endocrine Ven-do-kronN system Group of ductless glands that secrete hormones necessary for normal growth and development, reproduction, and homeostasis. The major endocrine glands are the hypothalamus, pitu¬ itary, PINEAL, THYROID, PARATHYROIDS, ADRENALS, islets of LANGERHANS in the PAN¬ CREAS, ovaries, and testes. Secretion is regulated either by regulators in a gland that detect high or low levels of a chemical and inhibit or stimu¬ late secretion or by a complex mechanism involving the hypothalamus and the pituitary. Tumours that produce hormones can throw off this bal¬ ance. Diseases of the endocrine system result from over- or underproduc¬ tion of a hormone or an abnormal response to a hormone. See illustration opposite on following page.
endocrinology Yen-do-kri-'nal-o-jeX Medical discipline dealing with regulation of body functions by hormones and other biochemicals and treatment of endocrine system imbalances. In 1841 Friedrich Gustav Henle first recognized “ductless glands,” which secrete products directly into the bloodstream. The field was essentially established in the early 20th cen¬ tury, when Ernest H. Starling, who introduced the term hormone , proposed that chemical and nervous regulation of physiological processes were linked. Endocrine therapy is based on replacing deficient hormones with purified extracts. Nuclear technology has led to new treatments; use of radioactive iodine for hyperthyroidism greatly reduced the need for thy¬ roid gland surgery. The detection of minute amounts of hormone with radioimmunoassays (see radiology) permits early diagnosis and treatment of endocrine disorders.
endogamy See exogamy and endogamy
endometriosis V.en-do-.me-tre-'o-sosV Disorder of the female repro¬ ductive system in which endometrium (uterine lining) grows in an abnor¬ mal location because some endometrial fragments traverse the fallopian tubes into the abdominal cavity and become embedded on structures there, usually the ovaries, rather than exiting the uterus via the vagina (during menstruation). Symptoms include pain on menstruation, sexual inter¬ course, defecation, and/or urination; heavy menstrual flow; blood in the urine; and infertility. Diagnosis is best made by laparoscopy. Treatment includes surgery and hormones to suppress ovulation for six to nine months.
endoplasmic reticulum Yen-do-'plaz-mik-ro-'tik-yo-bmX (ER) Membrane system within the cytoplasm of a eukaryotic cell (see eukary¬ ote), important in the synthesis of proteins and lipids. The ER usually makes up more than half the membrane of the cell and is continuous with the outer membrane of the nuclear envelope (see nucleus). There are two distinct regions of ER: the rough ER, or RER (so called because of the protein-synthesizing ribosomes attached to it), and the smooth ER (SER), which is not associated with ribosomes and is involved in the synthesis of lipids and the detoxification of some toxic chemicals.
endorphin \en-'dor-f3n\ Any of a group of proteins occurring in the brain and having pain-relieving properties typical of opium and related opiates. Discovered in the 1970s, they include enkephalin, beta- endorphin, and dynorphin. Each is distributed in characteristic patterns throughout the nervous system. Endorphins are released in response to pain or sustained exertion (causing, e.g., the “runner’s high”). They are also believed to have a role in appetite control, release of pituitary sex hor¬ mones, and shock. There is strong evidence that they are connected with “pleasure centres” in the brain, and they seem to be activated by acupunc¬ ture. Knowledge of their behaviour has implications for treating addic¬ tions and chronic pain.
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endoscopy ► Engels I 621
hypothalamus - pineal gland pituitary gland
-thyroid gland
parathyroid glands (behind thyroid)
adrenal glands
-islets of
Langerhans (in pancreas)
ovary (in female)
testis (in male)
Major glands of the human endocrine system. The hypothalamus stimulates the pitu¬ itary gland and influences food intake, weight regulation, fluid intake and balance, thirst, body heat, and the sleep cycle. Pituitary hormones stimulate growth, egg and sperm development, milk secretion, and release of hormones by other glands. The pineal gland may play a significant role in sexual maturation and the circadian rhythm. Thyroid hormones regulate the metabolic rate of tissues, stimulate the con¬ traction of heart muscle, and are necessary for normal growth and brain develop¬ ment before birth and during infancy. Parathyroid hormone regulates calcium, phosphorus, and magnesium levels. The adrenal glands regulate salt and water retention, some reactions of the immune system, and blood pressure. The islets of Langerhans regulate blood sugar levels. The ovaries and testes produce hormones that regulate the reproductive system and that produce male and female secondary sex characteristics.
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endoscopy \en-'das-ko-pe\ Examination of the body’s interior through an instrument inserted into a natural opening or an incision, usually as an outpatient procedure. Endoscopes include the upper gastrointestinal endo¬ scope (for the esophagus, stomach, and duodenum), the colonoscope (for the colon), and the bronchoscope (for the bronchial tubes). With fibre optics, much more maneuverable instruments can reach formerly inaccessible sites, while causing much less discomfort. Attachments can take tissue samples, excise polyps and small tumours, and remove foreign objects.
endotherm So-called warm-blooded animals; that is, those that main¬ tain a constant body temperature independent of the environment. The endotherms include the birds and mammals. If heat loss exceeds heat gen¬ eration, metabolism increases to make up the loss or the animal shivers to raise its body temperature. If heat generation exceeds the heat loss, mechanisms such as panting or perspiring increase heat loss. Unlike ecto- therms, endotherms can be active and survive at quite low external tem¬ peratures, but because they must produce heat continuously, they require high quantities of “fuel” (i.e., food).
Energia also called RKK Energia formerly OKB-1 Russian aero¬ space company that is a major producer of spacecraft, rockets, and mis¬ siles. Energia originated in 1946 as a department within a Soviet institute
conducting work on long-range missiles. Ten years later, under Sergey Korolyov, it became the independent design bureau OKB-1. In the 1950s it developed the R-7 (SS-6), the world’s first inter-continental ballistic missile; a modified R-7 placed the first artificial satellite into orbit (see Sputnik). OKB-1 was responsible for the U.S.S.R.’s commanding early lead in the “space race,” although it failed in its secret project to beat the U.S. to a manned Moon landing. In 1974 the conglomerate NPO Energia was created with OKB-1 at its center. A main focus for the company was the development and operation of space stations (see Salyut, Mir). In the early 1990s Energia became the main contractor for the Russian portion of the International Space Station (it provided the station’s Zvezda habi¬ tat and control module), but its role was later reduced. In 1994 it was renamed RKK Energia and partially privatized. After the dissolution of the Soviet Union in 1991, Energia partnered with multinational satellite launching services, to which it provided its Block DM upper stage for boosting payloads to geostationary orbit.
energy Capacity for doing work. Energy exists in various forms— including kinetic, potential, thermal, chemical, electrical (see electricity), and nuclear —and can be converted from one form to another. For example, fuel-burning heat engines convert chemical energy to thermal energy; batteries convert chemical energy to electrical energy. Though energy may be converted from one form to another, it may not be created or destroyed; that is, total energy in a closed system remains constant. All forms of energy are associated with motion. A rolling ball has kinetic energy, for instance, whereas a ball lifted above the ground has potential energy, as it has the potential to move if released. Heat and work involve the trans¬ fer of energy; heat transferred may become thermal energy. See also acti¬ vation ENERGY, BINDING ENERGY, IONIZATION ENERGY, MECHANICAL ENERGY, SOLAR ENERGY, ZERO-POINT ENERGY.