Secretion, transport, and feedback control of hormones
Hormone classes determine everything downstream
| Class | Examples | Receptor | Transport | Half-life |
|---|---|---|---|---|
| Peptide/protein | Insulin, GH, PTH, ACTH, LH/FSH, TSH | Cell surface (GPCR, RTK) | Free in plasma | Minutes |
| Steroid | Cortisol, aldosterone, sex steroids, vitamin D | Nuclear | Carrier protein bound | Hours |
| Amine - thyroid | T4, T3 | Nuclear | TBG, albumin, transthyretin | Days (T4 ~7d) |
| Amine - catecholamine | Adrenaline, noradrenaline | Cell surface | Free | Seconds |
- Peptide hormones are stored in granules and released on demand; steroid hormones are synthesised on demand and cannot be stored
- Only the free fraction is biologically active - anything that changes binding protein changes the total but not the free level
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