Endocrinology Central Online
Adrenal Glands - FAQs
 
The adrenal gland actually consist of two glands, each about the size of a grape and each of them wrapped around the top of each of the kidneys.

Each adrenal gland also consists of two parts:

  1. The outer layer is called the adrenal cortex.  This outer layer is responsible for secreting three types of hormones: 
      • Glucocorticoids (cortisol)
      • Mineralcorticoids (aldosterone)
      • Androgens (androstenedione, a precursor to testosterone) 

     2. The innner part of the adrenal glands is called the adrenal medulla and secretes a number of hormones that  act as neurotransmitters in the brain:

      • epinepherine
      • norepinepherine
      • dopamine.
  
Graphic Courtesy of Maricopa Community College 
 
The following chart shows the various hormones produced by the adrenal glands as a result of instructions from the hypothalamus gland by way of the pituitary gland.
 

ADRENAL GLAND

The Outer Layer (Adrenal Cortex)

Steroid Produced

Target or effect

glucocorticoids (Cortisol)

(Messenger is ACTH from the pituitary gland)

Cortisol belongs to a class of hormones called glucocorticoids, which affect almost every organ and tissue in the body. Scientists suspect that cortisol has possibly hundreds of effects in the body, however only a few major effects are currently known.

Cortisol's most important job is to help the body respond to stress and maintain metabolism:

  • helps maintain blood pressure and cardiovascular function
  • helps slow the immune system's inflammatory response in the case of trauma
  • helps balance the effects of insulin in breaking down sugar for energy
  • helps regulate the metabolism of proteins, carbohydrates, and fats
  • in men, provides hormonal messages (androstenedione) to the testes to produce testosterone
  • in women, it breaks down cholesterol to produce progesterone, a precursor to estrogen. 

Feedback mechanism:

The amount of cortisol produced by the adrenals is precisely balanced and is regulated by the hypothalamus through instructions to the pituitary gland,  both bean-sized organs close to each other at the base of the brain.

To maintain cortisol balance in the blood, the body's thermostat, the hypothalamus monitors cortisol levels and when they are too low, sends corticotropin-releasing hormone (CRH) to the pituitary gland . The pituitary responds by secreting ACTH (adrenocorticotropin), a hormone that stimulates the adrenal glands to produce cortisol. Completing the cycle, when the hyopthalamus senses that sufficient cortisol is present in the blood, it reduces its ACTH production and the adrenal glands cease their cortisol production.

For more information on how the adreal cortex interracts with the hypothalamus and the pituitary gland in a feed-back loop, click here.

Other Effects of Cortisol :

In Fetal Development : Glucocorticoids have multiple effects on fetal development. They promote maturation of the fetal lung and production of the surfactant (alvioli function)necessary for lung function when born. Pregnant women who have an underactive pituitary or adrenal insufficiency often lose their fetus or baby soon after birth due to pulmonary immaturity.

Cortisol Imbalance Conditions
  • Over production : Cushings disease (Primary - due to adrenal tumor (growth); Secondary - due to pituitary tumor or more commonly, to ingested steroids).
  • Underproduction: Addisons disease (Primary - usually due to autoimmune system attacking the adrenal cells; Secondary - due to pituitary malfunction causing underproduction of ACTH messaging to the adrenal glands).
  • Genetic Factors
    • Congenital adrenal hyperplasia (CAH) (very rare and is usually caught very early in childhood)
      The CAH gene is one that controls the amount of the special chemical (21-hydroxylase) that is necessary for the adrenal glands to produce cortisol. If this gene is missing, 21H is not produced and the adrenal glands are unable to produce cortisol.

      In this condition, the pituitary is told that not enough cortisol is circulating in the blood, so cholesterol levels are raised and is converted into androgen rather than the needed cortisol.

      In a fetus, the effect can be disastrous. If the fetus is gendered as female with chromosomes XX, the excessive androgen production while in the womb, may cause the  androgynous anomolies of which the following are examples:
      • Vagina, uterus, one ovary, penis, and one testicle
      • Vagina, no uterus or ovaries 
      • No vagina or penis
      • Vagina, uterus, two ovaries, penis & 2 testicles
      • Any other combinations of the above
mineralocorticoids (aldosterone)

Aldosterone belongs to a class of hormones called mineralocorticoids and is also produced by the adrenal glands.

Aldosterone maintains salt balance through hormonal communications with the kidneys, a function which is necessary to sustain life. It is a sodium stabilizer in the blood (absorption and re-absorption of salt) and the body's main blood pressure stabilizer. In other words, aldosterone stimulates the kidneys to conserve sodium (Na+) thus increasing blood water volume, and stimulates the kidneys to excrete potassium (K+) into the urine.

Aldosterone production is triggered by the production of the hormone Angiostenin II indirectly by the kidneys. When aldosterone is produced, its major target is the distal tubule of the kidney, where aldosterone stimulates exchange of sodium and potassium. The primary physiologic effects are:

  • Increased resorption of sodium i.e. sodium loss in urine is decreased under aldosterone stimulation.
  • Increased resorption of water, with consequent expansion of blood fluid volume.
  • Increased kidney filtering of potassium.

Feedback Mechanism:

There is a feedback loop between:

  • the liver which produces a prohormone called angiotensinogen
  • the kidneys that produce renin that combines with angiotensinogen to form angiostenin I
  • the lungs which convert angiostenin I to angiostenin II which is recognized by adrenal gland receptors
  • the adrenal glands that produce aldosterone
  • the pituitary gland that produces ADH, an anti-diuretic hormone and blood pressure regulator.

Feedback Process

  • The kidneys monitor potassium levels in the blood that flow through it.  Small increases in blood levels of potassium stimulate the kidneys to produce renin.
  • When the liver detects the renin, it produces angiotensinogen which combines with the renin to form the hormone angiotensin I
  • When the blood reaches the lungs, the lungs modify the angiotensin I to angiotensin II
  • When the adrenal glands detect the angiostenin II, they produce aldosterone

The kidneys will produce renin, and consequently angiotensin II under the following conditions:

  • if blood volume drops
  • if blood pressure drops
  • If sodium blood levels are too low
  • if there is trauma

Effects of Angiostenin II:

  • constricts the walls of arteries and capillaries to save/maintain blood pressure (in the case of trauma, can lead to shock)
  • stimulates the  the kidneys to reabsorb sodium ions causing an increase in water retension and thus higher blood volume
  • stimulates the adrenal cortex to release aldosterone that causes:
    •  the kidneys to reclaim still more sodium and thus water
    • potent anti-inflammatory effects on body tissues
    • immunosuppressive effects on body systems
  • increases the strength of the heartbeat
  • stimulates the pituitary to release aldosterone

Underproduction

 Addison's Disease . Addison's Disease often is indicated by underproduction of both cortisol and androstenone. If the cause is too little pituitary hormone instructions to the adrenal glands (ACTH), the  disease is called secondary adrenal insufficieny and is still classified as Addison's Disease .

The subsequent lack of aldosterone causes sodium (Na+) and potassium (K+ ) to be continually flushed out of the body system causing life-threatening lowered blood pressure and if not treated, renal (kidney failure) and even death. This condition is known as diabetic insipidus.

Overproduction:

When aldosterone production is excessively high, it causes increased sodium reabsorption into the blood and potassium loss through the urine. This condition is known as secondary hypertension.

Overproduction potential causes:  

1) Conn's syndrome (primary hyperaldosteronism) - usually caused by the presence of a tumor or growth on one or both of the adrenal glands that causes the gland to secrete excess aldosterone leading to low blood potassium and hypertension .

2) Bartter's Syndrome (secondary hyperaldo steronism) - Much like Cushings Disease, Bartter's Syndrome is the result of excess adrenal secretions, but in this case, the production is excess aldosterone.

androgens (androstenedione which is precursor to Tesosterone)

In normal cases, the Adrenal Cortex creates and maintains levels of testosterone and estrogen in males and females.

There is also a push-pull relationship between the immune and the endocrine systems.

  • In a healthy body - testosterone reduces inflammation by depressing auto-immune responses that attack the joints and muscles.
  • However, during a bacterial or viral infection the immune system takes over and reduces the amount of testosterone produced so immune responses can function and white blood cell production can increase.

Male - Under Production Low libido and lack of energy.
Male - Over-production Aggressiveness, easy to anger, impatience, greater body hair, excessive masturbation and/or sexual addiction.  Increases probability of infertility and testes & prostate cancer.
Female - Underproduction Minimized libido, lack of energy, and lack of ability to reach orgasm.
Female -  Overproduction

May cause some masculation (excessive body hair, lower voice, muscular buildup, enlarged clitoris).Increases susceptibility to infertility & ovarian & breast cancers.

In fetuses and children, If due to to lack of the CAH gene, it is called Congenital Adrenal Hyperplasia - see above  ).

The Inner Layer (Adrenal Medulla)

Steroid Produced

Target or effect

Adrenaline Epinephrine
 Norepinephrine

The Adrenal Medulla produces three hormones classified as catecholamines:

  • Adrenaline
  • Norepinephrine
  • dopamine.

These hormones are legacies from our prehistoric past and hunting days when we either fought or fled from situations. (Fight/Flight reaction). Adrenaline and Norepinephrine are produced immediately under severe mental or physical stress (within milli-seconds).

Circulating epinephrine and adrenaline causes:

  • increased rate and force of contraction of the heart muscle
  • blood vessel constriction - smaller diameter blood vessels increased resistance producing higher arterial blood pressure.
  • Dilation of bronchial tubes and alveoli allowing higher oxygen tranfer processes in pulmonary ventilation.
  • The breakdown of glycogen in skeletal muscle to provide glucose for energy production.
  • Stimulation of fat cell breakdown producing fatty acids for energy production in muscle tissues. Offsets the immediate depletion of immediate energy sources -blood glucose (above).
  • Increased metabolic rate and higher body heat production, mainly the effect of epinephrine.
  • Dilation of the pupils, especially in low light
  • Restriction of blood vessels close to the skin to force blood to flow to the major organs of the body. Can be seen in sallow or pale face of frightened person or of shock victim.
  • Inhibition or "almost shut down" of certain processes such as stomach activity.
  • immediate need to void urine or feces.

If these steroids are not produced in sufficient quantities due to adrenal insufficiency and we got into an accident, we would never come out of shock and would die.

  • Overproduction is usually caused by epinephrine-secreting tumors called pheochromocytoma or chromaffin cell tumors on the adrenal medulla that are also associated with unpredictable but potentially dangerous levels of hypertension. Surgery is usually the process to alleviate this problem. The tumor and all or part of the adrenal gland.

 

 

Dopamine

Dopamine when transmitted though the blood system to the brain has matching receptors within the basil ganglia (interior of the brain).

Dopamine provide assistance with the following activities:

  • Produces feelings of bliss (the pleasure chemical). Suppresses pain and increases pleasure.
  • Critical for executing smooth and controlled movements.
    • Underproduction: 
      • Parkinson disease which a person looses the ability to initiate controlled movements.
      • Disrupted or incoherent thought as in schizophrenia.
      • Poor working memory.
    • Overproduction:
      • Personality disorders of paranoia: too much dopamine in the limbic system and not enough in the cortex produces:
        • Mild: Severe introversion and social interaction inhibitions.
        • Serious: An overly suspicious personality given to bouts of paranoia.
 


©1998-2009 Medical Central Online™, All Rights Reserved.