BLOOD GLANDS: ENDOCRINE GLANDS.
The blood glands are the spleen, thyroid, thymus, suprarenal, pituitary, and pineal bodies. They each make a contribution of some kind to the blood which maintains its fitness to supply the material for the growth and nourishment of the various organs and tissues of the body in due balance. There fore they are also called organs of internal secretion or endocrine glands (Greek endon, within, and krinlin, to separate).
But they do not produce, like the salivary or sweat glands, a secretion that is carried along definite channels, and so an earlier name was ductless glands.
Of recent years an immense amount of research has been done by physiologists and physicians to unveil the mystery of the work of these structures, adding a new chapter to medical science more fascinating than its title endocrinology.
The development of the sex organs is also associated with the normal function of these endocrine glands.
The Spleen is the chief of these. It is situ ated in the belly to the left side of the stomach in the hypochondriac region (p. 190). Its posi tion in reference to the stomach is well shown in Fig. 109, p. 201, and by studying this figure in conjunction with Fig. 104, p. 198, a good idea may be obtained of its position in reference to the rest of the body. The spleen is popularly called "the melt." It weighs usually from 5 to 7 ounces, is an elongated, flattened body, 4 to 5 inches in length, and 3 inches broad. It is usually of a deep-red or a purplish colour. It is a gland of considerable importance, if we are to judge from its blood supply, for it re ceives an artery—the splenic artery—directly from the aorta, the chief blood-vessel of the body. See Plate XIV.
Its vein—the splenic vein—joins the portal vein, as we have already noted on p. 200. Its structure much resembles that of a lymphatic gland, already described. It has a fibrous sule, from which partitions, or trabeculte, pass inwards, dividing off the organ into spaces by the irregular work they form. In these spaces is closed spleen pulp, which consists of lular bodies of ous sizes—some like the white corpuscles of the blood, some larger, and others smaller. If a spleen
be cut open and looked at with the naked eye, small white round bodies, like sago grains, are seen scattered through it. These are the corpuscles of the spleen, or the Malpighian bodies of the spleen. They are masses of what has been called adenoid tissue (see p. 277), consisting of white cells in a net-work of fine fibres, and through each body passes a branch of the splenic artery. Fig. 127 shows a branch of the splenic artery (u), with the corpuscles (c) ated on its twigs (h). The blood passes from the capillaries of the artery into fine spaces among time spleen pulp, from these to larger spaces, and then on to the veins, which carry it away from the organ. In fact the spaces are of such a character that the blood from the artery filters through the pulp, just as fluid would pass through a sponge, and is then collected by the veins.
Functions of the Spleen.—Such a remark able structure suggests that the business of the spleen is to affect in some way the quality of the blood. As the blood filters through the spongy pulp, some important change is wrought in it by the active cells of the pulp, either in the way of removing from the blood-current old and worked-out red cells, or, as others believe, in the direction of adding to the blood new and active white cells, for the white cells of the spleen are not distinguishable from those of the blood. The blood coming from the spleen is said to be richer in white cells and poorer in red ones. It has been found that the spleen increases in size after a meal, being consider ably swollen five hours after a meal, remaining so for some time, and then returning to its usual size. So that it undergoes a regular alternate expansion and diminution in size. When, however, it is mentioned that the spleen has been wholly removed without any apparent ill effect, it will be understood how obscure is yet the question of its function.