Overview

The adrenal glands (also called Suprarenal glands) are paired endocrine glands which reside on the superior poles of each kidney. In adults each gland is approximately 5cm long and 3cm wide, although there is much variation between individuals. 

They are responsible for the production of many hormones, and play important roles in stress, infection and development. Death will result if they are lacking.

The adrenal glands are very well vascularised with three separate arterial supplies direct off the abdominal aorta. They have a surrounding capsule and are embedded in perineal fat along with their respective Kidney, giving optimum protection.

Image courtesy of https://commons.wikimedia.org/wiki/Image:Illu_adrenal_gland.jpg Public domain image 

Structure of the Adrenal Glands

Two fetal glands with different origins and functions merge during embryonic development to form each gland. This results in two parts with very different physiological roles:

An outer cortex

The primary role of the outer cortex is the synthesis and secretion of more than 25 steroid hormones collectively known as corticoids. The cortex is comprised of three layers of glandular tissue - Zona Glomerulosa, Zona Fasiculata, and Zona Reticularis, each responsible for the production of Mineralcorticoids, Glucocorticoids and Androgens respectively. Further information on each of these can be found by following the links.

An inner medulla

This is a thinner layer. It arises from the neural crest and is composed of modfiied sympathetic ganglia, responsible for secretion of catecholamines, particularly adrenalin and Noradrenalin. It shall not be considered further in this website.

Image courtesy of https://upload.wikimedia.org/wikipedia/commons/5/5c/Gray1185.png Public Domain image

Hormone synthesis

Mineralcorticoids, Glucocorticoids and Androgens are all classes of steroid hormones. The primary substrate for their synthesis is Cholesterol. The adrenal cortex has two sources of Cholsterol: either free cholestrol in the plasma, or de novo synthesis from acectate. 

For a diagram of the stages of steroid hormone synthesis click here: https://www.endotext.org/pediatrics/pediatrics9/figures9/figure1.gif