Histology Fact Sheet: Adrenal Gland

Adrenal Gland

The adrenal gland is found on the upper portion of each kidney. Because of where the adrenal gland is located, the adrenal gland is also called the suprarenal gland.

The adrenal gland is composed of an outer cortex and an inner medulla. The cortex and the medulla are derived from different embryonic tissues. The cortex and the medulla each produce and release their own type of hormones. The adrenal cortex is essential to life, but the adrenal medulla is not essential to life.

The hypothalamus of the brain has an effect on both regions of the adrenal gland. The adrenal cortex is regulated by a negative feedback loop involving the hypothalamus and the pituitary hormone adrenocorticotropic hormone (ACTH).  Nervous impulses from the hypothalamus regulate the adrenal medulla.

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Histology of the Adrenal Cortex

Upon examining the histology, it can be seen that the adrenal cortex consists of three different regions. Each region produces a different type of hormone.  The adrenal cortical hormones are all steroids.

The layers of the adrenal cortex, from the external side of the gland going deeper are: zona glomerulosa, zona fasciculata, and zona reticularis. The layers can be visualized on a histology slide. The respective hormones of each zone are: mineralocorticods (such as aldosterone), glucocorticoids (such as cortisol), and sex steroids. 

Mineralocorticoids are secreted by the outermost region of the adrenal cortex, the zona glomerulosa. The main mineralocorticoid is aldosterone.  Aldosterone works on the kidney to conserves sodium ions and water in the body.

Glucocorticoids are secreted by the middle region of the adrenal cortex, the zona fasciculata. The principal glucocorticoid is cortisol.  Cortisol increases blood glucose levels.

The innermost region of the adrenal cortex, the zona reticularis, secretes sex hormones. The action of the sex steroids secreted by the adrenal gland is usually overshadowed by the hormones secreted from the gonads (testes and ovaries). In women, the masculinization effect of adrenal androgen secretion may become visible after menopause, when ovarian estrogen secretion decreases.

Histology hint from Sarah Bellham: A mnemonic to remember the layers of the adrenal cortex and their respective products is:

"Go Find Rex; Make Good Sex"
(glomerulosa, fasciculata, reticularis)
(mineralocorticoid, glucocorticoid, sex steroids).

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Histology of the Adrenal Medulla

The adrenal medulla is the inner portion of the adrenal gland. 

The adrenal medulla develops from neural tissue. The cells of the adrenal medulla are chromaffin cells. They secrete the catecholamines (epinephrine and norepinephrine).  These two hormones are secreted in response to stimulation by sympathetic nerves,  especially during "flight or fright" situations.

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Sources:

Histology: A Text and Atlas
Michael H. Ross/Edward J. Reith

http://www.training.seer.cancer.gov; funded by the U.S. National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program, via contract number N01-CN-67006, with Emory University, Atlanta SEER Cancer Registry, Atlanta, Georgia, U.S.A.