Gland (Lat. glans, an acorn), in anatomy, the general name of a variety of organs whose functions are to elaborate the various products of secretion from the blood, to perform certain offices connected with absorption and assimilation, and to assist in preparing and maintaining the circulating fluid in a normal condition. Of the first class of glands the liver and the salivary glands are examples, of the second the mesenteric and lymphatic glands, and of the third the spleen. The true secreting glands are of various form, size, and structure, but are all constructed with special reference to the arrangement of the nucleated and epithelial cells and tubes or cavities which enter into their texture; their products are poured forth either on the outer surface of the body, or into some cavity or canal communicating extemaily, and the cells which effect the separation of their special secretions from the blood are generally in the relation of epithelium cells to the inversions of the skin or mucous membranes that form the greater part of their follicles or tubuli.
These cells generally minister to the act of secretion by absorbing from the blood its watery and saline ingredients, which they afterward exhale in the requisite proportions, and by generating at the same time a peculiar ingredient by their own powers of assimilation; thus producing a secreted fluid different in composition from the blood from which it was derived. The great majority of glands provided with ducts may be divided into three groups, according to the modes in which the cell-containing tubes are arranged: 1, the simple tubular glands, like the follicles of the stomach and intestines, which seem to be mere depressions in the mucous membrane, or elongated vesicles lined with secreting cells; 2, the aggregated or conglomerate glands, in which a number of follicles are grouped into lobules, and these again into lobes joined by loose areolar tissue, like the salivary, mammary, pancreatic, prostate, and lachrymal glands, and also the liver; 3, the convoluted tubular glands, as the perspiratory and sebaceous glands ending in dilatations, cul-de-sacs, or loops.
In all a large extent of secreting surface is packed in a small compass; while one end of the gland and duct opens on a free surface, the opposite end is closed, and has no direct communication with blood vessels or other canals. The glandular organs have been divided into two classes, according as their product is ex-crementitious and to be cast off, or to be used within the system; the former are called more properly excretory glands, and include the kidneys, and those which supply the cutaneous and pulmonary transpiration and the peculiar faecal matters of the lower part of the intestinal canal; the true secretory glands are the gastric, salivary, mammary, sebaceous, mucous, lachrymal, Brunners, and the pancreas. The kidneys, liver, mammary glands (secreting respectively urine, bile, and milk), and the pancreas are described under their proper titles; the salivary and gastric glands are noticed under Digestion; the sebaceous, ceruminous, odoriferous, and sudoriparous glands (secreting the oily, waxy, odorous, and perspiratory matters of the surface), are treated in the article Skin; the follicles of Lieberkuhn (in the small intestine), Brunner's glands in the duodenum, and the solitary glands most numerous in the crecal region, under Intestine; the lachrymal glands under Eye; and the so-called glands of Pacchioni and the pineal body or gland are alluded to in the article Brain. The air passages of the chest and head, the alimentary canal above the stomach, and the genito-uri-nary apparatus, are provided with solitary and aggregated glands and follicles for the secretion of their lubricating mucus; the tonsils are glandular masses principally, and there are numerous follicles in the posterior fauces, and in the neighborhood of the epiglottis and entrance to the larynx, whose diseased secretions and ulceration constitute the kind of folliculitis popularly called "clergyman's sore throat."-Another system is that of the vascular or ductless glands, which possess all the elements of glandular structure, except the efferent ducts; restoring therefore to the blood whatever they take from it, it is generally admitted that they perform some part in the process of sanguification, probably acting upon such nutrient materials as are taken up directly by the blood vessels without in the first instance passing through the absorbents.
These glands are the spleen on the left side of the abdominal cavity; the thymus gland, a foetal organ in the anterior mediastinum; the thyroid body, on the anterior portion of the neck; and the supra-renal capsules, surmounting the kidneys; these will be described in their alphabetical order. They are composed of vesicles or sacculi, simple and closed, or branched, of a delicate membrane surrounded with a vascular plexus, and filled with an albuminous fluid containing fat granules and nucleated cells. The opinion that these glands serve for the higher organization of the blood materials is supported by the fact that they are especially large and active during foetal life and childhood, when the most abundant supply of nutrient fluids is necessary. They are not essential to life in the adult; the thymus entirely disappears, the thyroid may be completely disorganized, and the spleen be removed (as has been often done in animals), without fatal consequences; the supra-renal capsules seem to be connected with the production of pigment, and. their morbid condition or atrophy is connected with the peculiar disease known as "bronzed skin."-The last group includes the absorbent glands, the patches of Peyer, the mesenteric, and the lymphatic glands.
The lacteals and the fluid they convey have been described under Absorption and Chyle. Peyer's glands, most numerous toward the ileo-caecal valve, are intimately connected with the lacteals; whether single or in clusters, they are always in that portion of the intestine which is opposite the mesentery; they are capsules, containing fatty and albuminous matters, with nuclear particles and cells, all apparently undergoing rapid changes; the exterior and interior of the capsules are freely supplied with blood. In the mesentery are the mesenteric glands, which bear the same relation to the lacteals as the absorbent glands to the lymphatics; each gland is enclosed by a fibrous sheath, which forms by its partitions an internal supporting framework; the intervening alveoli are filled with a grayish pulp, as in Peyer's patches, penetrated by a fine capillary plexus, and in free communication with the afferent and efferent ducts between which they are situated; the number of corpuscles of the chyle is greatly increased by passing through these glands, which perform a most important part in the blood-making or assimilating process. No lacteal or lymphatic reaches the terminal thoracic duct without passing through one or more of these glands.
In the lower vertebrata plexuses of lymphatics occupy the places of the glands of birds and mammals. Glands are situated all along the course of the lymphatic vessels, both superficial and deep-seated. Familiar examples are the glands in the groin, the seat of syphilitic and scrofulous abscesses, and often swollen from irritation of any portion of the lower extremity; the axillary glands in the armpit, often requiring surgical interference for enlargements and abscesses; and the glands on the sides of the neck, frequently the seat of scrofulous suppuration.
Ultimate Glandular Follicles. a. Membrane of the follicle, b. Layer of epithelium lining the follicle, seen in profile, c. Surface of epithelium cells, lining the whole interior of the follicle.
Mucous Glandule, from the Cavity of the Mouth. a. Investment of areolar tissue, b. Excretory duct, c, c. Secreting follicles, d. Branches of the excretory duct.