Chemical Coordination and Integration

Human endocrine system - hypothalamus, pituitary, pineal, thyroid, parathyroid, adrenal, pancreas, gonads

  • Father of Endocrinology [Study of endocrine system] is Thomas Addison
  • Endocrine glands are ductless glands that secrete a non nutrient, inter cellular messengers in trace amounts, called as Hormones directly in to the blood to reach the target organ.
  • Exocrine glands possess ducts to discharge the substances
  • Pancreas and Gonads are Heterocrine glands as they have both endo end exocrine functions.
  • Secretin was the first hormone to be discovered
  • Trophic hormones are also known as stimulating hormones
  • Hormones are with low molecular weight and are non antigenic.
  • ⇒ The Hypothalamus
  • Hypothalamus is the link between Endocrine and nervous systems, which contains [nuclei in] neurosecretory cells that produce hormones called as neurohormones which control the secretion of pituitary hormones.[Releasing hormones and Inhibiting hormones].
  • Pituitary gland is located in a bone like cavity, sella turcica in hypothalamus through a stalk called infundibulum.
  • Pituitary gland is the master gland as it secretes trophic hormones
  • Three parts of pituitary gland are Adenohypophysis (Anterior), Intermedial lobe, and Neuro hypophysis (Posterior)
  • Neurohypophysis is not a true pituitary gland as it just stores hormones from the hypothalamus in the herring bodies.
  • Human growth hormone (or) somatotrophin, Thyroid stimulating Hormone (TSH), Follicle stimulating hormone (FSH), Prolactin (PRL), Adrenocorticotrophic Hormone (ACTH), are the hormones of Adenohypophysis
  • Oxytocin and Vasopressin are the two hormones of posterior part of pituitary.
  • Intermediate lobe secretes MSH (melanocyte stimulating Hormone)
  • Gonadotrophic hormones secreted by Adenohypophysis are of 2 types – (i) FSH and (ii) LH (Luteinizing Hormones)
  • FSH in males causes spermatogenesis and in females causes growth of ovarian follicles and release of Estrogen.
  • LH in males activates interstitial cells to secrete male sex hormones (androgens) and hence called the ICSH [interstitial cell stimulating hormone] and in females stimulates corpus luteum to secrete progesterone.
  • PRL is the hormone of maternity
  • Oxytocin helps in contraction of smooth muscle cells of Uterus (during child birth) and mammary gland and so called as birth hormone (or) milk ejection hormone.
  • ADH (or) Vasopressin helps in the water retention in the body which acts on the distal part of nephron. [ADH (Anti – diuretic hormone) – Prevents diuresis]
  • Gigantism ; Acromegaly (disproportional gigantism) and dwarfism / Nanism / Ateliosis are diseases due to hyper and hypo secretion of Human growth hormone respectively.
  • Growth Hormone induces liver to produce somatomedins for bone growth.
  • ⇒ Pineal gland
  • Pineal gland, located in epithalamus that [weight ()0.1-0.2 g)] contains modified nerve cells (Pinealocytes) produces 2 hormones.
  • Serotonin, that regulates vasoconstriction and melatonin which maintains the biological clock [ Circadian rhythm] of human, ie. Sleep wake cycle, Temperature, menstrual cycle and metabolism.
  • ⇒ Tyroid gland
  • Thyroid is the largest gland that possess a bilobed structure at the either side of trachea connected by a flap called isthmus.
  • Thyroid tissue contain follicular and parafollicular cells to produce Triiodothyronine, (Thyroxine), Tetraiodothyronine (T3) and Thyrocalcitonin (TCT) respectively.
  • BMR, calcium balance, RBC formation and water electrolyte balance are important functions of thyroid gland.
  • Cretinism, Myxedema (Gull’s disease), Goitre (iodine deficiency), Hashimoto's thyroiditis (autoimmune) are the disorders of thyroid hormones due to its low production.
  • Hyper secretion of thyroid hormones will lead to graves' disease also known as Exophthalmic goitre, that gives a staring look.
  • Thyrocalcitonin, made up of 32 amino acids regulates (lessen) the blood calcium level
  • ⇒ Parathyroid gland
  • 4 glands (one pair in each lobe) at the back of thyroid gland are present to produce parathyroid hormone / parathormone (or) collip’s hormone to regulate the Ca2+ ions by increasing it due to re-absorption of Ca2+ ions from renal tubules, digested food and even from bone [bone – resorption, demineralization].
  • Hypoparathyroidism leads to hyper excitability, gooseflesh, muscular spasm and cooling of hands and feet.
  • Hyper disorder could lead to Osteoporosis and Hypercalciuria.
  • ⇒ Thymus gland :
  • The gland is located dorsal to heart and Aorta which is considered as first developing lymphoid organ, that undergoes atrophy in adult.
  • Thymosin, that helps in differentiation of T cells and B cells (cell mediated – Humoral mediated immunity) and Thymopoietin, that inhibits the secretion of ACh Neurotransmitter, are the two important hormones of thymus gland.
  • Myasthenia gravis is the result of abnormal secretion of thymosin.
  • ⇒ Adrenal gland :
  • This suprarenal gland contains cortex and medulla.
  • Medulla secretes Adrenaline and Nor, adrenaline (catechol – amines) which are called as emergency hormones / FFF hormones, that is responsible for Alertness, pupillary dilation, piloerection, sweating etc,
  • Cortex contains three layers namely, outer zona glomerulosa (zone – belt; glomerulosa – little balls), middle zona fasciculata (bundles) and Inner zona reticularis (network of fibres)
  • Outer layer secretes mineralocorticoid (Eg. Aldosterone – Na2+ retention) ;
  • Middle zone secretes glucocorticoid (Eg. Cortisol – Anti inflammatory reaction, RBC Production, carbohydrate metabolism).
  • Inner zone reacts androgenic steroids (male sex hormones).
  • Hypoglycemia, low aldosterone level, Addison’s disease (increased WBC production), Under secretion of sex hormones are the Hyposecretion disorders of adrenal hormones.
  • Pheochromocytoma, Diabetes mellitus, cushing’s disease (moon face, buffalo humps, abdomen dilation), Hypokalemia (decreased potassium levels) are disorders of Excessive secretion of Adrenal hormones.
  • Adrenal cortical tumour leads to
    (i) Virilism - affect females by imparting male character
    (ii) Hirsutism - affect females by imparting male character
    (iii) Gynacecomastia - enlarged breasts in male.
  • ⇒ Pancreas
  • Pancreas has islets of Langerhans in addition to the acinar cells, that possess 4 kinds of cells.
  • Alpha – glucagon (convert glycogen into glucose)
  • β (60 – 70 %) – insulin (antagonistic to glucagon)
  • D cells / Delta cells – Somatostatin (SS) – Suppress the release of digestive / Pancreatic hormones.
  • F cells – Pancreatic polypeptide (helps in release of digestive secretion)
  • ⇒ Gonads
  • Testes containing Leydig cells (or) interstitial cells, secretes androgens where testosterone is the principal androgen which stimulates the growth & development of male secondary sex organs such as seminal Vesicles, Prostate and Penis.
  • Eunuchoidism is the failure of secretion of testosterone.
  • Ovaries produce oestrogen, progesterone, Relaxin and Inhibin (and) Actin.
  • Estradiol is the principal feminizing Oestrogen.
  • Inhibit and Actin, inhibits and activates FSH and GnRH production.
  • ⇒ Gastro – Intestinal tract :
  • Gastrin stimulates gastric juice secretion and movements of stomach, which is secreted by pyloric region of stomach.
  • Secretin, CCK (cholecystokinin), Pancreatic polypeptide, somatostatin are secreted by Intestine.
  • ⇒ Heart and kidneys :
  • Atrial Natriuretic factor (ANF) that are produced from cardiocytes inhibits the release of renin and inhibits NaCl reabsorption of collecting duct.
  • Kidneys release Renin which acts upon angiotensinogen to convert it into angiotensin I and then into angiotensin II, which further secretes aldosterone that enhances sodium and water reabsorption from nephrons.

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