Pathophysiology
Summary
The adrenal cortex is divided into three layers: the zona glomerulosa (outer layer) produces mineralocorticoids like aldosterone; the zona fasciculata (middle layer), which synthesizes glucocorticoids ; and the zona reticularis (inner layer), responsible for androgen synthesis.
Adrenal insufficiency manifests in three major forms: primary adrenal insufficiency, arising from intrinsic defects in the adrenal cortex; secondary adrenal insufficiency, resulting from decreased ACTH secretion by the pituitary gland; and tertiary adrenal insufficiency, which occurs due to reduced CRH release from the hypothalamus.
In primary adrenal insufficiency, both cortisol and aldosterone are deficient, leading to a range of physiological abnormalities. Hypocortisolism reduces vascular tone, impairs gluconeogenesis leads to hypoglycemia. Hypoaldosteronism affects the Na/K ATPase in the collecting duct, resulting in hyperkalemia and hyponatremia, and ammonia production, which can contribute to type IV RTA.
Primary adrenal insufficiency can arise occur in both acute and chronic settings. A notably acute form is Waterhouse-Friderichsen syndrome, characterized by bilateral adrenal hemorrhage usually triggered by acute sepsis from Neisseria meningitidis. Acute bilateral adrenal hemorrhage can also result from anticoagulation therapy or disseminated intravascular coagulation (DIC). Addison's Disease is a chronic form with an insidious onset, often resulting from autoimmune destruction of the cortex (HLA B8, DR3, DR4). It is characterized by symptoms such as postural hypotension & salt wasting, as well as irregular menses or amenorrhea and skin hyperpigmentation from increased ACTH and MSH production.
Secondary adrenal insufficiency arises from pituitary dysfunction, leading to decreased ACTH and consequently reduced cortisol production. A hallmark of this condition is decreased cortisol levels with preserved mineralocorticoid production, as aldosterone production is regulated by RAAS.
Distinctively, secondary adrenal insufficiency lacks the hyperpigmentation common in primary adrenal insufficiency due to low MSH levels. It often coexists with deficiencies in other pituitary hormones such as LH, FSH, and TSH, making it commonly associated with broader pituitary disorders.
Tertiary adrenal insufficiency results when the hypothalamic secretion of CRH is inhibited, leading to decreased levels of ACTH and consequently reduced cortisol production. Chronic use of exogenous steroids is the most commonly etiology, and abrupt withdrawal may result in adrenal insufficiency or crisis. It can also develop from hypothalamic tumors or radiation.
Adrenal crisis is a life-threatening condition resulting from acute cortisol deficiency. It can be triggered by acutely stopping exogenous steroids, exposing low endogenous cortisol levels, or acute stress events like injuries or surgeries, These events demand an increase in endogenous cortisol production, and a lack of this cortisol response in individuals with adrenal insufficiency can also lead to an adrenal crisis.
Lesson Outline
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FAQs
Adrenal insufficiency is characterized by inadequate production of adrenal hormones. It can manifest in three forms: primary, secondary, and tertiary. Primary adrenal insufficiency arises from an intrinsic defect in the adrenal cortex, leading to decreased production of both cortisol and aldosterone. Secondary adrenal insufficiency is due to a lack of adrenocorticotropic hormone (ACTH) from the pituitary gland, affecting mainly cortisol production. Tertiary adrenal insufficiency is caused by insufficient corticotropin-releasing hormone (CRH) from the hypothalamus, also primarily affecting cortisol levels.
Acute primary adrenal insufficiency can be precipitated by bilateral adrenal hemorrhage, often resulting from anticoagulation therapy or disseminated intravascular coagulation (DIC). A severe form of this condition is Waterhouse-Friderichsen syndrome, characterized by bilateral adrenal hemorrhage in the context of acute sepsis, commonly due to Neisseria meningitidis infection.
Hypocortisolism, or cortisol deficiency, leads to decreased vascular tone, resulting in hypotension and shock. It also impairs gluconeogenesis, causing hypoglycemia. Hypoaldosteronism, a deficiency in aldosterone, leads to hyperkalemia and type 4 renal tubular acidosis due to reduced Na/K counter-transporter activity in the renal collecting ducts. Additionally, it causes hyponatremia and volume loss through increased renal excretion of sodium and water.
Addison's disease is a form of chronic primary adrenal insufficiency with an insidious onset. It is characterized by symptoms such as postural hypotension, salt wasting, and skin hyperpigmentation. The most common cause is autoimmune destruction of the adrenal cortex, although it can also be triggered by disseminated tuberculosis. Addison's disease is often associated with specific HLA types like B8, DR3, and DR4.
Long-term use of exogenous steroids suppresses the release of corticotropin-releasing hormone (CRH) from the hypothalamus and adrenocorticotropic hormone (ACTH) from the pituitary gland. This results in a decrease in endogenous cortisol production and results in adrenal atrophy. If steroid therapy is abruptly discontinued, the suppressed endogenous cortisol production becomes unmasked, leading to adrenal insufficiency. To mitigate this risk, it's advisable to taper off steroid therapy gradually.
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