Note 20 — Chapter VI · Digestion.

Glands. Glands are organs of various shapes and sizes, whose special work it is to separate materials from the blood for further use in the body, the products being known as secretion and excretion. The means by which secretion and excretion are effected are, however, identical. The essential parts of a gland consist of a basement membrane, on one side of which are found actively growing cells, on the other is the blood current, flowing in exceedingly thin-walled vessels known as the capillaries. The cells are able to select from the blood whatever material they require and which they elaborate into the particular secretion. In Fig. 47 is illustrated, diagrammatically, the structure of a few typical secreting glands. The continuous line represents the basement membrane. The dotted line represents the position of the cells on one side of the basement membrane. The irregular lines show the position of the blood-vessels.