ZOO 117 1.0
Histology
Glandular Tissues
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Glandular Epithelium & Glands
Glands develop during fetal life from epithelia by cells
proliferation & invasion of subjacent of connective tissue
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Exocrine Glands
Description – Ducts or tubes carry exocrine
products to epithelium. Retains their contact with
the epithelium surface.
They have a secretory potion & ducts
2 Types
•  Exocrine glands
•  Endocrine glands
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Exocrine Glands
Exocrine Glands
2 Types
Include the following diverse glands
•  Mucous secreting glands
•  Sweat & oil glands
•  Salivary glands
•  Liver & pancreas
1. Unicellular: One cell
2. Multicellular: Many cells
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Unicellular Exocrine Glands
These are the Goblet cells
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Multicellular Exocrine Glands
Posses two basic parts
•  Produce mucin
•  Mucin + H2O
Mucus
•  Protects & lubricate
many internal body
surfaces (small intestine
& respiratory tract)
•  Epithelium walled duct
•  Secretory unit
•  Classified in two ways
Classified by structure (branching & shape) of duct
•  Simple
•  Compound
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Exocrine Glands
Exocrine Glands
Secretory portion : Can be simple
Secretory portion : Can be branched
i.e. Compound glands
1. Tubular : short or long
2. Coiled:
1. Tubular
3. Acinar: round or globular
2. Acinar
3. Tubuloacinar
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Multicellular Exocrine Glands
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Multicellular Exocrine Glands
Characterized by Secretory
unit (mode or type)
•  Merocrine secretion:
Secretory vesicles released
via exocytosis. Mainly
proteins or glycoprotein s
•  Holocrine secretion:
Entire cell is destroyed
during secretion
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Multicellular Exocrine Glands
Characterized by
Secretory unit (mode or
type)
Multicellular Exocrine Glands
Exocrine glands with merocirne secretion can be
further divided in to: 3 types depending on the
nature of proteins or glycoproteins.
• Apocrine secretion:
Apical portion of the cell
is lost. (only cytoplasm +
excretory product).
•  Product is typically a
large lipid droplet.
•  Serous: Mostly water but may contain some
enzymes. Acinar cell of the Parotid salivary gland
& Pancreas
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Multicellular Exocrine Glands
•  Mucous : Contains strongly hydrophilic
glycoproteins called mucin. When they are
released become hydrated to mucus, a viscous
elastic, protective lubricant material. Sublingual
gland, Goblet cells
Thyroid Gland
•  Mixes: Serous and mucus. Submandibular
gland
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Thyroid Gland
Thyroid Gland
•  Located in the cervical
region anterior to lanrynx
•  Butterfly shaped 2
lobes
•  Lobes united by an
Isthmus
•  Largest endocrine
gland
•  Straddles the trachea
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Thyroid Gland
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Thyroid Gland
•  The thyroid gland contains numerous follicles,
composed of epithelial follicle cells and
colloid.
•  Also, between follicles are clear parafollicular
cells, which produce calcitonin.
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Function:
•  Synthesize thyroid hormones
•  Thyroxin (tetra-iodothyronine –T4)
•  Tri-iodothyronine (T3)
•  Important for growth, cell differentiation
•  Control of basal metabolic rate & oxygen
consumption in the cells
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Thyroid Gland
Thyroid Gland
•  Paranchyma composed of millions of thyroid
follicles.
•  Each follicle consists of
•  Simple epithelium
•  Central lumen: filled with gelatinous
substance; colloid.
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Thyroid Gland
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Thyroid Gland
•  Only endocrine glad
with large quantities of
secretory products are
stored.
•  Densely packed
separated by sparse
reticular connective
tissue
T.S.
of
thyroid
gland
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Follicular Cells
Parafollicular Cells / C. Cells
•  Range in shape from squamous to low
•  Found inside the basal
columnar
•  Variable in diameter
•  How to identify an active gland?
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More follicles with low columnar epithelial
cells & more squamous cells
lamina of the follicular
epithelium or
•  Isolated clusters
between follicular cells
•  Synthesis & secrete
calcitonin
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T4 and T3: Actions
•  increase synthesis of enzymes involved in
cellular respiration --> increase basal
metabolic rate
Control
•  Major regulator is
TSH
•  Release of TSH
stimulated by TRH
from hypothalamus
–  results in increased heat production.
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T4 and T3: Control
Release of TRH is
stimulated by cold,
pregnancy, low thyroxin
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