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Histology 1.4. Glands
Gland a single epithelial cell, or grouping of
cells specialized for secretion. Secretion
energy-consuming process by which the cell takes
up small molecules and transforms them via
intracellular biosynthesis into a more complex
product then actively releases it from the cell.
The product is utilized by the organism in
several ways. Excretion the organism gets rid
of harmful or toxic metabolic end-products or
useless waste material.
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Classification of glands I. Based on
morphology unicellular and multicellular Unicellu
lar, intraepithelial gland goblet cell
Intestinal epithelium simple columnar
epithelium (2) goblet cells (1) the arrow shows
the nucleus (3)
TEM image of the same type of unicellular
gland, the goblet cell
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CLASSIFICATION OF MULTICELLULAR GLANDS
With ducts exocrine glands Without ducts
endocrine glands
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CLASSIFICATION OF EXOCRINE GLANDS (based on
morphology)
Simple tubular Coiled tubular Branched
tubular Simple acinar Branched acinar
Compound tubular Compound acinar Compound
tubuloacinar
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SOME EXAMPLES Simple tubular gland intestinal
gland of Lieberkühn
Schematic drawing LM microphoto
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Coiled tubular gland sweat glands of the skin
Schematic drawing LM microphoto
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Branched tubular gland fundic glands in the
stomach
Schematic drawing LM microphoto
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Simple acinar gland Frog skin mucous and
toxin-producing glands
Compact form without lumen sebaceous gland
of mammalian skin
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Branched acinar gland larger sebaceous glands of
the skin
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Compound tubular gland esophageal gland
duct segment
capillary
secretory acini
capillary
lumen
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Compound tubuloacinar glands
Mandibular gland Parotid gland
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Composition of compound glands Parenchyma
composed of lobes and lobules, ducts The duct
system of the compound glands Acinus Inte
rcalated duct Striated (salivary
duct) Interlobular duct Lobar
duct Main duct
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Model of the gland a bunch of grapes berry
acinus
stalk of berry intercalated duct
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Intralobular striated (salivary) duct
Interlobular duct
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II. Type of secretory product

• Serous gland composed of acini with narrow
  lumen
• secretory cells have round, basally located
  nuclei
• tthe cytoplasm of the cells is basophilic

Pancreas (see the micrograph) and parotid
gland are purely serous producing thin watery
fluid rich in proteins (mainly enzymes)
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2. Mucous glands composed of acini with wide
lumen secretory cells have flattened nuclei at
the base their cytoplasm is very weakly stained
Esophageal glands (see the micrograph) are purely
mucous producing thick viscous fluid, rich
in mucopoly- saccharides for lubrication and
protection of internal body surfaces
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3. Seromucous glands mucous acini surrounded by
serous cells forming a demilune shape
The submandibular gland of some species (monkey,
human, cattle) is seromucous. Red arrows point
at mucous cells, bléue arrows point at the
demilume shaped gropu of serous cells (Demilune
of Gianuzzi)
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III. Modes of secretion

• Merocrine secretion
• The secretory process is an exocytosis
• The secretory cell remains completely intact
• Most of the glands secrete in a merocrine manner
• Exocrine pancreas Submandibular gland

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• 2. Apocrine secretion
• the secretum is gathered at the apical portion
  of the cell
• the secretum leaves the cell membrane-bounded
  (pinched off)
• the cell remains alive, but a part of it goes
  with the secretory droplet

Examples sweat and mammary glands
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• 3. Holocrine secretion
• the secretory cell gradually fills up with
  secretum
• the cell organelles degenerate
• the cell dies, its membrane breaks and the
  secretum empties

The sebaceous gland is a holocrine gland. Dead
cells are replaced by the mitotic divison of
basal cells
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Absorptive epithelium its main function is to
absorb. Morphology of these epithelial cells
exhibit cuticular border (intestine) or brush
border (kidney tubules). Please note at fine
structural level both are microvilli !
EM micrograph of the apical surface with
microvilli
Intestinal epithelium the arrow shows the
cuticular border
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Pigmented epithelium Epithelial cells contain
melamosomes brown color
EM
Pigmented epithelium in the eye at LM level
shows brown pigmentation. At EM level the
melanosomes appear as electron dense bodies in
the cytoplasm.
LM
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Sensory epithelia Main function is
sensation Types primary, secondary sensory
epithelium true nerve cells
Primary sensory epithelium olfactory epithelium
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Secondary type of sensory epithelia Example
sensory cells of the taste buds