Endocrine: Steroid Hormones - some facts for Step 1

·         Derived from Cholesterol

·         They all have similar structures

·         Only made in few organs for example

o   Adrenal cortex

o   Gonads produce sex hormones

Steroid Hormone Synthesis and Release

·         Cells that secrete steroid hormones have abundant SER

·         SER – location of steroid synthesis

·         Lipophilic and therefore easily diffuse across the cell membrane

·         Synthesized as needed EXCEPT for thyroid hormones

Transport in the blood & half life of steroid hormones

·         Lipophilic – not soluble in plasma

·         Most steroid hormones are bound to protein carrier molecules

o   Some have specific carriers – corticosteroid binding globulin

o   Others simply bind to general plasma protein – ie: albumin

o   Exception – adrenal androgens – no carrier proteins      

·         Half life of steroids are much longer than that of peptide hormones

·         There is always and equilibrium between bound hormones and unbound hormones.  So the ratio between the two in the plasma is constant.  Carriers release the hormone and they then simply diffuse across the cell.

·         Unbound (free) hormones are available to tissues

·         Free form creates the negative feedback à regulated!