Author/Editor		Poredoš, Pavel
Title		Struktura mikrocirkulacije
Translated title		Structure of the microcirculatory system
Type		članek
Source		Med Razgl
Vol. and No.		Letnik 35, št. Suppl 2
Publication year		1996
Volume		str. 1-8
Language		slo
Abstract		The microcirculatory system consists of blood vessels with a diameter smaller than 300 microns, i.e. capillaries, arterioles, precapillary sphincters and venules. The simplest structure is that of capillaries: their walls are built of layers of longitudinally arranged flat endothelial cells and a basement membrane. From the outside, individual pericytes and adventitial cells rest on the basement membrane. The structure of capillaries differs in different organs; they especially differ in permeability for different substances. Three types are distinguished: closed-continuous, perforated, i.e. fenestrated, and open or sinusoid capillaries. Arterioles have a slightly larger diameter than capillaries. Their walls consists of two layers. The inner wall is formed by endothelial cells and a basement membrane, while the outer is formed by one or two layers of circular smooth muscle cells separated by an incompletely developed internal elastic membrane. In large arterioles, similarly as in arteries, a third layer appears, i.e. an adventitia which is formed by longitudinally arranged sheaves of connective tissue. Arterioles have the largest total diameter in the arterial part of the circulatory system, they have therefore the largest influence on blood pressure and are called resistance vessels. The wall structure of venules is similar to that of capillaries, only their diameter is greater (20 micro m or more), while in larger venules in addition to a layer of endothelial cells and the basement membrane, individual smooth muscle cells appear. The composition of individual sections of the microcirculatory system differs from one organ to another, depending on their function. Their diameter also changes, primarily in dependence on the fullness of the circulatory system and activity of mechanisms for the regulation of blood flow.
Summary		Mikrocikrulacijo tvorijo žile, ki imajo premer manjši od 300 micro m, to so kapilare, arteriole, prekapilarni sfinktri in venule. V prispevku so prikazane splošne strukturne značilnosti različnih segmentov mikrocirkulacije. Najbolj enostavno zgradbo imajo kapilare, katerih stena je zgrajena iz plasti vzdolžno urejenih ploščatih endotelijskih celic in bazalne membrane. Od zunaj se bazalni membrani prilegajo posamezni periciti in adventicijske celice. Zgradba kapilar je v različnih organih različna, zlasti se razlikujejo po prepustnosti za različne snovi. Tako ločimo tri tipe kapilar: zaprta ali zvezna, luknjičasta ali fenestrirana in odprta ali sinusoidna kapilara. Arteriole imajo nekoliko večji premer kot kapilare. Stena arteriole sestoji iz dveh plasti. Notranjo plast tvorijo endotelijske celice in bazalna membrana, zunanjo pa ena do dve plasti krožnih gladkih mišičnih celic; vmes je položena nepopolno razvita notranja elastična membrana. Večje arteriole imajo podobno kot arterije še tretjo plast, adventicijo, ki jo tvorijo vzdolžno urejeni snopi vezivnega tkiva. Arteriole imajo največji skupni premer v arterijskem delu obtočil, zato imajo tudi največji vpliv na krvni tlak, in jih imenujemo uporovne žile. Venule imajo podobno zgradbo stene kot kapilare, le svetlina je širša (20 micro m in več); pri večjih venulah se poleg plasti endotelijskih celic in bazalne membrane pojavijo tudi posamezne gladke mišične celice. Sestava posameznih odsekov mikrocirkulacije se od organa do organa razlikuje, odvisno od funkcije, ki jo ta organ opravlja. Prav tako se spreminja tudi premer svetline, predvsem v odvisnosti od polnjenosti cirkulacijskega sistema in od aktivnosti mehanizmov uravnavanja pretoka krvi.
Descriptors		MICROCIRCULATION ARTERIOLES CAPILLARIES