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
are also observed. 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 |
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Prepares the body for "fright, fight or flight" and has many effects: |
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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.
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Adrenal Cortex |
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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.
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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).
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This is the end of this page but an introduction
to the endocrine system and information about
other aspects of it - such the locations
of and hormones secreted by the main endocrine
glands, conditions
that affect the endocrine system, and a page
about diabetes
are also included on this website.
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