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Human Adrenal Glands (part of the Endocrine
System)
This page is a simple summary of information about
the Adrenal Glands.
The 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:
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The human body normally* includes two
adrenal glands. |
These 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"). |
Click |
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for a diagram of the positions of
the Adrenal Glands - and other major endocrine
glands of the human body. |
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*
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). |
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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
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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
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The adrenal cortex consists of three concentric
zones of steroid-synthesizing cells: glomerulosa,
fasiculata and reticularis. Although the boundaries
between these zones are indistinct, each
of these zones has a characteristic arrangement
of cells. |
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Simple Diagram representing
the Adrenal Medulla (centre) and the Adrenal Cortex
(surround):
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Hormones
secreted by the Adrenal Glands: |
Adrenal Medulla |
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Adrenalin
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Prepares
the body for "fright, fight or flight"
and has many effects: |
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Action
of heart increased.
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Rate
and depth of breathing increased.
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Metabolic
rate increased.
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Force
of muscular contraction improves.
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Onset
of muscular fatigue delayed.
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Blood
supply to the bladder and intestines
reduced, their muscular walls relax,
the sphincters contract.
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Noradrenalin
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Similar
effects to adrenalin: |
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Constriction
of small blood vessels leading to increase
in blood pressure.
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Increased
blood flow through the coronary arteries
and slowing of heart rate.
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Increase
in rate and depth of breathing.
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Relaxation
of the smooth muscle in the intestinal
walls.
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Adrenal Cortex |
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Corticosteroids
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Glucocorticoids (e.g. cortisol, cortisone, corticosterone) |
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Utilization
of carbohydrate, fat and protein by the
body.
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Normal
response to stress.
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Anti-inflammatory
effects.
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Hypersecretion
of cortisol results in Cushings Syndrome.
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| Mineralocorticoids (e.g.
aldosterone) |
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Regulation
of salt and water balance.
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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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