Adrenal glands
The body has two adrenal (suprarenal) glands, one of which is located superior to each kidney.In the human, they are about 4-6cm long, 1-2cm wide & 0.5cm thick, and both may weigh about 15gm.
Each gland is surrounded by a thick connective tissue capsule that sends septa into the interior of the gland.
They are divisible by embryonic origin, structure, and function into cortex and medulla.
Adrenal Cortex
Structure in adults:
Cells of the adrenal cortex have the characteristic steroid-synthesizing cell structure (polygonal or rounded, with pale- staining central nucleus, acidophilic cytoplasm that contains many lipid droplets, abundant SER , mitochondria containing enzymes),
The suprarenal cortex consists of three concentric layers or zones:
a) zona glomerulosa.
b) zona fasciculate.
c) zona reticularis.
a. Zona glomerulosa :
this outermost cortical layer lies directly under the capsule.constitutes about 15% of adrenal volume.
composed of small cells arranged in form of clusters (glomeruli), separated by thin-walled capillaries.
ultrastructurally the cells contain well developed SER and comparatively little RER with scanty lipid droplets.
the cells of this layer secrete mineralocorticoids.
b. Zona fasciculata :
this middle layer of the cortex.
constitutes about 65% of adrenal volume .
Its cells form straight cords or columns (usually 2-3cells wide) separated by capillaries the columns are perpendicular to the organ surface.
ultrastructurally, the cells have prominent RER, extensive lipid vacuoles and characteristic small round or ovoid mitochondria.
Its cells produce glucocorticoids and some adrenal androgens.
c. Zona reticularis :
this innermost layer of the adrenal cortex.constitutes about 7% of adrenal volume.
consists of an anastomosing network of cell cords with capillary network closely apposed to the cell membranes.
Its cells are smaller and more acidophilic than those in the fasciculata and contain fewer lipid droplets, more mitochondria, many lipofuscin granules and prominent SER.
the reticularis and fasciculata seem to constitute a single functional zone, with the reticularis producing most of the glucocorticoids and adrenal androgens.
Normal function.
The adrenal cortex produces three types of steroid hormones.1. Mineralocorticoids mainly aldosterone: produced by the zona glomerulosa in response to angiotensin II, it stimulates sodium absorption by the distal renal tubules.
2. Glucocorticoids mainly cortisol and corticosterone: produced by the zona reticularis in response to ACTH and by the fasciculata after prolonged stimulation, glucocorticoids control carbohydrate metabolism and suppress the immune response by decreasing circulating lymphocytes and eosinophils.
3. Adrenal androgens: secreted by zona reticularis in response to ACTH and by fasciculata after prolonged stimulation, they produce musculinizing and anabolic effect.
Adrenal Medulla
Structure.
The adrenal medulla is composed of epithelial cells supported by a delicate connective tissue richly supplied by blood sinusoids.It contains two major cell types:a) chromaffin cells.
b) ganglion cells.
a. Chromaffin cells. Also known as pheochromocytes
these are the predominant cell type.they contain large nuclei and cytoplasmic granules that become brown when exposed to chromium salts for this reason, they are sometimes referred to as chromaffin cells.
the chromaffin cells synthesize and secrete norepinephrine and epinephrine in response to stimulation by preganglionic sympathetic nerve fibers, some cells are thought to produce serotonin in addition to epinephrine, the hormones are released by process of exocytosis.
with an electron microscope, the cells shows well developed Golgi complex, few profiles of RER, many oval mitochondria, and membrane bound cytoplasmic granules.
There are two types of chromaffin cells:-
1- cells secrete norepinephrine have dense core granules.
2- light cells secrete epinephrine have granules not so dense.
b. Ganglion cells: few parasympathetic ganglion cells present show typical
morphologic characteristics of autonomic ganglion cells (large, multipolar cells,
randomly distributed throughout ganglion, have large and ovoid nuclei mostly eccentric).
PINEAL GLAND
the pineal gland is also known as the epiphysis cerebri, or pineal body.
It is small flattened conical structure located just below the posterior end of the corpus callosum of the brain.
covered on its outer surface by pia mater which forms the capsule, from which number of fibrous trabeculae carrying the blood vessels and unmyelinated nerves extending into the interior of the gland and incompletely divide the parenchyma into poorly defined lobules of various size.
The pineal gland is composed of groups of cells called pinealocytes supported by astroglial cells.
A. Pinealocytes :
Structure.The pinealocytes are large neuron-like cells have extensive processes that are intertwined with the processes of the astroglial cells.
Pinealocytes are often arranged in rosettes, where several cells surround a central fibrillary area composed of cell processes directed towards a small capillary vessel.
With H&E stain, they have pink-staining cytoplasm and dark-staining irregular or lobate nuclei.
With silver stain, they exhibit long cytoplasmic processes that terminate as swellings close to blood capillaries stored in the terminal swellings are vesicles containing monoamines and polypeptide hormones.
The cells produce melatonin, which induces rhythmic changes in the secretions of the hypothalamus, pituitary and gonads, and is said to act as an endocrine transducer.The concentration of melatonin in the blood conform to a circadian rhythm, being higher during darkness and lowest during the day.
B. Astroglial Cells:
Also known as interstitial cells, these glialike cells have elongated nuclei that stain more heavily than those of the parenchyma.These cells have long cytoplasmic processes that contain a large number of intermediate filaments.
They are found around blood vessels and between clusters of pinealocytes.
They are indistinct unless specially stained.
The pineal gland has a rich blood supply and is innervated by sympathetic and parasympathetic nervous systems. In addition signals from retina arrive indirectly.
Concretions of calcified material called "brain sand" (corpora arenacia) accumulate within the astroglial cells and connective tissue of the pineal gland, progressively with age, these deposits are useful to radiologists because they serve as a landmark determine whether the pineal gland has been displaced laterally by a space-occupying lesion within the skull.