A textbook of human physiology / translated from [the] 6th German edition by W. Stirling.

  • Landois, Leonard
Date:
1888
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Licence: Public Domain Mark

Credit: A textbook of human physiology / translated from [the] 6th German edition by W. Stirling. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    145/980 page 93
    STRUCTUKE OF ARTERIES. blood and the fluids of the tissues. The fluid after it passes into the tissues consti- tutes the lymph, and acts like a stream irvujating the tissue elements.] I. The arteries are distinguished from veins by their thickev ivalb, due to the greater development of smooth muscular and elastic tissues—the middle coat (tunica media) of the arteries is specially thick, while the outer coat (t. adventitia) is relatively thin. [The absence of valves is by no means a characteristic feature.] A typical artery consists of three coats (tig. 68). (1) The tunica intima, or inner coat, consists of a layer of {a) irregular, long, fusiform nucleated squamous cells forming the excessively thin transparent endothelium, immediately in contact with the blood-stream. [Like other endothelial cells, these cells are held together by a cement substance, which is blackened by the action of silver nitrate.] Outside this lies a very thin, more or less fibrous, layer—mb-cijithelial layer—in which numerous spindle or branched protoplasmic cells lie em- beelded within a corresponding system of plasma canals. Outside this is an elastic lamina [b), which in the smallest arteries is a structureless or tibrous elastic membrane—in arteries of medium size it is a fenestrated membrane {Hcnle), while in the largest arteries there may be several layers of elastic lamim^ or fenestrated elastic membrane mi.Ked witli connective-tissue. [In some arteries the elastic membrane is distinctly iibrous, the fibres being chiefly arranged longitudinally. It can be stripped ofT, when it forms u brittle elastic membrane, which has a great tendency to curl up at its margins. In a transverse section of a middle-sized artery it appears as a bright wavy line, but the curves are probably produced by the partial collapse of the vessel. It forms an important guide to the piathologist, in enabling him to determine which coat of the artery is diseased.] In middle-sized and large arteries a few non-striped muscular fibres are disposed longitudinally between the elastic plates or lamina?. Along with the circular muscular fibres of the middle coat, they may act so as to narrow the artery, and they may also aid in keeping the lumen of the vessel open and of uniform calibre. (2) The tunica media, or middle coat, contains much non-striped muscle (c), which in the smallest arteries consists of transversely disposed non-striped muscular fibres lying between the endothelium and the T. adventitia, while a finely granular tissue with few elastic fibres forms the bond of union between them. As we proceed from the very smallest to the small arteries, the number of muscular fibres becomes so great as to form a well-marked fibrous ring of non- striped muscle, in which there is comparatively little connective-tissue. In the large arteries the amount of connective-tissue is considerably increased, and between the layers of fine connective- tissue numerous (as many as 50) thick, elastic fibrous or fenestrated laminte are concentrically arranged. A few non-striped fibres lie scattered amongst these, and some of them are arranged transversely, while a few have an oblique or longitudinal direction. The first part of the aorta and pulmonary artery, and the retinal arteries, are devoid of muscle. The descending aorta, common iliac, and popliteal have longitudinal fibres between the transverse ones. Longitudinal bundles lying inside the media occur in the renal, splenic, and internal spermatic arteries. Longitudinal bundles occur both on the outer and inner surfaces of the um- bilical arteries, wliich are very muscular. (3) The tunica adventitia, or outer coat, in the smallest arteries consists of a struc- tureless membrane with a few connective- tissue corjiuscles attached to it; in somewhat larger arteries there is a layer of fine fibrous elastic tissue mixed with bundles of fibrillai- connective-tissue (cl). In arteries of w«W/<' size, and in the largest arteries, the chief mass consists of bundles of fibrillar con- ^ . . nective-tissue containing connective-tissue ^^ipi'larjes corpuscles. The bundles cross each other in a variety of directions, and fat cells often lie between them. Next the media there are numerous fibrous or fenestrated elastic lamellre. In medium sized and small arteries the elastic tissue next the media takes the form of an inde- pendent elastic membrane (Henle's external elastic membrane). Bundles of non-striped muscle, arranged longitudinally, occur in the adventitia of the arteries of the penis, and in the renal, splenic, spermatic, iliac, hypogastric, and superior mesenteric arteries. II. The capillaries, while retaining their diameter, divide and reunite so as to form net- 69. The outlines of the nucleated endo- thelial cells with the cement blackened by the action of silver nitrate.
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