The adrenal medulla secretes catecholamines including adrenaline, noradrenaline, and dopamine. These hormones are synthesized from the amino acid tyrosine in the chromaffin cells of the adrenal medulla. Catecholamines act through intracellular mediators and have various effects, such as increasing heart rate, blood pressure, and blood glucose levels. Their secretion increases during stress, exposure to cold, and hypoglycemia to mobilize energy stores and restore homeostasis.

1. Adrenal Medulla
• Introduction.
• The part of adrenal gland consisting of
chromaffin tissues and which is an
essential part of the autonomic nervous
system is called Adrenal Medulla.
• The chromaffin cells are of two types.
• 1.Adrenaline Secreting Cells (90%)
• 2.Noradrenaline Secreting Cells (10%)
1

2. • Hormones of Adrenal Medulla.
• Adrenal medullary hormones are the amines
derived from catechol and so these hormones
are called catecholamines.
• Three catecholamines are secreted by
medulla,
• 1.Adrenaline or epinephrine.
• 2.Noradrenaline or norepinephrine.
• 3.Dopamine.
2

3. • Plasma Level of Catecholamines.
• Adrenaline 3ug/dL
• Noradrenaline 30ug/dL
• Dopamine 3.5ug/dL.
• Half-Life of Catecholamines.
• The half-life of Catecholamines is about 2
minutes.
• Mechanism of action.
• Hormones of adrenal medulla act through
intracellular mediator.
3

4. • Synthesis of Catecholamines.
Are synthesized from the amino acid tyrosine in
the chromaffin cells of adrenal medulla.These
hormones are formed from phenylalanine
also.But phenylalanine has to be converted into
tyrosine.
• Stages of synthesis of
Catecholamines.
1.Formation of tyrosine from phenylalanine in
the presence of enzyme phenylalanine
hydroxylase.
4

5. 2. Uptake of tyrosine from blood into the
chromaffin cells of adrenal medulla by
active transport.
3. Conversion of tyrosine into
dihydroxyphenylalanine (DOPA) by
hydroxylation in the presence of tyrosine
hydroxylase.
4. Decarboxylation of DOPA into
dopamine by DOPA decarboxylase.
5

6. 5. Entry of dopamine into granules of chromaffin
cells.
6. Hydroxylation of dopamine into noradrenaline
by the enzyme dopamine beta hydroxylase.
7. Release of noradrenaline from granules into
the cytoplasm.
8. Methylation of noradrenaline into adrenaline
by the most important enzyme called
phenylethanolamine-N-methyltransferase
(PNMT).PNMT is present in chromaffin cells.
6

7. • Functions of the hormones of
adrenal medulla.
1. Effect on Blood Vessels.
Noradrenaline has strong effects on blood
vessels.It causes constriction of blood
vessels throughout the body via alpha
receptors.So,it is called General
vasoconstrictor.The vasoconstrictor effect
of noradrenaline increases total peripheral
resistance.
7

8. 2. Effect on Circulation.
Adrenaline directly acts on the heart.It increases
the heart rate,so when pumping of the heart will
increases the cardiac output will also be
increased.
3. Effect on Blood Pressure.
Adrenaline acts on the heart and increases the
systolic blood pressure.The diastole blood
pressure may also rise somewhat or remain
unchanged.
8

9. 4. Effect on Respiration.
Adrenaline increases the rate and force
of respiration.
5. Effect on Carbohydrates.
Adrenaline increases the blood glucose
level.It is by increasing the glycogenolysis
in liver and muscle.So, a large quantity of
glucose enters the circulation.
9

10. 6. Effect on Fat.
Adrenaline causes mobilization of free fatty acid
from adipose tissues.catecholamines need the
presence of glucocorticoids for this action.
7. Effect on Skeletal Muscle.
Adrenaline causes severe contraction and quick
fatigue of skeletal muscle.It also causes
vasodilatation in skeletal muscles.
10

11. 8. Effect on Secretions.
Adrenaline increases the secretion of saliva and
sweating.
Regulation of secretion of Adrenaline
and Noradrenaline.
• Adrenaline and noradrenaline are secreted from
adrenal medulla in small quantities even during
rest.During stress conditions,due to
sympathoadrenal discharge,a large quantity of
catecholamines is secreted.
11

12. • Catecholamine secretion also increases in,
1.Exposure to Cold.
• During exposure to cold, adrenaline and
noradrenaline are secreted in large quantities.
• Catecholamines significantly increase the
muscular activity and sometimes produce
shivering so that, the body temperature increase.
12

13. 2.Hypoglycemia.
• Release of catecholamines increases
during hypoglycemia.
• These hormones increase the blood sugar
level by inducing glycogenolysis in muscle.
13