Adrenal Gland | Biology for JAMB PDF Download

Adrenal or Supra Renal Glands
Position, Origin & Structure :– 

• This gland was discovered by a scientist Eustachius.
• It is found on the head (anterior most part) of both the kidneys.
• Adrenal gland is ecto mesodermal in origin.

• It weights about 4 - 6 gm in man.
• Whole gland is surrounded by a fibrous capsule.
• Each gland has two parts :- Outer part of gland is called cortex and inner part is called medulla.
• Cortical portion is 80-90% and is develop from mesoderm of embryo.
• Medullar portion of this gland is made up of neural - ectoderm of embryo. Only 10 - 20% part is medullar part of gland.

Adrenal Cortex :– Most of the cells of this part are fatty. This portion is divided into three regions from periphery to centre.

1. Outer zone or Zona glomerulosa :-Mineralocorticoid hormones are secreted by this zone.

2. Middle zone or Zona fasciculata :-This zone secretes glucocorticoid hormones. In this region polyangular cells are arranged in the layers.

3. Inner zone or Zona reticularis :– Cells of this region are spread in the form of a network, these are arranged in layers. This zone secretes a small amount of sexhormones.

About 40-50 hormones are synthesized in adrenal cortex. All these hormones are of steroid nature. Their basic constituent is cholesterol. these are also called corticoids. Out of these 40-50 hormones, only 7-8 hormones are active.

1. Mineralocorticoids :– 2 main hormones fall under this category.

(1) Aldosterone (2) Deoxycorticosterone 

• These hormones are related with distribution of water in tissues and balance of electrolytes in the body.
• These hormones maintain the ionic balance of Cl-,K+, Na+ and water in the blood and ECF.
• Aldosterone hormone affects distal convoluted parts of uriniferous tubules & early Cortical tubule of kidneys.
• It basically activates the Na+ – K+ pump.
• It helps in reabsorption of Na+ & Cl- ions and controls the excretion of K+ ions.
• Aldosterone hormone is also known as salt retaining hormone it increases sodium concentration.
• An increase in Na+ ion concentration (than normal) in ECF is called Hypernatraemia.
• In hyposecretion of aldosterone hormone, there is a tremendous loss of ions of Na+, Cl- and HCO3--- by urination and K+ ions are increased in blood.

2. Glucocorticoids :– (Secretion control by ACTH).

Mainly hormone comes under this category is Cortisol. (Life saving hormone). 

Cortisol :– It is an important hormone secreted by zona fasciculata. It is also known as Hydrocorticosterone. Cortisol has a small amount of mineralocorticoid acitivity.

Metabolic Effect : On carbohydrate metabolism : Increases sugar in blood causes Hyperglycemia.

Protein metabolism : Cortisol causes lysis of proteins in some organs like lymphoid tissues (thymus, lymph node etc),muscles, bones, skin etc. (Deamination & urea formation stimulated or inhibit protein synthesis).

Fat metabolism :– 

(i) Facilitateslipolysis.

(ii) Promotes deposition of fat, in unusual sites of the body.

On nucleic acid metabolism :– Cortisol inhibits nucleic acid synthesis in all other tissues except liver where (i.e., in the liver) RNA synthesis is increased. . This hormone is "anti - inflammatory". This prevent the actions of WBC and collagen fibres in tissues, so used in diseases like oedema, arthritis/Rheumatism. This hormone is Immuno-suppressive, because it check the immune reactions by antibodies. So it is also used in allergy. Now a days, cortisols are used in transplantation of organs.

3. Sex - Hormones/Sex corticoids/Gonadocorticoids :–

• Sex hormones secreted by adrenals are called gonadocorticoids.
• They are secreted in very small amount by zona reticularis.
• Male hormones are called androgens and female hormones are called oestrogens.
• Both the hormones are secreted by men & women both, but sex hormones secreted by gonads inactivate the sex hormone of opposite sex secreted by adrenal gland.
• These hormones stimulate the muscles, external genitalia and sexual behaviour.
• Male hormone secreted by adrenal gland is mainly dehydroepiandrosterone [DHEA].
• Female sex hormones progesterone and estrogens are secreted in minute quantities.

Adrenal medulla :– Origin : The adrenal medulla develops from the neuroectoderm of the embryo.

Structure :The adrenal medulla consists of rounded groups of relatively large and granular cells. These cells are modified of sympathetic nervous system which have lost normal processes and have acquired a glandular function. These cells are called chromaffin cells or phaeochromocytes. These cells are connected with the preganglionic motor fibres of sympathetic nervous system, therefore, these are discussed together as sympatheticoadrenal system.

Hormones of Adrenal medulla :– Two hormones are secreted by this part. These collectively are called catecholamine.

These hormones are synthesized by chromaffin cells with Tyrosine amino acid. (A) Adrenaline or Epinephrine :– 

• This hormone is 80% part of the total hormones secreted by Adrenal medulla.
• It was termed as Emergency hormone by Walter Cannon, because this hormone prepares the body to face unavoidable emergency situations.

Functions of Adrenaline :– 

(1) It constricts the blood vessels of skin (Vaso constriction).

(2) The hormone enhances the flow of blood by vasodilation of blood vessels of brain, heart, liver and skeletal muscles. 

(3) Due to effect of this hormone, heart beat, blood pressure, BMR, amount of glucose in blood increases.

(4) Adrenaline enhances the heart beat and thus increases cardiac output, due to this, circulation of blood becomes faster.

(5) The hormone stimulates the trachea and bronchi muscles to relax, as a result of it, rate of breathing is increased.

So adrenaline hormone is used to cure asthma.

(6) It dilates the pupils of eyes. Goose flesh is observed due to its effect. It constricts the erecter pilli muscle of hair, and hair are raised.

(7) The hormone stimulates contraction in spleen, as a result of it, spleen pours its stored blood into blood stream.

(8) It checks the secretion of saliva and reduces the peristaltic movements in alimentary canal.

(9) Due to the effect of this hormone, clotting period of blood is reduced, the hormone also stimulates the uterus of female animals to contract.

• Adrenaline provides the body with an emergent chemical defence mechanism in stress conditions that threaten the physical integrity and chemical consistency of the body e.g. accident, restlessness, fear anger, mental tension, pain etc. It immediately prepares the body to face the emergency by a violent stress or alarm reaction.
• The cortisol hormone of adrenal cortex serves to maintain the body in living condition and recover it from the severe effects of stress reactions. Thus, an increased output of cortisol is  "life saving" in "shock conditions".

So it is also known as life-saving hormone.

• The hormones of adrenal medulla prepare the animal for fear, fight or flight in emergency conditions, (by excess secretion of these hormones) Adrenaline hormone is called 3F = FFF hormone and adrenal gland is called "triple F gland" (FFF gland)

(B) Noradrenaline or Norepinephrine hormone :– 

• It is only 20% part of total hormones secreted by adrenal medulla.
• It acts as vasoconstrictor, thus increases the blood pressure. Exception - It does not constrict coronary artery of heart.

Control of adrenal Secretion :– 

• Adrenocorticotropic hormone [ACTH] of anterior lobe of pituitary gland controls the hormones secreted by adrenal cortex.
• ACTH controls very little or even does not control the secretion of mineralocorticoids. These are controlled by Renin hormone secreted by kidneys.
• Pituitary gland does not control the secretion of adrenal medulla hormones, the adrenal medulla hormones secretion is controlled by nervous system.
• The amount of cortisol and ACTH in blood is maximum in the morning and minimum in early part of night.

IRREGULAR SECRETION OF ADRENAL HORMONE :– 

(i) Hyposecretion :– Addison's disease :- Hypoadrenalism 

• Caused due to hyposecretion of corticoid hormone of adrenal gland, following are some symptoms of addison's disease dehydration in the body, Blood pressure, BMR and body temperature are reduced, excretion of water and Na+ increase. The skin of hands, neck and face turns to bronze colour.
• Hyposecretion of corticoids causes reduction in amount of glucose in blood, it is called hypoglycemia. In this disease, patient may die, so hormones of adrenal gland are called life - saving hormones 

 (ii) Hypersecretion :– Cushing's syndrome (disease) :– 

• Due to hypersecretion of corticoids, body increases breadthwise or body becomes broad because excess deposition of fat under the skin (to cause moon face, fish mouth and buffalo hump). Protein catabolism increases in body.

Irregular growth of skin and bones is observed. Hyperglycemia occurs. Amount of Na and water increase in ECF, which is called oedema. Due to this B.P. also increases.

Conn's Disease :– (Primary aldosteronism)

•  Due to excess of mineralocorticoids, an imbalance of Na+, K+ is  observed. This disease is called "Conn's disease". Due to this disease there occurs irregularity in nervous system, as a result of that muscles get contracted Muscle weakness, hypertension and hypokalemia are observed.

 Sec. Hyperaldosteronism :–  Blood pressure increases, and excess mental tension and weakness in muscles are observed.

Adrenogenital Syndrome/Adrenal virilism/Pseudohermaphrodite :– In this case, girls develop male characters. eg. menstruation cycle is stopped, uterus and ovary are damaged and clitoris becomes enlarged. 

• If in a man, female sex hormone is secreted by adrenal is in excess amount, He will show feminine characters i.e. development of mammary glands this disorder is called gynaecomastia.
• If in a male, androgens are present in excess amount, it developes extra long penis. This defect is called macrogenitosomia i.g. manis, Armedilo.
• Adrenal gland is also known as 4 - S gland