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