Glands one or more cells that makes and secretes an aqueous fluid

Classified by: – Site of product release – endocrine or exocrine – Endo-in – Exo-out – Crine-secrete – Relative number of cells forming the gland – unicellular or multi-cellular

Endocrine Glands Ductless glands that produce hormones to be used internally. Secretions include amino acids, proteins, glycoproteins, and steroids Products are secreted to intracellular spaces; usually picked up by the capillaries to be distributed to the target organ(s) by the circulatory system Examples: pituitary, thyroid, and pancreas

Exocrine Glands More numerous than endocrine glands Secrete products onto body surfaces (skin) or into body cavities Examples: mucous, sweat, oil, and salivary glands Only important unicellular gland: goblet cell Multi-cellular exocrine glands: composed of duct and secretory unit

Goblet cell

Multicellular Exocrine Glands Classified according to: – Simple or compound duct type – Structure of their secretory units Figure 4.3

Merocrine secretion corresponds to the process of exocytosis. Vesicles open onto the surface of the cell, and the secretory product is discharged from the cell without any further loss of cell substance. Most glands – salivary, pancreas, eccrine sweat

Holocrine secretion designates the breakdown and discharge of the entire secretory cell. It is only seen in the sebaceous glands of the skin.