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ADRENAL GLANDSLecture 1Dr. Zahoor Ali Shaikh

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ADRENAL GLANDS

There are two Adrenal glands, one above each kidney.

Adrenal gland has outer cortex and inner medulla.

- Outer cortex secrete – steroid hormones

- Inner medulla secrete – catecholamine

(Epinephrine, Nor epinephrine)

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ADRENAL GLANDS

Adrenal cortex and adrenal medulla secrete hormones which belong to different chemical categories, whose function mechanism of action and regulation are totally different. Therefore there are TWO endocrine organs in Adrenal gland.

We will discuss adrenal cortex and then adrenal medulla.

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ADRENAL CORTEX Adrenal cortex secretes - Mineralocorticoids, Glucocorticoids, Sex

hormones Adrenal cortex has three layers 1. Zona glomerulousa [outer layer] –

mineralocorticoid - aldosterone 2. Zona Fasciculata [middle layer] 3. Zona Reticularis [inner layer]

Glucocorticoids & Sex hormones

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ADRENAL CORTEX

Adrenal cortex produces number of adrenocortical hormones, all of which are steroids derived from cholesterol.

Cholesterol is converted to pregnenolone and then by enzymatic action on pregnenolone, steroid hormones are produced.

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ADRENAL CORTEX Adrenal steroid hormones can be divided into

three categories: 1. Mineralocorticoids – Aldosterone, it affects

mineral that is electrolyte balance [Na+, K+ balance].

2. Glucocorticoids – Cortisol, plays major role in glucose metabolism but also in protein, lipid metabolism and in stress situation.

3. Sex hormones - Testosterone [male sex hormone] - Estrogen [female sex hormone]

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ADRENAL CORTEX Adrenal Steroid hormones [Aldosterone,

Glucocorticoids, sex hormones] are all lipophilic, therefore, immediately diffuse through plasma membrane of the cell into the blood.

In the blood, - Corticosteroids are carried by Alpha

globulin [transcortin]. - Aldosterone and Dehydroepiandrosterone

[DHEA] are carried by albumin.

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ALDOSTERONE

Aldosterone Action & Function Aldosterone acts on the distal

convoluted tubule and collecting tubule of the kidney and causes Na+ absorption and K+ excretion.

Na+ retention causes osmotic retention of water and expands ECF [Extra cellular fluid], which is important in long term regulation of blood pressure.

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ALDOSTERONE

Mineralocorticoids are essential for life.

WHY ?Because when Mineralocorticoids are

NOT there, there will be decrease plasma volume due to decreased Na+ and H2O. It will lead to decreased Blood Pressure and circulatory failure.

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CONTROL OF ALDOSTERONE SECRETION Control of Aldosterone secretion is

through 1. Renin-Angiotensin-Aldosterone

system [RAAS] which is regulated by decrease in

Na+ and decrease in blood pressure.2. Direct Stimulation of Adrenal cortex

by rise in plasma K+ concentration

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IMPORTANT NOTE

ACTH from anterior pituitary gland promotes the secretion of Cortisol, but not Aldosterone, therefore regulation of Aldosterone is largely independent of anterior pituitary control.

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GLUCOCORTICOIDS

GLUCOCORTICOID We will see 1. Metabolic Effects 2. Role in Adaptation of Stress

1. Metabolic Effects Cortisol plays important role in

carbohydrate, protein and fat metabolism.

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Metabolic Effects

Main function of Glucocorticoids is to increase blood glucose level.

HOW ? By Gluconeogenesis – conversion of non-

carbohydrate sources e.g. amino acids into carbohydrate within the liver.

Gluconeogenesis helps to maintain hepatic glycogen stores. Between meals or during fasting glycogen releases glucose in the blood to maintain glucose level.

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Metabolic Effects of Glucocorticoids Glucocorticoids inhibit glucose

uptake by the tissues but not the brain, as brain uses only glucose as its metabolic fuel.

Glucocorticoids stimulate protein breakdown in many tissues especially muscle.

Glucocorticoids facilitate lipolysis [breakdown of lipid], therefore release fatty acid.

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OTHER ACTIONS OF GLUCOCORTICOIDS Cortisol permits catecholamine to

induce vasoconstriction. Lack of Cortisol may cause

circulatory shock.

NOTE If any patient is on Cortisol and

undergoes surgery, the dose of Cortisol should be increased.

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2. Role of Glucocorticoid in Adaptation of StressHow Cortisol helps to adapt to stress ? Precise role is not known, but possible

explanation might be In case of stress e.g. surgery, accident, etc. - Increased glucose level by Cortisol will

help brain to work [As patient is not eating]. - Increased amino acid by Cortisol will help

in tissue repair. - Increased fatty acids available are used

by tissue as alternate fuel.

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OTHER EFFECTS OF CORTISOL

1. Anti inflammatory Cortisol blocks the production of

inflammatory chemical mediators e.g. leukotrines, prostaglandin.

- Cortisol suppresses migration of nuetrophil to the injured side.

2. Immunosuppressive Cortisol inhibits immune response by

interfering with antibody production by lymphocytes.

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USE OF CORTICOSTERIODS We use corticosteroids when

inflammatory response itself has become destructive e.g. rheumatoid arthritis.

In preventing organ transplant rejection.

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SIDE EFFECTS OF CORTICOSTEROIDS As immune response of the body are

suppressed, person has more chances to get infection.

OTHER SIDE EFFECTS - Gastric ulcer - High Blood pressure - High Blood sugar - Bone Osteoporosis - Menstrual irregularities

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REGULATION OF CORTISOL SECRETION Cortisol secretion is regulated by

ACTH, through negative feedback loop involving

Hypothalamus – pituitary – adrenal cortex axis.

ACTH acts on Zona Fasciculate and Zona Rectilularis.

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OTHER FACTORS THAT INFLUENCE CORTISOL SECRETION

Diurnal or Circadian Rhythm Effect Cortisol level is high in the morning

[awake] and low at the night [during sleep].

- Circadian Rhythm is regulated by biological clock [suprachismatic nuclei] of Hypothalamus and is related to sleep – wake cycle.

- Peak and low level are reversed in person who works at night and sleeps during the day.

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ADRENAL CORTEX – SEX HORMONES In both sexes [male and female]

adrenal cortex produces both androgens [male sex hormone] and estrogens [female sex hormone].

Under normal conditions, adrenal androgens and estrogens are not so abundant to induce masculinizing or feminizing effects.

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ADRENAL CORTEX – SEX HORMONES In female, adrenal androgen is

responsible for androgen dependent processes

e.g. pubertal growth spurt, Growth of axillary and pubic hair. Development and maintenance of

sex drive

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CONTROL OF ADRENAL CORTEX ANDROGENS It is ACTH that controls adrenal

androgen secretion [not the pituitary gnadotropic hormone].

In female, at the time of puberty, adrenal androgen secretion increases which initiates the development of androgen dependent processes.

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WHAT SHOULD YOU KNOW FROM THIS LECTURE? Adrenal Gland – Layers Secretion of Steroids Hormones by each layer Aldosterone – Action & Function Control of Aldosterone Secretion Glucocorticoids – metabolic effects, role in stress Glucocorticoids other effects Anti-inflammatory

and Immunosuppressive Side Effects of Corticoids Regulation of Cortisol Secretion, Diurnal Rhythm Secretion of Sex hormones by adrenal cortex

and their control

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