Histology
ENDOCRINE SYSTEM dr. Ahmed AlhuchamiADRENAL (SUPRARENAL) GLANDS
They are paired, flattened, triangular bodies that are located superior to the superior pole ofthe kidney. Both glands are weighing 8 gm. They are approximately 5x4x1 cm in diameter.
Adrenal gland is enclosed by a dense connective tissue capsule. Its stroma is composed of
rich network of reticular fibers that support the secretory cells.
Suprarenal gland has two parts that are of different embryonic origin, these are:
1. Cortex (90%) – derived from the genital ridge of the mesoderm.
2. Medulla (10%) – derived from neural crest cells.
Adrenal cortex:
It is subdivided into three concentric layers, which are not sharply defined (because they are
derived from the same embryonic origin). These are:
a) Zona glomerulosa
b) Zona fasciculata
c) Zona reticularis
Note: all cells of the adrenal cortex reveal ultrastructurall features of steroid-hormone
secreting cells.
Zona glomerulosa: characterized by being:
Thin outer layer (15%) that is located just under the capsule
Light microscopical exam shows that its cells are pyramidal and arranged in rounded
or arched groups that are surrounded by capillaries.
Their nuclei are rounded and central while cytoplasm is lightly basophilic
These cells are responsible for secretion of mineralocorticoids mainly aldosterone
(controls electrolytes –Na+ & K+ - homeostasis and water balance).
Zona fasciculata:
It is the thickest layer (65 – 80%) of the adrenal cortex
Cells are large polyhedral with rounded central nucleus and pale foamy cytoplasm.
These cells are arranged in parallel columns of 1or 2 cells thickness. Columns usually
run in right angle to the capsule. Cells' columns are separated by sinusoidal capillaries.
The cytoplasm of zona fasciculata cells contains numerous lipid droplets that contain
neutral fats, fatty acids, cholesterol and phospholipids. These substances represent
precursors for steroid hormones.
During slide preparation (by typical histological procedures) lipid is extracted, thus
gives vacuolated or spongy appearance to these cells and that's why they are called
Spongyocytes.
Zona fasciculata cells secret the following hormones:
i. Glucocorticoids (mainly cortisol and cortisone), which influence the
carbohydrate, lipid and protein metabolism.
ii. Gonadocorticoids (sex hormones - small amount of androgens).
Zona reticularis:
Thin layer (10%) that lies between zona fasciculata and medulla. It consists of small rounded
cells that are arranged in branching and anastomosing cords. Cells have rounded central
nucleus and deeply basophilic cytoplasm (because they contain fewer lipid droplets and more
lipofuscin pigment). This layer secrets the weak androgen (dehydroepiandrosterone -
DHEA) which is converted to testosterone in several other tissues.
Adrenal Medulla :
The adrenal medulla is composed of large, pale-staining polyhedral cells arranged in cords or
clumps and supported by a reticular fiber network. A profuse supply of sinusoidal capillaries
intervenes between adjacent cords and a few parasympathetic ganglion cells are present.
When medullary cells are exposed to an oxidizing agent such as potassium bichromate
(K2Cr2O2), caticholamines (adrenalin and noradrenalin) will be oxidized giving a brown
coloration to their cytoplasm, therefore these cells are called chromaffin cells and the
reaction is called Chromaffin reaction. Chromaffin cells can be considered modified
sympathetic postganglionic neurons, lacking axons and dendrites and specialized as
secretory cells.
Unlike cells of the cortex, medullary chromaffin cells contain many granules, contain one or more
Than other of the catecholamines, epinephrine or norepinephrine. About 80% of the
catecholamine secreted from the adrenal is epinephrine.
Medullary chromaffin cells are innervated by cholinergic endings of preganglionic
sympathetic neurons, from which impulses trigger hormone release by exocytosis.
Epinephrine and norepinephrine are released to the blood in large quantities during intense
emotional reactions, such as fright, and produce vasoconstriction, increased blood pressure,
changes in heart rate, and metabolic effects such as elevated blood glucose. These effects
facilitate various defensive reactions to the stressor (the fight-or-flight response). During
normal activity, the adrenal medulla continuously secretes small quantities of the hormones.
