Endocrine

• Endocrine System


  System that uses chemical messengers called hormones to regulate the body's internal environment
• Lecture Outline


  • Classification of Hormones
  • Mechanism of Hormonal Action
  • Endocrine Glands, Hormones, and Functions
  • Endocrine Disorders
• Hormones


  Chemical messengers secreted by endocrine glands that regulate the activity of target cells and tissues

  
• Glands


  Organs that secrete hormones and other substances
• Endocrinology


  The study of the endocrine system and its disorders
• Chemical messengers


  Substances that convey signals from one cell to another
• Mechanism of Hormonal Action

  1. Opening or closing channels

  2. Activating second-messenger systems

  3. Activated by first messenger

  4. Relays message to intracellular proteins that carry out dictated response

  
• Types of Chemical Messengers

  • Neurotransmitters and neuropeptides
  • Paracrines
  • Hormones
  • Neurohormones
• Neurotransmitters and neuropeptides


  Short-range chemical messengers that diffuse across narrow space to act locally on adjoining target cell
• Paracrines


  Local chemical messengers that exert effect only on neighboring cells in immediate environment of secretion site
• Hormones


  Long-range messengers secreted into blood by endocrine glands in response to appropriate signal, exerting effect on target cells some distance away from release site

  
• Neurohormones


  Hormones released into blood by neurosecretory neurons, distributed through blood to distant target cells

  
• Differences between Nervous and Endocrine System

  • Not provided

  
• Classification of Hormones


  • Hydrophilic hormones (proteins, peptides)
  • Lipophilic hormones (steroids)

  
• Hydrophilic hormones


  Highly water soluble, low lipid solubility
• Lipophilic hormones


  High lipid solubility, poorly soluble in water
• Peptide Hormone Synthesis


  1. Preprohormones

  2. Prohormones

  3. Active hormones

  4. Storage

  5. Exocytosis
• Steroid Hormones Synthesis


  1. Cholesterol modification

  2. No storage

  3. Release via diffusion

  
• Amine Hormones Synthesis


  1. Tyrosine precursor

  2. Storage (thyroid hormones in thyroglobulin, catecholamines in secretory vessels)

  3. Secretion (thyroid hormones T4 and T3, dopamine, norepinephrine, epinephrine)

  
• Hormonal Transport


  Hydrophilic hormones dissolved in plasma, bound to specific carrier proteins<|>Lipophilic steroids and thyroid hormones bound to plasma proteins like albumin<|>Catecholamines 50% circulate as free hormones, 50% loosely bound to albumin

  
• Mechanism of Action of Hormones


  1. Membrane receptors (hydrophilic peptides and catecholamines alter conformation of adjacent ion channels, activate second-messenger system)

  2. Internal receptors (lipophilic steroids and thyroid hormones bind to hormone response element)

  
• Hormone Regulation


  Effective plasma concentration affected by hormone's rate of secretion, metabolic activation/inactivation, binding to plasma proteins, rate of removal from circulation, and responsiveness of target cell receptors

  
• Hormone-Hormone Interactions


  • Permissiveness (one hormone present in adequate amounts for full exertion of another)
  • Synergism (complementary effects of several hormones)
  • Antagonism (one hormone causes loss of another hormone's receptors)
• Mechanisms of Hormone Regulation

  • Negative-feedback Control
  • Neuroendocrine Reflexes
  • Circadian and Other Biological Rhythms (diurnal, circalunadian, circannual)

  
• Complexity of Endocrine Function
• Endocrine Disrupting Chemicals


  Chemicals from household products and other sources that can mimic, antagonize or otherwise disrupt normal endocrine function
• Nonvertebrate Endocrinology
• Endocrine Disorders


  • Hyposecretion (primary vs. secondary, causes)

  Hypersecretion (primary or secondary, causes)

  Decreased responsiveness of target cells
• Pineal Gland


  Located in the center of the brain, secretes melatonin to regulate circadian rhythm. Suprachiasmatic nucleus and melanopsin also involved in circadian regulation.
• Pituitary Gland


  Located at the base of the brain, makes, stores, and releases hormones. Consists of posterior neurohypophysis and anterior adenohypophysis.

  
• Intermediate Lobe


  Found in some animals, poorly vascularized, secretes MSH
• Anterior Pituitary Hormones


  • Somatotropes (GH)

  Corticotropes (ACTH)

  Thyrotropes (TSH)

  Gonadotropes (LH, FSH)

  Lactotropes (Prolactin)

  
• Prolactin


  Involved in lactation, nurturing of young, reproduction, osmoregulation, growth, metabolism, water drive, metamorphosis, and behavioral effects in birds and mammals
• Posterior Pituitary Hormones


  ADH/Vasopressin (role in water balance, SIADH, diabetes insipidus)

  
• Medical Correlation: SIADH and Diabetes Insipidus
• Roles of Posterior Pituitary Hormones


  Involved in labor, lactation, partner preference, maternal behavior, social cognition, and anxiety. Dysregulation linked to autism.

  
• Endocrine Control of Growth

  Genetic determination of maximum growth capacity, adequate diet, freedom from chronic disease/stress, and normal levels of growth-influencing hormones like insulin, thyroid, and steroids.
• Growth Rate Patterns
• Normal Growth Curve
• Growth Hormone


  Primarily promotes growth indirectly by stimulating liver's production of IGF-I, also has metabolic effects increasing fatty acids and blood glucose.