17.4 hormone transport

lipid soluble hormones

• steroids, calcitriol, thyroid hormone

• do not dissolve in blood, REQUIRES transport protein

  • transport proteins are water soluble proteins synthesized by the liver

  • also has the added benefit of protecting hormones and preventing early destruction, prolonging biological half-life

  • temporary relationship

• called bound hormone when attached

  • serves as a readily available source

• called unbound (free) hormone when unattached

water-soluble hormones

• most biogenic amines and proteins

• readily dissolve within blood, do NOT generally require transport proteins

  • generally released directly into blood and transported to target cells

blood concentration: hormone release

hormone release and its concentration in blood are positively correlated

• increase in release results in higher blood concentration and vice versa

blood concentration: hormone elimination

typically eliminated thru:

1. enzymatic degradation, usually occurs in liver cells

2. through removal of hormone from the blood by kidneys using urine

3. uptake into target cells

• hormone elimination and blood concentration are negatively correlated

  • faster hm. elimination = lower blood conc. and vice versa

biological half life of a hormone

amount of time necessary to reduce hormone concentration within blood to one half-life of what had been originally secreted

• water-soluble = relatively short half life (few minutes or less to an hour)

• steroids usually = longest biological half-life due to transport protein protection preventing early destruction or loss

  • ex. testosterone HL is about 12 days

• shorter biological HL = more frequently it must be replaced to maintain its concentration in blood