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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Hormonal Coordination Page 1

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  • The ductless glands called endocrine glands secrete 'hormones' which act as chemical regulators.
  • The hormones may be amines, steroids or proteins.
  • Pituitary gland is also called master endocrine gland as its secretions control other endocrine glands.
  • Location: It is present within a small cavity called 'sella turcica' which is on ventral side of brain below hypothalamus.




Structure of Pituitary Gland


  • Pituitary gland is divided into two lobes.
  • Anterior part called Adenohypophysis and posterior called Neurohypophysis.
  • Adenohypophysis has three subdivisions, namely:


Lowermost largest - Pars distalis containing acidophils and basophils cells.


Upper narrow part - Pars tuberalis containing alveoli like cells.


Region between pars distalis and pars nervosa - Pars intermedia which is
almost absent in human beings.

  • Neurohypophysis has three regions, namely:


Lowermost large - Pars nervosa containing cells like neurons.


Pituitary stalk - contains pituicytes cells.


Median Eminence - contains pituicytes cells.

  • The capillaries derived from veins form portal system in adenohypophysis.




Hormones Secreted from Adenohypophysis


  • Seven hormones are secreted from pars distalis of adenohypophysis.
  • Growth Hormone (GH): Secreted by pars distalis. It is necessary for
    normal body growth. Therefore, called somatotropic hormone. Hyposecretion of GH results into 'dwarfism' where physical growth is stunted but mental growth is normal. Hypersecretion in children results into 'gigantism' where height is upto 7 feet or more. In adults, hypersecretion of GH results into 'acromegaly' where bones of jaws, nose, fingers, etc., grow abnormally.
  • Lactogenic Hormone (LTH): Also called 'Prolactin'. Produced in large amount after child birth. Thus, it stimulates secretion of milk by mammary glands.
  • Melanocyte Stimulating Hormone (MSH): It produces change in skin colour in lower vertebrates but in human beings, the function is not yet clear.
  • Thyroid Stimulating Hormone (TSH): It stimulates the secretion of thyroxine from thyroid gland. When thyroxine level from blood increases, it inhibits secretion of TSH.
    This is called feedback mechanism.
  • Adrenocorticotropic Hormone (ACTH): This stimulates cortical cells of adrenal gland to release their hormones.
  • Follicle Stimulating Hormone (FSH): It is a gonadotropic hormone which stimulates development of sperms in males and ova in females.
  • Luteinising Hormone (LH): It is a gonadotropic hormone. In males, it stimulates secretion of testosterone and it is also called interstitial cells stimulating hormone (ICSH). But, in females it stimulates secretion of progesterone and estrogen.




Hormones Released from Neurohypophysis:


  • The two hormones stored and released from neurohypophysis are antidiuretic hormone and oxytocin.
  • Antidiuretic Hormone (ADH): Also called vasopressin. It promotes the kidneys to
    reabsorb and conserve water. Hyposecretion of ADH results into excretion of dilute
    urine as little water is reabsorbed. This is called 'diabetes insipidus'. ADH also constricts blood vessels and increases blood pressure.
  • Oxytocin: In females, it produces contractions of uterus in expectant mothers. It
    also helps in ejection of milk from mammary gland after child birth. In males, the
    function is not yet known.




Thyroid Gland


  • Structure of thyroid gland: It is the largest, butterfly like endocrine gland in the human body.
  • Location: Thyroid gland is present below the larynx on the ventral side of the neck region.




Structure of Thyroid Gland


  • Thyroid gland consists of two lobes which are connected to each other by a region called 'isthumus'.
  • Thyroid gland has a thin covering called 'capsule' which is made up of connective tissue.
  • Internally capsule gives rise to many partitions called 'trabeculae' which divide the thyroid gland internally into many units called 'lobules'.
  • Each lobule contains smaller functional units called 'follicles'. Follicles are somewhat spherical in shape.
  • Single follicle: It has a lining of epithelial cells arranged in single layer. In the
    central cavity of each follicle is 'Colloid' which is a secretion of thyroid gland, rich in iodine. A protein called thyroglobulin is present in colloid.
  • In between several follicles is the presence of connective tissue called 'interfollicular' connective tissue.
  • 'Parafollicular' cells or 'C' cells are present in this connective tissue which secrete 'Calcitonin'.




Thyroid Hormones


  • Tri-iodothyronine, i.e., T3 and tetra-iodothyronine, i.e., T4 are the two hormones produced by thyroid gland. T3 contains three atoms of iodine and T4 contains four atoms of iodine.
  • T4 is produced in more quantities than T3, but it is less active than T3.
  • Functions of T3 and T4: Increase in metabolic rate, increase in oxidation and
    absorption of glucose, increase in the rate of protein synthesis, affects calcium and magnesium metabolism.
  • Calcitonin: This hormone is produced by the 'C' cells or 'Parafollicular cells'. It
    reduces the reabsorption of calcium from the bone. It inhibits the reabsorption
    of calcium in the renal tubules. Thus, calcium level from blood is brought down. It is also called thyrocalcitonin.




Hypothyroidism and Hyperthyroidism


  • Hypothyroidism: Insufficient production of thyroid hormones results into
    hypothyroidism. In children, hypothyroidism produces 'cretinism', where mental
    as well as physical growth of the child is stunted.
  • Hypothyroidism in adults produces 'myxoedema', where metabolic rate decreases,
    feeling of weakness, weight gain, loss of hair, low body temperature, etc. are the symptoms.
  • Hyperthyroidism: Over secretion of thyroid hormone results in hyperthyroidism. It results in high metabolic rate, loss in weight, production of excess metabolic heat, physical and mental restlessness. Sometimes the thyroid gland enlarges in size to cause 'Goitre'. It further results in exophthalmic goitre where eyes become large and protruding.




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