The human lungs are two in number and are the prime organ of respiration in humans. They are enclosed in the thoracic cavity. They are surrounded by the rib cage on all sides and they surround the heart as well as the pericardium. Both the lungs consist of a hilum each, through which the blood vessels enter and exit. The pulmonary veins carry blood that is oxygenated & transfers blood that is purified from the lungs to the heart and enter into the left atrium. The pulmonary arteries carry deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation. The hilum also contains lymphatics and lymph nodes. The lymph nodes are of special significance and get enlarged when there is an infection of the lung or in some other non-infectious conditions like sarcoidosis.
The two lungs are further divided into lobes. The right lung consists of three lobes and the left one has two lobes. The airways are the part of the lungs which are responsible for passage of air inwards and out and the smaller airways are responsible for transfer of gases. The airways start from the trachea which divides into the right and left bronchi which enter the right and left lungs respectively. The bronchi divide into the bronchioles and the terminal bronchioles, respiratory bronchioles, alveolar ducts and finally the alveoli. The bronchi, bronchioles and the terminal bronchioles are surrounded by cartilage, which enable the lumen to remain patent and allow passage of air. The respiratory bronchioles, alveolar ducts and the alveoli are called as the respiratory zone of the lungs as they are mainly responsible for the exchange of gases with the bloodstream. Both the lungs together have 300 to 500 million alveoli.
The human lungs are covered by pleurae. The pleurae have a visceral and parietal component enclosing the pleural cavity in between. The visceral pleura is the part of the pleura which lines the lungs and the parietal pleura lines the inner wall of the thoracic cage. Lung parenchyma refers to the alveolar tissue along with the respiratory bronchioles, alveolar ducts and the terminal bronchioles.
Functions of human lungs:
- The main function of the lungs in humans is respiration. The lungs convert deoxygenated blood into oxygenated blood, which is imperative for oxygen transfer to all the organs of your body.
- Apart from the main function of respiration it helps it also helps to filter out tiny blood clots formed in the veins.
- It also filters out micro air bubbles from the venous blood which may be produced in the blood following deep sea diving.
- Immunoglobulin A is synthesized by the human lungs and secreted into the bronchial secretions which play an important role to maintain the local immunity.
- It causes alterations in the partial pressure of carbon dioxide in the blood and thus helps maintain the pH of your blood.
- It helps in the conversion of angiotensin 1 to angiotensin 2 by the action of angiotensin converting enzyme.
- The mucus produced along the surface of the bronchial epithelium contains many glycoproteins like mucins, lysozymes etc. which contain antimicrobial properties.