24 Adrenal medulla physiology Flashcards
Adrenal medulla consists of ___________ cells which are homologous to ___________________ neurons.
chromaffin;
sympathetic postganglionic
What are the 2 main ways for blood to pass through the cortex to the medulla?
What is there difference in affecting PNMT?
- 80% cortical capillaries, exposed to cortisol to induce the enzyme PNMT
- 20% medullary artery, without breaking into capillary loops, only exposed to little cortisol
PNMT in medulla is for epinephrine synthesis
Which of the following about releasing catecholamines is wrong?
A. Acetylcholine is the NT from preganglionic sympathetic neurons for stimulation
B. NT depolarize chromaffin cells to cause Ca2+ influx and exocytosis of catecholamine-containing secretory granules.
C. Activating tyrosine hydroxylase is the rate limiting step
D. Long term stimulation from NT will cause tyrosine hydroxylase to hide
D
Can upgrade the TH
What is the importance of having cortisol in catecholamine synthesis?
Cortisol induce the expression of PNMT for the conversion of norepinephrine to epinephrine
State the flowchart of the synthesis of the catecholamine epinephrine.
Tyrosine —-TH—-> DOPA ——> dopamine ——> norepinephrine (20%) —PNMT—-> epinephrine (80%)
What will the catecholamines (epinephrine and norepinephrine) become later on?
norepinephrine: normetanephrine
epinephrine: metanephrine
> > > vanillylmandelic acid (VMA)
Which of the following is/are false?
A. EP and NP have 20-30 mins biological half lives
B. Urinary VMA are used clinically to assess the level of catecholamine production in patients
C. Urinary conjugated metanephrines are used clinically to assess the level of catecholamine production in patients
D. EP and NP used clinically to assess the level of catecholamine production in patients
A and D
they only have 2-3 mins of half live so B and C should be used as assessment rather than EP and NP
Which of the following is true?
A. Norepinephrine has higher affinity to beta receptors than epinephrine
B. Epinephrine aims at acting on target cells at point of release
C. Norepinephrine is produced from receiving signals (acetylcholine) from sympathetic ganglion
C
A: should be epinephrine has higher affinity to beta receptors
B: epinephrine acts on distant target cells
C: acetylcholine > sympathetic ganglion > norepinephrine > acts on target cells at point of release
Which of the following are short term stress response by catecholamines?
A. increased metabolic rate B. dilation of bronchioles C. liver converts glycogen to glucose D. decrease in blood pressure E. decreased digestive and kidney activity
All except D
should be increase in blood pressure
Which of the following are long term stress response by mineralocorticoids and glucocorticoids?
A. increase in blood sugar
B. increased in blood volume and pressure
C. retention of Na+ and water
D. increase sensitivity of the immune system
E. Proteins and fats converted to glucose or broken down for energy
All except D
should be suppression of immune system
State 5 effects of catecholamines on carbohydrate/fat metabolism and pancreatic hormone secretion.
- increase gluconeogenesis in liver to provide energy when stressed
- increase glycogenesis in liver and muscle
- increase lipolysis in adipose tissue
- inhibit insulin secretion
- stimulate glucagon secretion
- raise blood glucose levels
- raise free fatty acids and ketones levels
any 5
What is pheochromocytoma?
Where does it arise from?
- Catecholamine-producing neuroendocrine tumours (mostly benign) arising from chromaffin cells of adrenal medulla, and they secrete high levels of epinephrine and norepinephrine.
What is paraganglionoma?
Where does it arise from?
derived from extra-adrenal sympathetic/ parasympathetic ganglia; mostly secrete norepinephrine or dopamine, while the ones of parasympathetic origin are mostly non-secretory type silent tumors
List 3 signs or symptoms in patients with pheochromocytoma.
- sweating: mostly under sympathetic cholinergic effect
- headache
- hypertension (often severe)
- weakness/fatigue
- palpitations
