Adrenal Gland
Study Guide

Web address: http://www.cytochemistry.net/Endocrine_System/adrenal.htm

10/31/00
Gwen V. Childs, Ph.D.
Shorey 9/32;  Email: childsgwenv@uams.edu

To help you with your study, Read Gartner and Hiatt, pp 316-321 and follow the guide in the questions below. Also, consult the Lecture slides found at the following site:   http://www.cytochemistry.net/Endocrine_System/Adrenal_lecture_slides.htm

 Test yourself:  How much do you know about the adrenal glands?

Where would you find the adrenal glands? Why are they also called suprarenal glands?

Adrenal glands lie in pairs above each kidney in upright mammals. This is why they are sometimes called "supra-renal".

Define the two major regions in the gland. What are the three divisions of the cortex.  

From outside in, there is the capsule (connective tissue); cortex, and medulla.
The cortex includes:

How would you distinguish the cortical regions histologically? What are the major products of each of the cortical regions?   Name the regulatory hormone for each.

Zona Glomerulosa

Find it on this photo.  It is distinguished by grape-like clusters of cells that lie just under the capsule (blue stained region in photograph)

Secretes aldosterone.

Aldosterone itself is regulated by the renin-angiotensin system. Aldosterone stimulates distal tubules of Kidney to pump sodium across basal membrane and thereby attract water.  This raises blood pressure.

Zona Fasciculata

Photo shows capsule, Zona Glomerulosa and the lighter-staining Zona fasciculata.

The cells are arranged in cords (long rows) separated by capillaries.

Note the lipid droplets filling the cells.

Cells secrete glucocorticoids under the influence of ACTH (adrenocorticotropin). Where does ACTH come from and what cell type produces it?  An example of a glucocorticoid is "cortisol".  Cortisol raises blood glucose, thereby providing a source of energy for our responses to stress (in the flight or fight reaction).  It is also anti-inflammatory.

Zona Reticularis:

This is the zone right next to the medulla and  is seen as a branching network of smaller, dark cells.  These cells secrete precursors of androgens. They can be regulated also by ACTH.

  The steroids produced by the Zona reticularis are called Dehydroepiandosterone sulfate or,  DHEA sulfate.  This is converted to DHEA (which is a precursor for a steroid called androstenedione).  Once DHEA is secreted, it is converted further to androstenedione in peripheral tissues. 

 Androstenedione is the immediate precursor for testosterone, and dihydrotestosterone.   These active androgens have a different impact in males and females.

In males, the  testosterone produced from adrenal DHEA is very small relative to that produced by the testes.  Where in the testes is testosterone produced? Thus, this source is not a big contributor unless it is secreted in excess before puberty. Then it can cause premature penile enlargement and other virilizing effects.  What are the effects of testosterone in the male?

In females, the adrenal contributes most of the precursors for testosterone during the cycle.  However, as a rule, females produce only a very small amount. During midcycle  the ovarian thecal cells produce testosterone as a precursor for estrogens.  At this midcycle point, testosterone is also sent to the ovarian granulosa cells and it also serves as a precursor for estrogens in that cell type.  

In addition to its use as a precursor for estrogens, during puberty, testosterone is  responsible for normal pubic and axillary hair growth in females.  Excess secretion can cause excess hair growth, called "hirsuitism" and virilization.   Some females who complain of low sex drive benefit from testosterone therapy.   Therefore,  the adrenal steroids that are precursors for testosterone may have physiological functions similar to those in the male.  

Some studies show that DHEA itself may have important metabolic effects which inhibit atherosclerosis and prolong life in rabbits and perhaps humans.  Health food stores and shelves of vitamins often stock bottles of DHEA.  The benefits of this steroid are currently being explored.

What organelles are involved in the production of the steroid hormones in the cortex? What is the precursor molecule used by the cells?

Cholesterol is the precursor molecule for the steroid hormones described in the above section.  Steps in steroid biosynthesis also lead to the production of estrogens, progesterone (ovary) and testosterone (ovary and testes).   It is basically a 4 ring structure.  The  steroid hormones are formed by enzymes in two major organelles: Smooth endoplasmic reticulum and mitochondria with tubular or vesicular cristae.  The steps involve passing the steroid precursor and metabolites back and forth, in a volley-ball like fashion  as follows:

See the cartoons in the slide show: http://www.cytochemistry.net/Endocrine_System/Adrenal_lecture_slides.htm

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Steroid Volleyball

Each cell type expresses unique sets of enzymes in the SER and mitochondria to allow it to stop at a certain point in the pathway and thus produce only that steroid. 

 This pathway can be regulated by specific regulators for each of the steroid hormone producing cells.  The regulators may stimulate the production of the enzymes as well as the production and actions of the proteins that facilitate movement across the mitochondrial membranes (volleyball net).  More enzymes + more transport proteins at the volleyball net= higher levels of steroid hormones.

The following electron micrograph shows the close relationship between mitochondria and the SER.

Trace the arterial supply through the adrenal. Why might the supply to the cortex be of importance for the function of the medullary cells?

 The arterial supply is as follows:

1. Adrenal artery branches and penetrates cortex at multiple sites 
2. Breaks up into Capillary plexus under the capsule.
3. Capillaries descend to the medulla through the cortex.
4. Other branches of the cortical arteries go straight to the medulla.
5. Blood is collected in a central vein and leaves via the adrenal vein.

The arterial supply carries glucocorticoids (cortisol) which facilitates the synthesis of adrenaline (epinephrine).

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What is the structure and function of the cells in the adrenal medulla?

The Adrenal medulla has clusters of secretory cells. Venous channels lead to the Central vein which collects the secretory product.  Cells have basophilic cytoplasm with some rough endoplasmic reticulum.  Their secretory product is an "amine".  These are catecholamines called noradrenaline (norepinephrine) and adrenaline (epinephrine).   The hormones are secreted as part of the responses of the autonomic nervous system.  During the flight or fight reaction (response to stress), enzymes that convert noradrenaline to adrenaline are activated.  The regulation is by preganglionic fibers of the sympathetic nervous system, so you might say that the medullary cells are like "postganglionic cells that have lost their axon".   Instead, they secrete their adrenaline into the bloodstream.   The hormones are stored in secretory vesicles.  At the electron microscopic level, one would see cells with numerous secretory vesicles. They would also be innervated by nerve endings with clear vesicles, containing acetylcholine.

How would they respond in a stress reaction? Name some effects of the hormones produced and secreted.

Adrenaline has a number of activating effects on the body to allow it to respond to stress: speed up heart rate, promotes breakdown of glycogen to provide energy stores, etc.  The production of enzymes converting noradrenaline to adrenaline  is induced by cortisol from the adrenal cortex.  Thus, the blood supply to the cortex receives the cortisol and transmits it to the medulla, setting up a paracrine interaction that influences medullary secretion.

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See also the Adrenal Lecture Slides.

Last update: 10/15/2001
Web address: http://www.cytochemistry.net/Endocrine_System/adrenal.htm

Gwen V. Childs, Ph.D.
University of Arkansas for Medical Sciences
Shorey 9/32; (501) 686-7020
For questions or comments: childsgwenv@uams.edu

visitors since 10/23/2000