2. Adrenal glands
A small gland that makes steroid hormones, adrenaline, and noradrenaline. These
hormones help control heart rate, blood pressure, and other important body
functions. There are two adrenal glands, one on top of each kidney. Also called
suprarenal gland.
The adrenal gland lies at the upper pole of each human kidney. Each glands (1) is
pyramidal in shape (2) is approximately 2 to 3 cm in width, 4 to 6 cm long, 1 cm
thick and (3) weighs approximately 4g regardless of age, weight, or sex.
3. • The human adrenal cortex secretes three major classes of steroid
hormones that possess a wide range of physiological functions. These
include the (1) glucocorticoids, (2) mineralocorticoids, and (3) adrenal
androgens.
4. • Adrenocorticotropic hormone is made in the corticotroph cells of
the anterior pituitary gland. It is secreted in several intermittent pulses
during the day into the bloodstream and transported around the body.
Like cortisol, levels of adrenocorticotropic hormone are generally high
in the morning when we wake up and fall throughout the day and
lowest during sleep. This is called a diurnal (circadian) rhythm.
• Once adrenocorticotropic hormone reaches the adrenal glands, it binds
on to receptors causing the adrenal glands to secrete more cortisol,
resulting in higher levels of cortisol in the blood. It also increases
production of the chemical compounds that trigger an increase in other
hormones such as adrenaline and noradrenaline.
5. Clinical significance
• regulate the glucocorticoid (steroid) hormone cortisol
Plasma level and half life
• The daily output of this hormone is 10ng and the conc. In plasma is
3ng/dl
• Half life of ACTH is 10 minutes
Mode of action
• ACTH acts by the formation of cyclic AMP
6. • Actions of ACTH on Adrenal cortex
• Maintainence of structural integrity and vascularization of zona
fasiculata and zona reticularis of adrenal cortex
• Conversion of cholesterol into pregnenolone, which is the precursor
of glucocorticoids.
7. • Results of an ACTH test are often compared with the results of
cortisol tests and may show one of the following:
• High ACTH and high cortisol levels: This may mean Cushing's disease.
• Low ACTH and high cortisol levels: This may mean Cushing's
syndrome or a tumor of the adrenal gland.
• High ACTH and low cortisol levels: This may mean Addison disease.
• Low ACTH and low cortisol levels. This may mean hypopituitarism
8. Hypersecretion
• The effects of too much adrenocorticotropic hormone are mainly due to the increase in
cortisol levels. Higher than normal levels of adrenocorticotropic hormone may be due to:
• Cushing's disease – this is the most common cause of increased adrenocorticotropic
hormone. It is caused by a non-cancerous tumour called an adenoma located in the
pituitary gland, which produces excess amounts of adrenocorticotropic hormone. (Please
note, Cushing’s disease is just one of the numerous causes of Cushing’s syndrome).
• Rarely, a tumour outside the pituitary gland, producing adrenocorticotropic hormone
(also called ectopic adrenocorticotropic hormone tumour).
• Adrenal insufficiency including addison’s disease (although cortisol levels are low,
adrenocorticotropic hormone levels are raised).
• Congenital adrenal hyperplasia (a genetic disorder with inadequate production of
cortisol, aldosterone or both).
9. Hyposecretion
Lower than normal levels of adrenocorticotropic hormone may be due
to:
• Cushing's syndrome related to an adrenal tumour (endogenous) or
due to long term use of steroid medication for other diseases
(exogenous). Although adrenocorticotropic hormone levels are low,
cortisol levels are raised.
• Conditions affecting the pituitary gland, e.g. hypopituitarism.
• Side-effect of pituitary surgery or radiation therapy.
• Too little adrenocorticotropic hormone could lead to a poorly
functioning adrenal gland due to insufficient production of cortisol.
10. Screening test for cushing syndrome
• One is the measurement of 24-hour urinary free cortisol under
normal circumstances, <2% of the secreted cortisol appears in urine
as free cortisol. In general, a 24-hour urinary free cortisol
concentration <I00 microgram/day excludes the diagnosis of Cushing
syndrome, and concentrations >I20 microgram/day suggest the
diagnosis of Cushing syndrome.
• Another reliable and convenient screening test for Cushing syndrome
is the overnight low-dose dexamethasone suppression test (1 mg at
midnight) with measurement of serum cortisol (suppressed to <5
microgram/dL [I40 nmol/L) at 08:OO hours the following morning
