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Endocrinology 2nd major control system in the body
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Endocrinology 2nd major control system in the body

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  • 1. Endocrinology
    • 2 nd major control system in the body
    • “study of chemical messengers (hormones) secreted by endocrine glands and other tissues”
    • major role: to maintain homeostasis
    • coordinates many processes:
      • metabolism, respiration, excretion, reproduction
  • 2. Homeostasis
    • concept of Claude Bernard
    • individuals live with 2 environments:
      • external milieu
      • internal milieu
    • bodies control internal milieu > allows independence from external milieu
  • 3. Homeostasis
    • contents of “fluid environment”:
      • glucose
      • amino, fatty acids
      • Electrolytes
    • result: wide distribution of mammals to all types of habitats
  • 4. Feedback systems
    • endocrine and other sensory cells have “setpoint” for monitoring substances in blood
    • low levels > hormone released (e.g. Ca 2+ and parathyroid hormone)
    • some systems shut off due to negative feedback
    • some are regulated by positive feedback
  • 5.  
  • 6. Other mechanisms of regulation
    • Actions of opposing hormones
      • PTH and calcitonin
      • glucagon and insulin
    • the brain / pituitary connection
      • time of day
      • temperature
      • nutrition
  • 7. Types of cellular communication
  • 8. Subcategories of hormones
    • Neurohormones: produced by nerve cells
      • Neuropeptides
      • Nonpeptidergic neurohormones
      • Neuromodulators
  • 9.
    • Pheromones:
      • Released to exterior of animal
      • Modulates response of another animal
    • Lumones: released into lumen of GI tract
    • Chalones: inhibit mitosis
    • Growth factors: mitogenic peptides
    Subcategories of hormones, cont’d.
  • 10. Protein and peptide hormones
    • Made of amino acids
    • Variable in size (e.g., TRH=3 amino acids)
    • Ring structures may be present (e.g., oxytocin, vasopressin)
    • Many synthesized in precursor form > modified prior to secretion (e.g., insulin; Fig. 1.8)
    • Some consist of two peptide chains (e.g., pituitary glycoproteins)
    • Possible glycosylation
    • Transmembrane receptors
  • 11. Hormones derived from tyrosine
    • Enzymes present in cells determine which catecholamine will be synthesized
    • Tyrosine > DOPA > dopamine > norepinephrine > epinephrine (handout)
    • Catecholamines can be hormones, neurotransmitters
    • Transmembrane receptors
    • Thyroid hormones (thyroxine, triiodothyronine) also derived from tyrosine
      • T3 > 2 tyrosines with 3 iodine atoms (Fig. 5.3)
      • T4 > 2 tyrosines with 4 iodine atoms
    • Nuclear receptors
  • 12. Steroid hormones
    • Derived from cholesterol
    • Glucocorticoids (e.g., cortisol), mineralocorticoids (aldosterone)
    • Gonadal steroids (progesterones, androgens, estrogens)
    • “ generational” relationships
    • Enzymes present in cell determine steroids produced
    • nuclear receptors
    • bind to proteins in blood > extends half-life
    • in liver, conjugated to glucuronic acid or sulfated > inactivated
  • 13. Terms to include:
    • DNA, gene, codon, structural gene (“coding sequence”), regulatory regions, introns, exons
    • Transcription, RNA polymerase, RNA, mRNA
    • Translation, ribosomes, tRNA, amino acids, amino terminus, carboxy terminus
  • 14. Peptide synthesis
    • nucleotide sequence of gene dictates amino acid sequence of peptide
    • sequence is transcribed into RNA
    • introns splicing occurs
    • mRNA leaves nucleus
    • translation occurs on ribosomes
    • peptides transported to RER and then Golgi for modification(s) and packaging
  • 15.  
  • 16. Prohormones
    • “ precursors” to peptide hormones
    • often, peptides are spliced from much larger hormones
    • examples:
      • oxytocin
      • gonadotropin-releasing hormone (GnRH)
    • precursors are packaged with endopeptidases in secretory vesicles
  • 17.  
  • 18. Peptide circulation and metabolism
    • half-life = time required for half of molecules to be cleared / inactivated
    • short a.a. sequence > short half life
    • inactivated by peptidases
    • drug design
    • peptides activate membrane-bound receptors on target cells

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