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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Part-3: Watch this video for the topic from 1:08 to 17:02
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