The Function of the Adrenal Glands

They are required e.g. during stress situations, for proper kidney functioning, for fat , amino acid and glucose metabolism, and they also release sex hormones. The adrenal glands sit just above each kidney, which gives them their other name, suprarenal glands. Each adrenal gland consists of two sections: the inner adrenal medulla and the outer adrenal cortex. The hormones produced by each part produce very different actions within the body.

Why do we have the adrenal medulla? The secretory cells of the adrenal medulla release epinephrine and norepinephrine. Both belong chemically to the group of catechola-mines. Nerve impulses from the sympathetic neurons of the hypothalamus regulate the secretion of both hormones, and their functions enhance those of the sympathetic autonomic nervoussystem.

What roles do epinephrine and norepinephrine play? Epinephrine (adrenaline) and norepinephrine (noradrenaline) are secreted during stress situations. Their release signals the body to produce fight or flight behaviour. Norepinephrine is secreted in small amounts. It mainly causes vasoconstriction in the skin, viscera, and skeletal muscles, which raises blood pressure and produces alarm-awareness in the body.

Epinephrine is secreted in larger amounts. In turn, the heart rate accelerates and the force of contraction increases. It also induces vaso-constriction in skin and viscera and vasodilation in skeletal muscles. Epinephrine dilates the bronchioles, decreases peristalsis, and stimulates the liver to transform glycogen to glucose. It increases the cell respiration rate and the use of fats for energy. Indeed, both epinephrine and norepinephrine effects are very similar to those of sympathetic activity. Therefore, the hormones are also called sympathomimetic, which means they mimic sympathetic nervous activation. Our body has two systems, one neuronal and one hormonal, that together ensure proper, fast and adaptive body reactions in stressful (often: dangerous) situations. Epinephrine release from adrenal glands is in fact more effective than sympathetic stimulations, because the hormone very strongly increases energy production and cardiac output.

Is there a difference to the hormones of the adrenal cortex? The adrenal cortex produces various steroid hormones. They fall into three classes, mineralocorticoids, glucocorticoids, and sex hormones. The sex hormones are the female estrogens and the male androgens. In the adrenal cortex only very small amounts are secreted (the main sources of sex hormones are the reproductive organs). The biological importance of adrenal gland sex hormone secretion is not fully researched.

What function does aldosterone exactly have? Aldosterone is a mineralocorticoid. The target organs of aldosterone are the kidneys, where it controls the reabsorption of sodium ions and the excretion of potassium ions by the kidney tubules. Aldosterone increases the rate of sodium ion (Na+) re-uptake into the blood and potassium ion (K+) excretion into urine.

Among the signals that stimulate the secretion of aldosterone are a deficiency of sodium, when blood loss or dehydration lowers blood pressure, or an elevated blood level of potassium.

Low blood pressure and/or low blood volume activate the renin-angiotensin feedback of the kidneys. Angiotensin II induces vaso-constriction and stimulates aldosterone secretion. Sodium reabsorption and water retention by aldosterone help to restore blood volume and blood pressure to normal.

What role does cortisol play? Cortisol is a member of the hormonal group called glucocorticoids. It increases the use of fats and excess amino acids for energy production. In turn, it decreases the use of glucose (“glucose-sparing effect”). It also reserves glucose for the brain energy balance. Cortisol is also secreted during different physiological stress situations. Most cells, except the neurons, use fatty acids and amino acids for cell respiration. Neurons are actually dependent upon glucose as an energy source. During stress situations, proper brain function is only guaranteed when the body cells shut down their glucose consumption and oxidate fats and amino acids instead. Cortisol does exactly this and, thus, ensures that glucose will be available to the brain.

Another very important function is the anti-inflammatory effect. During inflammation, histamine from damaged tissues opens peripheral capillaries. Lysosomes from damaged cells release their enzymes, which help break down damaged tissue. These effects get blocked by cortisol, which also stabilizes the lysosomal membranes (tissue destruction get prevented).

What happens if the cortisol level is out of the normal range? With a normal cortisol level, the inflammation processes are limited. In the case of too much cortisol, the immune response decreases.

And the function of ACTH and CRH? ACTH (adrenocorticope hormone) is the direct stimulus for cortisol secretion and is produced in the anterior pituitary gland. ACTH is stimulated again by CRH (corticotropin releasing hormone) from the hypothalamus.

BIBLIOGRAPHY 1. Holt EH, Peery H: Basic Medical Endocrinology, 4th edition, Elsevier 2009. 2. http://dict.leo.org. 3. www.dict.cc. 4. www.webster-dictionary.org.

EXERCISE: 1. Where is ACTH produced? a. thyroid gland b. kidneys c. anterior pituitary gland d. hypothalamus

2. What is the trade name of epinephrine? a. noradrenaline b. adrenaline c. aldosterone d. cortisol

3. Where is cortisol secreted? a. adrenal cortex b. adrenal medulla c. hypothalamus d. liver

Youll find the answer on: http://tinyurl.com/weiterbildung-englisch

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Kontakt: mail@lobitz-seminare.de, www.lobitz-seminare.de

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Lösung für Exercise:

Answer: 1. c Answer: 2. b Answer: 3. a

The Function of the Adrenal Glands

Why do we have the adrenal medulla?

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The Function of the Adrenal Glands

Why do we have the adrenal medulla?

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