cyst(redirected from Uveal cyst)
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cyst,abnormal sac in the body, filled with a fluid or semisolid and enclosed in a membrane. Cysts can be congenital but are usually acquired, the most common locations being the skin and the ovaries. Sebaceous cysts of the skin, known as blackheads or whiteheads, occur when dirt or other material blocks the oil glands of the skin, preventing secretions from escaping. Retention cysts develop in glandular organs when ducts are blocked, commonly in kidney tubules, mammary glands, and sweat glands. Most cysts can be aspirated for treatment and/or cytology (diagnostic purposes); often cysts require surgical removal.
a cavity appearing in tissues and body organs as a result of various pathological processes.
True cysts are lined with epithelium or endothelium; false cysts have no special lining. Cysts are classified according to the mechanism of their development. Retention cysts form upon the disruption of the efflux of any glandular secretion which leads to dilatation of the gland or duct (for example, with clogging of the ducts of sebaceous, salivary, or mammary glands). Ramollissement cysts arise in compact tissue when the tissue softens (with hemorrhage, inflammation, necrosis) in a limited section (for example, a brain cyst, after infarction or hemorrhage). Dysontogenetic cysts form from a cystlike transformation of embryonic canals and fissures (for example, branchiogenetic cysts, from the vestiges of the gill slits) or from a defect in the development of an organ (for example, cystic kidneys). Tumorous cysts arise most often in glandular, vascular, or bone tumors for a variety of reasons (cystadenoma, lymphangioma). Traumatic cysts form with traumatic displacement of the epithelium and its embedding in the underlying tissues (epithelial cysts of the fingers, palms, iris). Parasitic cysts represent the vesicular stages (cysticerci) of tapeworms (Echinococcus, Cysticercus). The dimensions, structure, and external manifestations of cysts depend on their origin. Treatment is principally surgical.
V. V. SEROV
|Table 1. The Cyrillic alphabet|
|Letters and names||Numerical value||Greek uncial||Letters and names||Numerical value||Greek uncial|
|1Letters whose shape has changed 2Letters later dropped from the Russian alphabe:|
Note: The names of some letters have meanings as words; they are shown in parentheses
|ձ az (I)||1||ձ||ϰ kher||600||ϰ|
|б buki||ѡ omega2||800||ѡ|
|ß vedi (know [imper.])||2||ß||ц tsy||900|
|ɾ glagol’ (word; verb)||3||ɾ||y cherv’ (worm)||90|
|A dobro (good)||4||Δ||Ш sha|
|Є es!’ (is)||5||Є||Ш shcha|
|zhivete ([you] live)||ъ er|
|S zelo2 (very)||6||Ѕ||ъI ery|
|Z zemiia’ (earth)||7||Z||ь er’|
|Ι i2 (and)||10||Ι||ъ iat’2|
|H izhe’ (which; who)||8||H|
|ĸ kako (how)||20||ĸ||10 Iu|
|Λ liudi (people)||30||λ||(i)ia1|
|M myslete ([you] think)||40||m||(i)e1|
|N nash1 (our)||50||N||A ius malyi2|
|O on (he)||70||O||ѫ ius bol’shoi2|
|П pokoi (rest)||80||П||Љ iotized ius malyi2|
|p rtsy||100||P||ѭ iotized ius bol’shoi2|
|C slovo (word)||200||C||Ҙ ksi = (xi)2||60|
|T tverdo (hard)||300||T||Ψ psi2||700|
in the life cycle of many unicellular organisms, a stage characterized by the presence of a protective sheath, also called a cyst.
In animals (some flagellates, rhizopods, sporozoans, infusorians). resting cysts and reproductive cysts are distinguished. The thick jelly-like or solid walls of resting cysts consist of chitinous substances that sometimes become mineralized. The cysts form under unfavorable conditions, for example, when a body of water dries up or freezes over. In parasites, resting cysts ensure the transfer of one host to another through the external environment. Some protozoans can exist in cyst form for many months or years (for example, the genus Colpoda about 16 months, the genus Oicomonas about 5½ years, and the species Peridinium cinctum about 16½ years). Reproductive cysts have a thin wall and exist only for the short time during which their contents divide into several independent organisms.
In plants (peridinians, chrysomonads, Euglena), cysts result from compression of the body and extrusion onto the surface of a solid and virtually impermeable wall. Encystment usually occurs when environmental conditions deteriorate; it helps the organism to withstand the unfavorable period. When conditions turn favorable, the cysts germinate and their contents escape from the wall. A cyst usually produces a single new individual, but its contents sometimes divide, with several new individuals emerging from the cyst. In other words, reproduction occurs.