1st Lec on Endocrine Histology by Dr Roomi

8/3/2019 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.

1st Lec on Endocrine Histology by Dr Roomi

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1st Lec on Endocrine Histology by Dr Roomi