Physio lec 2

• Hypothalamus


  TRH/CRH/GnRH/GHRH-SRIF/PIF
• Anterior Pituitary


  GH/TSH/ACTH/FSH/LH/Prolactin/MSH?
• Posterior Pituitary


  ADH/Oxytocin
• Pancreas


  insulin/Glucagon
• Parathyroid


  PTH/Calcitonin
• Placenta


  HCG/HPL
• somatostatin


  Growth Hormone Inhibitory Hormone
• Protein hormones


  Synthesized in endoplasmic reticulum and Golgi apparatus
• Steroid hormones


  Cholesterol derivative (adrenal and sex hormones). Not stored!
• Amine hormones


  Tyrosine derivatives (Thyroid hormones). Enzymes in cytoplasm!
• Protein hormones


  Lipophobic (hydrophilic), cannot diffuse through cell membrane, bind to receptors on cell surface
• Steroid hormones


  Lipophilic (fat-soluble), can freely diffuse through cell membrane and bind to intracellular receptors
• Protein hormones require membrane receptors to transmit their signal, while lipophilic hormones can directly cross the cell membrane and interact with intracellular receptors
• Feedback mechanism


  Negative is most common, positive rare e.g. LH surge in ovulation
• Receptor regulation


  Down-regulation vs. up-regulation e.g. progesterone receptors in uterus and estrogen receptors in ovary during ovulation
• Cellular mechanisms of hormone action


  1. Receptor mediated 2nd messenger mechanism

  2. Tyrosine kinase mediated: Insulin and GH

  3. Receptor mediated Trans-activation: steroid hormones and amine hormones (T3 and T4)
• Receptor mediated 2nd messenger mechanism


  • H+R= HR complex, HR activates G protein, activates adenylate cyclase, other 2nd messengers include Ca++ and calmodulin, DAG & IP3, GMP
• Tyrosine kinase mediated


  • Enzyme phosphorylation of receptor
• Trans-activation


  • Receptors in cytoplasm or nucleus, H+R= HR complex, HR dimerize and bind SRE of DNA, translation and protein expression
• Pineal hormones


  • Pineal gland secretes Melatonin, serotonin and others
  • Functions: Circadian rhythm, Reproductive and sexual regulation, Other?
• Physiology of Melatonin Secretion


  Melatonin is a serotonin derivative induced in the absence of light
• Melatonin and Circadian Rhythm


  Melatonin controls biological clock, has anticancer and antioxidant effects
• Hypothalamic hormones


  • Hypothalamus is a collecting center for information concerning internal well-being of body, used to control secretions of many globally important pituitary hormones
• Hypothalamic hormones


  TRH/CRH/GnRH/GHRH-SRIF/PIF
• Thyroid stimulating Hormone


  Stimulates thyroid gland
• Adrenocorticotropin Hormone


  Stimulates adrenal gland
• All tropic hormones are in pituitary and release this hormone to stimulate target gland
• Dopamine


  Only inhibitory neurotransmitter
• Hypothalamic-hypophyseal portal circulation


  • Hormones exit hypothalamus to stimulate or inhibit anterior pituitary secretion of a specific hormone
• Anterior pituitary hormones stimulate testosterone production
• Growth hormone


  Protein polypeptide, secretion is pulsatile, not constant level, peaks 2 hours before midnight
• Somatomedins


  Insulin like growth factors, work by tyrosine kinase receptor similar to insulin
• Factors affecting GH secretion


  • Stimulated by hypothalamus, negative feedback
• GH functions


  • Direct actions, Indirect actions or Somatomedins (IGF) mediated actions: GH induces IGF production
• GH


  Stimulates cellular and linear growth, increases glucose blood synthesis, has diabetogenic effect
• Regulation of GH secretion

  • Pulsatile pattern, variable and uncontrollable
• Gigantism and acromegaly are pathophysiology of excess GH secretion, dwarfism is pathophysiology of deficient GH secretion
• Prolactin


  Chemistry similar to GH, promotes growth of mammary alveoli, has metabolic role
• Prolactin secretion regulation


  Stimulated by GnRH, inhibited by dopamine (PIF)
• Prolactin levels


  Normally inhibited during pregnancy by high estrogen and progesterone, increase after delivery when these drop