Adrenal Hormones -1

7/29/2019 Adrenal Hormones -1

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Adrenal Hormones-1

G. Prabhakar Rao


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Overview

The adrenal gland cortex synthesizes andsecretes two major classes of steroid hormonesthe adrenocorticosteroids (glucocorticoids andmineralocorticoids) and the adrenal androgens.

The adrenal cortex is divided into three zones that

synthesize various steroids from cholesterol. The outer zona glomerulosa produces

mineralocorticoids (for example, aldosterone),which are responsible for regulating salt and

water metabolism. Production of aldosterone is regulated primarily

by the reninangiotensin system.


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Overview

The middle zona fasciculata synthesizesglucocorticoids (for example, cortisol),which are involved with normal

metabolism and resistance to stress.

The inner zona reticularis secretesadrenal androgens (for example,dehydroepiandrosterone).


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Overview Secretion of these steroids controlled by pituitary

adrenocorticotropic hormone [ACTH also calledcortictropin].

ACTH is released in response to the hypothalamiccorticotropin-releasing hormone (CRH also calledcorticotropinreleasing factor).

Glucocorticoids serve as feedback inhibitors ofcorticotropin and CRH secretion.

Hormones of the adrenal cortex are used in replacementtherapy:

1. In the treatment and management ofasthma andrheumatoid arthritis.

2. In the treatment ofsevere allergic reactions.

3. In the treatment of some cancers.


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Adrenal (supra renal) glands

There are two adrenal glands, situated on the upper poleof each kidney enclosed within the renal fascia.

The outer part is the cortex and the inner part themedulla. The adrenal cortex is essential to life but the

medulla is not. Adrenal cortex: It produces three groups of steroid

hormones from the cholesterol. They are collectivelycalled as adrenocorticoids (corticosteroids, corticoids).

1. Glucocorticoids

2. Mineralocoticoids

3. Sex hormones (androgens)


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Glucocorticoids

Cortisol(hydrocortisone), corticosteroneand cortisone are the main glucocorticoids.

They are essential for life, regulating

metabolism and responses to stress. Secretion is stimulated by ACTH from the

anterior pituitary and by stress.


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The functions of glucocorticoids

Gluconeogenesis (formation of new sugar from, forex : protein) and hyperglycaemia ( raised bloodglucose level.

Lipolysis (breakdown of triglycerrides into fattyacids and glycerol for energy production).

Stimulating breakdown of protein, releasingamino acids, which can be used for synthesis ofother proteins, e.g. enzymes, or for energy (ATP)

production. Promotion of reabsorption of sodium and water

from renal tubules (a minaralocorticoid effect).


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Mineralocorticoids (aldosterone)

Aldosterone is the main mineralocorticoid. It functions are associated with the maintenance

ofwater and electrolyte balance in the body.

It stimulates the reabsorption of sodium by the

renal tubules and excretion of potassium in the

urine.

Sodium reabsorption is also accompanied by

retention of water and therefore aldosterone isinvolved in the regulation of blood volume and

B.P too.


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Mineralocorticoids (aldosterone)

The bloodpotassium levels regulates the

amount ofaldosterone produced by the

adrenal cortex.

When the blood potassium level rises, morealdosterone is secreted.

Low blood potassium has the opposite effect.

Angiotensin also stimulates the release ofaldosterone.


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Adrenocorticosteroids The adrenocorticoids bind to specific

intracellular cytoplasmic receptors in targettissues.

The glucocorticoid receptors widelydistributed throughout the body.

The mineralocorticoid receptors confinedmainly to excretory organs, such as the kidney,colon, salivary and sweat glands.

The receptorhormone complex translocates

into the nucleus, where it attaches to genepromoter elements, acting as a transcriptionfactor to turn genes on or off, depending on thetissue.


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Glucocorticoids

Cortisol is the principal human glucocorticoid.

Normally, its production with a peak early inthe morning and then a secondary smaller

peak in the late afternoon.

Factors such as stress and levels of thecirculating steroids influence secretion.


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Promote normal intermediary metabolism

Glucocorticoids favorgluconeogenesisthrough increasing amino acid uptake bythe liver and kidney and elevating activities

of gluconeogenic enzymes. They stimulate protein catabolism and

lipolysis, thereby providing the buildingblocks and energy that are needed for

glucose synthesis.


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Promote normal intermediary metabolism

Glucocorticoid insufficiency may resultin hypoglycemia (for example, duringstressful periods or fasting).

Lipolysis results as a consequence of theglucocorticoid augmenting the action of

growth hormone on adipocytes, causing

an increase in the activity of hormone-sensitive lipase.


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Increase resistance to stress

Glucocorticoids raise plasma glucose levels,which provide the body with the energy it requires to

combat stress caused, for example, by trauma,

fright, infection, bleeding, or debilitating disease.

Glucocorticoids can cause a modest rise in bloodpressure, apparently by enhancing thevasoconstrictor action of adrenergic stimuli onsmall vessels.

Individuals with adrenal insufficiency may respond toseverestress by becoming hypotensive.


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Alter blood cell levels in plasma

Glucocorticoids cause a decrease ineosinophils, basophils, monocytes, andlymphocytes by redistributing them from

the circulation to lymphoid tissue.

In contrast to this effect, they increase theblood levels of hemoglobin,

erythrocytes, platelets, andpolymorphonuclear leukocytes.


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Have anti-inflammatory action

The most important therapeutic property of the

glucocorticoids is their ability to dramatically reducethe inflammatory response and to suppressimmunity.

Also involved is the indirect inhibition ofphospholipase A2 blocks the release ofarachidonicacidthe precursor of the prostaglandins andleukotrienes from membrane-bound phospholipid.

Cyclooxygenase-2 synthesis in inflammatory cells isfurther reduced, lowering the availability ofprostaglandins.

In addition, interference in mast cell degranulationresults in decreased histamine and capillarypermeability.


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Affect other components of the

endocrine system

Feedback inhibition ofcorticotropin

production by elevated glucocorticoids

causes inhibition of furtherglucocorticoid

synthesis as well as further production ofthyroid-stimulating hormone.

In contrast, growth hormone production is

increased.


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Can have effects on other systems

Adequate cortisol levels are essential for normalglomerular filtration.

High doses of glucocorticoids stimulate gastricacid andpepsin production and may exacerbate

ulcers. Effects on the central nervous system that influence

mental status have been identified.

Chronic glucocorticoid therapy can cause severebone loss.

Myopathy leads patients to complain ofweakness.


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Q & A

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Adrenal Hormones -1

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