The adrenal gland is divisible into two distinct different parts – Cortex and medulla that are developmentally and functionally independent.
It has a connective tissue capsule containing a few elastic and smooth muscle fibres.
From this many delicate trabeculae, enclosing capillaries, penetrate into the cortex and the corticomedullary junction.
The framework of cortex consists of a network of reticular fibres.
Cortex
- The cells which occupy greater part of the gland are divided into three zones.
- The outer thin Zona glomerulosa, next to capsule.
- A middle thick Zona fasciculata
- An inner moderately thick Zona reticularis which abuts on the medulla.
- Zona glomerulosa: consists of short columnar cells, closely packed, in groups or in columns forming arcs immediately below the capsule. They have deep staining nuclei and basophilic cytoplasm. (In the horse it is called as zona arcuata).
- Zona fasciculata: consists of columns of large polyhedral cells arranged radially in the form of anastomosing cords extending between both the zones above and below. Cell have central nuclei, one or two in each cell, and cytoplasm is basophilic and appear vacuolated because in routine staining technique, the lipoid droplets in the cytoplasm gets dissolved. The vacuolation gives a spongy appearance and hence the cells are often referred to as spongiocytes.
- Zona reticularis: consists of anastomosing cells cords. The cells are cuboidal and have deeply staining spherical nuclei. The cytoplasm stains deeply in some, lightly in others and may contain pigment. Lipoid droplets are less in number in these cells. There are sinusoids in the zone.
Medulla
- The cells of this part are arranged in groups or irregular cords surrounded by sinusoids. The cells are polygonal and show numerous fine granules in the cytoplasm. The nuclei are large, centrally located and stain lightly. The granular content of the cytoplasm varies in different cells.
- The cells are arranged in such a way that one pole of the cell is directed towards a capillary and the other pole towards a vein. When the gland tissue is fixed in fluid containing potassium dichromate, fine brown granules are seen throughout these cells. This is due to chromaffin reaction. The cells are therefore called pheochrome cells.
- These granules are readily stained with basic stain. In addition to chromaffin cells there are single group of sympathetic ganglion cells.
Functions
- The adrenal cortex produces numerous substances mostly steroids and based on their action they have been grouped into three classes. There is also some evidences to indicate that each of these classes is apparently secreted by one particular zone of cortex.
- Mineralo-corticoids – (aldosterone) regulate water and electrolyte balance chiefly Na and K secreted by zona glomerulosa cells.
- Gluco-corticoids – (cortisone and hydrocortisone) influences carbohydrate metabolism, favour catabolism of proteins and also have anti-inflammatory, anti-allergic, anti-rheumatic properties. They inhibit lymphoblastic activity and also antibody formation. These are produced by cell of zona fasciculata.
- Sex anabolic hormones (weak androgens, 17-ketosteroids oestrogen and progesterone) These are concerned with the development of secondary sexual characteristics and have an anabolic action on protein metabolism. These are produced by cell of zona reticularis.
- The Medulla secretes Epinephrine and Nor-epinephrine. These increases blood pressure and cardiac output, and cause vasoconstriction and raise blood sugar level.
