Acinus

ACINUS (Latin-berry, primarily grape), the terminal secretory department of acinar (otherwise alveolar, grape-like) glands, having the form of a larger or smaller round or oval vesicle (in contrast to the elongated tubular terminal department of tubular glands). Simple acinar, or vesicular, glands, consisting of one cell and an excretory duct in the form of a neck, are found, besides in invertebrates (myriapods), in amphibians (mucous and poison glands of the skin); they usually also include the sebaceous glands of the skin, consisting of several sacs opening with a wide duct into the hair follicle. Complex acinar glands consist of a system of branching excretory ducts, the caliber of which becomes smaller as they branch, and terminal secretory cells of various shapes (round or oval) attached to the terminal departments of the excretory duct. These include some salivary glands (usually serous), glands of the bronchial mucous membrane, etc. (among glands with internal secretion-the thyroid gland). The acinus has a clearly defined own structureless membrane-membrana propria, on which the glandular epithelial cells are located in a more or less regular layer; the lumen of the acinus may vary, depending on the type of gland and its functional state (see individual glands); outside, the own membrane is usually adjacent to basket-like cells of muscular character; each acinus is enveloped in a thin network of connective tissue, in which blood capillaries and thin nerve trunks branch, from which terminal branches penetrate under the own membrane and end on the glandular cells with their terminal apparatuses, mostly in the form of buttons.-The acinus is also the designation of a unit of lung territory, corresponding to the branching of the so-called terminal bronchus (see Lungs). Acinus, acinar-terms that have become widespread in anatomical classifications of pulmonary tuberculosis.