Adrenal Medulla
Medulla is the inner part of adrenal gland and it forms 20% of the mass of adrenal gland. It is
made up of interlacing cords of cells known as chromaffin cells. Chromaffin cells are also
called pheochrome cells or chromophil cells. These cells contain fine granules which are
stained brown by potassium dichromate.
Types of chromaffin cells
Adrenal medulla is formed by two types of chromaffin cells:
1. Adrenaline-secreting cells (90%)
2. Noradrenaline-secreting cells (10%).
HORMONES OF ADRENAL MEDULLA
Adrenal medullary hormones are the amines derived from catechol and so these hormones
are called catecholamines.
Catecholamines secreted by adrenal medulla
1. Adrenaline or epinephrine
2. Noradrenaline or norepinephrine
3. Dopamine.
PLASMA LEVEL OF CATECHOLAMINES
1. Adrenaline : 3 μg/dL
2. Noradrenaline : 30 μg/dL
3. Dopamine : 3.5 μg/dL
HALF-LIFE OF CATECHOLAMINES
Half-life of catecholamines is about 2 minutes.
SYNTHESIS OF CATECHOLAMINES
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.
ACTIONS OF ADRENALINE AND NORADRENALINE
Adrenaline and noradrenaline stimulate the nervous system. Adrenaline has significant
effects on metabolic functions and both adrenaline and noradrenaline have significant effects
on cardiovascular system.
MODE OF ACTION OF ADRENALINE AND NORADRENALINE –ADRENERGIC
RECEPTORS
Actions of adrenaline and noradrenaline are executed by binding with receptors called
adrenergic receptors, which are present in the target organs.
Adrenergic receptors are of two types:
1. Alpha-adrenergic receptors, which are subdivided into alpha-1 and alpha-2 receptors
2. Beta-adrenergic receptors, which are subdivided into beta-1 and beta-2 receptors.
.
, ACTIONS
Circulating adrenaline and noradrenaline have similar effect of sympathetic stimulation. But,
the effect of adrenal hormones is prolonged 10 times more than that of sympathetic
stimulation.
1. On Metabolism (via Alpha and Beta Receptors)
Adrenaline influences the metabolic functions more than noradrenaline.
i. General metabolism: Adrenaline increases oxygen consumption and carbon dioxide
removal. It increases basal metabolic rate. So, it is said to be a calorigenic hormone
ii. Carbohydrate metabolism: Adrenaline increases the blood glucose level by increasing the
glycogenolysis in liver and muscle. So, a large quantity of glucose enters the circulation
iii. Fat metabolism: Adrenaline causes mobilization of free fatty acids from adipose
tissues.Catecholamines need the presence of glucocorticoids for this action.
2. On Blood (via Beta Receptors)
Adrenaline decreases blood coagulation time. It increases RBC count in blood by contracting
smooth
muscles of splenic capsule and releasing RBCs from spleen into circulation.
3. On Heart (via Beta Receptors)
Adrenaline has stronger effects on heart than noradrenaline. It increases overall activity of the
heart, i.e.
i. Heart rate
ii. Force of contraction
iii. Excitability of heart muscle
iv. Conductivity in heart muscle
4. On Blood Vessels (via Alpha and Beta-2 Receptors)
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’. Vasoconstrictor effect
of noradrenaline increases total peripheral resistance. Adrenaline also causes constriction of
blood vessels.
5. On Blood Pressure (via Alpha and Beta Receptors)
Adrenaline increases systolic blood pressure by increasing the force of contraction of the
heart and
cardiac output. But, it decreases diastolic blood pressure by reducing the total peripheral
resistance.
Noradrenaline increases diastolic pressure due to general vasoconstrictor effect by
increasing the total peripheral resistance. It also increases the systolic blood pressure to a
slight extent by its actions on heart.
6. On Respiration (via Beta-2 Receptors)
Adrenaline increases rate and force of respiration. Adrenaline injection produces apnea,
which is known as adrenaline apnea. It also causes bronchodilation.
.
Medulla is the inner part of adrenal gland and it forms 20% of the mass of adrenal gland. It is
made up of interlacing cords of cells known as chromaffin cells. Chromaffin cells are also
called pheochrome cells or chromophil cells. These cells contain fine granules which are
stained brown by potassium dichromate.
Types of chromaffin cells
Adrenal medulla is formed by two types of chromaffin cells:
1. Adrenaline-secreting cells (90%)
2. Noradrenaline-secreting cells (10%).
HORMONES OF ADRENAL MEDULLA
Adrenal medullary hormones are the amines derived from catechol and so these hormones
are called catecholamines.
Catecholamines secreted by adrenal medulla
1. Adrenaline or epinephrine
2. Noradrenaline or norepinephrine
3. Dopamine.
PLASMA LEVEL OF CATECHOLAMINES
1. Adrenaline : 3 μg/dL
2. Noradrenaline : 30 μg/dL
3. Dopamine : 3.5 μg/dL
HALF-LIFE OF CATECHOLAMINES
Half-life of catecholamines is about 2 minutes.
SYNTHESIS OF CATECHOLAMINES
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.
ACTIONS OF ADRENALINE AND NORADRENALINE
Adrenaline and noradrenaline stimulate the nervous system. Adrenaline has significant
effects on metabolic functions and both adrenaline and noradrenaline have significant effects
on cardiovascular system.
MODE OF ACTION OF ADRENALINE AND NORADRENALINE –ADRENERGIC
RECEPTORS
Actions of adrenaline and noradrenaline are executed by binding with receptors called
adrenergic receptors, which are present in the target organs.
Adrenergic receptors are of two types:
1. Alpha-adrenergic receptors, which are subdivided into alpha-1 and alpha-2 receptors
2. Beta-adrenergic receptors, which are subdivided into beta-1 and beta-2 receptors.
.
, ACTIONS
Circulating adrenaline and noradrenaline have similar effect of sympathetic stimulation. But,
the effect of adrenal hormones is prolonged 10 times more than that of sympathetic
stimulation.
1. On Metabolism (via Alpha and Beta Receptors)
Adrenaline influences the metabolic functions more than noradrenaline.
i. General metabolism: Adrenaline increases oxygen consumption and carbon dioxide
removal. It increases basal metabolic rate. So, it is said to be a calorigenic hormone
ii. Carbohydrate metabolism: Adrenaline increases the blood glucose level by increasing the
glycogenolysis in liver and muscle. So, a large quantity of glucose enters the circulation
iii. Fat metabolism: Adrenaline causes mobilization of free fatty acids from adipose
tissues.Catecholamines need the presence of glucocorticoids for this action.
2. On Blood (via Beta Receptors)
Adrenaline decreases blood coagulation time. It increases RBC count in blood by contracting
smooth
muscles of splenic capsule and releasing RBCs from spleen into circulation.
3. On Heart (via Beta Receptors)
Adrenaline has stronger effects on heart than noradrenaline. It increases overall activity of the
heart, i.e.
i. Heart rate
ii. Force of contraction
iii. Excitability of heart muscle
iv. Conductivity in heart muscle
4. On Blood Vessels (via Alpha and Beta-2 Receptors)
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’. Vasoconstrictor effect
of noradrenaline increases total peripheral resistance. Adrenaline also causes constriction of
blood vessels.
5. On Blood Pressure (via Alpha and Beta Receptors)
Adrenaline increases systolic blood pressure by increasing the force of contraction of the
heart and
cardiac output. But, it decreases diastolic blood pressure by reducing the total peripheral
resistance.
Noradrenaline increases diastolic pressure due to general vasoconstrictor effect by
increasing the total peripheral resistance. It also increases the systolic blood pressure to a
slight extent by its actions on heart.
6. On Respiration (via Beta-2 Receptors)
Adrenaline increases rate and force of respiration. Adrenaline injection produces apnea,
which is known as adrenaline apnea. It also causes bronchodilation.
.
