Gland

A small organelle or a larger organ consisting of organelles which produces substances and secretes these substances into the body (endocrine secretion) or on body surfaces (exocrine secretion).

Glands can be differentiated according to the type of secretion:

• exocrine, e.g. sweat gland, sebaceous glandn, mammary glands
• endocrine, e.g. hormonal glands that release their secretion into the bloodstream

Differentiation according to construction:

• tubular, tubular
• acinous, grape-shaped
• alveolar, vesicular

Differentiation according to viscosity of secretion:

• serous, rather aqueous
• mucous, rather slimy, viscous

https://en.wikipedia.org/wiki/Gland