PINEAL GLAND
Also called pineal body, epiphysis
cerebri
is an endocrine or neuroendocrine
gland that regulates daily body
rhythm.
It develops from neuroectoderm of
the posterior portion of the roof of
the diencephalon and remains
attached to the brain by a short
stalk.
In humans, it is located at the
posterior wall of the third ventricle
near the center of the brain.
The pineal gland is a flattened, pine
cone–shaped structure
It measures 5 to 8 mm high and 3 to5
mm in diameter and weighs between
100 and 200 mg.
A.sh The pineal gland contains two types of parenchymal cells:
Pinealocytes
Interstitial (glial) cells. Pineal gland, sheep - H&E
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The parenchyma of the pineal gland
looks rather homogeneous at low
magnification. A few blood vessels
are visible criss-crossing through the
gland. At higher magnification three
types of nuclei can be distinguished.
Small dark nuclei belong to the
astrocytes found in the pineal gland.
Pinealocytes have larger, lighter and
round nuclei, which are surrounded
by a broad rim of light cytoplasm.
Most nuclei present are the nuclei
of pinealocytes. Endothelial cell
nuclei are found in association with
the vessels and capillaries traversing
the tissue. Both pinealocytes and
astrocytes have long processes
which give the tissue between the
nuclei its "stringy" appearance. The interstitial (glial) cells constitute
about 5% of the cells in the gland.
In addition to the two cell types,
the human pineal gland is characterized
by the presence of calcified concretions called
brain sand
It appears to be derived from precipitation of
calcium phosphates and carbonates on carrier
proteins that are released into the cytoplasm
when the pineal secretions are exocytosed A.sh Melatonin
is released in the dark and regulates reproductive function in mammals by inhibiting
A.sh
the steroidogenic activity of the gonads
Production of gonadal steroids is decreased by the inhibitory action of melatonin on
neurosecretory neurons located in the hypothalamus (arcuate nucleus) that produce
GnRH.
Inhibition of GnRH causes a decrease in the release of FSH and LH from the anterior
lobe of the pituitary gland. In addition to melatonin, extracts of pineal glands from
many animals contain numerous neurotransmitters, such as serotonin, norepinephrine,
dopamine, and histamine, and hypothalamic-regulating hormones, such as
somatostatin and TRH.
Clinically, tumors that destroy the pineal gland are associated with precocious (earlyonset) puberty.
Animal studies demonstrate that information relating to the length of daylight reaches
the pineal gland from photoreceptors in the retina.
The pineal gland thus influences seasonal sexual activity. Recent studies in humans
suggest that the pineal gland has a role in adjusting to sudden changes in day length,
such as those experienced by travelers who suffer from jet lag.
In addition, the pineal gland may play a role in altering emotional responses to the
reduced length of day during winter in temperate and subarctic zones known as
seasonal affective disorder (SAD) Endocrine Pancreas
(Islets of Langerhans) DR.SHATARAT ENDOCRINE PANCREAS
Islets of Langerhans
Low power
High power ENDOCRINE PANCREAS
•
Cells in the islets of Langerhans
• Alpha – secrete glucagon
• Beta – secrete insulin
• Delta – secrete somatostatin and gastrin
• PP – secrete pancreatic polypeptide First described by Langerhans in 1869 (as an observation
on the urine of pancreactictomized dogs).
In 1893 Gustave-Edouard Laguesse (1861-1927) attached
the name Langerhans to the structures. Langerhans did not
suggest any function for them. The book has been reprinted
with an English translation by H. Morrison. Spherical-oval cellular masses between the acini of the
pancreas.
Variable in size and number of cells in them.
They form ~ 1 million secretroy units.
Not homogeneously distributed and increase in number
towards the tail.
Surrounded by a very thin capsule.
They have the same embryological origin as the rest of the
pancreas (endoderm). Section of an adult human pancreas stained for
glucagon (green) and insulin (red) In H & E cells show variation in staining
reaction between acidophilia and basophilia.
E.M. shows typical poly peptide secreting
cells with variable amount of granules.
Immunohistochemistry is the only accurate
method to differentiate between cells. Major pancreatic cells cell
Cell
Location
%
α
Peripheral
~ 20 Glucagon
↑ Blood glucose level;
↑ glycogenolysis and lipolysis
β
Central
~ 70 Insulin
↓ Blood glucose level
δ
Scattered
5-10 Somatostatin
Inhibits release of other cells
F (PP)
Scattered
<1
Secretion
Pancreatic
polypeptide
Function
↑ activity of chief cells, ↓ bile
secretion.
↓ pancreatic enzyme and HCO3
secretion.
↓ intestinal motility
