Adrenal Cortex
IMPORTANCE OF ADRENAL GLANDS
Adrenal glands are called the ‘life-saving glands’ or ‘essential endocrine glands’. It is
because the absence of adrenocortical hormones causes death within 3 to 15 days and absence
of adrenomedullary hormones, drastically decreases the resistance to mental and physical
stress.
FUNCTIONAL ANATOMY OF ADRENAL GLANDS
There are two adrenal glands. Each gland is situated on the upper pole of each kidney.
Because of the situation, adrenal glands are otherwise called suprarenal glands. Each gland
weighs about 4 g.
PARTS OF ADRENAL GLAND
Adrenal gland (Fig. 70.1) is made of two distinct parts:
1. Adrenal cortex: Outer portion, constituting 80% of the gland
2. Adrenal medulla: Central portion, constituting 20% of the gland.
HISTOLOGY OF ADRENAL CORTEX
Adrenal cortex is formed by three layers of structure. Each layer is distinct from one another.
1. Outer zona glomerulosa
2. Middle zona fasciculata
3. Inner zona reticularis.
HORMONES OF ADRENAL CORTEX
Adrenocortical hormones are steroids in nature, hence the name ‘corticosteroids’. Based on
their functions, corticosteroids are classified into three groups:
1. Mineralocorticoids
2. Glucocorticoids
3. Sex hormones.
MINERALOCORTICOIDS
Mineralocorticoids are the corticosteroids that act on the minerals (electrolytes), particularly
sodium and potassium.
Mineralocorticoids are:
1. Aldosterone
, 2. 11-deoxycorticosterone.
SOURCE OF SECRETION
Mineralocorticoids are secreted by zona glomerulosa of madrenal cortex.
FUNCTIONS OF MINERALOCORTICOIDS
Ninety percent of mineralocorticoid activity is provided by aldosterone.
Life-saving Hormone
Aldosterone is very essential for life and it maintains the osmolarity and volume of ECF. It is
usually called life-saving hormone because, its absence causes death within 3 days to 2
weeks. Aldosterone has three important functions.
It increases:
1. Reabsorption of sodium from renal tubules
2. Excretion of potassium through renal tubules
3. Secretion of hydrogen into renal tubules.
Actions of aldosterone are:
1. On Sodium Ions
Aldosterone acts on the distal convoluted tubule and the collecting duct and increases the
reabsorption of sodium. During hypersecretion of aldosterone, the loss of sodium through
urine is only few milligram per day. But during hyposecretion of aldosterone, the loss of
sodium through urine increases (hypernatriuria) up to about 20 g/day. It proves the
importance of aldosterone in regulation of sodium ion concentration and osmolality in the
body.
2. On Extracellular Fluid Volume
When sodium ions are reabsorbed from the renal tubules, simultaneously water is also
reabsorbed. Water reabsorption is almost equal to sodium reabsorption; so the net result is the
increase in ECF volume. Even though aldosterone increases the sodium reabsorption from
renal tubules, the concentration of sodium in the body does not increase very much because
water is also reabsorbed simultaneously. But still, there is a possibility for mild increase in
concentration of sodium in blood (mild hypernatremia). It induces thirst, leading to intake of
water which again
increases the ECF volume and blood volume.
3. On Blood Pressure
Increase in ECF volume and the blood volume finally leads to increase in blood pressure.
Aldosterone escape or escape phenomenon Aldosterone escape refers to escape of the kidney
from salt-retaining effects of excess administration or secretion of aldosterone, as in the case
of primary hyperaldosteronism.
4. On Potassium Ions
Aldosterone increases the potassium excretion through the renal tubules. When aldosterone is
deficient, the potassium ion concentration in ECF increases leading to hyperkalemia.
Hyperkalemia results in serious cardiac toxicity, with weak contractions of heart and
development of arrhythmia. In very severe conditions, it may cause cardiac death. When
aldosterone secretion increases, it leads to hypokalemia and muscular weakness.
5. On Hydrogen Ion Concentration
While increasing the sodium reabsorption from renal tubules, aldosterone causes tubular
secretion of hydro- gen ions. To some extent, secretion of hydrogen ions is in exchange for
sodium ions. It obviously reduces the hydrogen ion concentration in the ECF. In normal
conditions, aldosterone is essential to maintain acidbase balance in the body. In
hypersecretion, it causes alkalosis and in hyposecretion, it causes acidosis.
6. On Sweat Glands and Salivary Glands
Aldosterone has almost the similar effect on sweat glands and salivary glands as it shows on
renal tubules. Sodium is reabsorbed from sweat glands under the influence of aldosterone,
IMPORTANCE OF ADRENAL GLANDS
Adrenal glands are called the ‘life-saving glands’ or ‘essential endocrine glands’. It is
because the absence of adrenocortical hormones causes death within 3 to 15 days and absence
of adrenomedullary hormones, drastically decreases the resistance to mental and physical
stress.
FUNCTIONAL ANATOMY OF ADRENAL GLANDS
There are two adrenal glands. Each gland is situated on the upper pole of each kidney.
Because of the situation, adrenal glands are otherwise called suprarenal glands. Each gland
weighs about 4 g.
PARTS OF ADRENAL GLAND
Adrenal gland (Fig. 70.1) is made of two distinct parts:
1. Adrenal cortex: Outer portion, constituting 80% of the gland
2. Adrenal medulla: Central portion, constituting 20% of the gland.
HISTOLOGY OF ADRENAL CORTEX
Adrenal cortex is formed by three layers of structure. Each layer is distinct from one another.
1. Outer zona glomerulosa
2. Middle zona fasciculata
3. Inner zona reticularis.
HORMONES OF ADRENAL CORTEX
Adrenocortical hormones are steroids in nature, hence the name ‘corticosteroids’. Based on
their functions, corticosteroids are classified into three groups:
1. Mineralocorticoids
2. Glucocorticoids
3. Sex hormones.
MINERALOCORTICOIDS
Mineralocorticoids are the corticosteroids that act on the minerals (electrolytes), particularly
sodium and potassium.
Mineralocorticoids are:
1. Aldosterone
, 2. 11-deoxycorticosterone.
SOURCE OF SECRETION
Mineralocorticoids are secreted by zona glomerulosa of madrenal cortex.
FUNCTIONS OF MINERALOCORTICOIDS
Ninety percent of mineralocorticoid activity is provided by aldosterone.
Life-saving Hormone
Aldosterone is very essential for life and it maintains the osmolarity and volume of ECF. It is
usually called life-saving hormone because, its absence causes death within 3 days to 2
weeks. Aldosterone has three important functions.
It increases:
1. Reabsorption of sodium from renal tubules
2. Excretion of potassium through renal tubules
3. Secretion of hydrogen into renal tubules.
Actions of aldosterone are:
1. On Sodium Ions
Aldosterone acts on the distal convoluted tubule and the collecting duct and increases the
reabsorption of sodium. During hypersecretion of aldosterone, the loss of sodium through
urine is only few milligram per day. But during hyposecretion of aldosterone, the loss of
sodium through urine increases (hypernatriuria) up to about 20 g/day. It proves the
importance of aldosterone in regulation of sodium ion concentration and osmolality in the
body.
2. On Extracellular Fluid Volume
When sodium ions are reabsorbed from the renal tubules, simultaneously water is also
reabsorbed. Water reabsorption is almost equal to sodium reabsorption; so the net result is the
increase in ECF volume. Even though aldosterone increases the sodium reabsorption from
renal tubules, the concentration of sodium in the body does not increase very much because
water is also reabsorbed simultaneously. But still, there is a possibility for mild increase in
concentration of sodium in blood (mild hypernatremia). It induces thirst, leading to intake of
water which again
increases the ECF volume and blood volume.
3. On Blood Pressure
Increase in ECF volume and the blood volume finally leads to increase in blood pressure.
Aldosterone escape or escape phenomenon Aldosterone escape refers to escape of the kidney
from salt-retaining effects of excess administration or secretion of aldosterone, as in the case
of primary hyperaldosteronism.
4. On Potassium Ions
Aldosterone increases the potassium excretion through the renal tubules. When aldosterone is
deficient, the potassium ion concentration in ECF increases leading to hyperkalemia.
Hyperkalemia results in serious cardiac toxicity, with weak contractions of heart and
development of arrhythmia. In very severe conditions, it may cause cardiac death. When
aldosterone secretion increases, it leads to hypokalemia and muscular weakness.
5. On Hydrogen Ion Concentration
While increasing the sodium reabsorption from renal tubules, aldosterone causes tubular
secretion of hydro- gen ions. To some extent, secretion of hydrogen ions is in exchange for
sodium ions. It obviously reduces the hydrogen ion concentration in the ECF. In normal
conditions, aldosterone is essential to maintain acidbase balance in the body. In
hypersecretion, it causes alkalosis and in hyposecretion, it causes acidosis.
6. On Sweat Glands and Salivary Glands
Aldosterone has almost the similar effect on sweat glands and salivary glands as it shows on
renal tubules. Sodium is reabsorbed from sweat glands under the influence of aldosterone,
