Glands

GLANDS

Glands  Develop

from epithelium that invaginated the connective tissue forming secretory units  Consists of: Parenchyma  The

secretory & ductal epithelial cells

Stroma  The

supporting connective tissue elements

CLASSIFICATION Based on:  Site of secretion  Presence or Absence of Duct  Number of Cells  Shape of Secretory Unit  Type of Secretion  Mechanisms of Secretion

Based on Site of secretion Exocrine glands Endocrine glands Paracrine glands

Presence or Absence of Duct  Exocrine:

with ducts  Endocrine: ductless glands (adrenal glands, Thyroid, parathyroid, etc)

Based on Number of Cells  Exocrine

Glands:

 Unicellular The

glands

gland is a single cell, like the goblet cell

 Multicellular

Glands

Based on Branching of Duct  Simple

glands  Compound glands

Based on Shape of Secretory Unit  Acinar

or alveolar (sac or flask like)

 Ex.

Exocrine pancreas  Small sebaceous glands  Tubular  Ex.

(straight, coiled, branched)

Sweat gland-coiled  Intestinal gland-straight  Pyloric gland-branched

Based on Type of Secretion  Mucus:

a viscous material, which usually protects or lubricates cell surfaces  Serous: watery and often rich in enzymes  Mixed: contain both mucus & serous substances

Based on Mechanisms of Secretion  Merocrine

glands (ex. parotid gland)

The secretory cells release their contents by exocytosis  Apocrine

glands (ex. Lactating mammary gland)

Part of the apical cytoplasm of the secretory cells is released along with the contents  Holocrine

glands (ex. Sebaceous gland)

The entire secretory cell along with its contents is released in the process of secretion.

Basic Organization of Multicellular Glands A

capsule surrounds the gland, sending extensions called septa of connective tissue dividing the glands into lobes and lobules.  Ducts that are located  Between

lobes are interlobar ducts  Within lobes are intralobar ducts  Between lobules are interlobular ducts  Within lobules are intralobular ducts  (Ex.

Striated & intercalated ducts)

Endocrine Glands  Unicellular:

ex. Individual endocrine cells in gastrointestinal and respiratory epithelia  Multicellular: ex. Adrenal gland  Lacks a duct system and release secretions into capillaries.