Describe the control, secretions and functions of
renal andadrenal hormones
This covers the production of adrenal hormones. Information specific to catecholamines receptor function can be found under adrenoreceptors, whilst detailed information on specific agents, including structure-activity relationships, is in the pharmacopeia.
The adrenal glands are paired triangular glands at the superior pole of the kidney. The gland can be divided into:
- Adrenal cortex
Consists of three layers which produce steroid hormones (A good mnemonic is GFR for the layers, and ACT(H) for hormones)
- Zona Glomerulosa
Predominantly produces mineralocorticoids (aldosterone).
- Zona Fasciculata
Predominantly produces glucocorticoids (cortisol).
- Zona Reticularis
Predominantly produces sex steroids (testosterone).
- Zona Glomerulosa
- Adrenal medulla
Aldosterone is the key mineralocorticoid hormone, accounting for 95% of mineralocorticoid activity:
- Release is stimulated by:
- Increased serum K+
- Increased Angiotensin II
- Decreased osmolarity
- Increased ACTH
- Decreased serum pH
- Acts to increase sodium and water retention (and removal of potassium), via:
Cortisol (hydrocortisone) is the primary glucocorticoid in the body, accounting for 95% of endogenous glucocorticoid effect. Cortisol is:
- Produced at ~15-30mg.day-1
- Released in response to ACTH
ACTH is released in response to CRH, which is:
- Released in response to stress
- Modulated by circadian rhythms, and demonstrates diurnal variation:
- CRH peaks just before waking
- CRH troughs during sleep
Cortisol has effects on many organ systems, and in physiological amounts cause:
- Increased sensitivity to catecholamines
- Increases fluid retention
(Essentially anti-insulin effects):
To provide substrates, it also stimulates:
- Decreased glucose uptake
Naturally occurring catecholamines include:
Synthesis of catecholamines occurs in the adrenal medulla, which is a modified sympathetic ganglion composed of chromaffin cells.
- Synthesis and release is dependent on ACh release by the presynaptic neuron
Unlike many other hormones, catecholamine secretion is not a negative-feedback loop.
Process of catecholamine synthesis:
- Tyrosine is concentrated in the adrenal medulla
- Tyrosine is hydroxylated to DOPA by tyrosine hydroxylase
This is the rate-limiting step, and is probably the best enzyme to remember.
- DOPA is decarboxylated to dopamine
- Dopamine is converted to noradrenaline
- Noradrenaline is converted to adrenaline by PNMT (Phenylethanolamine N-methyltransferase)
This may only occur in the adrenal medulla.
Plasma half-lives of noradrenaline and adrenaline are small as a consequence of their metabolism and elimination.
- Extraneuronal uptake in the lungs, liver, kidney, and GIT
- Neuronal uptakeby sympathetic nerve endings
- Inactivation by MAO in nerve cytoplasm
- Inactivation by COMT in the liver and kidney
- Brandis K. The Physiology Viva: Questions & Answers. 2003.
- Chambers D, Huang C, Matthews G. Basic Physiology for Anaesthetists. Cambridge University Press. 2015.