Endocrine System Flashcards
The pituitary gland is composed of glandular epithelial tissue and neural (secretory)
tissue. It is centrally located at the base of the brain, where it
lies in a saddle-shaped depression of the sphenoid bone called the sella turcica.
The pituitary gland has two functional components:
anterior lobe (adenohypophysis), and posterior lobe (neurohypophysis). Between
them, we can found pars intermedia.
Adenohipophysis (anterior lobe) has the typical organization of endocrine tissue
where the cells are organized in clumps and cords separated by fenestrated sinusoidal
capillaries. Using histochemical techniques with mixtures of acidic and basic dyes we
can identified two group of cells according to their staining reaction: chromophile
(basophils (10%)andacidophils (40%)andchromophobes (50%).
- *Acidophil cells** have red, basophilic cells blue and **chromophobe cells unstained
cytoplasm. **
In a pars intermedia, we can found different-sized follicles filled with colloid (CF)
which represent the residual lumens of Rathke’s pouch and small groups of cells
chromophobes and basophils cells arranged in cords, located around the cysts.
The pars nervosa contains the nonmyelinated axons and their nerve endings dilatated
in a form of neurosecretory called Herring bodies. In the posterior lobe we can found
specialized glial cells called pituicytes associated with the capillaries.
Pineal gland or epiphysis cerebri is neuroendocrine gland located at the posterior
wall of the third ventricle near the center of the brain.
Epiphysis is a small gland covered with a capsule (modified pia mater) from which
surface starts septas which separate glandular tissue in a lobular clumps. It contains
two types of parenchymal cells: pinealocytes and interstitial (glial) cells. Pinealocytes
are the chief cells of the pineal gland.
They are arranged in clumps or cords. As a consequence of a precipitation of calcium
phosphates and carbonates in pineal gland, during the time it develops calcified
concretions called corpora arenacea or brain sand.
Because they are opaque to X-rays they serve as convenient markers in radiographic
and computed tomography (CT) studies.
The thyroid gland is located in the anterior neck region adjacent to the larynx and
trachea; and consists of two large lateral lobes connected by an isthmus, a thin band
of thyroid tissue.
A thin connective tissue capsule surrounds the gland and sends trabeculae into the
parenchyma that partially outline irregular lobes and lobules.
Thyroid follicles constitute the functional units of the gland.
A thyroid follicle, spherical cyst-like structure, has a wall lined with a simple
cuboidal/low columnar epithelium called a follicular epithelium composed of
follicular and parafollicular cells. The central part of follicles contain a gel-like mass
called colloid.
Follicular cells (principal cells) produce the thyroid hormones T4 and T3.
Parafollicular cells (C cells) located in the periphery of the follicular epithelium
secrete calcitonin.
The parathyroid glands are small endocrine glands arranged in two pairs (superior
and inferior parathyroid glands) located in the connective tissue on the posterior
surface of the lateral lobes of the thyroid gland.
The parathyroid glands are closely associated with the thyroid gland.
The parathyroid gland is surrounded by a thin connective tissue capsule from which
extend septa and goes into the gland and divides it into poorly defined lobules. In the
glandular tissue, we can found fat cells, which numbers increase with age.
In the parathyroid gland we can recognize principal and oxyphil cells.
Principal (chief) cells are small, polygonal cells, with a centrally located nucleus and
the pale-staining, slightly acidophilic cytoplasm. They are producing parathyroid
hormone, who regulates calcium and phosphate levels in the blood.
Oxyphil cells constitute are more rounded, considerably larger than the principal
cells, and have a distinctly acidophilic cytoplasm (high amount of mitochondria),
arranged in a single or in cluster formation.
They have a flattened triangular shape and are embedded in the perirenal fat at the
superior poles of the kidneys.
The adrenal glands are covered with a thick connective tissue capsule from which
trabeculae extend into the parenchyma, carrying blood vessels and nerves.
The secretory parenchymal tissue is organized into two distinct regions:
1. The cortex (adrenal cortex-steroid secreting portion) which lies beneath the
capsule, and
2. The medulla (catecholamine secreting portion) which lies deep in the center of
the gland.
The adrenal cortex is divided into three zones on the basis of the arrangement of its
cells:
a) zona glomerulosa: composed of cells arranged in closely packed ovoid clusters and
curved columns. They are producing aldosterone, which is functions control of blood
pressure.
b) zona fasciculata: composed of cells arranged in long straight cords separated by
sinusoidal capillaries. They are producing glucocorticoids that regulate glucose and
fatty acid metabolism.
c) zona reticularis: composed of cells arranged in anastomosing cords separated by
fenestrated capillaries. They are producing weak androgens.
The medulla consists of pale-staining epithelioid cells called chromaffin cells
(medullary cells), connective tissue, numerous sinusoidal blood capillaries, and
nerves.
Numerous of myelinated nerve fibers pass directly to the chromaffin cells of the
medulla and when they stimulate them, cells release their secretory products -
catecholamines.
