Endocrine glands
Author: Dr. R. Menaka
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Endocrine organs are glands whose products are secreted into the blood, to affect tissues distant from the site of secretion. These secretory products are hormones.
Adrenal Gland
Pituitary Gland:
The different parts of the gland are the
i. adenohypophysis and
ii. neurohypophysis
i. Adenohypophysis- the mature adenohypophysis has several distinct parts: the cranial
pars distalis, the pars intermedia, and the pars tuberalis
Pars distalis- The cells of the pars distalis can be characterized as acidophilic and basophilic types. The acidophils produce growth hormone and prolactin, the basophils produce thyroid stimulating hormone, adrenocorticotrophic hormone, and gonadotrophic hormones.
Pars intermedia- The pars intermedia is pressed up close to the neurohypophysis. The
pars intermedia secretes MSH, or intermedin.
Pars tuberalis is not yet known to secrete any hormones.
Neurohypophysis- The pars nervosa is a place of storage and release of hormones made in the brain. The two hormones associated with it are oxytocin and vasopressin. Instead of neurotransmitters, these hormones are made in the brain's supraoptic and paraventricular areas, then carried to the pars nervosa in the axons that end at the surface of capillaries.
Pineal Gland
Histologically, the pineal gland is made up of pinealocytes, the functional cells and manufacture the pineal hormone melatonin (5-methoxy-N-acetyl-tryptamine). These cells are large and lightly stained in H&E, with a rounded nucleus. The astrocytes also present but cannot be seen on H&E stained slide.
Thyroid Gland
The basic unit of the gland is thyroid follicles. The thyroid follicles are hollow, which is lined by simple cuboidal epithelium. The amorphous material present inside thyroid follicles is colloid, an inactive storage form of the gland's secretion.
In certain regions between the follicles, C-cells or clear cells are present . Sometimes these cells are called parafollicular cells. These are oval shaped, larger, and more lightly stained than the follicular cells are. They are often hard to identify in H&E preparation. The C-cells do not produce colloid; they produce the hormone calcitonin.
Adrenal Gland
The adrenal gland has a distinct cortex and medulla.
The coretx consists of 1. Zona glomerulosa, 2. Zona fasiculata and 3. Zona reticularis
1. Zona glomerulosa.
The adrenal gland is surrounded by a distinct connective tissue capsule. The layers of cells immediately beneath the capsule are organized into the zona glomerulosa. They form arcades or small arches of cells.
Deep to this layer is a second distinct region. where the cells form somewhat more regular rows, radiating away from the center of the gland. This is the zona fasciculata,
The cells in that region of the cortex closest to the medulla. They are organized into anastomosing cords to form a network-like zona reticularis. Separating the rows and cords of cells are irregular vascular channels, or sinusoids.
The Adrenal Medulla
The cells of the adrenal medulla are characteristic of catecholamine compounds. The adrenal medulla produces the catecholamine hormones epinephrine and norepinephrine. These medullary cells shows the chromaffin reaction.