How are inspiration and expiration take place in humans?
The inflow (inspiration) and outflow (expiration) of air occur between the atmosphere and lungs by the expansion and contraction of lungs. Inspiration: It is the process by which fresh air enters the lungs. The external intercostal muscles present between the ribs contract and pull these ribs and sternum upward and outward increasing the volume to the thoracic cavity. The diaphragm becomes flats and gets lowered by the contraction of its muscles thereby increasing the volume of the thoracic cavity. The abdominal muscles relax and allow the compression of the abdominal organ by the diaphragm As the volume of the thoracic cavity increases and as a result, there is a decrease in air pressure in the lungs. The greater pressure outside the body causes air to flow rapidly into the nostrils through the respiratory tract to the lungs. Expiration: It is a process by which foul air (CO2) is expelled out from the lungs. Internal intercostal muscles contract so that they pull in ribs downward and inward decreasing the size of the thoracic cavity. The muscle fibres of the diaphragm relax making it convex, decreasing the volume of the thoracic cavity. Contraction of abdominal muscles compresses this abdomen and pushes it towards the diaphragm. The overall volume of the thoracic cavity decrease and foul air goes outside from the cavities of alveoli through the respiratory tract.
