· They are also known as supra-renal gland because they are located on the top of each kidney.
· The human body has two adrenal glands that release chemicals called as hormones into the bloodstream. These hormones affect many parts of the human body.
· Each adrenal gland weight 4-5 gm in adults.
· Adrenal glands are first detected at 6 weeks of gestation.
Adrenal glands are small, conical yellowish bodies which are composed of two types of tissues. Adrenal glands are two, triangular shaped organs that measures about 1.5 inches in height and 3 inches in length. There is one pair of small rounded bodies lying across top of each kidney. Each adrenal gland is comprised of two distinct regions:
1) Adrenal Cortex:
· It is the outer part of the gland which is firm, pale yellowish tissue.
· It is derived from the mesoderm of embryo.
· This part of the adrenal gland secretes a number of steroid hormones. Glucocorticoides are steroid hormone from the adrenal cortex, which influences metabolism of carbohydrates for example, Cortisol and Cortisone. They increase the blood glucose level by increasing formation of carbohydrates from protein by the process of gluconeogenesis and also by conversion of glycogen to glucose in the liver by the process of glycogenolysis.
· Some other steroid hormone from the adrenal cortex influences the external sex characters; these are known as sex corticoids.
· Adrenal cortex is further divided into three concentric layers:
a) Zona Reticularis: It is the inner layer of the cortex whose cells are arranged in net like fashion.
b) Zona Fasciculata: It is the middle layer of the cortex. It is the widest of all three layers.
c) Zona Glomerulosa: It is the outermost layer of the cortex which is composed of five layers of compactly arranged cells.
There are three groups of steroid hormone which are secreted by adrenal cortex.
· They regulate the balance of water and electrolytes in our body.
· Aldosterone is the mineralocorticoide found in our body.
· They mainly act on renal tubules.
· The steroid hormones which influence salt and water metabolism are known as mineralocorticoides.
· They reduce the loss of sodium from the body through urine, sweat etc and decrease the excretion of potassium. These hormones help in the retention of water by the body along with sodium and hence maintain salt and water balance.
· Mineralocorticoides stimulating the re-absorption of sodium and water and also etion of potassium and phosphate from the body.
· The main function of mineralocorticoid is to maintain the electrolytes balance, body fluid volume, osmotic pressure and blood pressure of the body.
· These are the hormones which regulates metabolism of carbohydrates, proteins and fats.
· Cortisol is the main glucocorticoides found in our body.
· Cortisol stimulates the liver for the synthesis of carbohydrates from non- carbohydrates sources like amino acid and glycerol. This process is known as gluconeogenesis.
· Glucocorticoides stimulates gluconeogenesis, lipolysis and proteolysis.
· Inhibition of cellular uptake and utilization of amino acid is performs by glucocorticoides.
· Cortisol is involved in the maintenance of cardiovascular system.
· Also help in the proper functioning of kidney.
· Cortisol produces anti- inflammatory reaction and also functions in suppression of immune response.
· Glucocorticoides stimulates the production of RBC.
· Adrenal cortex also produces a small quantity of androgenic steroids i.e. sex hormone (androgens) both in male and female.
· These hormones are secreted as DHEA (Dehydroxy Epiandosterone) which acts as a precursor of both testosterone and estrogens.
· It plays a major role in the growth of axial, pubic and facial hair during puberty.
· Development of acne is also due to sexoxorticoides in young girl.
· They also play an important role in the development of embryo. (foetus)
2) Adrenal Medulla:
· It is the inner, central part of the adrenal gland.
· The medulla of each adrenal secretes two amines, epinephrine (adrenaline) and nor- epinephrine (nor- adrenaline).
· These hormones regulate the blood pressure, heart beat, respiration, contraction and relaxation of smooth muscles and other activities controlled by the sympathetic nervous system.
· Epinephrine also increases levels of blood glucose, oxygen consumption and heat production. During stress epinephrine is secreted and it produces increased blood pressure, rapid and stronger heart beats and release of more sugar from the liver to the blood by the process of glycogenolysis to provide more material for increased oxidation and production of energy.
Activation of Adrenaline and Nor- adrenaline:
Both hormones belong to the category of compounds known as Catecholamines and are secreted in response to any kind of stress, danger and during emergency situations like fall in blood pressure, increase in sugar level, increased respiration rate and heart beat etc. The CNS at the time of stress stimulates the adrenal medulla to release both these hormones. These are also known as emergency hormone or fight or flight hormone. These hormones serve following purposes:
a) Increases alertness
b) Dilation of pupil
c) Increase in heart beat
d) Increased respiration rate.
e) It also stimulates the breakdown of glycogen due to which the concentration of glucose increases in the blood.
f) It stimulates the breakdown of lipids and proteins.
Endocrine glands are ductless glands and their secretions are known as Hormones. They are chemical messengers which are secreted in trace amounts and affects the target organ of the body.
Pituitary gland release several hormones which regulate the functioning of different parts of the body. Growth hormone, PRL, TSH, ACTH, LH, FSH, MSH, oxytocin and vasopressin are the hormones released by the pituitary gland.
Thyroid glands are located in our neck region and secretes thyroxine, TCT and calcitonin hormone. On the other hand Parathyroid gland is located on the posterior side of thyroid gland and release PTH.
Gonads,testes in male and ovary in female are the reproductive glands which secretes hormones that helps in the reproduction of male and female. Testes secrete androgen, inhibin,AMF and ovary release estrogen and progesterone.
Pancreas is a composite gland which function as both exocrine and endocrine gland. The endocrine pancreas consists of islets of langerhans. Alpha cells of pancreas secretes glucagon and beta cells release insulin.
Thymus gland is a lymphoid organ that secretes the peptide hormone thymosin. Thymus gland promotes the development of specific cell of the immune system called as T- lymphocytes.
Pineal gland is an endocrine gland found in the cerrebral ventricle in the brain midline. Pineal gland release melatonin hormone which controls circadian rhythm of the body.
Hypothalamus is the basal part of the brain which contain neuro-secretory cells called nuclei These nuclei produce hormones which regulate the functioning of pituitary hormones.