Essay on Adrenal Gland (937 Words)

Essay on Adrenal Gland (937 Words)!

Adrenal Glands are two small yellowish glands located on superior to kidney .Each adrenal gland, structurally and functionally divides into two main regions – outer and inner medulla. The tissue in these two regions differs in origin and hence functions independently of each other.

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Adrenal Cortex:

Adrenal cortex, derived from mesoderm is essential for life. It consists of fatty cholesterol containing glandular cells which secretes 40 different steroid hormones, collectively called corticoids. Adrenal cortex is further divided into 3 regions on the basis of corticoids secretion. These are –

(a) Zona glomerulosa secretes mineralocorticoids

(b) Zona fasciculata secretes glucocorticoids

(c) Zona reticularis secretes sex corticoids (also secreted by zona fasiculata).

I. Mineralocorticoids:

i. Regulate electrolyte and water balance in body, sweat, bile, urine and saliva.

ii. Major mineralocorticoids are – aldosterone, deoxycorticosterone

iii. The major mineralcorticoid, which is secreted almost independently of ACTH from the pituitary, is aldosterone.

iv. Aldosterone secretion is controlled mostly by the levels of potassium and sodium in serum and a blood pressure control system called the renin-angiotensin system. (Renin-angiotensin system is discussed in excretory system)

v. Aldosterone is also called ‘salt retaining hormone’ whose secretion is controlled by Renin-angiotensin system.

vi. The principle action of aldosterone is the retention of sodium. Therefore, aldosterone profoundly affects fluid balance by effecting intracellular and extracellular fluid volume.

vii. Aldosterone has the opposite effect on serum levels of potassium as it is lost in the urine in exchange for sodium in the renal tubules.

viii. Salivary and sweat glands are also influenced by aldosterone to save sodium and the intestine increases the absorption of sodium in response to aldosterone.

ix. Hypersecretion due to adrenal cortical tumor lead to Conn’s syndrome. It is also called aldosteronism and is characterised by

a. Rise in blood volume and blood pressure but without oedema (collection of fluid in the subcutaneous tissue)

b. Muscular weakness

c. High Na⁺ and low K⁺ level in blood plasma resulting in kidney damage with polyuria and tetany and metabolic disorder.

II. Glucocorticoids:

i. Concerned with normal metabolism

ii. Important glucocorticoids are Cortisol and corticosterone.

iii. The major glucocorticoid is Cortisol.

iv. Cortisol has important actions in the control and metabolism of carbohydrates, lipids, and proteins and assists in the metabolic reaction to stress, especially chronic stress.

v. It causes glucose to be liberated from the liver by increasing glucose production from fatty acids (byproducts of lipid breakdown) and amino acids.

vi. Cortisol causes the tissues to take up less glucose from the blood and mobilizes fat breakdown.

vii. The net effect is to increase serum glucose concentrations which are protective for the brain in that cases it cannot use any other fuel source than glucose.

viii. It also stimulates protein breakdown for glucose formation in all tissues except the liver where it stimulates protein synthesis.

ix. At high concentrations (greater than physiologic) glucocorticoids (such as hydrocortisone or prednisone) are useful for the treatment of allergies and inflammation. Hence, they have anti-inflammatory effects.

Hypersecretion results in cushing syndrome:

It occurs due to elevated level of plasma Cortisol and related hormones due to carcinoma or formation of tumor in cortex region.

It is characterised by

i. High sugar level in blood

ii. Loss of sugar in urine

iii. Loss of weight

iv. High Na⁺ and low K⁺ concentration in plasma

v. Abnormal obesity (Red moon face and buffalo hump) and wasting of limb muscles

Hyposecretion of both mineralocorticoids (aldosterone) and glucocorticoids (Cortisol):

Addison’s disease:

It is due to underactivity of the adrenal cortex which may be due to destruction of cells by disease like TB. Characterised by

i. Excessive loss of Na⁺, Cl^– and HCO₃^–

ii. Increased K⁺ level in blood

iii. Dark bronze colour pigmentation of skin

iv. Decreased resistance to infection

v. Low blood pressure

vi. Weakness, anaemia, vomiting and diarrhoea weaken the body.

III. Sex corticoids:

i. Secreted by both zona reticularis and zona fasciculata.

ii. They include: androstenedione, androsterone and dehydroepiandrosterone etc.

iii. They have the same functions as sex hormones of testes

iv. They have minor role only as are produced in small quantities

v. Promotes secondary sex characteristics of male type

vi. It also includes small amount of female sex hormones like estrogen and progesterone.

vii. Excessive secretion of sex corticoids (androgen) due to tumor of adrenal cortex result in virilism and hirsutism in female and gynaecomastia in male.

Adrenal Medulla:

Adrenal Medulla is actually an extension of the nervous system. It forms the central core of adrenal gland consists of glandular cells called chromaffin cells which one stimulation by sympathetic system, secretes tow hormones –

(i) Adrenaline

(ii) Noradrenaline

Both epinephrine and norephrinesysthesized from the amino acid tyrosine. Tyrosine is formed by hydroxylation of phenylalanine in the adrenal. Secretion of adrenaline is 5- 10 times higher than the non-adrenaline. Epinephrine, dopamine and Norepinephrine are collectively called catecholamines.

Adrenaline:

1. Amine hormone

2. Secreted by adrenal medulla on stimulation by sympathetic nervous system for meeting an emergency or stress condition, like injury, pain, fear, accident, grief, fall in blood pressure etc. hence called emergency hormone.

3. It increases blood pressure, BMR

4. Acts as vasodilator

5. Increases respiration rate

6. Increases sugar level in blood by stimulating glycogenolysis in liver and skeleton muscles

7. Slows down peristalsis

8. Hypersecretion of adrenaline causes hypertension, high level of sugar in the blood and urine, high metabolic rate, nervousness and sweating etc.

Nor-adrenaline:

1. Amine hormone

2. more or less it resembles adrenaline in its biological effects excepts that it operates during normal state, exercise

3. It has lesser effect on cardiac activity and produce greater constriction of blood vessels in muscles.