Veterinary Histology and Embryology

CLASSIFICATION OF GLANDS

• The glands of the body are classified as exocrine or endocrine.
• Exocrine glands have ducts which carry out the secretion to an epithelial surface, while endocrine glands are ductless and pour their secretion into the blood or lymph.

Exocrine gland

• The exocrine gland consists of a secretory portion and a duct.
• The secretory portion is arranged as a cluster of secretary cells known as a secretory unit, which has a central lumen, which opens into the first portion of the ductular system.
• The exocrine glands can be classified in several different ways based on the shape and form of the secretory unit, nature of secretion and mechanism of secretion.

Endocrine gland

• Certain glands are lacking in ducts and are termed endocrine glands.
• The endocrine glands secrete specific chemical substance called hormones which have specific effects on the other tissue or organs of the body e.g., thyroid, parathyroid, pituitary etc.
• The secretions of these glands are conveyed directly into the blood stream.
• To facilitate this endocrine glands have numerous sinusoids forming an extensive network, surrounding the secretory cells, which are usually arranged in small groups, follicles or anatomizing cords of cells.