gland

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gland,

organ that manufactures chemical substances. A gland may vary from a single cell to a complex system of tubes that unite and open onto a surface through a duct. The endocrine glands, e.g., the thyroid, adrenals, and pituitary, produce hormones that are secreted directly into the bloodstream (see endocrine systemendocrine system
, body control system composed of a group of glands that maintain a stable internal environment by producing chemical regulatory substances called hormones.
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). Exocrine glands secrete their substances onto an external or internal body surface. Most exocrine glands, e.g., the salivary and lacrimal glands, release their secretions through ducts. However, some open directly onto a body surface, as in the sebaceous glands of the skin and the digestive glands of the intestinal mucosa. A simple exocrine gland may consist only of a tube lined with secretory cells. In more complex types, clumps of cells produce the secretion and a duct or system of ducts discharges the secreted material. Some glands have dual functions, e.g., the liver, pancreas, ovary, and testis produce both a secretion that is emitted through a duct and a hormone that is taken up by the blood. Such structures are called mixed glands. Among the substances produced by exocrine glands in humans are sweat, lubricants like mucus and tears, and digestive juices. There are specialized exocrine glands in the animal world that produce such substances as the shells of bird eggs, spiderwebs, and the cocoons of the silkworm larvae. Simple glands are also common in the plant kingdom. The sweet nectar of flowers and the resinous pitch of pine trees are substances produced by plant glands.

Gland

A structure which produces a substance or substances essential and vital to the existence of the organism and species. Glands are classified according to (1) the nature of the product; (2) the structure; (3) the manner by which the secretion is delivered to the area of use; and (4) the manner of cell activity in forming secretion. A commonly used scheme for the classification of glands follows.

  • I. Morphological criteria
  • A. Unicellular (mucous goblet cells)
  • B. Multicellular
  • 1. Sheets of gland cells (choroid plexus)
  • 2. Restricted nests of gland cells (urethral glands)
  • 3. Invaginations of varying degrees of complexity
  • a. Simple or branched tubular (intestinal and gas-tric glands)—no duct interposed between surface and glandular portion
  • b. Simple coiled (sweat gland)—duct interposed between glandular portion and surface
  • c. Simple, branched, acinous (sebaceous gland)—glandular portion spherical or ovoid, connected to surface by duct
  • d. Compound, tubular glands (gastric cardia, renal tubules)—branched ducts between surface and glandular portion
  • e. Compound tubular-acinous glands (pancreas, parotid gland)—branched ducts, terminating in secretory portion which may be tubular or acinar
  • II. Mode of secretion
  • A. Exocrine—the secretion is passed directly or by ducts to the exterior surface (sweat glands) or to another surface which is continuous with the external surface (intestinal glands, liver, pancreas, submaxillary gland)
  • B. Endocrine—the secretion is passed into adjacent tissue or area and then into the bloodstream directly or by way of the lymphatics; these organs are usually circumscribed, highly vascularized, and usually have no connection to an external surface (adrenal, thyroid, parathyroid, islets of Langerhans, parts of the ovary and testis, anterior lobe of the hypophysis, intermediate lobe of the hypophysis, groups of nerve cells of the hypothalamus, and the neural portion of the hypophysis)
  • C. Mixed exocrine and endocrine glands (liver, testis, pancreas)
  • D. Cytocrine—passage of a secretion from one cell directly to another (melanin granules from melanocytes in the connective tissue of the skin to epithelial cells of the skin)
  • III. Nature of secretion
  • A. Cytogenous (testis, perhaps spleen, lymph node, and bone marrow)—gland “secretes” cells
  • B. Acellular (intestinal glands, pancreas, parotid gland)—gland secretes noncellular product
  • IV. Cytological changes of glandular portion during secretion
  • A. Merocrine (sweat glands, choroid plexus)—no loss of cytoplasm
  • B. Holocrine (sebaceous glands)—gland cells undergo dissolution and are entirely extruded, together with the secretory product
  • C. Apocrine (mammary gland, axillary sweat gland)—only part of the cytoplasm is extruded with the secretory product
  • V. Chemical nature of the product
  • A. Mucous goblet cells (submaxillary glands, urethral glands)—the secretion contains mucin
  • B. Serous (parotid gland, pancreas)—the secretion does not contain mucin

gland

[gland]
(anatomy)
A structure which produces a substance essential and vital to the existence of the organism.
(engineering)
A device for preventing leakage at a machine joint, as where a shaft emerges from a vessel containing a pressurized fluid.
A movable part used in a stuffing box to compress the packing.

gland

1
1. a cell or organ in man and other animals that synthesizes chemical substances and secretes them for the body to use or eliminate, either through a duct (see exocrine gland) or directly into the bloodstream (see endocrine gland)
2. a structure, such as a lymph node, that resembles a gland in form
3. a cell or organ in plants that synthesizes and secretes a particular substance

gland

2
Engineering a device that prevents leakage of fluid along a rotating shaft or reciprocating rod passing through a boundary between areas of high and low pressure. It often consists of a flanged metal sleeve bedding into a stuffing box
References in periodicals archive ?
Polymorphous low-grade adenocarcinoma (PLGA) is an uncommon salivary gland tumor that usually arises from a minor salivary gland.
Lobular carcinoma ofintraoral minor salivary gland origin: report of twelve cases.
A clinicopathologic study of 196 intraoral minor salivary gland tumours.
Tumors of all histologies were included, but tumors of the minor salivary glands were not included in this study because of limitations imposed by the ICD-O system.
26] Studies are needed to characterize the histologic and temporal salivary gland changes that involve the ducts, acini, or matrix constituents in both the major and minor salivary glands of HIV-infected patients.
A parapharyngeal mass is most often caused by a pleomorphic adenoma of the deep parotid gland or minor salivary glands.
In the minor salivary glands, the most common location is the lip; other areas of involvement are the buccal mucosa, palate, tongue, retromolar area, and floor of the mouth.
4) This condition usually affects the minor salivary glands of the hard palate (77% of cases); it has also been reported in the major salivary glands, nasal cavity, lip, trachea, and larynx.
Morphological studies revealed that the minor salivary glands of RA patients were highly infiltrated with lymphocytes and that the alterations also included fibrosis, acinar atrophy and lymphoplasma cell sialadenitis (14,15).
Mucus extravasation cysts or mucoceles are an extremely common lesion of the minor salivary glands.
In this test, the health care professional removes a few minor salivary glands from inside your lower lip.
It usually originates in the parotid gland; the minor salivary glands and the upper respiratory tract are involved only infrequently.