Adrenal Medulla Flashcards
1
Q
What are the parts of Nervous System?
A
- Central and Peripheral: The central nervous system (CNS) includes the brain and spinal cord, and the peripheral nervous system (PNS) is all the nerves that branch out from the spinal cord and the brain and travel throughout the body.
- Somatic and Autonomic: The somatic nervous system regulates the movement of skeletal muscles, and the autonomic nervous system controls involuntary actions such as heart rate, digestion, and perspiration.
2
Q
What is the role of the autonomic nervous system?
A
- Regulates the operation of the internal organs to support the activity of the body as a whole.
- Not under voluntary control.
- Divided into two parts.
3
Q
What is the role of Autonomic Nervous System?
A
Parasympathetic Nervous System: Promotes restorative functions
- Constricts pupils
- Constricts bronchi
- Decreases heart rate
- Increasing digestion
Sympathetic Nervous System: Prepares the body for activity
- Dilates pupils
- Dilates bronchi
- Increasing heart rate
- Decreasing digestion
- Increase metabolism, inc glucose
- Increasing blood to muscles
4
Q
How is signal communication in the nervous system?
A
- Neurones are the principle functional unit of the nervous system – collection of neurones form nerves.
- The communication between neurones and target cells occurs at synapses.
- Neurotransmitters (NTs) are vital for this communication and examples include adrenaline, noradrenaline, acetylcholine and glutamate.
5
Q
How does the ANS communicate?
A
6
Q
What are adrenal medulla?
A
- Lie in the retroperitoneum above the upper poles of the kidneys. Medulla comprises about 10% of the weight.
- Specialist endocrine organ, part of the sympathetic nervous system, composed mainly of chromaffin cells.
- Non-essential organ, however it helps you deal with physical emotion or stress.
7
Q
What is the nerve and blood supply to the Adrenal medulla?
A
Nerve Supply
- The adrenal medulla is innervated by pre-ganglionic fibres of the sympathetic NS.
- These release acetylcholine and enkephalines at their synapses.
Blood Supply
- The adrenal gland derives blood from the adrenal branches the inferior phrenic artery.
8
Q
What Hormones of the Adrenal Medulla?
A
The adrenal medulla secretes catecholamines from chromaffin cells.
- Adrenaline is synthesised mainly in the medulla.
- Noradrenaline synthesised by medulla, CNS and PNS.
- Small amounts of dopamine are produced by the medulla, but it is mostly produced in the NS.
9
Q
How is secretion of Catecholamines controlled?
A
Catecholamines are found in the adrenal medulla stored in intracellular granules.
- Secreted by exocytosis into the bloodstream in response to acetylcholine from the splanchnic nerve.
- Cortisol stimulates PNMT activity. Cortisol is present in high concentrations in most of the medulla due to venous blood flow from the cortex.
10
Q
What is importance of Catecholamines?
A
- Emergencies and emotional reactions
- Hypoglycaemia, fasting
- Thermogenesis
- Blood Pressure
- Shock
11
Q
What are Adrenergic Receptors?
A
Catecholamines work by stimulating adrenergic receptors. These are transmembrane proteins which couple to G proteins. Various classes and subclasses of adrenergic receptors:
- Alpha 1
- Alpha 2
- Alpha 3
- Beta 1
- Beta 2
These different classes allow the same catecholamine to exert differing effects on different effector cells.
12
Q
What is the action of Noradrenaline?
A
- Synthesised mostly as a sympathetic neurotransmitter.
- Stimulates non-thermoregulatory ‘stress’ sweat glands.
- Stimulates vascular α1-adrenergic receptors causing hypertension, increased cardiac contraction and dilatation of the pupils
- ↑ Affinity for β1 – increases cardiac contraction and rate
- Less affinity for β2 – vasodilation and hepatic glycogenolysis.
- β3 receptors on fat cells are also stimulated.
13
Q
What is the action of Adrenaline?
A
- Stimulates α1 - causing hypertension, increased cardiac contraction and dilatation of the pupils
- β1 receptors - increases cardiac contraction and rate
- Adrenaline activates β2 receptors causing vasodilatation in skeletal muscle so variable effect on BP.
- Stimulates hepatic glycogenolysis, lipolysis and increases the basal metabolic rate.
14
Q
What is Phaeochromocytoma and Paraganglioma (PPGL)?
A
- Phaeochromocytoma – Is a tumour arising from adrenomedullary chromaffin cells that commonly secrete one or more catecholamines.
- Paraganglioma – Is a tumour arising from extra adrenal chromaffin cells of the sympathetic paravertebral ganglia.
15
Q
What are Paraganglioma?
A
- Incidence is 2 to 8 per million per year.
- Prevalence of PPGL in patients with hypertension is 0.2 – 0.6%.
- More common in 4th and 5th decades of life, but can occur at any age.
- 10% Malignant, 10% bilateral, 10% extra-adrenal.
- At least 1/3 have a genetic component.
- They are rarely biochemically silent.
16
Q
What are symtpms during or following Paroxysms?
A
- Hypertension
- Headahe
- Sweating
- Forceful heart beat with or without tachycardia
- Anxiety or fear of impending death
- Tremor
- Fatigue or exhaustion
- Nausea or Vomiting
- Abdominal or Chest Pain
- Visual disturbances
17
Q
What are symtpms during or following Paroxysms?
A
- Increased sweating
- Cold hands and feet
- Weight loss
- Constipation
18
Q
What are Genetic conditions associated with PPGLs?
A
Multiple Endocrine Neoplasia Type 2
- Mutation in the RET protoncogene
- Two subtypes (a and b), in either subtype phaeosdevelop.
- MEN 2A – Hyperparathyroidism, MTC and phaeo
- MEN 2B – As 2A but mucosal neuromas and marfinoidbody habitus
Von Hippel-Lindau Disease
- Mutation of VHL suppressor gene. Develop hemangioblastomas in the retina, cerebellum and spinal cord plus phaeo.
Von Recklinghausen’s Neurofibromatosis
- Patients develop visible subcutaneous neurofibromas. Due to mutation in NF-1 tumour suppressor gene. 5% develop phaechromacytos.
Familial Paragangliomas
- Mutations in the genes of the mitochondrial complex II, succinate dehydrogenase (SDH).
- SDHB – Multiple adrenal phaeochromocytoma, head and neck paragangliomas plus renal cell carcinoma. High frequency of malignancy.
- SDHC – Head and neck paragangliomas
- SDHD – Adrenal phaeochromocytoma, head and neck paraganglioma and extra-adrenal paragangliomas.
MAX and TMEM127 Mutations
- Adrenal tumours.
19
Q
What are Neuroblastoma?
A
15% Paediatric oncology deaths.
- Malignant, aggressive tumours.
- Most primary tumours arise in the abdomen with at least half occurring in the medulla.
- Dopamine, HVA or methoxytyraminereleased in most cases.
- Patients are treated with surgery, chemotherapy, radiotherapy and biotherapy
20
Q
Which patients should be screened for PPGL?
A
- Patients with severe hypertension
- Hypertensive patients with suspicious symptoms
- Young hypertensives
- Radiological evidence of adrenal mass
- Family History of PPGL
21
Q
How are PPGL’s biochemically tested?
A
Initial biochemical testing for PPGLs should include measurement of urinary fractionated metadrenalines or plasma free metadrenalines.
- Measurement of metadrenalines is superior to catecholamines. Due to conversion to o-methylated metabolites in chromaffin cells.
- Initial evidence showed plasma free metadrenalines may have better diagnostic sensitivity for hereditary PPGLs. Both methods have sensitivities >95% and specificities >90%.
22
Q
How are Urine and Plasma catocholamines tested?
A
Urine
- 24 hour urine sample is measured so that ‘attacks’ aren’t missed (unless short).
- Sample must be collected into acid bottle.
- HPLC with either ED or MS/MS is the method of choice for all.
Plasma
- The patient should be supine with appropriate reference ranges.
- Samples must be stored in fridge within 15 mins of being taken, then spun within 6 hours.
- Various methodologies.
23
Q
What are interferences of Biochemical Testing?
A
- Medical conditions – heart failure, MI, sleep apnoea
- Exercise
- Emotional stress
- Foods
- Mostly increase the normetadrenalineand dopamine, metadrenaline not affected as much
- Drugs
24
Q
What are Biochemical Testing follow ups for patient with positive test results?
A
- More than 75% of all PPGLs can be identified by the extent and nature of increased results.
- Elevations of both met and normet are rare as FPs.
- Findings of solitary increases in either met or normet >3x the cut off are rare findings.
- Medications and other interfering causes should always be considered in the borderline cases.
- In borderline cases a clonidine stimulation test can distinguish true positives from false positives.
25
What is the prinicple and preparation of Clonidine Suppression Test?
* Clonidine is a α2-adrenoreceptor agonist that inhibits neuronal noradrenaline release in patients without PPGL.
* Withdraw sympatholytic drugs 48 hours before testing.
26
What is the Procedure and interpretation of the Clonidine Suppression Test?
Procedure
* Insert a venous cannula.
* After 20 mins of supine rest take a blood sample for plasma metadrenalines.
* Administer clonidine orally at a dose of 300 µg/70g body weight.
* After 3 hours take another blood sample for plasma metadrenalines.
Interpretation
* A normal result is indicated by a suppression of normetadrenaline by more than 40%.
27
How is a Phaeochromacytoma diagnosed?
* Ultrasound Scanning
* CT Scanning
* MRI Scanning
* Metaiodobenzylguanidine (MIBG) Scanning
* Octreotide Scanning
* Venous catheterisation – rarely done
* PET scanning
28
What is the pre-operative management of Phaeochromacytomas?
* Patients are at risk of hypertensive crisis before surgery and hypotensive after.
* Patients need to be treated with oral antihypertensives, α-blockers are the first choice but β-blockers, calcium channel blockers and ACE inhibitors can be used.
* **Phenoxybenzamine is the α-blocker of choice and binds irreversibly.**
29
How are Phaeochromacytomas treated definitively?
* **Surgical removal of the tumour** – usually laparoscopic.
* Chemotherapy may be used for metastatic disease and 131I-MIBG.
30
What are post operative complication of treating phaeochromacytoma?
* Hypotension
* Hypoglycaemia
* Hypertension
31
How are patients treated for Phaeochromacytomas followed up?
* Regular measurement of blood pressure.
* Soon after surgery measurement of urine metadrenalines. Lifelong monitoring is recommended.
* Family studies may be required.
* Follow up patients with known genetic phaeochromocytoma.
32
What is the chemical method for Catecholamines?
* Fluorometric method uses the trihydroxyindolereaction which oxidises noradrenaline and adrenaline. Acidic ferricyanide is used to form trihydroxyindolewhich can be measured by fluorescence detection.
* Sensitivity is acceptable for urine not plasma
* Technically demanding and uses harmful chemicals.
* Prone to interference/quenching - antibiotics, anti-hypertensives.
* Can be used for detection in High Performance Liquid Chromatography
33
What is the Pisano method?
Urine Metadrenalines
* Acid hydrolysis
* Cation exchange extraction
* Wash
* Elute met and normet with Ammonia
* Oxidise in periodate, pH6
* Spectrophotometric measuremen to 350 + 360 nm
34
What are the disadvatages of the Pisano Method?
* Prone to interference tricyclics, anti-hypertensives, diet: (vanillin-rich foods - bananas, chocolate)
* Cannot separate met and normet
35
What is the Urine HMMA and Urine HVA?
Urine HMMA
* Similar method to met and normet but no hydrolysis
* Ethyl acetate extraction.
* Spectrophotometric measurement at 350 + 360 nm
* Simple but prone to interference
Urine HVA
* Spectrometry and fluorometric methods
* Oxidised in KFeCN
* 3 stage ion-exchange clean-up
36
What is Urine HVA?
*
37
What are Problems with the Chemical Methods?
* Assays are laborious, tedious and therefore often badly performed
* Interferences which cause poor specificity: drugs (tricyclics, anti-hypertensives), diet, quenching (fluorescence)
* Poor sensitivity
No longer used in clinical medicine.
38
What are PNMT and COMT assays for?
* **PNMT assay =** specific for noradrenaline only
* **COMT assay =** non-specific (any catechol group)
39
What are drawback to Radioenzymatic Assays in mesuring hormones?
* EXPENSIVE
* TIME-CONSUMING
* DIFFICULT
40
What are advantages and Disadvantages of using Immunoassays for biochemical testing?
**Advantages**
* Minimal expense of instrumentation.
* Kit methods that are simple to se up.
* Minimal operator expertise required.
**Disadvantages**
* High cost of kit method consumables.
* Lengthy sample prep and analysis times.
* Each metabolite must be measured separately.
* Difficult to identify presence of interferences.
* Poor accuracy.
* Poor sensitivity.
* Not possible to measure MT.
41
What are types of Chromatography?
* **GC-MS** (Expensive and needs specialist operator)
* **HPLC-ED**
* **HPLC-MS/MS** (Improve Specificity and Sensitivity)
42
What are the principles of HPLC-ED?
* Sample is introduce to the HPLC column and separated.
* The column is connected to an ED cell, an electrochemical sensor where a reaction takes place at an electrode.
* Electrochemically active substances that elute from the column undergo an electrochemical reaction, electrons are transferred resulting in an electrical current.
43
What does HPLC-ED do?
* Exploits the electroactive properties of cats and mets.
* Allows SIMULTANEOUS MEASUREMENT of NORADRENALINE, ADRENALINE, DOPAMINE, NORAMETANEPHRINE, METANEPHRINE and HMMA, HVA in urine.
* Requires acid hydrolysis to get free mets.
44
What are Advantages and Disadvanatages of HPLC-ED?
**Advantages**
* Minimal consumable costs for in house methods.
* Relative simplicity of operation.
* Some kit methods available but higher consumable costs.
* Moderate analytical sensitivity.
* Can identify chromatographic interferences.
* Can measure MT.
**Disadvantages**
* Moderate capital cost of instrumentation.
* Cumbersome sample preparation.
* Prone to analytical interferences.
* Low sample throughput.
45
What is LC-MS/MS?
* LC-MS/MS separates and quantifies according to mass to charge ratio of the analyte of interest.
* Recommended method for both urine and plasma.
* Very sensitive and specific.
* Modern systems allow fast run times \<3 mins.
* Mets are easily ionisable – electrospray ionisation used.
* Acid hydrolysis on urine not always required.
* Multiple reaction monitoring is used.
46
What are advantages and disadvantages of LC-MS/MS?
**Advantages**
* Minimal consumable costs.
* High sample throughput.
* Sample preparation is relatively simple.
* High sensitivity.
* High specificity and relative freedom from interferences.
* Can measure MT.
* High versatility of LC-MS/MS methods.
**Disadvantages**
* High capital cost of instrumentation.
* High level of operator expertise required.
* Need to develop in house methods, however companies have applications to use.
47
What are recommendations, what and how to measure PPGLs?
* Initial biochemical testing for PPGLs should include measurement of urinary fractionated metadrenalinesor plasma free metadrenalines.
* Liquid chromatography with either ED or MS should be used for diagnosis of PPGL.
