Vasculization

VASCUlIZATION (from Lat. vas- vessel), an anatomical term characterizing the supply of a given organ or region with vessels. It should denote both lymph and the supply of blood (by veins and arteries), but usually under the term V. is understood only the blood supply. Thus, the question is one of the richness or poverty of an organ or region in blood vessels. V. includes the concepts of 1) the number of vascular trunks approaching the organ, 2) the ways of their origin, branching, and anastomosing, 3) the order and manner of entry into the organ, and 4) the branching of vessels within the substance of the organ and their anastomosing. Ultimately, the measure of V. is the number of small blood vessels contained in 1 cubic cm of the organ's tissue, or the maximum amount of blood flowing through it in a unit of time. Krogh's observations confirm the long-known fact that the amount of blood flowing through an organ varies extremely, depending on whether the organ is at rest or working. In a resting muscle, for example, most capillaries are in a collapsed state, and the blood brought by the artery passes in large quantity directly into the veins through the medium of shunt channels. The vascularization of tissues and organs of the human body is far from uniform. The tissue of the pituitary gland, thyroid gland, and, generally, so-called internal secretion organs is more vascularized than muscular, bony, and, especially, connective tissue. Previously, it was thought that cartilages have no vessels, but at present vessels have been found in them as well. Tendon tissue also has its V., though a very limited one. There are organs that have no vessels at all (cornea, nails, hair). In contrast to them, so-called parenchymatous organs (such as the spleen, liver, and kidney) represent tissue that is 80% composed of blood vessels and only 20% of connective tissue stroma and cells specific to the given organ. One must distinguish between extra- and intra-organ systems of vessels. The first is composed of trunks approaching the organ from various sources, and, besides the number and place of origin of branches, is characterized by the manner of branching and anastomosing. One distinguishes (Shchvunkenko and his school) the trunk and diffuse types of branching, the main features of which are a greater or lesser length of the main trunk supplying blood (sometimes its absence) and the early or more gradual origin of branches. For mobile organs (such as the small intestine, non-fixed parts of the large intestine) or those subject to frequent pressure (palm, sole), a significant development of anastomoses in the form of so-called arcades (Descomps and Lalaubie) is noted. They may also be found in less mobile organs but which had a mesentery in the embryonic period (spleen). It should be noted that the question of collaterals (see), which have great regulatory significance for the nutrition of the organ in the extra-organ system, is important. The intestinal hemorrhages observed during kidney operations (and vice versa) apparently have as their cause the ascending thrombosis of these extra-organ collaterals of the corresponding vein. The place of entry of blood vessels into the organ is usually called the hilus. For surgeons, the shape of the hilus, or rather its area, is significant, since the character of operative procedures in the removal of an organ is determined by the number of vessels entering the organ and their distribution (cf. accessory vessels of the kidneys and spleen). The network of blood vessels inside the organ constitutes the so-called intra-organ system. For parenchymatous organs, such as the lung, liver, spleen, and kidney, the order of arrangement of the larger branches has great practical significance (direction of incisions!), or, more precisely, the presence and topography of poorly and avascular areas. Research in this direction (the school of Shchvunkenko) has elucidated the principle of the spiral or radial distribution of poorly vascularized areas, which is probably connected with embryogenesis—the formation of these organs from several primordia. The presence of collaterals, which, unlike those located in the extra-organ system, are called local, is also significant. The fact of the individual variability of the methods of V. and the possibility of linking some of its features to the shape of the organ has been established; here, the lobular embryonic form, in which a diffuse type of branching is more common, and the presence of distant anastomoses are of importance. The distribution of vessels in the skin has great significance for plastic operations. It has been established that skin vessels are more developed on the flexor surfaces of the limbs and follow a course corresponding to the direction of Langer's tension lines. In pathology, the term V. is used to denote the process of new vessel formation in certain pathological products; for example, one speaks of V. of a thrombus (see) during its organization; of V. of fibrinous exudate in the lung during so-called carcination (see Pneumonia). V. is a common phenomenon during the development of granulation tissue, as well as during regeneration and in some tumors, for example, in angiosarcomas.