ENDOCRINOLOGY

• Endocrine system is a network of ductless glands that secrete hormones directly into the blood.
• Endocrine system is controlled by hormones synthesis instead of the degradation.
• Hormones - a chemical signals produced by specialized cells secreted into the blood stream and carried to a target tissue.
• Hormones

  Major Functions:

  1. To maintain the constancy of chemical composition of extracellular and intracellular fluids.
  2. Control metabolism, growth, fertility
  3. response to stress
• The majority of endocrine functions are regulated through the pituitary gland, which in turn is controlled by secretion from the hypothalamus.
• 2 feedback mechanism of hormones:

  1. Positive feedback system (PFM)
  2. Negative feed back system (NFM)
• Positive Feedback system - it is a system in which an increase in the product results to elevation of the activity of the system and the production rate.
• Give example of PFM.

  Gonadal, thyroidal, adrenocortical hormone
• Negative feedback system - it is a system in which an increase in the product results to decreased activity of the system and the production.
• Types of NFM:

  1. Long FM
  2. Short FM
  3. Ultrashort FM
• Types of Hormone ACTION

  1. Endocrine
  2. Paracrine
  3. Autocrine
  4. Juxtacrine
  5. Intracrine
  6. Exocrine
  7. Neurocrine
  8. Neuroendocrine
• Endocrine

  • Secreted in one location and released into blood circulation.
  • Binds to a specific receptor to elicit physiological response.
• Paracrine

  • Secreted in endocrine cells and released into interstitial space.
  • Binds to a specific receptors in adjacent cell and affects its function.
• Autocrine

  • Secreted in endocrine cells and sometimes released into interstitial space.
  • Binds to specific receptor on cell of origin resulting to self-regulation of its function.
• Juxtacrine

  • Secreted in endocrine cells and remains in that same cellular space in relation to plasma membrane.
  • acts on immediately adjacent cell by direct cell-to-cell contact.
• Intracrine

  • Secreted in endocrine cells and functions inside the origin of synthesis.
• Exocrine

  • Secreted in endocrine cells and released into lumen of gut, and affects their functions.
• Neurocrine

  • secreted in neurons and released into extracellular space.
  • Binds to a receptors in nearby cell and affects its function.
• Neuroendocrine

  • secretd in neurons and released from nerve endings
  • interact with receptors of cells at distant site.
• 3 classification of hormones (according to composition or structures)

  1. Peptides and proteins
  2. Steroids
  3. Amines
• Classification of hormones

  Water-soluble: Peptides and proteins

  Wtaer-insoluble: steroids
• Peptides and proteins - cannot cross the cell membrane due to their large molecular size.
• In steroids, cholesterol as a common precursor.
• Amines - intermediary between steroids and protein hormones. Derived from an amino acid.
• Examples of amines;

  1. Epinephrine
  2. Norepinephrine
  3. Triiodothyronine
  4. Thyroxine
• Examples of steroids:

  (CAP.TEA)

  1. Aldosterone
  2. Cortisol
  3. Estradiol
  4. Progesterone
  5. Testosterone
  6. Activated Vitamin D3