Chap. 7 Endocrine System

• Signaling


  Different forms of signaling
• Hormones


  Chemical signals secreted into the circulatory system that communicate regulatory messages within the body

  
• Hormones


  • Reach all parts of the body, but only target cells have receptors for that hormone

  
• Endocrine system


  System that secretes hormones to coordinate slower but longer-acting responses to stimuli

  
• Nervous system


  System that conveys high-speed electrical signals along neurons
• Hypothalamus


  Plays a central role integrating the endocrine and nervous systems

  
• Human endocrine glands


  • Hypothalamus
  • Pineal gland
  • Pituitary gland
  • Thyroid gland
  • Parathyroid glands
  • Adrenal glands
  • Pancreas
  • Ovaries
  • Testes

  
• Organs containing endocrine cells

  • Thymus
  • Heart
  • Liver
  • Stomach
  • Kidneys
  • Small intestine

  
• Polypeptide hormones


  Most hormones are either peptides or proteins
• Amine hormones


  Derived from amino acids
• Steroid hormones


  Produced by the adrenal cortex and the gonads
• Hormone solubility


  Varies in their solubility in aqueous and lipid-rich environments
• Cellular response pathway


  1. Reception

  2. Signal transduction

  3. Response
• Water-soluble hormones


  Secreted by exocytosis, travel freely in the bloodstream, bind directly to cell-surface receptors

  
• Lipid-soluble hormones


  Diffuse across cell membranes, travel in the bloodstream bound to transport proteins, diffuse through the membrane of target cells
• Water-soluble hormone pathway


  1. Hormone binds to receptor protein on target cell surface

  2. Interaction triggers events leading to change in cytoplasmic function or gene transcription
• Lipid-soluble hormone pathway


  1. Hormone penetrates target cell's plasma membrane and binds to intracellular receptor

  2. Signal-receptor complex acts as transcription factor, typically activating gene expression
• Epinephrine pathway


  1. Epinephrine binds to G-protein-coupled receptors on liver cells

  2. Triggers release of messenger molecules that activate enzymes

  3. Results in release of glucose
• Lipid-soluble hormone response is usually a change in gene expression
• Pathway for water-soluble hormones

  1. Binding of a hormone to its receptor

  2. Initiation of a signal transduction pathway

  3. Responses in the cytoplasm

  4. Enzyme activation

  5. Change in gene expression

  
• Pathway for water-soluble hormones

  1. Epinephrine

  2. G protein

  3. Adenylyl cyclase

  4. G protein-coupled receptor

  5. GTP

  6. ATP

  7. cAMP

  8. Second messenger

  9. Inhibition of glycogen synthesis

  10. Promotion of glycogen breakdown

  11. Protein kinase A
• Pathway for lipid-soluble hormones

  The response is usually a change in gene expression<|>Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus<|>Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes
• Hypothalamus


  A region of the lower brain that contains different sets of neurosecretory cells<|>These cells produce neurohormones that are released from the posterior pituitary, or neurohypophysis, and to the anterior pituitary, or adenohypophysis

  
• Posterior pituitary hormones


  • Oxytocin
  • Antidiuretic hormone (ADH)
• Oxytocin


  Induces uterus contractions during childbirth and causes milk ejection during nursing
• Antidiuretic hormone (ADH)


  Increases water retention in the kidneys<|>Maintains blood osmolarity
• Anterior pituitary hormones


  • FSH, follicle-stimulating hormone
  • LH, luteinizing hormone
  • TSH, thyroid-stimulating hormone
  • ACTH, adrenocorticotropic hormone
  • Prolactin
  • MSH, melanocyte-stimulating hormone
  • Endorphin
  • Growth hormone

  
• Tropic hormones


  Hormone produced by one endocrine gland that targets another endocrine gland

  
• Nontropic hormones


  Hormone that directly stimulate target cells to induce effect
• Tropic hormones


  • FSH
  • LH
  • TSH
  • ACTH
• Nontropic hormones


  • Prolactin
  • MSH
  • Endorphin
• Growth hormone (GH)


  Promotes growth directly and has diverse metabolic effects<|>Stimulates the production of growth factors by other tissues
• Non-pituitary hormones


  • Thyroid hormones
  • Parathyroid hormones
  • Insulin and glucagon
  • Adrenal hormones
  • Sex hormones
  • Melatonin
• Thyroid hormones


  Triiodothyronine (T3) and thyroxine (T4)<|>Play crucial roles in stimulating metabolism and influencing development and maturation

  
• Hypothyroidism


  Too little thyroid function, can produce symptoms such as weight gain, lethargy, cold intolerance
• Hyperthyroidism


  Excessive production of thyroid hormone, can lead to high temperature, sweating, weight loss, irritability and high blood pressure
• Goiter


  Enlarged thyroid gland caused by insufficient dietary iodine
• Calcitonin


  Secreted by the thyroid gland, stimulates Ca2+ deposition in the bones and secretion by the kidneys, thus lowering blood Ca2+ levels
• Parathyroid hormone (PTH)


  Has the opposite effects on the bones and kidneys, and therefore raises Ca2+ levels<|>Also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food
• Glucagon


  Produced by alpha cells in the pancreas