3. Made up of chromaffin cells- structural and
functional equivalent of undifferentiated SNS
postganglionic neurons.
Contains granules that stores catecholamines
Epinephrine/ adrenaline secreting type- 90%
Norepinephrine/ noradrenaline secreting type- 10%
Very few dopamine secreting cells also
Receive sympathetic preganglionic cholinergic
innervation
Epinephrine is the medulla's principal
secretory product
4. Adrenal medulla can be considered as a
sympathetic ganglia
Some pre-ganglionic fibers pass through the
sympathetic chain (without relay) and
terminate on the adrenal medulla where cell
bodies of post- ganglionic fibers are located but
the axons are degenerated
5.
6. HORMONES SECRETED BY ADRENAL
MEDULLA
CATECHOLAMINES
EPINEPHRINE – Major output
NOR EPINEPHRINE
DOPAMINE
8. EFFECT OF GLUCOCORTICOIDS
PNMT is induced by glucocorticoids
Also promotes normal growth of adrenal medulla
In adrenocortical deficiency, epinephrine
synthesis is reduced
9. RELEASE OF CATECHOLAMINES
PRE GANGLIONIC ENDINGS – SECRETE Ach
Ach binds to NN receptors in adrenal medullary cells
Depolarization of cell
Opening of voltage gated Ca2
+ channels
Ca2
+ influx
Ca2+ mediated exocytosis
Release of epinephrine, nor epinephrine & dopamine
directly into blood stream
10. METABOLISM OF
CATECHOLAMINES
1. REUPTAKE INTO THE ADRENERGIC NERVE
ENDINGS – MAJOR FATE
2. DESTRUCTION BY TISSUE ENZYMES
MONO AMINE OXIDASE (MAO)
CATECHOL-O-METHYL TRANSFERASE (COMT)
METABOLITES
METANEPHRINE, NOR METANEPHRINE & VMA
(Vanilyl mandelic acid)
11.
12. PLASMA LEVELS
NOR EPINEPHRINE – 300pg/ml
EPINEPHRINE – 30 pg/ml
DOPAMINE – 35pg/ml
Epinephrine- predominant catecholamine in
adrenal medulla, but Nor epinephrine is mainly
synthesised in sympathetic nerve endings.
13. REGULATION OF SERETION OF
ADRENAL MEDULLA
STRESS- As a part of stimulation of sympathetic
system. (Sympatho adrenal sysem)
As a preparation for fight, fright or flight
HYPOGLYCEMIA
exercise, trauma, anger, anxiety, pain etc
14. MECHANISM OF ACTION
Acts on α and β receptors
α receptors- α1 and α2
β receptors- β1, β2 and β3
β receptors- coupled to adenylyl cyclase- increase
cAMP
α1 receptor- acts through IP3 and DAG
α2 receptor- inhibitory, decrease cAMP
15. Epinephrine acts more on β receptors
Norepinephrine acts more on α receptors
β Adrenergic receptors have a higher affinity for
epinephrine compared with NE.
α Adrenergic receptors have a higher affinity for
NE
17. • EFFECT ON CVS (SHORT NOTE)
➢ Epinephrin
Increases heart rate, force of contraction and thus
cardiac output→ Increases Systolic BP (β)
Vasoconstriction of renal, sphlanchnic and cutaneous
blood vessels (α1)
Vasodilation of skeletal and hepatic circulation- β2
vasodilation effect of epinephrine overrides the
vasoconstriction effect and therefore, total peripheral
resistance falls
Diastolic BP decreases and Pulse pressure widens
aim- to divert blood from splanchnic and cutaneous
circulation to the exercising (active) muscles, while
maintaining the cerebral and coronary blood flow
18. ➢ Norepinephrine
Blood vessels - Vasoconstriction ( α1) and
increase in Peripheral resistance
DBP increases
Some degree of tachycardia and increased
myocardial contractility and increase in SBP
But activates baroraceptor reflex resulting in
decrease in heart rate and cardiac output
IN HUMANS (INTACT HEART) AS THE BP IS INCREASED
BARORECEPTOR REFLEX WILL OPERATE TO CAUSE
BRADYCARDIA.
THIS EFFECT IS MORE STRONG FOR NOR EPINEPHRINE
The action of catecholamines on blood pressure needs the presence
of glucocorticoids.
19. EFFECT ON SMOOTH MUSCLES
Via α1 – constriction of sphincters of bowel & bladder
Via β2 – relaxation of smooth muscle of walls of
various visceral organs
EFFECT ON THERMOGENESIS
Epinephrine increase BMR
21. EFFECTS ON CNS
Acting on reticular formation – cause alertness
Adrenaline secretion increases during ‘fight or flight
reactions’ after exposure to stress
EFFECTS ON RESPIRATORY SYSTEM
via β2 - bronchodilatation
ACTION IN THE EYES
via α1 – constriction of radial muscles of iris to cause
mydriasis
22. EFFECTS ON PLASMA POTASSIUM LEVEL
Both Epinephrine & Norepinephrine cause (via
β2)
an initial rise in plasma K+ – due to release of K+
from liver
followed by a prolonged fall – due to increased
entry of K+ into muscle
23. On skin:
(i) Contraction of pilomotor muscles →
piloerection of hair
(ii) On sweat glands → localized sweating on
palm and sole, called adrenergic sweating.
24. DOPAMINE- ACTIONS
Increases cardiac output and systolic BP
Vasodilation in vital organs
Renal vasodilation maintains urine output and
causes natriuresis
Causes vasoconstriction in other parts
Useful in cardiogenic shock (Give reason)
25. FUNCTIONS OF ADRENAL MEDULLA
EMERGENCY FUNCTION
preparation for flight or fight
DEFENCE AGAINST EXPOSURE TO COLD
due to the calorigenic effect – increase heat
production
decrease heat loss due to cutaneous
vasoconstriction
DEFENCE AGAINST HYPOGLYCEMIA
catecholamines cause rapid rise in blood sugar
level
26. Applied Physiology
1. Hyposecretion of catecholamines → No adverse
effects (Adrenal medulla is not essential for life).
2. 2. Hypersecretion of catecholamines:
Pheochromocytoma
27. PHEOCHROMOCYTOMA (SHORT NOTE)
Tumour of adrenal medulla
Concentration of epinephrine and norepinephrine
increases
Features
Sustained hypertension/ episodic hypertension
Increased BMR
Profuse sweating
Hyperglycemia
Loss of appetite and weight
28. DIAGNOSIS
Increased concentration of catecholamines
Increased excretion of metanephrine and VMA
Treatment
Surgical removal of the tumour
Adrenergic antagonist for symptom relief
