Basic concepts of endocrine system

Coordination of body functions
1. Neurotransmitters
  1. Released by axon terminals of neurons into synaptic junctions
  2. Act locally to control nerve cell functions
2. Endocrines
  1. Secreted by glands/ specialized cells into the circulating blood
  2. Influence the function of cells at other location in the body
3. Neuroendocrines
  1. Secreted by neurons into the circulation
  2. Influence the function of cells at other location in the body
    1. E.g. hypothalamic hormones
4. Paracrines
  1. Secreted by cells --> extracellular fluid (ECF)
  2. Affect neighbouring cells (i.e. other than those that produced the hormone )
    1. E.g. Action of sex steroid on the ovary
5. Autocrines
  1. Secreted by cells --> ECF
  2. Affect the same cells that produced them (i.e. site of production)
    1. E.g. Release of insulin from pancreatic B-cells can inhibit its release from the same cells
6. Cytokines
  1. Are peptides secreted by cells --> ECF
  2. Can function as autocrines, paracrines/ endocrines
    1. E.g. interleukins
Body's 2nd largest communication system
Serves to REGULATE, INTEGRATE, & COORDINATE diff. physiological processes by means of hormones
Hormonal regulations: 4 areas
1. 1. Digestion, utilization & storage of nutrients
  1. E.g. Gut hormones, insulin
2. 2. Growth & development
  1. E.g. Growth hormones, FSH, LH
3. 3. Water & electrolyte balance
  1. E.g. PTH, aldosterone, ADH
4. 4. Reproductive functions
  1. E.g. Estrogen, testerone
Hormones
1. Mode of action
  1. Def.
    1. Chemical messengers secreted by endocrine organs
    2. Released in small quantities into blood & upon delivery by the circulation to target cell
    3. Act to regulate reactions that elicit a typical response
      1. Endocrine action
2. Chemical structures
  1. 3 categories
    1. Amines & amino acids
      1. Derived from single aa (Tyrosine)
        E.g Norepinephrine & epinephrine
      2. Derived from 2 iodinated tyrosine aa residues
        E.g. Thyroid hormones
    2. Peptides (<20 aa) & Proteins (>20 aa)
      1. Small
        E.g. thyrotropin-releasing hormone (3 aa)
      2. Large & Complex
        E.g. Growth hormone & FSH (approx. 200 aa)
    3. Steroids
      1. Derived from cholesterol
        E.g. Testosterone, oestrogen & progesterone
3. Synthesis
  1. Protein & peptide hormones
    1. Synthesized in rough ER
    2. Usually synthesized as precursor hormone --> modification
      1. E.g. Insulin contains an extra aa when synthesized
    3. Packed & stored in granules/ vesicles by Golgi & secreted when required
    4. May exist as free hormone & circulates unbound in blood/ complexed with specific binding proteins
  2. Steroid hormones
    1. Synthesized in smooth ER/ mitochondria
    2. Certain steroids --> precursors for production of other hormones
      1. E.g. In adrenal cortex: progesterone --> aldosterone, cortisol/ androgens
    3. Carried by specific carrier proteins
4. Metabolism & excretion

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Basic concepts of endocrine system

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	Created by Mandy Ng almost 10 years ago