7.10. The function of adrenal medulla. Adaptation to environmental stress.

Question 1

I. Adrenal medulla
1. What are the features of adrenal medulla?

Answer 1

Question 2

I. Adrenal medulla
2. Explain SYM control in adrenal medulla

Answer 2

• In the adrenal medulla: preganglionic SYM fibers synapse on chromaffin cells of the medulla.
• The chromaffin cells do not form another synapse, but rather start secreting NE + E into the bloodstream

Question 3

I. Adrenal medulla
3. What are the receptors for the synapses in adrenal medulla?

Answer 3

• The receptors for the synapses are nicotinic ACh receptors (nAChR)

Question 4

I. Adrenal medulla
4. Name a major enzyme that you can find in adrenal medulla?

Answer 4

PNMT (Phenylethanolamine N-methyltransferase) –
=>NE -> E

Question 5

II. Epinephrine synthesis
1. What are the features of PNMT (Phenylethanolamine N-methyltransferase)?

Answer 5

PNMT is stimulated by cortisol and catalyzes the conversion of NE -> E
- Cortisol (GC) is produced in zona fasciculata of the adrenal cortex
- The blood flowing from the cortex through the medulla is the only place where the [cortisol] is high enough for this stimulatory effect to occur

Question 6

II. Epinephrine synthesis
2. What are the 5 steps of Epinephrine synthesis?

Answer 6

Question 7

II. Epinephrine synthesis
3. What are the features of epinephrine production in adrenal medulla?

Answer 7

Normally, the medulla produces 80% E and 20% NE, but this varies based on the cortisol production.

Question 8

II. Epinephrine synthesis
4. Where does NE and E source of our body come from?

Answer 8

• 100% of the body’s E comes from the adrenal gland, but only 30% of the blood plasma NE is from the adrenal gland
  => remaining 70% of NE comes from SYM nerve terminals

Question 9

II. Epinephrine synthesis
5. What happen when ACh from the SYM fibers comes in contact with chromaffin cell receptors?

Answer 9

• When ACh from the SYM fibers comes in contact with chromaffin cell receptors, it increases permeability of Na+, and this induces an influx of Ca2+
• The Ca2+ in turn causes aggregation of chromaffin granules, which are then exocytosed.

Question 10

II. Epinephrine synthesis
6. What are the features of Beta2-receptor

Answer 10

• Remember that the Beta2-receptor has a higher affinity for E compared to NE.
• If E is present, then all the Beta2-effects are stronger.
• These receptors are present in blood vessels and liver, among other places.
  => This leads to vasodilation and the adrenaline metabolic effects like glycolysis/fuel mobilization

Question 11

III. Adrenal medulla secretion
1. How is “Adrenal medulla secretion” stimulated?

Answer 11

Question 12

III. Adrenal medulla secretion
2A. How can major stresses affect affect adrenal medulla secretion?

Answer 12

Question 13

III. Adrenal medulla secretion
2B, Which hormone that major stresses activate?

Answer 13

Major stresses almost simultaneously activate CRH (corticotropin-releasing hormone) and ADH from the HT

Question 14

III. Adrenal medulla secretion
2C. What is the molecular mechanism of CRH?

Answer 14

• CRH stimulates ACTH secretion from anterior pituitary
  -> ACTH stimulates cortisol production in the adrenal cortex
  -> cortisol stimulates production of catecholamines

(+ NE increases CRH release -> (+)-feedback)

Question 15

III. Adrenal medulla secretion
2D. How do Cortisol + catecholamines work together?

Answer 15

• Cortisol + catecholamines work together to increase glucose production and shift glucose use towards the CNS and away from the PNS

Question 16

III. Adrenal medulla secretion
2E. What is the role of Epinephrine?

Answer 16

• E also rapidly activates the release of FFAs, which can be used as fuel in the heart and muscle, while cortisol helps facilitate lipolysis

Question 17

III. Adrenal medulla secretion
2F. What is the effect of both cortisol and E?

Answer 17

• Both cortisol and E ↑ the BP and CO to improve the circulation to the vital organs, while E causes blood to divert away from the circulation of the intestines, kidney and skin

Question 18

III. Adrenal medulla secretion
3A. How do NE and CRH work together?

Answer 18

Question 19

III. Adrenal medulla secretion
3B. CRH input to other hypothalamic neurons inhibits appetite, sexual activity and GH + gonadotropin release
=> This is reinforced by which hormone?

Answer 19

This is reinforced by the high levels of cortisol, which also suppress growth and ovulation

Question 20

IV. Make a schematic diagram to explain Adaptation to environmental stress by adrenal medulla

Answer 20