1st Lec on Endocrine Histology by Dr Roomi
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HISTOLOGY OF
ENDOCRINE GLANDS
BY
DR. MUDASSAR ALI ROOMI (MBBS, M. Phil.)
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GENERAL CLASSIFICATION OF GLANDS
1) Exocrine Glands Glands that secrete their
products onto the apical surface directly OR via
epithelial ducts that are connected to the apical
surface e.g. salivary gland.
2) Endocrine Glands - Glands that release their
products directly in the blood stream. The
secretion passes through the basal surface of thecell into the blood stream. Endocrine glands lack
a duct system e.g. pituitary gland.
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ENDOCRINE GLANDS
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Adrenal (suprarenal)Glands
Located near superior pole of each kidney
Have separate and distinct embryologic origin,structure, and function
Covered with a connective tissue capsule and consist ofouter cortex and inner medulla
Fenestrated capillaries and large vessels are presentthroughout both regions
Cortex is subdivided into three zones: zonaglomerulosa, zona fasciculata, and zona reticularis(GFR)
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ADRENAL GLANDS
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ZONA GLOMERULOSA:
The cells in zona glomerulosa are arranged
into ovoid groups or clumps and surrounded by numerous sinusoidal
capillaries
The cytoplasm of these cells stains pink andcontains few lipid droplets.
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ZONA FASCICULATA:
The middle and the widest cell layer is the zonafasciculata (80 % of adrenal cortex).
The cells of the zona fasciculata are arranged invertical columns or radial plates.
Because of the increased amount of lipid dropletsin their cytoplasm, the cells of the zona
fasciculata appear light or vacuolated after anormal slide preparation.
Sinusoidal capillaries between the cell columnsfollow a similar vertical or radial course.
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ZONA RETICULARIS:
The third and the innermost cell layer is the
zona reticularis. This cell layer borders on the adrenal medulla.
The cells of the zona reticularis form
anastomosing cords surrounded by sinusoidalcapillaries.
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ADRENAL MEDULLA:
The medulla is not sharply demarcated from thecortex.
The cytoplasm of the secretory cells of the medullaappears clear.
After tissue fixation in potassium bichromate, calledthe chromaffin reaction, fine brown granules become
visible in the cells of the medulla. These granules indicate the presence of the
catecholamines epinephrine and norepinephrine in thecytoplasm.
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Cortex of adrenal gland
Under direct influence of ACTH from pituitary
gland
Release three types of steroid hormones:
mineralocorticoids, glucocorticoids, andandrogens
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Cells in zona glomerulosa secrete mineralocorticoids,primarily aldosterone
Aldosterone release is caused by decreased arterialblood pressure and low sodium levels or high
potassium level. Juxtaglomerular apparatus in kidney initiates the renin
angiotensin pathway to increase blood pressure
Aldosterone increases sodium reabsorption and
increased water retention by distal convoluted tubules(DCT).
Increased fluid volume increases blood pressure andinhibits further release of aldosterone
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Cells ofzona fasciculata secrete
glucocorticoids, of which cortisol and
cortisone are important
Glucocorticoids are released in response to
stress, increase metabolism and glucose
levels, and suppress inflammatory responses
Cells ofzona reticularis produce weak
androgens (e.g DHEA)
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Medulla of adrenal gland
Cells are modified postganglionic sympatheticneurons that became secretory (MCQ)
Action controlled by sympathetic division of
autonomic nervous system, not pituitary gland. Cells contain catecholamines (epinephrine and
norepinephrine) and respond to acute stress
Epinephrine (80%), norepinephrine (20%).
Prepares the individual for flight or fight responseby activating maximal use of energy and physicaleffort.
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Nerve supply of adrenal gland
the adrenal medulla receives input from thesympathetic nervous system throughpreganglionic fibers originating in the thoracicspinal cord from T5T11.
Because it is innervated by preganglionicsympathetic nerve fibers, the adrenal medullacan be considered as a specialized sympatheticganglion.
Unlike other sympathetic ganglia, however, theadrenal medulla lacks distinct synapses andreleases its secretions directly into the blood.
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Fetal Adrenal Cortex
At birth in humans the adrenal gland is larger than that of the adult andproduces up to 200 mg of corticosteroids per day, twice that of an adult.
At this age, a layer known as the fetal or provisional cortex, comprising80% of the total gland, is present between the thin permanent cortex andan under-developed medulla.
The fetal cortex is thick and contains mostly cords of large, steroid-secreting cells under the control of the fetal pituitary. The principalfunction of the cells is secretion of sulfated DHEA which is converted inthe placenta to active estrogens, which mostly enter the maternalcirculation.
The fetal adrenal cortex is an important part of a fetoplacental unit whichaffects both endocrine systems during pregnancy but whose physiological
significance remains largely unclear. After birth, the provisional cortex undergoes involution while the
permanent cortex organizes the three layers (zones)
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Adrenal Medulla
The adrenal medulla is composed of large, pale-stainingpolyhedral cells arranged in cords or clumps and supportedby a reticular fiber network.
A profuse supply of sinusoidal capillaries intervenes
between adjacent cords and a few parasympatheticganglion cells are present.
Medullary parenchymal cells, known as chromaffin cells,arise from neural crest cells, as do the postganglionicneurons of sympathetic and parasympathetic ganglia.
Chromaffin cells can be considered modified sympatheticpostganglionic neurons, lacking axons and dendrites andspecialized as secretory cells.
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One disorder of the adrenal medulla is
pheochromocytoma, a tumor of its cells that
causes hyperglycemia and transient elevations
of blood pressure (hypertension)
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Tumors of the adrenal cortex can result in excessiveproduction of glucocorticoids (Cushing syndrome) oraldosterone (Conn syndrome).
Cushing syndrome is most often (90%) due to apituitary adenoma that results in excessive productionof ACTH; it is rarely caused by adrenal hyperplasia oran adrenal tumor.
Excessive production of adrenal androgens has littleeffect in men, but precocious puberty (in boys) andhirsutism (abnormal hair growth) and virilization (ingirls) are encountered in prepubertal children.
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Cushing syndrome
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Addison disease
It is adrenocortical insufficiency is caused by
destruction of the adrenal cortex in some
diseases e.g. tuberculosis.
The signs and symptoms suggest failure of
secretion of both glucocorticoids and
mineralocorticoids by the adrenal cortex.
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