Describe/ explain the mechanism of breathing/ gaseous exchange in mammals.

Inhalation/inspiration/breathing in.
-Internal intercostal muscles relax; while external intercostal muscles contract; this causes the rib cage (ribs) to move upwards and outwards; the diaphragm muscles contract; which causes the diaphragm to flatten from its normal dome shape;
-This increases the volume of thoracic cavity; and decreases the pressure inside it; the atmospheric pressure being higher than the pressure inside the thoracic cavity forces air to rush into the lungs; through the nose and trachea inflating the lungs;
-Oxygen is in higher concentration in the alveolar cavity than blood (in the capillary); it then diffuses into the capillary through the epithelium of alveolus, capillary wall/endothelium and the plasma into the red blood cells where it combines with haemoglobin;
-Carbon (IV) oxide is in higher concentration in blood than alveolar cavity; hence diffuses out of blood into alveolar cavity and is expelled during exhalation;
Expiration/exhalation/breathing out
-Internal intercostal muscles contract while external intercostal muscles relax; this causes the rib cage to move downwards and inwards; the diaphragm muscles relax; causing the diaphragm to assume a dome shape;
-These movements decrease the volume of the thoracic cavity while increasing pressure;
-These movements decrease the volume of thoracic cavity; and increase pressure inside it; the air is forced out of the lungs into the atmosphere; and the lungs deflate;