User:CFCF/sandbox/Lungs
From Wikipedia, the free encyclopedia
A major organ of the respiratory system, each lung houses structures of both the conducting and respiratory zones. The main function of the lungs is to perform the exchange of oxygen and carbon dioxide with air from the atmosphere. To this end, the lungs exchange respiratory gases across a very large epithelial surface area—about 70 square meters—that is highly permeable to gases.[1]
Lung | |
---|---|
Details | |
System | Respiratory system |
Identifiers | |
Latin | pulmo |
Greek | pneumo (πνεύμων) |
Anatomical terminology |
The human lungs are the organs of respiration. Humans have two lungs, a right lung and a left lung. The right lung consists of three lobes while the left lung is slightly smaller consisting of only two lobes (the left lung has a "cardiac notch" allowing space for the heart within the chest).[2] Together, the lungs contain approximately 2,400 kilometres (1,500 mi) of airways and 300 to 500 million alveoli.
Estimates of the total surface area of lungs vary from 30-50 square metres up to 70-100 square metres (1076.39 sq ft) (8,4 x 8,4 m) in adults — which might be roughly the same area as one side of a tennis court.[3] However, such estimates may be of limited use unless qualified by a statement of scale at which they are taken (see Coastline paradox and Menger sponge).
Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 992 kilometres (616 mi). The lungs together weigh approximately 1.3 kilograms (2.9 lb), with the right lung weighing more than the left.
The pleural cavity is the potential space between the two serous membranes, (pleurae) of the lungs; the parietal pleura, lining the inner wall of the thoracic cage, and the visceral pleura, lining the organs themselves–the lungs. The respiratory system includes the conducting zone, which is part of the respiratory tract, that conducts air into the lungs.
The parenchyma of the lung, only relates to the functional alveolar tissue, but the term is often used to refer to all lung tissue, including the respiratory bronchioles, alveolar ducts, terminal bronchioles, and all connecting tissues.[4]
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart. Their principal function is to transport oxygen from the atmosphere into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere. A large surface area is needed for this exchange of gases which is accomplished by the mosaic of specialized cells that form millions of tiny, exceptionally thin-walled air sacs called alveoli.
To understand the anatomy of the lungs, the passage of air through the nose and mouth to the alveoli must be studied. The progression of air through either the mouth or the nose, travels through the nasopharynx, oropharynx, larynx, and the trachea (windpipe). The air passes down the trachea, which divides into two main bronchi; these branch to the left and right lungs where they progressively subdivide into a system of bronchi and bronchioles until the alveoli are reached. These many alveoli are where the gas exchange of carbon dioxide and oxygen takes place.[5]
Breathing is driven by muscular action; in early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, which is still found in amphibians. Reptiles, birds and mammals use their musculoskeletal system to support and foster breathing.
Medical terms related to the lung often begin with pulmo-, such as in the (adjectival form: pulmonary) or from the Latin pulmonarius ("of the lungs"), or with pneumo- (from Greek πνεύμων "lung").