HYPOTHALAMUS
· Hypothalamus is actually a part of the nervous system.· Also known as the master of the endocrine orchestra (previously pituitary gland was called so).
· Controls the pituitary gland directly and others indirectly.
· Hormones released by the hypothalamus are:
a. Growth hormone-releasing hormone (GHRH): Stimulates anterior pituitary to release Growth Hormone.
b. Growth hormone inhibiting hormone/Somatostatin: Inhibits release of Growth hormone.
c. Thyrotropin Releasing Hormone (TRH): Stimulates anterior pituitary to release TSH.
d. Corticotropin-Releasing Hormone (CRH): Stimulates anterior pituitary to release ACTH.
e. Gonadotropin-Releasing Hormone (GRH): Stimulates anterior pituitary to release FSH and LH.
f. Prolactin Inhibiting Hormone (PIH/Dopamine): Inhibits release of Prolactin from the anterior pituitary.
a. Growth hormone-releasing hormone (GHRH): Stimulates anterior pituitary to release Growth Hormone.
b. Growth hormone inhibiting hormone/Somatostatin: Inhibits release of Growth hormone.
c. Thyrotropin Releasing Hormone (TRH): Stimulates anterior pituitary to release TSH.
d. Corticotropin-Releasing Hormone (CRH): Stimulates anterior pituitary to release ACTH.
e. Gonadotropin-Releasing Hormone (GRH): Stimulates anterior pituitary to release FSH and LH.
f. Prolactin Inhibiting Hormone (PIH/Dopamine): Inhibits release of Prolactin from the anterior pituitary.
· Hypothalamus controls Sex, Sleep, Hunger, Thirst, Temperature, Appetite, Fatigue, Circadian rhythm, fluid balance.
PITUITARY GLAND
· Pituitary (hypophysis) regulates so many body activities, it has been nicknamed the 'master gland' or 'the conductor of the endocrine symphony'.· Pituitary lies in the sella turcica of the sphenoid bone and is attached to the hypothalamus by a short infundibular stalk.
· In man, it is normally oval in shape and measures about 1.3 cm in diameter and weighs about 0.5 gram, It is slightly larger in women.
· Based on anatomy and embryology, the pituitary can be divided into two parts: Adenohypophysis (Anterior) and Neurohypophysis (Posterior).
 |
| Structure of pituitary gland |
· Adenohypophysis is large in size and ectodermal in origin and is derived from the Rathke's pouch.
· The smaller neurohypophysis is developed from neural cells present in the floor of the third ventricle and is a diencephalic down growth connected to the hypothalamus.
· It is also known as Hypophysis cerebri.
· Six type s of chromophil cells have been identified in the anterior pituitary these are:
a. Somatotropes
b. Mammotropes
c. Mammosomatotropes
d. Corticotropes
e. Thyrotropes
f. Gonadotropes
· Chromophobe of unknown function are also present.
· Supporting cells called folliculostellate cells are also present.
· Supplied by internal carotid artery, drain into dural venous sinuses.
PARTS OF THE PITUITARY GLAND
| Part | Adenohypophysis | Neurohypophysis |
|---|---|---|
| Lobes | Anterior & Middle | Posterior |
| Characters | Has Secretory cells, Vascular connection with Hypothalamus, Secrete hormones in response to releasing hormones from Hypothalamus |
Hae Neuro secretary cells, Neural connection with Hypothalamus, Hormones are actually produced in Hypothalamus and stored and released from here. |
| Source of Development |
Rathke's pouch (Ectoderm) |
Neuroectoderm |
A. Hormones released from Anterior Pituitary
1. Growth Hormone (GH) or Somatotropin· It is a polypeptide hormone that is synthesized by somatotropes of the anterior pituitary.
· Its molecular weight is 22000 and is made up of 191 amino acids in a single chain.
· It is also produced by recombinant gene technology.
· It is also produced by recombinant gene technology.
a. Regulation of secretion:
· GHRH Its secretion is regulated by two hypothalamic hormones: GHRH (Growth Hormone Releasing Hormones) and somatostatin.
· GHRH Its secretion is regulated by two hypothalamic hormones: GHRH (Growth Hormone Releasing Hormones) and somatostatin.
· GHRH stimulates the secretion of GH and somatostatin inhibit its secretion.
· Hypocalcemia, fasting, stress, glucagon oestrogen and androgen are the factors that stimulate the secretion but glucose, cortisol and fatty acids inhibit the secretion.
· Hypocalcemia, fasting, stress, glucagon oestrogen and androgen are the factors that stimulate the secretion but glucose, cortisol and fatty acids inhibit the secretion.
b. Functions
· It is an anabolic hormone and requires adequate nutrition and insulin.
· It helps the synthesis of protein, DNA, RNA, collagen chondrin and increases the cell size and number. promotes the linear growth of the skeleton by its action on epiphyseal cartilage.
· It stimulates the growth of all the tissues of the body.
· It also stimulates the growth of connective tissues and muscle skin, intestine pancreas adrenal and increases the organ size.
· In the liver, it promotes gluconeogenesis.
· It activates the protein anabolism. So it decreased secretion also help in wasting muscle of old age.
· It stimulates the fat metabolism for the production of energy. So it has a ketogenic effect when insulin level is low.
· It is diabetogenic and antagonizes the actions of insulin in the skeletal muscles and adipose tissues but not in the liver.
· It is an anabolic hormone and requires adequate nutrition and insulin.
· It helps the synthesis of protein, DNA, RNA, collagen chondrin and increases the cell size and number. promotes the linear growth of the skeleton by its action on epiphyseal cartilage.
· It stimulates the growth of all the tissues of the body.
· It also stimulates the growth of connective tissues and muscle skin, intestine pancreas adrenal and increases the organ size.
· In the liver, it promotes gluconeogenesis.
· It activates the protein anabolism. So it decreased secretion also help in wasting muscle of old age.
· It stimulates the fat metabolism for the production of energy. So it has a ketogenic effect when insulin level is low.
· It is diabetogenic and antagonizes the actions of insulin in the skeletal muscles and adipose tissues but not in the liver.
c. Disorders
c. 1. Hyposecretion of growth hormone
· Low secretion of growth hormone causes retarded growth called dwarfism which is characterized by smaller body size, sexual immaturity and head generally larger than the body.
c. 1. Hyposecretion of growth hormone
· Low secretion of growth hormone causes retarded growth called dwarfism which is characterized by smaller body size, sexual immaturity and head generally larger than the body.
c.2. Hypersecretion of growth hormone
· Over secretion of growth hormone results in gigantism, before puberty.
· In gigantism, the skeleton grows rapidly so adults attain a height of 7to 8ft, limbs are generally disproportionately longer.
· In hypersecretion of the growth hormone in adults increase the thickness of the lower jaw, hand, feet and nose producing gorilla-like appearance called acromegaly
· Over secretion of growth hormone results in gigantism, before puberty.
· In gigantism, the skeleton grows rapidly so adults attain a height of 7to 8ft, limbs are generally disproportionately longer.
· In hypersecretion of the growth hormone in adults increase the thickness of the lower jaw, hand, feet and nose producing gorilla-like appearance called acromegaly
2. Thyroid Stimulating Hormone:
· It is a glycoprotein secreted by thyrotropes of the anterior pituitary gland.
· Its molecular weight is 28000 and is made of two subunits called alpha and beta subunits.
· It is a glycoprotein secreted by thyrotropes of the anterior pituitary gland.
· Its molecular weight is 28000 and is made of two subunits called alpha and beta subunits.
· Alpha subunit consist of 96 aminoacids and beta has 110 aminoacids.
· Beta subunit is responsible for biological activity.
· Beta subunit is responsible for biological activity.
a. Regulation of secretion
· The secretion and synthesis of TSH is controlled by the hypothalamic neurohormone (TRH)
· Exposure to cold fasting and oestrogen stimulates the TSH secretion and inhibits the secretion of cortisol, dopamine, CCK, somatostatin.
· The secretion and synthesis of TSH is controlled by the hypothalamic neurohormone (TRH)
· Exposure to cold fasting and oestrogen stimulates the TSH secretion and inhibits the secretion of cortisol, dopamine, CCK, somatostatin.
b. Functions
· It stimulates iodine uptake, organification of iodine, facilitate the synthesis of thyroid hormone and secretion of Thyroid hormones (T3 and T4)
· It stimulates the growth of Thyroid glands
· It stimulates iodine uptake, organification of iodine, facilitate the synthesis of thyroid hormone and secretion of Thyroid hormones (T3 and T4)
· It stimulates the growth of Thyroid glands
3. Adrenocorticotrophic hormone (ACTH) or Adrenocorticotropin
· This hormone is secreted by basophil cells and polypeptides in nature and is made up of a single chain of 39 amino acids.
· Its secretions are regulated by the hypothalamic hormone, CRH.
· ACTH Production is stimulated by increased secretion of CRH.
· Increase levels of cortisol suppress the ACTH secretion.
· Its molecular weight is 4500.
· It controls the growth of the adrenal cortex and synthesis of cortisol, so essential to life.
· Its molecular weight is 4500.
· It controls the growth of the adrenal cortex and synthesis of cortisol, so essential to life.
· The adrenal cortex atrophies in absence of ACTH.
· ACTH also acts on adipose tissue and increase the fatty acid concentration in blood.
· The adrenal cortex is the main target organ of ACTH. So secretion of the adrenal cortex acts throughout the body to increase the rate of gluconeogenesis, protein catabolism and fat catabolism (lipolysis), skin pigmentation, increase adrenal blood flow and control the secretion of glucocorticoids.
· ACTH is also used in the treatment of hypersensitivities, inflammatory reaction, rheumatism
· Hyposecretion of ACTH causes atrophy of adrenal gland and hypersecretion causes excessive growth of adrenal cortex.
· Stimulates the secretion of cortisol.
· Hyperpigmentation is the symptom of hypersecretion of ACTH.
· The adrenal cortex is the main target organ of ACTH. So secretion of the adrenal cortex acts throughout the body to increase the rate of gluconeogenesis, protein catabolism and fat catabolism (lipolysis), skin pigmentation, increase adrenal blood flow and control the secretion of glucocorticoids.
· ACTH is also used in the treatment of hypersensitivities, inflammatory reaction, rheumatism
· Hyposecretion of ACTH causes atrophy of adrenal gland and hypersecretion causes excessive growth of adrenal cortex.
· Stimulates the secretion of cortisol.
· Hyperpigmentation is the symptom of hypersecretion of ACTH.
4. Gonadotrophic Hormones
a. Follicle-stimulating hormone (FSH)
· It is one of the three gonadotropins.
· It is a glycoprotein secreted by gonadotropes.
· Its molecular wt is 33000. It has an alpha subunit of 92 amino acids and a beta subunit.
· It is regulated by hypothalamic neurohormone GnRH.
· It is regulated by hypothalamic neurohormone GnRH.
· In females, it leads to the growth and maturation of Graffian follicles with Estrogen production and prepares them for ovulation.
· In males, it stimulates spermatogenesis by inducing the development of germinal epithelium in seminiferous tubules.
b. Luteinizing hormone (LH)
· This hormone is a glycoprotein in nature and molecular weight of 28000 and is secreted by gonadotropes.
· This hormone is a glycoprotein in nature and molecular weight of 28000 and is secreted by gonadotropes.
· In females, luteinizing hormone is responsible for final ovulation and producing oestrogen.
· In males, it stimulates the interstitial cells of the testes to produce testosterone.
5. Luteotrophic hormone or Prolactin (LTH)
· It is also known as a lactogenic hormone.
· It is also known as a lactogenic hormone.
· It is secreted by lactotrophs of the adenohypophysis.
· Its molecular weight is 22000, polypeptide in nature and has 199 amino acids.
· Its secretion is under constant inhibition of the hypothalamus.
· Prolactin inhibiting and prolactin-releasing factors have antagonism on the secretion of prolactin.
a. Functions:
· It stimulates lactation in pregnant females by promoting the development of the mammary gland.
a. Functions:
· It stimulates lactation in pregnant females by promoting the development of the mammary gland.
· Its action in males is not known.
b. Disorders:
· In women hypersecretion of prolactin can result in infertility and hyposecretion can lead to the loss of milk production.
· In men hyposecretion decreases the secretion of testosterone synthesis and causes impotence.
b. Disorders:
· In women hypersecretion of prolactin can result in infertility and hyposecretion can lead to the loss of milk production.
· In men hyposecretion decreases the secretion of testosterone synthesis and causes impotence.
6. Intermediate lobe or Pars intermedia
· This part of the pituitary is located in between the anterior lobe and posterior lobe of the pituitary gland.
· Nowadays, it has been referred to as the part of the anterior lobe of the pituitary because both have been same embryological origin (from RATHKES POUCH).
· This lobe secretes a hormone called intermedin or melanocyte-stimulating hormone (MSH).
· In the case of fish, amphibians, reptiles and humans it helps in the darkening and dispersion of melanophores.
· Its regulation is controlled by sunlight.
· Its regulation is controlled by sunlight.
· Lack of skin pigmentation is due to its absence and causes albinism.
B. Posterior lobe or Neurohypophysis
· The posterior lobe of the pituitary is originated as an outgrowth of the primitive brain, infundibulum from the floor of the brain.· It is made up of nervous tissue and consists of the termination of many neurosecretory fibres of neurosecretory cells.
· This lobe secretes two types of hormones:
1. Oxytocin
2. Vasopressin
· This lobe secretes two types of hormones:
1. Oxytocin
2. Vasopressin
· These two hormones are octapeptides in nature.
· It is synthesized in the supraoptic nucleus whereas oxytocin is formed in the paraventricular nucleus.
· These hormones after synthesis combine with a binding protein called neurophysins.
· There are two neurophysins: neurophysin–I and Neurophysin-II.
· Oxytocin binds with the neurophysin–I and Vasopressin bind with the neurophysin–II.
1. Oxytocin or Pitocin
· Secretion of oxytocin results from two reflexes:
a. Milk ejection reflex: continuous milk suckling increases the oxytocin synthesis and lactation also increases.
· Oxytocin release is inhibited by pain, fear and stress.
b. Parturition reflex: the oxytocin acts on the myoepithelial cells of the nipple.
· It causes them to contract and squeeze the milk out of the alveoli of the mammary gland.
· Functions:
· Functions:
· It is an important uterus contracting hormone.
· It also gives rise to contracting of smooth muscle in the mammary gland and resulting in milk secretion.
· It also gives rise to contracting of smooth muscle in the mammary gland and resulting in milk secretion.
· So-called milk ejection hormone also.
· It is minimal anti-diuretic.
· It is minimal anti-diuretic.
· It has also physiological significance because it stimulates to contract the gall bladder, intestine and urinary bladder.
2. Vesopressin or Pitressin (ADH)
· This hormone is also called anti-diuretic hormone because it promotes water retention in the kidneys.
· It is released in response to stress and dehydration.
· Its secretion is regulated by continuous changes in osmolality and volume of body fluids.
· The osmoreceptors present in the hypothalamus is sensitive to 1% change in body fluids.
· The condition of water deprivation and plasma osmolarity increases the help in more secretion of ADH.
· Cortisol, alcohol and thyroxine reduce the ADH secretion.
· Functions:
· It stimulates reabsorption of water by distal convoluted tubules and collecting tubules of the kidney.
· Functions:
· It stimulates reabsorption of water by distal convoluted tubules and collecting tubules of the kidney.
· It reduces chloride absorption.
· It causes contraction of all plain muscles of the body except heart and uterus.
· Large quantities of this hormone cause the rise of arterial pressure, coronary vessels contraction, renal vasoconstriction and hyperglycemia.
· Disorder:
· It causes contraction of all plain muscles of the body except heart and uterus.
· Large quantities of this hormone cause the rise of arterial pressure, coronary vessels contraction, renal vasoconstriction and hyperglycemia.
· Disorder:
Its hyposecretion causes diuresis and diabetes insipidus characterized by polyuria and polydipsia) whereas hypersecretion causes anti-diuresis (small urine volume).
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