- 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).
- 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.