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Insulin secretion

  1. Insulin is a polypeptide anabolic hormone containing two chains of amino acids linked by disulfide bridges
  2. Insulin secretion begins at 12 weeks.
  3. Beef insulin differs by three amino acids from a human, Pork insulin differs from human insulin by only one amino acid.
  4. Insulin is synthesized in the rough endoplasmic reticulum of the B cells. It is then packaged in Golgi apparatus and expelled by exocytosis.
  5. The half-life of insulin in the circulation in humans is about 5 min
  6. The normal concentration of insulin in fasting normal humans is 0–70 U/mL. The amount of insulin secreted in the basal state is about 1 U/h, with a fivefold to tenfold increase following ingestion of food. The average amount secreted per day in a normal human is about 40 U.







Amino acids (leucine, arginine, others)


Intestinal hormones (GIP, GLP-1, gastrin, secretin, CCK)

α Adrenergic stimulators

β-Keto acids

β Adrenergic blockers




Thiazide diuretics

Cyclic AMP

K+ depletion

β-Adrenergic stimulators





Microtubule inhibitors


GLUT Transporter for facilitated diffusion of glucose


Basal glucose uptake

Placenta, blood-brain barrier, brain, red cells, kidneys, colon, many other organs


Act as B-cell glucose sensor

B cells of islets , liver


Basal glucose uptake

Brain, placenta, kidneys


Insulin-Dependent glucose uptake

Skeletal and cardiac muscle, adipose tissue,


Fructose transport

Jejunum, sperm 

  1. Maximum triglycerides are in chylomicrons
  2. Exogenous (Dietary) triglycerides are maximum in chylomicrons.
  3. Endogenous triglycerides are max. in VLDL.
  4. Stress induced Hyperglycemia is mediated through increased epinephrine, Cortisol and glucagon causing gluconeogenesis.
  5. Insulin is synthesized on a large scale bases by recombinant technology. Melatonin is synthesized & secreted by pineal gland
  6. Melanocyte stimulating hormone (MSH) is secreted by intermediate pituitary gland ACTH level is highest during early morning.
  7. Dopamine acts as hypothalamic prolactin inhibiting hormone and decreases prolactin secretion.
  8. Polyuria & diabetes insipidus occur due to decrease in ADH secretion.
  9. Iodine uptake is seen in thyroid gland salivary gland mammary gland gastric placenta, ciliary body of eye & choroid plexus.
  10. 1, 25 dihydroxy cholecalciferol (steroid) causing bone mineralization by increasing intestinal Ca*+ absorption.
  11. Adrenal medullary hormones (Adrenaline,Nor-Adrenaline, Dopmine) are not essential for life.
  12. Adrenal cortex is essential for life. The mineratocorticoids & glucocorticoids are essential for life.
  13. Increase in plasma Na+ inhibits aldosterone secretion & acute decline in plasma Na+ stimulates its secretion.
  14. GABA - exerts an inhibitory action on GnRH secretion before onset of puberty. Glutamate - has an excitatory effect & whose levels increase at the onset of puberty.
  15. A surge in LH secretion triggers ovulation. Action of LH are
  16. Stimulates ovulation
  17. Formation & maintenance of corpus luteum.
  18. Formation of progesterone in the corpus luteum from the lutein cells.
  19. Progesterone is thermogenic which increase body temperature during ovulation.
  20. FSH acts on granulosa cells in female and Sertoli cells in male.
  21. Zinc is secreted by prostate, and prostaglandins from seminal vesicle.
  22. Spermatozoa are stored in epididymis.
  23. Spermatozoa maturation and motility acquired during their passage through epididymis.
  24. Further maturation and capacitance occur within female genital tract.

Sertoli cells

  1. They provide nutrition to the developing sperm cells. Q
  2. maturation of spermatozoa called spermiogenesis
  3. They phagocytoze the injured or dead sperm cells Q
  4. They are the basis: of blood testis barrier Q
  5. They secrete androgen-binding protein (ABP), inhibin and MIS. Q
  6. They do not synthesize androgens, but they contain aromatase, the enzyme responsible for conversion of androgens to, estrogens and they can produce estrogens. Q
  7. Inhibin inhibits FSH secretion
  8. MIS causes regression of the mullerian ducts is in males during fetal life.


Leydig cells (Interstitial Cells)

They are nest of cells present between the seminiferous tubules in testes. They secrete testosterone into bloodstream

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