Glands | Biology for Grade 11 PDF Download

Glands of Epithelium

• A cell or group of cells which secrete chemical substances are called glands.
• All glands are composed of epithelium tissue.
• Glands originate from all three germinal layers.
• The cells are generally columnar or cuboidal.

Types of Glands

(A) On the basis of presence of secretory duct, glands are of 3 types:

(a)  Endocrine Gland  – Secretory duct absent

Endocrine Glands

(b)  Exocrine Gland –  Secretory duct present       

(c)  Heterocrine/Mixed Gland – Both endocrine & exocrine parts are present

(B) On the basis of nature of secretion , glands are of 3 types:

(i) Eccrine/Apocrine/Merocrine Gland

• In these glands secretory cells secrete substances by simple diffusion (Exocytosis).
• No part of cytoplasm is destroyed in secretion.
• Maximum sweat glands of humans, paws of rabbit, Goblet cells, salivary gland, tear gland, intestinal gland, mucous gland.

(ii) Apocrine Gland

• In this type of glands secretory products are collected in apical part of secretory cell. 
• Apical portion is also shed along with secretory matter.
• Secretory cells gain their lost part of cytoplasm by process of regeneration.
• Examples- mammary glands, sweat gland of arm pit, pubic region, skin around anus, lips, nipples etc.
• Largest sweat gland of body are found around nipples. – Areola mamme.
• In Rabbit seat glands  of this type are found on lips and skin around lips.

(iii) Holocrine Gland

• The production or secretion is shed with whole cell leading to its destruction.
• Example : Sebaceous, meibomian & zeis gland.