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 system). 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 group of cells with a communal secretory function. Exocrine glands incorporate a duct, or a system of ducts like tributaries leading to a river, which open onto an external or internal body surface. Some are simple or spiral pits(such as sweat glands in the skin or those which secrete acid and enzymes into the stomach) with a few secreting cells in their depths; others vary in size and complexity from the small salivary glands to the mammary glands (breasts). Endocrine glands by contrast are ductless, and secrete hormones directly into the bloodstream. The activity of all glands is regulated by chemical or nervous signals, or both. Molecules in the local environment, or brought by the blood, or released from nerve endings of the autonomic nervous system bind to cell membrane receptors, starting a sequence of signals within the cells which results in an increase (or decrease) in extrusion of their own particular secretion.

The nodular enlargements which can be felt under the skin in association with an infection (such as those in the neck with a sore throat) are commonly called swollen ‘lymph glands’, but they are not secretory and are more correctly called lymph nodes.

Stuart Judge

gland A group of cells or a single cell in animals or plants that is specialized to secrete a specific substance. In animals there are two types of glands, both of which synthesize their secretions. Endocrine glands discharge their products directly into the blood vessels; exocrine glands secrete through a duct or network of ducts into a body cavity or onto the body surface. Secretory cells are characterized by having droplets (vesicles) containing their products. See also secretion.

In plants glands are specialized to secrete certain substances produced by the plant. The secretions may be retained within a single cell, secreted into a special cavity or duct, or secreted to the outside. Examples are the water glands (hydathodes) of certain leaves, nectaries (see nectar), and the digestive glands of certain carnivorous plants.

gland¹ / gland/ • n. an organ in the human or animal body that secretes particular chemical substances for use in the body or for discharge into the surroundings. ∎  a structure resembling this, esp. a lymph node. ∎  Bot. a secreting cell or group of cells on or within a plant structure. gland² • n. a sleeve used to produce a seal around a piston rod or other shaft.

gland Cell or tissue that manufactures and secretes special substances. There are two basic types. Exocrine glands make such substances as hydrochloric acid, mucus, sweat, sebaceous fluids and enzymes, and secrete these usually through ducts to an external or internal body surface. Endocrine glands contain cells that secrete hormones directly into the bloodstream. See also endocrine system

gland (gland) n. an organ or group of cells that is specialized for synthesizing and secreting certain fluids, either for use in the body or for excretion. See endocrine gland, exocrine gland, secretion.

gland A cell or group of cells that is specialized for the secretion of a particular substance.

gland XVII. — F. glande, later form of OF. glandre (see next).

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