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The lungs of mammals have a spongy texture and are honeycombed with epithelium having a much larger surface area in total than the outer surface area of the lung itself. The lungs of humans are typical of this type of lung.
Breathing is largely driven by the diaphragm below, a muscle that by contracting expands the cavity in which the lung is enclosed. The rib cage itself is also able to expand and contract to some degree.
As a result, air is sucked into and pushed out of the lungs through the trachea and the bronchial tubes or bronchi; these branch out and end in alveoli which are tiny sacs surrounded by capillaries filled with blood. Here oxygen from the air diffusesThis article is about the physical mechanism of diffusion. For alternative meanings, see diffusion (disambiguation). Diffusion is the spontaneous spreading of something such as particles, heat, or momentum. The phenomenon is readily observed when a drop o into the blood, where it is carried by hemoglobinHaemoglobin ( BE) or hemoglobin ( AE), is the iron-containing oxygen-transport metalloprotein in the red cells of the blood in mammals and other animals. The molecule consists of globin, the apoprotein, and four haem groups, an organic molecule with an ir.
The deoxygenated blood from the heartThis page is about the muscular organ, the Heart . For other meanings of the word, see Heart (disambiguation). The heart ( Latin cor is a hollow, muscular organ that pumps blood through the blood vessels by repeated, rhythmic contractions. The term cardia reaches the lungs via the pulmonary arteryThe pulmonary arteries carry blood from the heart to the lungs. They are the only arteries (other than umbilical arteries in the fetus) that carry deoxygenated blood. In the human heart, the pulmonary trunk begins at the base of the right ventricle. It is and, after having been oxygenated, returns via the pulmonary veinThe pulmonary veins carry blood from the lungs to the left atrium of the heart. They are the only veins in the adult human body that carry oxygenated blood.s.
The lungs are located inside the thoracic cavityThe thoracic cavity is the chamber of the human body (and other animal bodies) that is enclosed by the ribcage and the diaphragm. It houses # the lungs, # the heart, # the thoracic aorta, # the main pulmonary artery and its branches, # the thymus gland, #, protected by the bony structure of the rib cage and enclosed by a double-walled sac called pleura. The inner layer of the sac adheres tightly to the outside of the lungs and the outer layer is attached to the wall of the chest cavity. The two layers are separated by a thin space called the pleural cavity that is filled with pleural fluid; this allows the inner and outer layers to slide over each other, and prevents them from being separated easily.
The lungs of vertebrates are closely related (i.e. homologous) to the swim bladders of fish (but not to their gills). The evolutionary origin of both are thought to be outpocketings of the upper intestines. This is reflected by the fact that the lungs of a fetus also develop from an outpocketing of the upper intestines (see ontogeny and phylogeny). The article on swim bladders contains further details about the evolutionary origin of these two organs.
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