Endocrine System Histology
A) PITUITARY GLAND
Tropic hormones (ACTH, FSH, LH, TSH)
● Trophic hormones (Prolactin, GH)
● NEUROHYPOPHYSIS / POSTERIOR PITUITARY (pars nervosa +
infundibulum)
●
i) branched glial cells (pituicytes) are most abundant
ii) unmyelinated axons of neurons with cell bodies in supraoptic &
paraventricular hypothalamic nuclei
ADENOHYOPHYSIS / ANTERIOR PITUITARY
1. Pars distalis (75% of adenophypophysis; cords of chromophils &
chromophobes interspersed with capillaries & reticular CT within a
fibrous capsule)
●
i) Chromphils (secretory cells with hormones stored in cytoplasmic granules)
include: acidophils (somatotrophs, lactotrophs) & basophils (corticotrophs,
gonadotrophs, thyrotrophs) with somatotrophs being the most abundant,
thyrotrophs the least.
ii) Chromphobes (stain weakly) include stem cells & degranulated chromphils.
2. Pars tuberalis (gonadotropins)
3. Pars intermedia (corticotrophs, chromophobes, colloid-filled cysts
derived from lumen of embryonic hypophyseal pouch)
B) PARATHYROID GLANDS
– Small, polygonal, pale / faintly acidophilic principal (chief) cells, with
cytoplasmic granules containing PTH. With increasing age, they get
replaced with adipocytes.
– Larger, clustered, very acidophilic, degnerated chief cell derivatives
called oxyphil cells. They are present in smaller number & are more
common in the older.
C) THYROID GLAND
– Fibrous capsule from which septa extend into parenchyma, dividing it
into lobules, carrying blood vessels, nerves & lymphatics.
– Parenchyma is composed of epithelial thyroid follicles of variable
sizes, each with a central colloid filled acidophilic lumen.
– Follicle epithelium is composed of:
i) Follicular cells / thyrocytes with basal RER & apical microvilli, that vary in
shape (squamous when inactive, cuboidal when normally functioning, columnar
when active)
ii) Parafollicular / C cells are found inside basal lamina of follicular epithelium or
as isolated clusters b/w follicles. They are larger than follicular cells, stain less
intensely, have smaller amount of RER & granules containing calcitonin.
D) ADRENAL GLANDS
●
Adrenal Medulla
Pale-staining polyhedral chromaffin cells arranged in cords, supported by a
reticular fiber network, separated by sinusoidal capillaries. These cells are
modified sympathetic postganglionic neurons, lacking axons & dendrites, & are
specialized as secretory granular cells (releasing E, NE)
●
Adrenal Cortex
Cells have acidophilic cytoplasm rich in lipid droplets, with central nuclei
i) Zona glomerulosa (15% cortex) has small closely packed round cords of
columnar or pyramidal cells with many capillaries (produce mineralocorticoids)
ii) Zona fasciculata (65-80% cortex) has larger, pale-staining polyhedral cells
rich in lipid droplets, arranged in cords (secrete glucocorticoids)
iii) Zona reticularis (10% cortex) has small, dark staining cells in irregular
branching cords, containing fewer lipid droplets, more lipofuscin pigment
(mainly secrete androgens, DHEA)
E) PANCREAS
– Spherical masses of endocrine cells embedded within acinar exocrine
tissue of pancreas, surrounded by capsule.
– Pancreatic islets mostly present in gland’s tail (constitute about 1-2%
of organ’s total volume), are polygonal, pale-staining than surrounding
acinar cells, arranged in cords separated by fenestrated capillaries.
i) A (alpha) cells secrete glucagon & are located peripherally
ii) B (beta) cells secrete insulin, are most numerous, located centrally
iii) D (delta) cells secrete somatostatin, are scattered
iv) PP cells, within pancreatic head, secrete pancreatic polypeptide