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Endocrinology > Adrenal medullary > Flashcards

Adrenal medullary Flashcards

1
Q

What is the adrenal medulla?

A

It is the specialist endocrine organ, part of the sympathetic nervous system, composed mainly of chromaffin cells. It deals with physical emotion and stress

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2
Q

Describe the nerve supply of the adrenal medulla?

A
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3
Q

What hormones are released by the cells of the adrenal medulla?

A

The hormone secretion by the adrenal medullary involves catecholamines from chromaffin cells.

  • Adrenaline synthesised in medulla
  • Noradrenaline synthesis in medulla, PNS and CNS
  • Dopamine synthesied by NS, and some by medulla
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4
Q

What allows quick release of hormones in the adrenal medulla?

A

Because the ANS, specifically the sympathetic division, exerts direct control over the chromaffin cells, the hormone release can occur rather quickly.

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5
Q

How are catecholamines released?

A

Catecholamines are stored in intracellular granules of the medull, which exocytose into the blood stream in response to acetylcholamine from the splanchnic nerve

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6
Q

How are catecholamines synthesised?

A

The adrenal medulla is the principal site of the conversion of the amino acid tyrosine into the catecholamines; epinephrine, norepinephrine, and dopamine.

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7
Q

What is cortisols role in the metabolism of catecholamines?

A

Cortisol is present in high concentrations in most of the medulla due to venous blood flow from the cortex. Cortisol stimulate PNMT activity (last enzyme of pathway), which ensures the metabolism goes to completion

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8
Q

What two enzymes are crucial in the metabolism of catecholamines? (dopamine->nor/adrenaline->mets)

A

The metabolism occurs quite rapidly as it is catalysed by catechol-o-methyltransferase (COMT) and monoamine oxidase (MAO).

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9
Q

Why is it important for the metabolism of catecholamines to be rapid?

A

Prolonged expression can cause congestive heart failure.

- MAO deactivates hormones

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10
Q

How are the waste products of catecholamines lost?

A

Further modification by adding sulphates allow them to be excreted in the urine -> investigations

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11
Q

What is the biochemical effect of catecholamines?

A

The catecholamines are important in emergencies, emotional reactions, hypoglycaemia, fasting, thermogenesis, blood pressure and shock. The catecholamines do not act alone, but rather through interactions with other hormones: insulin, glucagon, cortisol, renin, and thyroxine.

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12
Q

How do catecholamines exert their function?

A

By binding to adrenergic receptors. The classes of receptors are: alpha (1,2,3) or beta (1,2). Each one stimulates a seperate effector

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13
Q

Describe noradrenalines actions

A

Synthesised as a sympathetic neurotransmitter

  • stimulates vascular alpha1 causing hypertension and increased cardiac contraction, dilation of pupils
  • Stimulates non-thermoregulatory stress sweat glands
  • Increased affinity for beta1 causing increased cardiac contraction and rate
  • Less affinity for beta-2 causes vasodilation and hepatic glyconeogenesis
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14
Q

Describe adrenalines actions

A

Stimulates both alpha-1 and beta-1 receptors with the same effects as noradrenaline. Adrenaline also activates beta2 receptors causing vasodilation in skeletal muscle with variable effect on BP

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15
Q

Overall effect of adrenaline release

A

Stimulates hepatic glycogenolysis, lipolysis, and increases the basal metabolic rate (things during stress to serve during flight or fight resposne).

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16
Q

What are some catecholamine secreting tumours?

A

Phaeochromocytoma and paraganglioma (PPGL)

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17
Q

What are phaeochromocytomas?

A

Tumour arising from adrenomedullary chromaffin cells that commonly secrete one or more catecholamines.

18
Q

What are paragangliomas?

A

A tumour arising from extra adrenal chromaffin cells of the sympathetic paravertebral ganglia.

19
Q

What are the clinical symptoms during/following paroxysms (PPGL/phaeo)?

A
  • hypertension,
  • headache,
  • sweating,
  • forceful heartbeat,
  • anxiety,
  • tremor,
  • fatigue,
  • nausea,
  • abdominal chest pain and visual disturbances.
20
Q

What are the clinical symptoms between paroxysms (PPGL/phaeo)?

A
  • increased sweating,
  • cold hands and feet,
  • weight loss and constipation.
21
Q

What is meant by paroxysms?

A

Sudden attack - release of catecholamines

22
Q

What genetic conditions are associated with PPGLs?

A
  • Multiple endocrine neoplasia type II (MEN2)
  • Von Hippel-Lindau disease
  • Von Recklinghausen Neurofibromatosis
  • Familial parangliomas
  • MAX mutations
  • TMEM127 mutations
23
Q

What are MEN2?

A

Multiple endocrine neoplasia T2 (MEN2) is a mutation in the RET protooncogene. Two subtypes a and b. MEN2A causes hyperparathyroidism, MTC and phaeocytochromas. MEN2B same as 2A but mucosal neuromas and marfanoid body habitus

24
Q

What is Von Hippel-Lindau disease?

A

Caused by a mutation of VHL suppressor gene.

- Develop hemangioblastomas in the retina, cerebellum and spinal cord plus phaeocytochromas

25
Q

What is Von Recklinghausen Neurofibromatosis ?

A

Visible subcutaneous neurofibromas due to a mutation in NF-1 tumour suppressor gene. 5% develop phaeocytochromas.

26
Q

What is familial parangliomas?

A

caused by mutations in the genes of the mitochondrial complex II, succinate dehydrogenase (SDH).

  • SDHB causes multiple adrenal phaeochromocytoma, head and neck paragangliomas plus renal cell carcinoma
  • High frequency of malignancy
  • Mutation in SBHC causes head and neck paragangliomas
  • Mutations to SBHD cause adrenal phaeochromatocytoma, head and neck paraganglioma and extra renal paragangliomas
27
Q

What tumours are formed by MAX and TMEM127 mutations?

A

Adrenal tumours

28
Q

What are neuroblastomas?

A

These are malignant aggressive tumours of the medulla. Secretes dopamine, HVA or methoxytyramine.

29
Q

How are neuroblastomas treated?

A

Either surgery, chemo, radiotherapy or biotherapy

30
Q

Who should be screened for PPGLs?

A

The risk groups

  • Severe hypertension (180/120)
  • young hypertensives
  • hypertensive patients with suspicious symptoms
  • radiological evidence of adrenal mass
  • patients with genetic conditions
  • family history of PPGL
31
Q

What inital biochemical analysis is available to diagnose PPGLs?

A
  • Initial testing should include urinary fractioned metadrenalines or plasma free metadrenalines
  • Measuring metadrenalines is superior to catecholamines because catecholamines are unstable.
32
Q

Following positive inital test, what is an appropriate follow up test for PPGLs?

A
  • Elevations in both mets and normets do not require follow up tests.
  • Rest requires clonidine stimulation test to distinguish between true positives from false negatives
33
Q

What sample types are most appropriate for PPGL tests?

A

Urine or plasma

34
Q

What urine test is taken in PPGL investigations?

A

24hr urine sample to ensure no attacks are missed

- Collected in an acid bottle and measured using HPLC with either ED or MS/MS

35
Q

What cautions have to be taken for the plasma sample type for PPGL?

A

Highly unstable so must be stored in a fridge 15min from collection. Must be spun within 6h of collection.

36
Q

What are some interferences to the biochemical testing?

A

Medical conditions

  • heart failure
  • MI
  • sleep apnoea

Others:

  • exercise
  • diets
  • emotional stress
37
Q

Describe the diagnosis of PPGL

A
  • Measure urinary fractionated metadrenalines and normetadrenaline in a 24hr urine test
  • A solitary increase >3x upper reference limit indicates PPGL likely - followup are imaging
  • Whilst a solitary increase in either met or normet<3x could be a false possitive so repeat could be necessary. If the repeat is on the boarderline then undertake a clonidine stimulation test
38
Q

What is the clonidine suppression test?

A

Clonidine is a alpha2 adrenoreceptor agonist inhibiting neuronal noradrenaline release in healthy patients.

  • 20min after supine rest take plasma sample for metadrenalines
  • Administer clonidine orally at does of 300ug/70g.
  • After 3 hours measure plasma metadrenalise

Intepretation
- Normal test indicate suppression of normets by more than 40%

39
Q

Why is important to have elucidated all the information about the PPGL before doing a genetic investigation?

A

Allows the user to find the genetic defect quicker and at a lower cost

40
Q

Treatment of PPGL

A

Pre-operative management

  • Ensure the patient does not suffer from the other biochemical complications associated with the disease
  • Patients need to be treated with oral antihypertensives, alpha blockers (e.g. phenoxybenzamine) are the first choice but beta-blockers, calcium channel blockers and ACE inhibitors can be used.
41
Q

What are some post operative risks of PPG?

A

Patients are at risk of hypertensive crisis before surgery and hypotensive after

Endocrinology (12 decks)

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