The function of respiration is to provide oxygen to the cells and remove carbon dioxide, which is a waste product of cell metabolism. The lung is the main organ of respiration. The lung consists of two parts-
1. The conducting airways, which bring air to the alveoli.
2.the alveoli, where gas exchange takes place.
The conducting airways- Two nostrils lead to one trachea, which divide into two bronchi, which further divides into bronchioles. There are 20-23 subdivisions of bronchioles and one million terminal bronchioles. Conducting airways do not take part in gas exchange.
Alveoli- The ends of the bronchioles have air sacs or alveoli. Gas exchange occurs in these and there are about 300 million alveoli. They are lined by thin membranes. The total surface area of alveoli is about 70 meters squared or 40 times the surface area of the body. Blood has to be brought to these alveoli to be purified, or for gas exchange to take place. The right heart is the pump which drives venous blood or impure blood into one blood vessel, the pulmonary trunk. It divides and subdivides several times until ultimately, blood flows through the thin walled blood vessels which surround the alveoli. The surface area of these capillaries is roughly 70 meters squared. The right side of the heart is a low pressure system. The driving pressure is about 10 mmHg. The purified areas from the alveoli are collected by different set of pulmonary veins. And this is taken to the left side of the heart, to be pumped to various parts of the body. The circulatory and respiratory systems function simultaneously and precisely to supple oxygen to and eliminatory carbon dioxide from the body.
Respiration is controlled by the central nervous system. There are respiratory centers in the medulla, which are influenced by peripheral centers, which are sensitive to oxygen and carbon dioxide levels in the blood. The respiratory process is facilitated by the muscles which are also controlled by the brain. The respiratory system can be affected by diseases at any of these levels, leading to problems in breathing.