Gland

A gland is an organ in an animal's body that synthesizes a substance such as hormones for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland).

Structure

Glands are organs that synthesizes a substance such as hormones for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland). Numerous glands exist throughout the human body.

Development

Every gland is formed by an ingrowth from an epithelial surface. This ingrowth may in the beginning possess a tubular structure, but in other instances glands may start as a solid column of cells which subsequently becomes tubulated.

As growth proceeds, the column of cells may divide or give off offshoots, in which case a compound gland is formed. In many glands, the number of branches is limited, in others (salivary, pancreas) a very large structure is finally formed by repeated growth and sub-division. As a rule, the branches do not unite with one another, but in one instance, the liver, this does occur when a reticulated compound gland is produced. In compound glands the more typical or secretory epithelium is found forming the terminal portion of each branch, and the uniting portions form ducts and are lined with a less modified type of epithelial cell.

Stuffing box

A stuffing box is an assembly which is used to house a gland seal. It is used to prevent leakage of fluid, such as water or steam, between sliding or turning parts of machine elements.

Gland

A gland is a general type of stuffing box, used to seal a rotating or reciprocating shaft against a fluid. The most common example is in the head of a tap (faucet) where the gland is usually packed with string which has been soaked in tallow or similar grease. The gland nut allows the packing material to be compressed to form a watertight seal and prevent water leaking up the shaft when the tap is turned on. The gland at the rotating shaft of a centrifugal pump may be packed in a similar way and graphite grease used to accommodate continuous operation. The linear seal around the piston rod of a double acting steam piston is also known as a gland, particularly in marine applications. Likewise the shaft of a handpump or wind pump is sealed with a gland where the shaft exits the borehole.

Gland (botany)

In plants, a gland is defined functionally as a plant structure which secretes one or more products. This may be located on or near the plant surface and secrete externally, or be internal to the plant and secrete into a canal or reservoir. Examples include glandular hairs, nectaries, hydathodes, and the resin canals in Pinus.

Notable examples

Salt glands of the mangrove

The salt glands of mangroves such as Acanthus, Aegiceras, Aegialitis and Avicennia are a distinctive multicellular trichome, a glandular hair found on the upper leaf surface and much more densely in the abaxial indumentum. On the upper leaf surface they are sunken in shallow pits, and on the lower surface they occur scattered among long nonglandular hairs composed of three or four cells. Development of the glands resembles that of the nonglandular hairs until the three-celled stage, when the short middle stalk cell appears. The salt gland continues to develop to produce two to four vacuolated cells at the level of the epidermis, the stalk cell with an almost completely cutinized wall, and at least eight terminal cells. The terminal cells have a thin, perforated cuticle which separates from the cell walls apically, leaving an enclosed cavity between them. The secreted salt evaporates and forms visible crystals.