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Lec.6: The Adrenal Cortex
Lecture Objectives:
Identify the regional production of adrenal cortex hormones
the actions of the produced hormones
the regulatory mechanism and the disorders of the secreted hormone
Adrenal Glands
Are small, triangular glands loosely attached to the kidneys, divided into two regions:
1) Adrenal cortex (outer part of the adrenal gland) contains:
a. Zona glomerulosa: Secretes mineralocorticoids (aldosterone)
b. Zona fasciculate: Secretes is glucocorticoids (cortisol).
c. Zona reticularis: Primary secretion is androgens (male sex hormone)
2) adrenal medulla (inner part of the adrenal gland) is a modified post-ganglionic neurons
connected to sympathetic neurons.
Hormones produced by the adrenal cortex are referred to as corticosteroids, comprise
mineralocorticoids, glucocorticoids and androgens.
Zona Glomerulosa Outermost zone – just below the adrenal capsule secretes
mineralocorticoids. Mineralocorticoids are involved in regulation of sodium, potassium
and acid-base homeostasis. the mineralocorticoid of most importance is aldosterone
Zona Fasciculata is the Middle zone – between the glomerulosa and reticularis, Primary
secretion is glucocorticoids. Glucocorticoids, are involved the blood glucose homeostasis.
However they have additional effects in protein and fat metabolism. The glucocorticoid
of most importance is cortisol.
Zona Reticularis is the Innermost zone – Primary secretion is androgens
adrenal cortex hormone are steroids and derived from cholesterol
Glucocorticoid:
They have widespread metabolic effects on carbohydrates, fat and protein metabolism,
cortisol:
1) stimulates gluconeogenesis(which is the synthesis of glucose from noncarbohydrates
substrates, such as amino acids )
2) Increases lipolysis in adipose tissue.
3) Increases proteolysis and amino acid release in the muscle.
4) control the activity of the immune system
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Regulation of glucocorticoid Secretion:
ACTH is the main stimulus to cortisol secretion; three factors regulate ACTH and
therefore cortisol secretion:
1) Negative feedback control. ACTH release from the ant. pitutary gland is stimulated
by hypothalamic CRH ,increased plasma cortisol suppress CRH secretion.
2) Stress as (surgery, emotional stress) leads to sudden large increase in CRH and ACTH
secretion, the negative feedback control is temporarily overridden.
3) The diurnal rhythm of plasma cortisol, which is related to the sleeping –waking
cycle, cortisol is highest at the morning and fall to lowest level at the onset of sleep.
Glucocorticoid transport:
In the circulation 90% of glucocorticoid is protein bound mainly to cortisol –binding
globulin.
The biologically active form of cortisol in the plasma is the free (unbound).
The cortisol is removed from the plasma by the liver and converted to metabolically
inactive compound excreted in the urine as conjugated metabolites usually as
glucuronides. A small amount of cortisol is excreted unchanged in the urine. Urine
cortisol excretion is related to the free cortisol.
o Cortisol excess leads to a condition known as Cushing diseases, the excess cortisol may
be due adrenal hypersecretion (primary) or secondary to hypothalamic or pitutary
hypersecretion.
o Low cortisol result either from adrenal problem (Addison dis) or secondary to ACTH
deficiency (pitutary level)
o the following biochemical lab tests can be helpful to investigate the hypothalamic-pit-
adrenocorticoal axis:
CRH, ACTH, plasma cortisol (free and total),
24 hour urinary cortisol.
loss of cortisol diurinal rhythm
in addition to tests that suppress or stimulate the hormone.
Mineralocorticoid
The main mineralocorticoid is aldosterone (which is a steroid hormone), its main
function is to conserve Na
+
mainly by facilitating Na
+
reabsorption and in enhance the
secretion of K
+
in the distal renal tubules.
Aldosterone is the main regulator of water and electrolytes balance as well as blood
pressure, it increase blood pressure through blood volume expansion.
The regulators of aldosterone are:
1) The renin angiotensin system is the most important system controlling aldosterone
secretion, renin is a proteolytic enzyme produced by juxtaglomerular apparatus of the
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kidney and released in response to a decrease in the circulating blood volume, or Na
+
loss.
2) Renin converts angiotensinogen in the plasma to angiotensin I which is then converted
by angiotensin converting enzyme to angiotensin II which stimulate aldosterone
secretion.
3) Potassium; increase in plasma K
+
, leads to increase aldosterone secretion which will
lead to increase in urine K
+
excretion.
4) ACTH: this controlling mechanism is not very important except in stress condition.
5) No specific aldosterone binding protein has been demonstrated.
Underproduction, or hypoaldosteronism, leads to the low plasma Na and high plasma K
Hyperaldosteronism (elevated aldosterone) generally results from adrenal cancers. The
two main resulting problems:
1) Hypertension and edema due to excessive Na+ and water retention.
2) Accelerated excretion of potassium ions (K+). K+ loss leads to muscle weakness.
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