LECTURE 2
MS.C. JENAN M.
Glandular Epithelium : are formed by cells specialized to secrete. Its originate from
epithelial cells that leave the surface where they developed and penetrate into the
underlying connective tissue .
Gland Definition: cells or aggregation of cells that synthesizes a substance to be
released either in the blood stream or into cavities inside the body or its outer surface.
Glands are Classified According to their Mechanism of Secretion to :
 Exocrine Glands : Secrete their products via ducts onto the apical (or epithelial)
surface . example sweat gland.
 Endocrine Glands : Release their products into blood stream. These glands lack a
duct system and secrete into the blood or lymph. For example : thyroid gland.
 Mixed Glands : composed of two parts exocrine and endocrine . e.g. pancreas gland.
Exocrine Glands Clasification :
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According to a number of cells ( unicellular , multicellular )
According to structure ( simple , compound )
According to method of secretion ( apocrine , merocrine , holocrine )
According to product secreted ( serous , mucus , mixed)
Unicellular Glands : mucus – secreting goblet cells are the only example of these
single –celled glands in man found in trachea and the small intestine.
Multicellular Glands : these glands have many cells and they are divided into:
Simple glands – Glands of this type have an unbranched duct into which the cells
secrete which classified into:
1. Simple tubular glands : this type of gland has a single, straight, tubular. Secretory
cells line the entire duct which open on the apical surface e.g. crypts of lieberkuhn
2. Simple coiled tubular glands: sweat glands are almost the only example of asimple
coiled tubular glands each consist of a single tube that is tightly coiled in three
dimensions.
3. Simple branched tubular glands. Are found mainly in the stomach. The mucussecreting glands of the pyloric part of the stomach are shown in this example
4. Simple alveolar ( acinar ) glands. Simple acinar glands occur in the form of pockets
in epithelial surfaces . in this example of the mucus-secreting glands of the penile
urethra
5. Simple branched acinar gland : sebaceous glands provide a good example, this
gland consists of several secretory acini that empty into a single excretory duct.
Compound glands : These glands have a highly branched duct system.can be
classified into :
1. Compound tubular glands : in this type The secretory cells at the ends of the ducts
are in the form of tubules. Brunner’s glands of the duodenum are compound tubular
glands.
2. Compound alveolar glands : these glands differ from other compound glands in
that the ducts end is alveoli e.g. the lactating mammary gland
3. Compound tubulo- alveolar glands : these glands also have a highly branched duct
system, but some of the ducts end as tubules and others end as alveoli e.g. salivary
glands
Secretion from exocrine glands may accur in one of three way:
 Apocrine : a portion of cell containing secretions is released as it separates from rest
of the
cell . e.g.; Mammary glands
 Merocrine: secretions pass through the cell membranes of the secretory cell
e.g, pancreatic acinar cells
 Holocrine : entire secrtory cells disintegrate and are released a long with their
contents .e.g. sebaceous glands
Nature of secretion :
 Serous glands: secrete a watery often protein-rich product. The pancreas and
parotid glands are entirely serous in composition
 Mucous glands : a viscous product , rich in carbohydrates e.g.sublingual glands.
 Mixed ( serous-mucous ) : these glands secrete both protein and mucous e.g. the
salivary glands.
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