endorcrine

• Endocrine system


  Regulates the body using chemical messengers (hormones) secreted by cells
• Nervous system


  Regulates the activity of muscles and glands via electrochemical impulses (action potentials)
• Differences between endocrine and nervous systems


  • Endocrine system: Influence/regulate the system by use of chemical messengers
  • Nervous system: Regulates activity of muscles and glands via electrochemical impulse

  
• Hormones


  Molecules released into the blood that act as chemical messengers to regulate specific body functions
• Major processes controlled by hormones


  • Reproduction
  • Growth and development
  • Maintenance of electrolyte, water and nutrient balance in the blood
  • Regulation of cellular metabolism and energy balance
  • Mobilization of body defenses

  
• Endocrinology


  The scientific study of hormones and the endocrine organs

  
• Types of glands


  • Exocrine glands (non-hormonal substances)
  • Endocrine glands (ductless glands that produce hormones)
• Endocrine system


  Regulates the body using chemical messengers (hormones) secreted by cells
• Nervous system


  Regulates the activity of muscles and glands via electrochemical impulses (action potentials)
• Differences between the endocrine and nervous systems


  • Endocrine system: Influence/regulate the system by use of chemical messengers; Secreted by cells
  • Nervous system: Regulates activity of muscles and glands via electrochemical impulse (action potentials)
• Hormones


  Molecules released into the blood that act as chemical messengers to regulate specific body functions
• Major processes controlled by hormones


  • Reproduction
  • Growth and development
  • Maintenance of electrolyte, water and nutrient balance in the blood
  • Regulation of cellular metabolism and energy balance
  • Mobilization of body defenses
• Endocrinology


  The scientific study of hormones and the endocrine organs
• Types of glands


  • Exocrine glands: non-hormonal substances (sweat/saliva); Carry substances to a membrane surface
  • Endocrine glands: ductless glands; produce hormones. Release their hormones into surrounding tissue fluid.
• Examples of endocrine glands


  • Pituitary
  • Thyroid
  • Parathyroid
  • Adrenal
  • Pineal

  
• Example of neuroendocrine gland

  • Hypothalamus

  
• Examples of non-endocrine organs that contain endocrine tissue


  • Pancreas
  • Gonads (ovaries/testes)
  • Placenta
  • Heart
  • Kidney
  • Adipose tissue
  • Thymus
• Pancreatic Islets (Islets of Langerhans)


  Scattered clusters of endocrine cells within the pancreas, containing beta cells that produce insulin and alpha cells that produce glucagon
• Thyroid gland


  Consists of numerous follicles, with scattered clusters of endocrine cells called C cells or parafollicular cells that produce calcitonin

  
• Adrenal glands


  Contain the adrenal cortex and adrenal medulla, with small clusters of endocrine cells in the medulla that release adrenaline (epinephrine) and noradrenaline (norepinephrine)
• Pineal gland


  Located in the brain, contains scattered pinealocytes that produce melatonin
• Gastrointestinal tract


  Contains scattered endocrine cells in the mucosa that release hormones like gastrin, secretin, and cholecystokinin to regulate digestive processes
• Hypothalamus


  Contains scattered neurosecretory cells that produce and release hormones that control various functions of the pituitary gland

  
• Heart


  Contains scattered endocrine cells called atrial natriuretic cells in the atria that release atrial natriuretic peptide (ANP) in response to increased blood pressure
• Skin


  Contains some scattered endocrine cells that release hormones involved in melanin production and skin pigmentation regulation
• Testes and ovaries


  Contain scattered endocrine cells that produce sex hormones like testosterone, estrogen, and progesterone
• Kidneys


  The juxtaglomerular apparatus contains clusters of endocrine cells that release renin, an enzyme involved in blood pressure regulation
• Autocrines


  Short-distance chemical signals that exert effects on the same cells that secrete them
• Paracrines


  Short-distance chemical signals that affect other cells in the same tissue, other than the ones that secreted the chemicals
• Three major types of hormones & hormone-like structures


  • Amino acid-based (majority): biogenic amines, peptides, proteins
  • Steroid-based: derived from cholesterol
  • Eicosanoids: hormone-like structures made from arachidonic acid
• Hormones act through two major mechanisms


  Second messengers or by activating specific genes
• Cyclic AMP signaling mechanism


  1. Hormone binds receptor

  2. Receptor activates G protein

  3. G protein activates adenylate cyclase

  4. Adenylate cyclase converts ATP to cyclic AMP

  5. Cyclic AMP activates protein kinases
• Cyclic AMP


  A common second messenger that can have many different effects in different cells, depending on the specific protein kinases and substrates available
• PIP2-calcium signaling mechanism


  Phospholipase C splits PIP2 into diacylglycerol (DAG) and inositol triphosphate (IP3), which releases calcium ions that act as a second messenger
• Insulin signaling


  Insulin receptor is a tyrosine kinase enzyme that is activated when insulin binds, providing docking sites for intracellular relay proteins that initiate a series of protein phosphorylations to trigger specific cell responses
• Lipid-soluble hormones


  Can diffuse through the cell membrane to bind to intracellular receptors and directly activate genes
• IP3


  Releases Ca2+ from intracellular storage sites = Free Calcium
• Ca2+ takes on second messenger role


  1. Directly alters the activity of specific enzymes & channels

  2. Binds to intracellular regulatory protein, calmodulin
• cGMP


  Cyclic guanosine monophosphate. Second messenger for selected hormones
• Insulin


  Hormone that works without second messengers