Cyst

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.

Table 1. The Cyrillic alphabet
Cyrillic			Cyrillic
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
Oyuk1	400		θ tita2	9
ϕ	500	Φ	γ izhitsa2

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.