Life Sciences Glossary: Hormones of Neurohypophysis and Hypothalamus

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Hormones of Neurohypophysis

  • Antidiuretic hormone (ADH) or Vasopressin (Petersen) .
  • Oxytocin or Pitocin

Antidiuretic Hormone

  • ADH is related with Concentration of urine.
  • ADH promotes reabsorption of water from glomerular filtrate.
  • Vasopressin released by pituitary is antidiuretic.
  • Alcohol inhibits secretion of ADH, so increases the urine output.
  • Hypo secretion of ADH results in diabetes insipid us.
  • When the amount of ADH decreases in blood, micturition (passing out of urine) increases.

Oxytocin

  • Oxytocin (Pitocin) stimulates the contraction of the smooth muscles of uterus inducing labour pain for childbirth.
  • Oxytocin activates smooth muscles of uterus; it is administered to aid parturition (birth hormone) .
  • In a pregnant woman having prolonged labour pains, if childbirth has to be hastened, it is advisable to administer oxytocin which activates smooth muscles of uterus.
  • Oxytocin induces contraction of the mammary gland muscles, help in the flow of milk from mammary glands to mouth of child, hence called ‘milk ejection hormone.’

Hypothalamus

Hypothalamus secretes both releasing and inhibitory hormones controlling the secretion some anterior pituitary hormones.

  • Thyrotrophic releasing hormone (TRH) .
  • Corticotrophin releasing hormone (CRH) .
  • Growth hormone releasing hormone (GH-RH) .
  • Growth hormone release inhibiting hormone (Somatostatin) .
  • Prolactin- releasing factor (PRF) .
  • Prolactin- inhibiting factor (PIF) .
  • Gonadotropin – releasing hormone (GN RH) .
  • MSH – releasing hormone (MRH) .
  • MSH inhibiting hormone (MRIH) .

Thyroid Gland

  • The name ‘thyroid’ was introduced by Thomas Wharton in 1656. It is derived from Greek ‘Throes’ a shield. Thyroid gland is a median endocrine gland located below larynx. It is beloved in bird and mammals (single lobed in reptiles) right and left lobes are connected by a narrow nonlinear median part called ‘isthmuses.’
  • In adult, thyroid measures 3 - 7 kms. In length and weighs about 25 gram. It is the largest endocrine gland in the body Thyroid is composed of spherical called thyroid follicles. The thyroid hormones are stored in the lumen of follicle, the extracellular space. The wall of follicles is made of two types of cells, principal cells and par follicular cells. The principal cells manufacture the thyroid hormones namely tetra dodo threonine (T4) and tri- iodothyronine (t3) . Thyroxin (T4) is synthesized from iodine and an amino acid called tyrosine. The greatest concentration of iodine is found in thyroid. The iodine content of thyroxin is about 65 % . Kendall (1914) was first to prepare crystals of thyroxin. Secretion of thyroxin is inversely proportional to the blood level of thyroxin (feedback mechanism) . Thyroxin՚s main function is to control metabolism and it regulates the basal metabolic rate. Thyroxin increases catabolism, produces energy and increases the body temperature.
  • This process is called calorigenic effect. Thyroxin also helps to regulate tissue growth and development. Thyroxin also initiates, regulates and plays a key role in the metamorphosis of frog՚s tadpole. Hypo secretion of thyroxin retards and hyper secretion enhances the rate of metamorphosis. Addition to thyroxin or iodine in pond water induces and enhances metamorphosis in the tadpoles. On removing thyroid gland from tadpole, it will remain tadpole throughout life.

Cretinism

Hypo secretion of thyroxin during the growth years or birth. It is called childhood hypothyroidism. Two important symptoms are dwarfism and mental retardation.

Myxedema

(Gulls disease) . It is adulthood hypothyroidism. Lack of thyroxin causes the body to retain water. Patient suffers from slow heart rate, low body temperature, muscular weakness, etc.

Simple Goiter

It is caused by lower intake of iodine through diet. Goiter is the swelling of neck due to enlargement of thyroid. Table salt is often iodized to prevent goiter.

Exophthalmic Goiter (Grave՚s Disease)

  • It is hyperthyroidism. Eyeballs protrude due to accumulation of mucus in eye orbits; metabolic rate is abnormally high.
  • The par follicular cell (C- cells) of thyroid secrete a non-iodized hormone called ‘thyrocalcitonin’ or calcitonin (TCT) . Calcitonin lowers the amount of calcium and phosphate in the blood. Calcitonin retards bone dissolution (osteoplastic action) and stimulates excretion of calcium in urine. Calcitonin lowers calcium in the extracellular fluid (ECF) .

Hashimoto՚s Disease

  • It is an auto immune thyroid disorder discovered by Japanese surgeon Haskar Hashimoto. It is characterized by the production of antibodies in response to thyroid antigens. It is also known as suicide of thyroid.
  • The thyroid disorders are more frequent in females than in males.

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