ADRENAL GLANDS - PowerPoint Presentation

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ADRENAL GLANDS

BY DR. APEKSHA PANWAR DEPARTMENT OF KRIYA SHARIR HAMC

FUNCTIONAL ANATOMY OF ADRENAL GLANDS

The two adrenal glands each weighing about 4gms lie at the superior poles of the two kidneys.Each gland is composed of two distinct parts the Adrenal medulla and the Adrenal Cortex.The Adrenal Cortex secreates an entirely group of hormones called Corticosteroids.

Histologically adrenal cortex comprises of three distinct zones:

1-

Zona Glomerulosa is the outermost zone.2- Zona Fasciculata is the middle zone.3- Zona Reticularis is the innermost zone. The Zona Glomerulosa consists of cells that are small with a moderate number of lipid inclusions.The Zona fasciculata consists of cells that are large and have a high cytoplasmic nuclear ratio with more lipid inclusions.

FETAL ADRENAL GLAND

The fetal adrenal glands begins developing at 3-4 weeks of gestation and is seen as the primordium.Around the 6-8 weeks of gestation there is rapid enlargement of the adrenal glands, where cells in the cortex differentiate to form fetal zone, and an outer layer called the definitive zone.About this time sympathetic neural cells invade the primordium of the adrenal cortex and these cells differentiate into chromaffin cells which are able to synthesize and store catecholamines.The

fetal

zone is capable of synthesizing steroids by 8

th to 10th week of gestation.At the time of birth the fetal adrenal gland comprises of fetal cortex which is about 80% of the gland and an outer layer which is about 20% called the true cortex.The fetal

cortex undergoes a reduction in size

upto

about 50% of its size at birth within the first month.

ACTH regulates fetal cortisol secretions and the feedback regulation of ACTH is established by 8th – 10 th week of gestation.

MECHANISM OF SYNTHESIS OF ADRENAL

HORMONESLong term stress causes Hypothalamus to release Corticotropin releasing hormones.These corticotropin releasing hormones targets anterior pituitary to secreate ACTH hormones.

ACTH

secreated

target cells of Adrenal gland to stimulate Adrenal Cortex.Now the three distinctive layer of Adrenal Cortex secreates adrenal hormones namely: 1- Zona Glomerulosa- secreates Mineralocorticoids. 2- Zona Fasiculata – secreates Glucocorticoids. 3- Zona Reticularis-

secreates

Androgens.

Adrenal Medulla is stimulated by nerves. Brain send signals to spinal cord.

Sympathetic nerves which are leaving the spinal cord targets the Adrenal Medulla.Adrenal Medulla secreates two types of hormones:1- Adrenaline2- Nor Adrenaline.

These two hormones increases the sympathetic activity and triggers the fight and flight response.

ACTIONS OF MINERALOCORTICOIDS

Kidneys plays a major role in controlling Blood Pressure.When there is decrease in Blood Pressure the kidneys will reabsorb water and sodium back into the blood and reabsorb or secreate potassium in exchange.Increase in water and sodium in the blood will then increase blood pressure.Aldosterone secreates

by Zona Glomerulosa stimulates this exchange process thereby increasing Blood Pressure.

Aldosterone

primarily works in the distal part of the Nephron.Aldosterone stimulates water and sodium retention thereby causing increase in Blood Pressure.Aldosterone increases reabsorption of sodium and simultaneously increases secretion of potassium by renal tubular epithelial cells.Excess Aldosterone causes sodium to be reabsorbed by the tubules. Therefore as a result the extracellular fluid volume increases almost as much as the retained sodium.This Aldosterone mediated increase in extracellular fluid volume leads to increase in arterial pressure.

ACTIONS OF GLUCOCORTICOIDS

1-Effect of Cortisol on Carbohydrate MetabolismCortisol increases the enzymes required to convert amino acids into glucose in the liver cells.It causes mobilization of Amino Acids from the extrahepatic tissues mainly from muscle.Causes a moderate decrease in the rate of glucose utilization by most cells in the body.Both increased rate of gluconeogenesis and moderate reduction in the rate of glucose utilization by the cells causes blood glucose concentrations to rise.Rise in blood glucose concentration stimulates secretion of Insulin.

2-Effect of Cortisol on Protein Metabolism

Cortisol reduces the protein stores in essentially all body cells except those of the liver.

It decreases Protein Synthesis.Cortisol increases liver and Plasma Proteins.Cortisol causes increased conversion of Amino Acids to glucose.

3- Effect of Cortisol on Fat Metabolism

Cortisol promotes mobilization of fatty acids from adipose tissue.It increases the concentration of free fatty acids in the plasma.Despite the fact that cortisol can cause a moderate degree of fatty acids mobilization from adipose tissue, many people with excess cortisol secreation develop a peculiar type of obesity with excess deposition of fats in the chest and head regions of the body.

ADRENAL MEDULLA

The Adrenal Medulla occupies the central 20% of the Adrenal Gland and is functionally related to sympathetic nervous system.It is made up of interlacing cords of cells known as chromaffin cells or pheochrome cells.Adrenal medulla is formed by two types of Chromaffin cells:1-Adrenaline secreating cells(90%).

2-Nor adrenaline

secreating

cells(10%).Hormones of the Adrenal Medulla are the amines derived from Catechol so these hormones are called Catecholamines.Catecholamines secreated by Adrenal Medulla are:1- Adrenaline or epinephrine2- nor adrenaline or nor epinephrine.

ACTIONS OF ADRENALINE AND NOR

ADRENALINEAdrenaline and Nor Adrenaline stimulate the nervous system.Adrenaline has significant effects on metabolic functions.Both Adrenaline and Nor Adrenaline have significant effects on cardiovascular system.Actions of Adrenaline and Nor Adrenaline are executed by binding with receptors called Adrenergic receptors.

Adrenergic receptors are of two types:

1- Alpha Adrenergic receptors.

2- Beta Adrenergic Receptors.Circulating adrenaline and nor adrenaline have similar effects of sympathetic stimulation.Adrenaline acts through both alpha and beta receptors equally.Nor adrenaline acts mainly through alpha receptors and occasionally through beta receptors.

Adrenaline influences the metabolic functions more than noradrenaline.

Adrenaline increases oxygen consumption and carbon dioxide removal.It increases the metabolic rate so called Calorigenic hormone.Adrenaline causes the blood glucose level by increasing the glycogenolysis.Adrenaline causes mobilization of free fatty acids.Adrenaline decreases blood coagulation time.It increases the overall activity of heart.It causes constriction of blood vessels throughout the body.

Adrenaline increases systolic blood pressure by increasing the force of contraction of the heart.

Nor adrenaline increases diastolic pressure due to general vasoconstrictor effect by increasing the total peripheral resistance.

Adrenaline causes contraction of arrector pilli muscle.

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