Endocrine physiology

• Hormone


  Achemical substance released by a group of cells to control the function of other types of cells.

  -all cells have the capacity to produce hormones.

  -play a key role in regulating almost all body functions.
• Growth hormone releasing hormone (GHRH)


  Hormone released by the hypothalamus that stimulates the release of growth hormone
• Arcuate nucleus


  • Nucleus in the hypothalamus that releases GHRH
  • Stimulated by high amino acid levels, hypoglycemia, low fatty acids, exercise, healthy stress
• Growth hormone release


  1. GHRH released from arcuate nucleus

  2. Circulates through hypophyseal portal system

  3. Stimulates somatotrophs in anterior pituitary to secrete growth hormone
• Growth hormone (GH)


  Hormone secreted by anterior pituitary in response to GHRH
• Growth hormone binds to receptor


  Activates JAK-STAT signaling pathway
• Insulin-like growth factor-1 (IGF-1)


  Protein produced by liver in response to GH that mediates many of GH's effects
• Effects of IGF-1


  • Increases amino acid uptake in muscle
  • Stimulates protein synthesis in muscle, leading to muscle hypertrophy
  • Increases osteoblast and osteoclast activity, enhancing bone growth and remodeling
  • Stimulates collagen type 1 production in bone
• Growth hormone and IGF-1 play crucial roles in regulating muscle growth and bone development
• Peptide hormones


  Water-soluble hormones that cannot pass through cell membranes
• Steroid hormones


  Lipid-soluble hormones that can pass through cell membranes
• Peptide hormone receptor pathway

  1. Hormone binds to receptor on cell membrane

  2. Receptor activates G-protein

  3. G-protein activates effector enzyme (adenylate cyclase)

  4. Effector enzyme converts ATP to cAMP

  5. cAMP activates protein kinase

  6. Protein kinase phosphorylates target proteins
• 1. protein coupled receptors


  • 7 transmembrane domains
  • Coupled to G-proteins
• 1. stimulatory protein

  2. protein that activates adenylate cyclase when bound to GTP
• GTPase


  Enzyme that converts GTP to GDP, turning off G-protein
• Protein kinase


  Enzyme that phosphorylates target proteins, causing diverse effects
• Steroid hormone receptor pathway

  1. Hormone enters cell and binds to intracellular receptor

  2. Receptor-hormone complex binds to DNA and regulates gene transcription
• Examples of peptide hormones

  • FSH
  • LH
  • Growth hormone
  • Glucagon
  • Parathyroid hormone
  • Insulin
  • Oxytocin
  • ADH
• Examples of steroid hormones

  • Testosterone
  • Estrogen
  • Progesterone
  • Aldosterone
  • Cortisol
  • Vitamin D
  • Thyroid hormones
• GQ protein


  A different type of G-protein from the G-stimulatory protein
• Oxytocin


  Hormone produced by the posterior pituitary gland
• Paraventricular nucleus


  Nucleus in the hypothalamus that secretes oxytocin
• Oxytocin release during childbirth

  1. Stretching of the cervix activates stretch receptors

  2. Stretch receptors send signals to the hypothalamus

  3. Hypothalamus activates the paraventricular nucleus to secrete oxytocin

  4. Oxytocin binds to receptors on uterine smooth muscle cells

  5. Increases intracellular calcium levels

  6. Enhances uterine contractions to push out the baby
• Oxytocin release during breastfeeding


  1. Suckling of the nipple activates mechanoreceptors

  2. Mechanoreceptors send signals to the hypothalamus

  3. Hypothalamus releases oxytocin

  4. Oxytocin binds to myoepithelial cells surrounding milk glands

  5. Increases intracellular calcium levels

  6. Causes contraction of myoepithelial cells

  7. Ejects milk (milk letdown reflex)
• Oxytocin


  Also associated with feelings of love, compassion and emotional bonding (the "cuddle hormone")
• Hypersecretion


  Excessive production of oxytocin
• Hyposecretion


  Insufficient production of oxytocin
• Hypersecretion of oxytocin is rare, but can occur with administration of synthetic oxytocin (pitocin) to induce stronger uterine contractions during childbirth
• Hyposecretion of oxytocin can lead to uterine inertia, where the mother has difficulty pushing the baby out during childbirth
• Rare cases of hyposecretion can also occur due to postpartum hemorrhaging affecting the blood supply to the hypothalamus
• Endocrine glands are ductless
• Target cells


  cells that contain specific receptors for a particular hormone.
• The response of a receptor to a hormone is not static. If placed in low levels of hormone it will behave different that when placed in high levels.

  If you expose a receptor to a hormone where the circadian rhythm has disappeared, the response will be different.
• Peptide hormones

  synthesized in the ER as preprohormone-> posttranslational modification to prohormone-> hormone packaged in the Golgi body.
• Steroid hormones

  usually bound to carrier proteins hence have a longer half-life and slower clearance compared to peptide hormones.

  Alter function of already existing proteins whereas peptide hormones stimulate the production of new proteins.
• Amine hormones


  derived from Tyrosine or Tryptophan.

  • Trp= Melatonin
  • Tyr= catecholamines- behave like peptide hormones
  • Tyr= thyroid hormones- behave like steroid hormones
• Antidiuretic hormone (ADH)


  Also called vasopressin, it is a hormone that regulates water balance in the body
• ADH


  • Produced by the supraoptic nucleus in the hypothalamus
  • Stored and released from the posterior pituitary gland
• Stimuli for ADH release

  • Low blood pressure
  • High plasma osmolality (high solute, low water concentration)
• Osmo-receptors


  Specialized receptors in the brain that detect changes in blood osmolality