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The lung
is an organ belonging to the respiratory system and interfacing to the circulatory system of air-breathing vertebrates. Its function is to exchange oxygen from air with carbon dioxide from blood. The process in which this happens is called "external respiration" or breathing. There are also nonrespiratory functions of the lungs. Medical terms related to the lung often start in pulmo- from the Latin word pulmones for lungs.
Mammalian lungs
The lungs of mammalis 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 diffuses into the blood, where it is carried by hemoglobin.
The deoxygenated blood from the heart reaches the lungs via the pulmonary artery and, after having been oxygenated, returns via the pulmonary veins.
Location
The lungs are located inside the thoracic cavity, 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 left lung is smaller than the right one to give way for the heart.
Evolutionary origins
The lungs of vertebrates are closely related (i.e. homologous) to the gas 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.
Nonrespiratory functions of the lungs
In addition to respiratory functions such as gas exchange and regulation of hydrogen ion concentration, the lungs also:
influence on the concentration of biologically active substances and drugs used in medicine in arterial blood
filter out small blood clots formed in the systemic veins
serve as a physical layer of soft, shock-absorbent protection for the heart, which the lungs flank and nearly enclose.
Tuberculosis is an infection with the bacterium Mycobacterium tuberculosis, which most commonly affects the lungs (pulmonary TB) but can also affect the central nervous system (meningitis), lymphatic system, circulatory system (miliary TB), genitourinary system, bones and joints.
Other names for the disease are:
TB (short for tuberculosis)
Consumption (TB seemed to consume people from within with its symptoms of bloody cough, fever, pallor, and long relentless wasting)
Wasting disease
White plague (TB sufferers appeared markedly pale)
Phthisis (Greek for consumption) and phthisis pulmonalis
Scrofula (swollen neck glands)
King's evil (so called because it was believed that a king's touch would heal scrofula)
Pott's disease of the spine
Miliary TB (x-ray lesions look like millet seeds)
Tabes mesenterica (TB of the abdomen)
Lupus vulgaris (the common wolf - TB of the skin)
Tuberculosis is the most common major infectious disease today, infecting two billion people or one-third of the world's population, with nine million new cases of active disease annually, resulting in two million deaths, mostly in developing countries.
Most of those infected (90 percent) have asymptomatic latent TB infection (LTBI). There is a 10 percent lifetime chance that LTBI will progress to active TB disease which, if left untreated, will kill more than 50 percent of its victims. TB is one of the top three infectious killing diseases in the world: HIV/AIDS kills 3 million people each year, TB kills 2 million, and malaria kills 1 million.
The neglect of TB control programs, HIV/AIDS, and immigration has caused a resurgence of tuberculosis. Multiple drug resistant strains of TB (MDR-TB) is increasing. The World Health Organization declared TB a global health emergency in 1993.
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This article is licensed under the GNU Free Documentation License.
It uses material from the Wikipedia article "Lungs"
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