CHAPTER 10 : ENDOCRINE SYSTEM

• Endocrine system


  Composed of endocrine glands and specialized endocrine cells located throughout the body
• Endocrine glands and cells


  Secrete minute amounts of chemical messengers called hormones into the bloodstream, rather than into a duct
• Hormones


  Travel through the general blood circulation to target tissues or effectors
• Characteristics of the endocrine system

  • Target tissues have receptors for a specific hormone
  • Hormones produce a particular response in the target tissues
• Classes of chemical messengers

  • Autocrine
  • Paracrine
• Autocrine


  Released by cells and have a local effect on same cell type
• Autocrine example


  • eicosanoids
• Paracrine


  Released by cells that affect other cell types in close proximity
• Paracrine example


  • somatostatin
• Endocrine system functions


  • Regulation of metabolism
  • Control of food intake and digestion
  • Modulation of tissue development
  • Regulation of ion levels
  • Control of water balance
  • Regulation of cardiovascular function
  • Control of blood glucose and other nutrients
  • Control of reproductive functions
  • Stimulation of uterine contraction and milk release
  • Modulation of immune system function
• Types of hormones


  • Water-soluble hormones
  • Lipid-soluble hormones
• Water-soluble hormones


  Include proteins, peptides, amino acids, most common type of hormone
• Water-soluble hormone examples


  • growth hormone, antidiuretic, prolactin
• Lipid-soluble hormones


  Include steroids and eicosanoids
• Lipid-soluble hormone examples


  • Luteinizing hormone, androgens
• Stimuli that control hormone secretion

  • Humoral stimuli
  • Neural stimuli
  • Hormonal stimuli
• Humoral stimuli


  Blood-borne chemicals that can directly stimulate the release of some hormones
• Neural stimuli


  Following action potentials, neurons release a neurotransmitter into the synapse with the cells that produce the hormone
• Hormonal stimuli


  Hormone secretion that, in turn, stimulates the secretion of other hormones
• The same three types of stimuli (humoral, neural, and hormonal) can stimulate or inhibit hormone release
• Control by humoral stimuli

  Blood-borne chemicals directly stimulate hormone release
• Control by neural stimuli


  Neurons release neurotransmitter to stimulate hormone release
• Control by hormonal stimuli


  One hormone stimulates the secretion of another hormone
• Humoral inhibition of hormone release

  Involves the actions of companion hormones, with each performing an opposite function to maintain homeostasis
• Neural inhibition of hormone release

  Inhibitory neurotransmitter prevents the target endocrine gland from secreting its hormone
• Hormonal inhibition of hormone release

  Some hormones are inhibitory, reducing the release of the hormone being controlled
• Example of hormonal inhibition

  • Thyroid hormones can control their own blood levels by inhibiting their anterior pituitary tropic hormone
• Negative feedback


  Hormone's secretion is inhibited by the hormone itself once blood levels have reached a certain point
• Positive feedback


  Exemplified by tropic hormone action
• Most hormones are regulated by negative-feedback mechanism
• Hormone receptors


  A hormone can stimulate only the cells that have the receptor for that hormone
• Receptor site


  The portion of each receptor molecule where a hormone binds
• Receptor specificity


  The receptor site has specificity, allowing only one hormone to bind to it
• Hormone families


  Some hormones, such as epinephrine, can bind to a "family" of receptors that are structurally similar
• Lipid-soluble vs water-soluble hormone receptors

  Lipid-soluble hormones bind to nuclear receptors, water-soluble hormones bind to membrane-bound receptors
• Nuclear receptors


  Can be located in the cytoplasm, but then move to the nucleus when activated
• Hormone-nuclear receptor complex


  Interacts with nuclear DNA to regulate specific gene transcription
• Water-soluble hormone receptors


  Interactions are with membrane-bound receptors, that are proteins that extend across the cell membrane
• Water-soluble hormone receptor activation

  Turns on intracellular enzymes that ultimately cause the response dictated by the hormone-receptor interaction
• Lipid-soluble hormone action


  Stimulate protein synthesis by regulating the transcription of specific mRNA molecules