Human Adrenal Glands (part of the Endocrine System)

Here is a simple summary of information about the adrenal glands. Information on this page is likely to be appropriate for first-level courses such as AS and A-Level Human Biology, ITEC Anatomy and Physiology, and other courses in Health Sciences.

The location(s) of the Adrenal Glands:

The human body normally* includes two adrenal glands.

They are located immediately anterior to the kidneys, and are encased in a connective tissue capsule that is usually partially buried in an island of fat. The adrenal glands lie beneath the peritoneum. That is, they are retroperitoneal.

* In some circumstances (e.g. in the cases of certain types of tumours), one or more of the adrenal glands may be surgically removed. For further information about this see: http://www.endocrineweb.com/adrenal.html (Norman Endocrine Surgery Clinic).

The Structure of the Adrenal Glands:

The most obvious aspect of the structure of the adrenal glands is their partitioning into two distinctive components: the paler medulla (centre), and the darker cortex (surround). Both of these tissues contain many blood vessels, hence they may be described as "richly vascularized".

Adrenal Medulla

The medulla consists of many large columnar cells called chromaffin cells. These synthesize and secrete catecholamines.

There are also some ganglion cells. Blood from throughout the adrenal gland collects into large medullary veins to exit the gland.

Adrenal Cortex

The adrenal cortex consists of three concentric zones of steroid-synthesizing cells called the:

  • glomerulosa
  • fasiculata, and
  • reticularis.

Although the boundaries between these zones are indistinct, each of these zones has a characteristic arrangement of cells.

Simple Diagram representing the Adrenal Medulla (centre) and the Adrenal Cortex (surround):

Hormones secreted by the Adrenal Glands:

Adrenal Medulla

  • Adrenalin

Prepares the body for 'fright, fight or flight' ('FFF') and has many effects:

  • Noradrenalin

Similar effects to adrenalin:

  • Constriction of small blood vessels leading to increase in blood pressure.
  • Increased blood flow through the coronary arteries and slowing of heart rate.
  • Increase in rate and depth of breathing.
  • Relaxation of the smooth muscle in the intestinal walls.

Adrenal Cortex

  • Corticosteroids

Glucocorticoids (e.g. cortisol, cortisone, corticosterone)

  • Utilization of carbohydrate, fat and protein by the body.
  • Normal response to stress.
  • Anti-inflammatory effects.
  • Hypersecretion of cortisol results in Cushings Syndrome.

Mineralocorticoids (e.g. aldosterone)

  • Regulation of salt and water balance.
  • Hypersecretion of Alderosterone decreases the potassium in the body (affecting nerve impulse transmission and leading to muscular paralysis).

See also an introduction to the endocrine system and information about aspects of it such the locations of and hormones secreted by the main endocrine glands and conditions that affect the endocrine system including diabetes.

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