and carbon dioxide is removed from the tissues. Breathing is an automatic, rhythmic mechanical process, which delivers O2 to the tissues and removes CO2 from the tissues.
Alveoli: The exchange of gases between the external environment and cells of the body takes place in the individual alveolus. Oxygen and carbon dioxide exchange passively between the pulmonary capillaries and the alveoli; These gases move along their partial pressure gradients, i.e- from high to low.
Function of the Respiratory System
Protection: Cilia, both in the upper airways and trachea, beat and move mucous continually towards the mouth. Macrophage Alveolar macrophages phagocytose inhaled particulate matter and pathogens.
Thermoregulation: Heat loss from the respiratory system helps the body regulate internal body temperature.
Respiratory Mechanics
Differential pressure during inspiration: At the end of expiration, just before the beginning of inspiration, the pressure inside the lung is the same as the atmospheric pressure outside the body. 15/29 When the diaphragm actively contracts, the internal lung volume increases and the pressure inside the lung decreases. The change in internal pressure causes air to rush into the lungs and down its pressure gradient.
Differential pressure during expiration: At the end of inspiration, the diaphragm relaxes passively. The lung volume decreases and this causes the internal pressure inside the lungs to increase to a level higher than atmospheric pressure outside the body.
Lung elasticity and surface tension effects: the ability of the lungs’ elastic tissue to recoil during expiration. Elastins are elastic fibers present in the walls of the alveoli, which allow the lungs to return to their resting volume after expiration.
Pulmonary surfactant: Pulmonary surfactant is a phospholipid, similar to those found in a lipid bilayer surrounding human cells. It is made by pneumocytes in the lungs.
