HORMONAL ACTION

1.   Hormones are molecules:
     -     produced by endocrine glands
     -     secreted into blood stream.
     -     transported all over the body
     -     act on target organs.

2.   2 groups of hormones (according to mode of action):

     -     steroid hormones
     -     peptide hormones

3.   Steroid hormones:

     -     eg: oestrogen, progesterone + testosterone
     -     derived from blood lipid cholesterol.
     -     are lipids
     -     so can enter cells easily
     -     by passing through phospholipids (part of plasma membrane).

 

4.   In cytoplasm:
     -     hormone binds to a protein receptor
     -     forms a hormone-receptor complex
     -     then moves into nucleus
     -     binds to specific region of the DNA.
     -     activates genetic transcription
     -     which produces mRNA
     -     then diffuses out of nucleus
     -     into cytoplasm
     -     binds to ribosomes
     -     translate into protein

 

5.   Peptide hormone:
     -     eg: adrenaline, glucagons + insulin.
     -     derived from amino acids.
     -     are polar (thus cannot enter cells easily)

6.   Peptide hormone:

     -     binds to the protein receptor (on the membrane)
     -     forming a hormone-receptor complex
     -     which then activates a membrane enzyme (adenylate cyclase).
     -     then catalyses the conversion of ATP to cAMP (2nd messenger).
     -     initiates a complex chain reaction (cascade effect)
     -     which simplifies response of the hormone.