- Zonareticularis is the inner zone and consists of cells arranged in branching cords which secrete sexcorticoids.
- They are associated with deposition of protein in muscles and retention of nitrogen.
- These hormones are secreted as DHEA ( Dehydroxyepiandrosterone). Which is a precursor of both testeosterone and oestrogens.
Adrenal medulla
• The adrenal medulla is completely surrounded by the cortex. It is an outgrowth of tissue from the same source as the nervous system and its functions are closely allied to those of the sympathetic part of the autonomic nervous system.
• It is stimulated by its extensive sympathetic nerve supply to produce adrenaline or epinephrine and noradrenaline or norepinephrine in the ratio of 1:4. These are commonly called as catecholamines.
(a) Adrenaline : It is associated with potentiating the conditions needed for fight or flight.
- When the body is under stress, homeostasis is disturbed.
The immediate response is sometimes described as preparing for fight or flight
- These hormones increasesalertness, pubillary dilation, sweating etc. Both these hormones increases heart beat, strength of heat contraction and rate of respiration.
(b) Nor-adrenaline: This is the postganglionic chemical transmitter of the sympathetic nervous system. The main function of nor-adrenaline is the maintenance of blood pressure by causing general vasoconstriction, except of the coronary arteries.
Hormones disorders
(a) Hypersecretion of glucocorticoids
- Hyper secretion of cortisol ( cushing’s syndrome ) has a wide variety of effects but they may not all be present at the same time. These include.
• Painful adiposity of the face ( moon face), neck and trunk
• Excess protein catabolism, causing thinning of subcutaneous tissue and muscle, wasting, especially of the limbs.
• Suppression of growth hormone, causing arrest of growth in children.
• Osteoporosis and kyphosis, if vertebral bodies are involved
• Susceptibility to infection due to reduced febrile response, depressed immune response and phagocytosis, impaired migration of phagocytes.
• Insomnia, excitability, euphoria, psychotic depression.
• Hypertension menstrual disturbances, peptic ulceration
(b) Hyposecretion of glucocorticoids
Inadequate secretion of cortisol causes diminished gluconeogenesis, low blood glucose, muscle weakness and pallor.
(c) Hypersecretion of mineralocorticoids
Excess aldosterone (conn’s syndrome) affects kidney function, causing
• Excessive reabsorption of sodium chloride and water causing hypertension
• Excessive excretion of potassium causing hypokalemia, which leads to cardiac arrhythmia and muscle weakness.
(d) Hyposecretion of mineralocorticoids
Hypoaldosteronism results in failure of kidneys to regulate sodium, potassium and water excretion, leading to
- Blood sodium deficiency and potassium excess
- Dehydration, low blood volume and low blood pressure
• Addison’s disease is due to the hyposecretion of all adrenal cortex hormones. There is electrolyte upset with low plasma Na+ through increased urinary elimination and high plasma K+, reduced blood volume, lower blood pressure, marked anaemia, hypoglycaemia, great muscular
weakness, nausea, vomiting, diarrhoea and bronze pigmentation.
(e) Hypersecretion of sexcorticoids
• Virilism is due to excessive secretion of sex corticoids caused by adrenal tumour results in appearance of male secondary characters in females like male voice, beard moustaches, stoppage of menstruation and growth of clitoris.
• Hirsutism is presence of facial and excess body hair in females due to adrenal virilism.
Kidney
The kidneys produce hormones that affect the function of other organs. For example, a hormone produced by the kidneys stimulates red blood cell production. Other hormones produced by the kidneys help regulate blood pressure and control calcium metabolism.
• The kidneys secrete three hormones: rennin, erythropoietin and calcitriol
• Whenever the rate of ultrafiltration falls, the cells of their juxtaglomerular complex secrete and release into blood a compound named renin. It acts upon a plasma protein angiotensinogen, speparating a compound called angiotensin – II from it.
• Angiotensin –II accelerates heart beat and constricts arterioles, thereby increasing blood pressure. This enhances the rate of ultrafiltration.
• Simultaneously, the angiotensin-II stimulates adrenal corten to secrete aldosterone and enhances water and sodium reabsorption from nephrons. These factors also elevate blood pressure.
• The oxygen shortage stimulates the kidney cells to secrete a hormone named erythropoietin ( a circulating glycoprotein) into the blood.
• Erythropoietin stimulates the bone marrow to increase the production of RBCs.
• Vitamin D exists in two forms: Calciferol or D2 and cholecalciferol or D3
• Calcitriol is the active form of vitamin cholecalciferol( D3).It promotes absorption of Ca+2 and phosphrous in the small intestine and accelerates bone formation.
Pancreas
• The pancreas lies inferior to the stomach in a bend of the duodenum. It is both an exocrine and an endocrine gland.
• Pancreas has group of cells called islets of Langerhans. These produce endocrine secretions. Four kinds of cells have been identified in the islets
- Alpha cells ( about 15%) produce glucagon.
- Beta cells (about 65%) produce insulin.
- Delta cells or D-cells ( about 5%) produce somastostatin.
- F cells: Pancreatic polypeptide cells (15%) produce pancreatic polypeptide.
• Glucagon stimulates the liver to convert stored glycogen into glucose in the blood. Glucagon is controlled by feedback in accordance with the level of glucose in the blood. When the blood sugar rises, the secretion of glucagon is suppressed and when it drops the secretion of glucagon is stimulated. Glucagon is also called an ‘antiinsulin’ hormone.
• Insulin is antagonistic to glucagon. Insulin decreases the level of glucose in the blood. It acts by increasing the rate at which glucose out of the blood and into the cells and by stimulating muscle cells to take up sugar from the blood and convert it to glycogen.
• Like glucagon, insulin is primarily regulated by feedback from the blood glucose concentration.
• When the blood sugar level drops, the secretion of insulin is suppressed. When the blood sugar level increases, the secretion of insulin is stimulated.
• It promotes protein synthesis in tissue from amino acids and reduces catabolism of proteins. It is an anabolic hormone. It increases the synthesis of fat in the adipose tissue from fatty acids and reduces the breakdown and oxidation of fat.
• Somatostatin seems to suppress the release of hormones from the pancreas and digestive tract.
• Pancreatic polypeptide inhibits the release of digestive secretion of the pancreas.
• The most common endocrine disorder of the pancreas is the diabetes mellitus ( hyperglycemia), now recognized to exist in two forms – insulin dependent and non insulin dependent.
• The insulin dependent diabetes mellitus ( IDDM) is caused by a failure of the Beta cells to produce adequate amounts of insulin while the non-insulin dependent diabetes mellitus ( NIDDM) appears to involve failure of insulin to facilitate the movement of glucose into the cells.
• In both disorders the blood glucose concentration is elevated above the normal range.
• Some of the glucose is excreted in the urine and water follows the glucose, causing excessive urination and dehydration of body tissues. The causes excessive thirst ( polydipsia). The cells are unable to utilize their proteins for it. The person becomes very weak. Degradation of fats
increases, producing ketone bodies ( ketosis). Blood cholesterol level rises.
• Hypoglycemia occurs when the blood glucose level falls below normally. Symptoms of hypoglycemia include weakness, profuse sweating irritability, confusion, unconsciousness and convulsions.
Gonads
• Gonads are the sex glands, the ovaries and the testis. They produce ova and sperm respectively but also secrete hormones.
Male sex hormones
- Male sex hormones or androgens are produced by testis.They are secreted by Leydig cells or interstitial cells found in the connective tissue around seminiferous tubules. Androgens are steroid hormones produced under control of ICSH ( LH) of pituitary gland with maximum activity at
puberty. Two common androgens are testosterone and androsterone. Dihydrosterone is the active form of testosterone.
- Testosterone is first produced during foetal growth under the influence of chorionic gonadotropin of placenta. There is a spurt of testosterone production at the age of 10-13 years when puberty begins. Testosterone production declines after the age of 50 years. At the time of puberty
testosterone causes development of male secondary sex organs external / accessory male sex characters, growth of body tissue, broadening of shoulders, growth of muscles, higher metabolism, increased sebaceous gland activity, normal skin and formation of sperms through
spermatogenesis is mainly due to FSH. Development of external genitalia in the male foetus is under the control of testosterone produced by testes. Deficient androgen secretion causes eunuchoidism
Eunuchoidism
- Eunuchoidism is a hormonal disorder due to non-secretion of testosterone in a genetically male individual. The secondary male sex organs are under developed and nonfunctional. The accessory male character fails to develop. Spermatozoa are not formed. Castration is artificial removal
of testes. Secondary male characters do not differentiate. Castrated human males are called eunuchs.
Female sex hormones
- They belong to both steroid and protein categories. The hormones are secreted by growing graafian/ ovarian, corpus luteum and placenta.
1. Estrogens
They are steroid hormones secreted by growing ovarian follicles under instructions from anterior pituitary through FSH. Estrogens include estradiol, estriol and estrone. Estradiol is the principal estrogen. Its maximum concentration is found at the time of puberty. Later it shows cyclic rise and fall during menstrual cycle. During pregnancy estradiol is secreted by placenta. At puberty the hormone is required for development of female secondary sex organs, external / accessory female sex characters, body contour and onset of menstrual cycle. Later on the hormone helps in maintaining the traits and organs in reproductive tract. During menstrual cycle, estrogen released from growth ovarian follicle inhibits FSH secretion and stimulates LH secretion from pituitary increasing blood supply to uterine epithelium.
2. Progesterone
It is a steroid hormone secreted by corpus luteum under the influence of LH of anterior pituitary in the second half of menstrual cycle and hCG of placenta during pregnancy. The placenta also secretes the hormone. Routinely progesterone causes temporary changes in endometrial
lining of uterus for receiving egg. During pregnancy it helps in attaching embryo to uterine wall development of placenta, maintenance of pregnancy and growth of secretory alveoli in mammary glands. Progesterone checks ovulation. Hyposecretion results in abortion and misconception.
3. Relaxin
The proteinaceous hormone is secreted by corpus luteum towards the close of gestation period for loosening of pelvic ligaments. Softening dilating and relaxing of uterus for decreasing discomfort of carriage and easy child birth.
4. Human Chorionic Gonadotropin ( hCG)
The proteinaceous hormone is secreted by placenta for maintaining corpus lutoum,hCG is urine is an indication of pregnancy.
5. Human placental Lactogenic hormone (HPL)
The hormone produced by placenta prepares the mammary glands to secrete milk.
6. Inhibin / Actin
Hormones produced by corpus luteum, placenta and testes that inhibits or activates gonadotrophic activity of pituitary gland and hypophysis.
Puberty related endocrine abnormalities
Hypogonadism
- Defect or injury to hypothalamus, pituitary testes or ovaries. In male hypogonadism, there is deficient production of testosterone due to hypofunction of Leyding cells or deficient formation of sperms on account of hypofunction of sertoli cells. Both the defects may be present. Male musculature and male secondary sexual characteristics do not develop. In female hypogonadism there is deficient secretion of estrogen, little development of secondary sexual characters of females and nondevelopment of reproductive cycles.
Precocious puberty
- It is early maturation of primary sex organs. Ovary before the age of 11 years and testes before the age of 12 years. Sexual pseudoprecosity in boys occurs due to excess formation of testosterone as there is tumour growth in testes or adrenals. It results in early enlargement of pensis,
development of pubic and axillary hair, faster body growth, masculinisation and then stunting . Similarly, sexual pseudoprecosity in girls results from excessive production of estrogen due to tumours in ovaries / adrenals. Breast and pubic hair develop early but ovarian cycle does not occur.
Gynaecomastia
Normally-developing pubertal males may be at risk for gynecomastia that is part of the normal developmental process. Normal male infants also may have gynecomastia. Gynecomastia results from an imbalance in hormone levels in which levels of estrogen (female hormones) are increased relative to levels of androgens (male hormones).
- It is the development of breast tissue in males due to
(i) Perturbation of estrogen to androgens ratio.
(ii) Temporary increase in circulating estrogen during neonatal period and during puberty.
(iii) Decreased testosterone in later life
Other organs which secrete hormones
Heart
- It produces a peptide hormone atrial natriuretic factor ( ANF) in case of hypertension. The hormone inhibits renin ( in kidneys) and ADH secretion ( in pituitary)
Salivary glands
- The glands produce proteinaceous hormone parotine required for calcification of teeth.
Gastrointestinal mucosa
1. Gastrin
It is produced by pyloric mucosa and duodenum ( small quantity by γ-cells in pancreas) in response to presence of food in stomach. Stimulus is provided by vagus nerve. Gastrin stimulates secretion of gastric juices and churning movements of stomach. Hypersecretion produces gastric
ulcers and other gastric problems.
2. Motilin
It is secreted by duodenum in response to food and acidity. Motilin controls motility of stomach and intestine
3. Secretin
Entry of HCl in duodenum stimulates secretion of secretin from duodenal mucosa. The hormone stimulates secretion of water and bicarbonate in bile and pancreatic juice. It inhibits stomach movements and secretion of gastric juice. Secretion was the first hormone to be isolated.
4. Enterogastrone
It is believed to be produced by duodenum in response to chyme. Enterogastrone stops digestive activity in stomach.
5. Cholecystokinin
It is produced by duodenum and jejunum in response to presence of food. Cholecystokinin stimulates the flow of pancreatic enzymes and contraction of gall bladder.
6. Pancreazymin
The hormone is believed to be secreted by duodenal mucosa and required for the flow of pancreatic juice. Both cholecystokinin and pancreazymin are now believed to be one structure.
7. Enterocrinin
The hormone secreted by duodenal mucosa stimulates crypts of Lieberkuhan for secretion of succus or intestinal juice.
8. Duocrinin
Intestinal hormone that stimulates secretion of mucus and HCO3 from Brunner’s gland
9. Villikinin
Intestinal hormone that stimulates movements of intestinal villi
10. Gastric Inhibitory Peptide ( GIP)
It is secreted by mucosa in the upper part of small intestine in response to fat and protein in chyme,monosaccharides also have a stimulating effect. GIP inhibits gastric mobility and secretion for slowing down of passage of food. It stimulates insulin secretion.
Hormones which always remains in tissue fluid
Never reach blood stream but remain in ECF
1. Neurohormones : Secreted by nodesof axons of nerve cells, Acetylcholine and Norephrine are the main neurohormone. Acetylcholine causes muscles to contract, activates pain responses and regulates endocrine and REM sleep functions.
2. Prostaglandin: Called local hormones. They are fatty acid, Many types, Kidney, gonads, seminal vesicle, thymus, brain organ and cells secrete these hormone in EC. Function in the contraction and relaxation of smooth muscle, the dilation and constriction of blood vessels,
control of blood pressure, and modulation of inflammation.
3. Kinins : Called as “First aid hormone”, reducesblood pressure by expanding blood vessels. Secreted at the time of chemical change in ECF
4. Pheromones or Ectohormones: effect the other animal’s behavior and mode of life of same species. , are volatile andtravel through air from place to place
Three tyeps
1. Sex-Pheromone : These attact male and female animal for reproduction Examples Muskone, Civetone
2. Aggregation pheromone: Sendingmessage to othermember of the socity of insect, to help in aggregation Example Geradial in honeybee
3. Alarm pheromones: Alarm other member of same species of insect. Example Formic acid in ants.
Distinguish
EnzymeVs Hormone
Vitamins Vs Hormone
Feedback loop of the male reproductive system
Corticotropin releasing hormone or CRH feedback mechanism