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Endo-Repro I > Adrenal Medulla > Flashcards

Adrenal Medulla Flashcards

1
Q

What is the first step in catecholamine synthesis?

A

Tyrosine is converted into DOPA by tyrosine hydroxylase.

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2
Q

What is the second step of catecholamine synthesis?

A

DOPA is converted into dopamine by DOPA decarboxylase.

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3
Q

What is the third step of catecholamine synthesis?

A

Dopamine is converted into norepinephrine by Dopamine beta-hydroxylase.

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4
Q

What is the fourth and final step of catecholamine synthesis?

A

The conversion of norepinephrine into epinephrine by phenylethanolamine-N-methyltransferase (PNMT).

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5
Q

What is the rate limiting step of catecholamine synthesis?

A

The first step (tyrosine hydroxylase).

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6
Q

What inhibits tyrosine hydroxylase?

A

Norepinephrine.

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7
Q

What does DOPA decarboxylase use as a co-factor?

A

Pyridoxal phosphate.

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8
Q

What happens to the end product of DOPA decarboxylase (dopamine)?

A

The dopamine is packaged in secretory vesicles.

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9
Q

Where is dopamine beta-hydroxylase located?

A

It is membrane bound in the vesicles dopamine is packaged in.

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10
Q

What does dopamine beta-hydroxylase use as a co-factor?

A

Vitamin C.

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11
Q

What is the signal for catecholamine synthesis?

A

Acetylcholine released from pre-ganglionic sympathetic fibers (nicotinic receptors)

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12
Q

What is another name for the chromaffin cells of the adrenal medulla?

A

Pheochromocytes.

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13
Q

Where is phenylethanolamine-N-methyltransferase located?

A

In the chromaffin cell cytosol.

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14
Q

How does norepinephrine leave the secretory vesicle? (remember that PNMT is in the cytosol).

A

It passively diffuses out of the secretory vesicle.

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15
Q

How does epinephrine (converted from NE by PNMT in the cytosol) get back into the secretory vesicle?

A

Epinephrine re-enters the secretory vesicle by ATP-dependent active transport (monoamine transporter or VMAT-1).

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16
Q

What effect does cortisol have on PNMT?

A

An increase in stress hormones (such as glucocorticoids) or nerve impulses due to stress can cause PNMT to convert more norepinephrine into epinephrine.

17
Q

How does COMT degrade epinephrine and norepinephrine?

A

COMT converts epinephrine into metanephrine and norepinephrine into normetanephrine.

18
Q

How does monoamine oxidase (MOA) metabolize catecholamines?

A

It converts intracellular (sympathetic neuron) norepinephrine into DHPG. DHPG then diffuses fropm the neuron.

19
Q

What is the fate of DHPG?

A

It is metabolized by aldehyde dehydrogenase (AD) or COMT into VMA.

20
Q

What else can MAO metabolize?

A

MAO can also convert metanephrine and normetanephrine into VMA.

21
Q

What is another route of metabolism for catecholamines and metanephrines?

A

They can be conjugated by the liver (sulfate or glucuronide).

22
Q

How are catecholamines excreted?

A

In the urine (renal).

23
Q

What GPCR subtype are α1 adrenoceptors?

A

α1 adrenoceptors are Gq receptors.

24
Q

What is the general effect of α1 adrenoceptor stimulation?

A

α1 adrenoceptors generally cause smooth muscle contraction.

25
Q

What does α1 adrenoceptor stimulation cause?

A
  • Vasoconstriction (increased BP)
  • Mydriasis (pupillary dilation)
  • Intestinal sphincter contraction
  • Bladder sphincter contraction
26
Q

What GPCR subtype are α2 adrenoceptors?

A

α2 adrenoceptors are Gi receptors.

27
Q

What is the general effect of α2 adrenoceptor stimulation?

A

α2 adrenoceptors generally serve to suppress sympathetic outflow.

28
Q

What does α2 adrenoceptor stimulation cause?

A
  • Decreased sympathetic outflow
  • Decreased insulin release
  • Decreased lipolysis
29
Q

What GPCR subtype are β1 adrenoceptors?

A

β1 adrenoceptors are Gs receptors.

30
Q

What is the general effect of β1 adrenoceptor stimulation?

A

β1 adrenoceptors generally increase sympathetic outflow.

31
Q

What does β1 adrenoceptor stimulation cause?

A
  • Increased heart rate
  • Increased cardiac contractility
  • Increased renin release
  • Increased lipolysis
32
Q

What GPCR subtype are β2 adrenoceptors?

A

β2 adrenoceptors are Gs receptors.

33
Q

What is the general effect of β2 adrenoceptor stimulation?

A

β2 adrenoceptors generally serve to counteract the effects of α adrenoceptor activation.

34
Q

What does β2 adrenoceptor stimulation cause?

A
  • Vasodilation
  • Bronchodilation
  • Increased lipolysis
  • Increased insulin release

Endo-Repro I (12 decks)

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