Endocrine

• Endocrine system


  Involve secretory cells which lack outflow ducts
• Modes of hormone delivery

  • Endocrine
  • Neuroendocrine
  • Paracrine
  • Neurocrine
  • Autocrine
• Chemical classes of hormones

  • Peptide hormones
  • Amines
  • Steroids
  • Iodothyonines
• Receptor Signal Transduction


  1. Recognition

  2. Transduction

  3. Action of second messenger (e.g. cAMP)
• Intracellular hormone receptors


  • Typical for steroid and thyroid hormones
  • Lipid-soluble hormones pass through cell membrane
  • Hormone molecules bind to specific cytosolic receptors
  • Formed complex binds to specific regions on genes/DNA
  • Transcription of mRNA is initiated and gene expression is controlled
• Primary response


  Direct regulation of transcription of only a small number of genes by hormone-receptor complex
• Secondary response


  Activation of other genes by protein products of primary response
• Permissive action


  Requirement of presence of a hormone for other hormones to exert effects
• Antagonistic effects


  Opposing effects of two different hormones on same target cell or tissue
• Synergism


  Enhanced response of tissue/organ to combination of at least two hormones, exceeding individual actions
• Endocrine glands develop from embryonic Rathke's pouch and the type of tissues are epithelial
• Hormones released by neurohypophysis are synthesized by the hypothalamus (from nervous tissue)
• Adrenal cortex of amniotes is equivalent to interrenal organs of bony fishes
• In fishes, there are fewer and larger islets within the pancreas or along the bile duct
• Mammalian ovaries also produce relaxin which is a nonsteroid hormone
• All vertebrates have androgens
• Pineal gland functions as a photoreceptor in lower vertebrates
• Juxtaglomerular cells are analogous to the teleost UROPHYSIS (which produce urotensins) and the corpuscles of Stannius in fish kidneys
• Ultimobranchial bodies are found in all vertebrates except mammals and agnathans; homologous with thyroid parafollicular cells in mammals
• Thyroxin (T4) and triiodothyronine (T3) are secreted by the thyroid gland.
• Chemical messenger


  Any substance produced by a cell and plays a physiological role in the control of the activity of another cell

  
• Hormone


  • Any substance elaborated by one cell to regulate another cell
  • Serve as the body's chemical messengers
• Tropic Hormone


  Hormone which regulates the secretions of other endocrine tissues or organs
• Neurohormone


  Hormone produced by a nerve cell
• Neuropeptide


  Peptidergic neurohormone (i.e. a neurohormone comprised of chains of amino acids)
• Neuromodulator


  Hormone that modulates the response of a neuron to a neurotransmitter or another hormone
• Neuroregulatory


  Generalized term for any neurohormone that acts as a neurotransmitter or neuromodulator

  
• Pheromones


  Chemical messengers released to the exterior of an animal to stimulate a response in another member of the same species
• Lumones


  Chemical messengers released into the lumen of the gastrointestinal tract
• Chalones


  • Putative cellular mitotic inhibitors
  • Inhibit the proliferation of immature cells
• Growth factors


  • Mitogenic substances
  • Can affect the growth of cells that promote or inhibit mitosis
• The endocrine systems involve secretory cells which lack outflow ducts
• Half-life of a hormone

  Duration of time required to decrease the concentration of a circulating hormone by half

  
• Oxytocin is a peptide hormone with a half-life of a few hours
• Growth hormone can last several days to several months, depending on the organisms and amount of growth hormone released
• Factors influencing hormone concentrations in the blood

  • Rate of hormone synthesis & secretion from the source gland into the blood
  • Rate of removal of the hormone from the blood
• Ways hormones are cleared from the plasma

  • Metabolic destruction
  • Binding with the tissues
  • Excretion by the liver into the bile
  • Excretion by the kidneys into the urine

  
• Endocrine mode of hormone delivery

  • Source cell: endocrine gland (usually epithelial)
  • Hormones are released by the endocrine gland and into the bloodstream such that they can be transported to the target tissue
• Neuroendocrine mode of hormone delivery

  • Source cell: nerve cell
  • Neurohormones are released into the bloodstream for transmission
• Neurocrine mode of hormone delivery

  • Source cell: neuron
  • Target cell: neuron
  • Exhibited via chemical synapses
  • Neurotransmitters are the chemical messengers being delivered from the presynaptic cell to the postsynaptic cell