HS1 - Adrenal Medulla

L42/43

Adrenal medulla

• Part of the autonomic nervous system

• Specialized ganglia supplied by sympathetic preganglionic neurones (ACh as a transmitter)

• Synthesises catecholamines

• Main site for adrenaline synthesis

• Not essential for life

• Deepest part of adrenal gland

What do adrenal medulla cells release

Adrenaline and noradrenaline

!!! Cateocholiamine synthesis

Noradrenaline is synthesises in 3 steps from tyrosine

!!! What happens to catecholamines after synthesis

Transported into syaptic vesicles using a specialised transporter (vesicular monoamine transporter)

!!! Regulation of catecholamine release

Cortisol can supplement (not replace) SNS activation to help increase adrenaline secretion

If adrenaline has no -ve feedback, how is it reduced

Breakdown of adrenaline in liver and kidneys

Uptake into nerve terminals

!!! systemic effects of adrenaline

Why do we need adrenaline in addition to SNS [check what SNS is] innervation

Phaeochromocytoma

• Excess catecholamines

• Tumour of chromaffin cells

  • Causes over secretion

  OR

• Dramatic episodes

  • Sudden stressor (exercise, rapid posture change)

How is phaeochromocytoma diagnosed

Adrealine is too short-lived to measure directly, so urine is measured for its metabolites (such as VMA)

OR

Scan adrenals using MIBG (iodinated tracer which

mimics noradrenaline and is concentrated into

adrenal medulla cells)

How is phaeochromocytoma treated

Surgery (removal of tumour)

• Catecholamine crisis risk must be managed

  • First, alpha blocker prevents vasoconstriction

  • Second, beta blocker minimises cardiac stimulation

  • Order is important to prevent hypertensive crisis due to inhibition of beta mediated vasodilation

If surgery is not an option, then hypertensive drugs may help

Hypofunction of adrenal medulla

Medulla is no necessary, so no clinical problems who gaf

Adrenal glands summary