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ZOO 117 1.0
Histology
Dr. Dinithi Peiris
Dept. of Zoology
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Thyroid Follicular
Cells
1.  Thyroglobulin synthesis
begins in the rER,
Carbohydrate are added in
the rER & the Golgi
complex,
Thyroglobulin is releases
into the lumen of the follicle
from vesicles at the apical
surface of the cell.
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Thyroid Follicular
Cells
2. The uptake of
circulating iodide
is accomplished in
the thyroid
follicular cells by a
membrane
transport protein.
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Thyroid Follicular
Cells
This protein, called the
Na/I symporter (NIS),
is located in the
basolateral membrane
of the follicular cells
and simultaneously
carries two molecules,
sodium and iodide.
Thyroid Follicular
Cells
4. Thyrosin resides of
thyroglobulin bind to 1
or 2 iodine atoms
covalently.
•  Two iodinated parts of
thyrosin (still part of
Thyroglobulin)
congugated by
oxidation coupling
reaction to form T3 & T4
Thyroid Follicular
Cells
3. Iodine is transferred
into the follicle cavity
by an anion
transporter.
Oxidation to active
iodine is initiated by
thyroid peroxidase
Thyroid Follicular
Cells
• Under influence of TSH, the
follicular cells engulf
iodinated thyroglobulin.
• Thyroglobulin is broken
down by lysosomal enzymes
into thyroid hormone.
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Thyroid Follicular Cells
Thyroxin
control
Thyroxin
control
X
Hypothyroidism
•  A deficiency in dietary iodide
consumption (=endemic
goiter)
•  Surgical removal of the
thyroid gland
•  Radioactive iodine treatment
• external radiation
What if no
iodine in diet?
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Hyperthyroidism
Examples of Thyroid Diseases
Most common cause: Graves'
disease: an autoimmune condition in
which the body's immune system
tricks the thyroid into producing too
much thyroid hormone.
1° Hypothyroidism
Thyroid Gland - Calcitonin
•  polypeptide produced by
parafollicular cells.
Hyperthyroidism
Thyroid Gland - Calcitonin
•  Control:
responds
directly to
blood calcium
levels
•  Very rapid
effect
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Thyroid Gland - Calcitonin
The Liver
•  actions: decreases blood
calcium levels by:
–  stimulating osteoblasts
(Ca2+ uptake and
incorporation into
bone)
–  inhibiting osteoclast
activities (osteoclasts
break down bone
matrix releasing
calcium)
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The Liver
• The largest single organ in
the human body.
• In an adult, weighs about
1.5 kg (2%) of the body wt.
& is roughly the size of a
football.
• Located in the upper righthand part of the abdomen,
behind the lower ribs
The Liver
•  70% - 80% of the blood in the liver comes from
the portal vein.
•  Rest comes from the hepatic artery.
•  Elimination occurs via bile.
•  Covered by a thin connective tissue; Glisson s
Capsule.
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The Liver
The Liver
•  Has 4 lobes
•  Right & left lobes
•  Right lobe
are separated by
•  Left lobe
the falciform
•  Qaudate lobe
ligament
•  Quadrate lobe
Anterior surface
The Liver
•  Caudate lobe is
separated from right
lobe by depression of
inferior vena cava.
Posterior surface
• Quadrate lobe is
inferior to caudate
lobe between lobe &
gallbladder.
Liver Lobule
•  Functional unit of the liver
•  Based on the direction of the blood flow.
•  Consists of hepatic plates radiates from the central
vein towards the periphery. Plates are separated by
hepatic sinusoids. *
•  Central venule: central vein
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Liver lobule
Liver lobule
•  At the corners of lobules are portal canal or
portal triad.
•  Portal triad consists of:
•  A portal venule (branch of portal vein),
embedded in connective tissue.
•  An arteriole ( branch of hepatic artery)
•  Duct of cuboidal epithelium or bile duct
•  Lymphatic vessel.
Liver lobule
Liver lobule
Blood
vessels,
nerves, bile
duct
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Liver lobule
Liver lobule
•  Hepatocyte functions are of different categories.
Connective tissue
•  Hence, liver lobules are described 3 ways
depending on:
•  Secretion of protein factors in to blood;
Classic hepatic/liver lobule
•  Secretion of bile components: Portal lobules
•  Removal of oxygen & small compounds from
blood; Liver acinus.
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