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Anatomy?Physio > AP Adrenal > Flashcards

AP Adrenal Flashcards

1
Q

Describe the hormones secreted by adrenal cortex.

A

The adrenal gland secretes steroid hormones such as cortisol and aldosterone. It also makes precursors that can be converted to sex steroids (androgen, estrogen). A different part of the adrenal gland makes adrenaline (epinephrine).

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2
Q

Anatomy of adrenal gland

A

Adrenal glands are paired organs located in the retroperitoneal area near the superior poles of the kidneys

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3
Q

Structure & Function of Adrenal Gland

A

Cortex: Comprises 80% of gland and is derived from mesoderm

Medulla; Comprises of 20% of gland and is derived from ectoderm

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4
Q

Adrenal Medulla

A

¢Functionally related to sympathetic nervous system

¢Chromaffin cells (neuroendocrine cells) in adrenal medulla secretes catecholamines like epinephrine & norepinephrine into blood on sympathetic stimulation

¢Effects of secreted epinephrine & norepinephrine mimic sympathetic stimulation

¢More widespread effect than direct sympathetic stimulation

¢Influences all organs & tissues of body

¢Epinephrine stimulates cardiac output & metabolic activity throughout body

¢Norepinephrine promotes vasoconstriction & dilates pupils of eyes

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5
Q

Adrenal Medulla…cont’d

A

-Catecholamines

  • ¢Derived from tyrosine (non essential amino acid)
  • —Phenylalanine → Tyrosine → Dopamine → Norepinephrine → Epinephrine

¢Pheochromocytoma

  • —Catecholamine-secreting tumor that arises from chromaffin cells of the adrenal medulla
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6
Q

Adrenal Cortex

Corticosteroids

A

Corticosteroids

¢Mineralocorticoids

—Zona glomerulosa

—Affects electrolytes of ECF like sodium and potassium

Aldosterone

¢Glucocorticoids

—Zona fasciculata

—Increase blood glucose concentrations

Cortisol

¢Androgens

—Zona reticularis

—Similar to testosterone

Dihydroepiandrosterone

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7
Q

Synthesis of Adrenocortical Hormones

A

¢Cholesterol enters adrenal cortex cells in form of low-density lipoproteins (LDL)

¢ACTH stimulates uptake of LDL & liberation of cholesterol

¢ACTH & angiotensin II stimulate conversion of cholesterol to pregnenolone

  • —Rate-limiting step in synthesis of adrenocorticosteroids
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8
Q

Transport of Corticosteroids in Blood

A

¢Cortisol largely (90–95%) bound to plasma proteins in blood

  • —Cortisol-binding globulin plays primary role
  • Binding prolongs lifetime in plasma (t½ = 60–90 min

¢Aldosterone less extensively (-60%) bound to plasma proteins in blood

  • —Shorter lifetime in plasma (t½ . 20 min)

¢Cortisol & aldosterone metabolized primarily in liver

  • —Metabolites excreted partially in bile (-25%) & remainder by kidneys (-75%)
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9
Q

Aldosterone

A
  • Critical role in regulation of electrolytes (K+, Na+ & Cl–) in extracellular fluids
  • Absence of aldosterone leads to
  • —↑ K+, ↓ Na+ & ↓ Cl– in plasma
  • —Marked reductions in blood & extracellular fluid volumes & cardiac output
  • —Fatal condition unless mineralocorticoid administered
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10
Q

Functions of Aldosterone

A

-Aldosterone triggers Na+ reabsorption & K+ secretion by renal tubular epithelial cells

  • —Predominant effect on principal cells of collecting tubules
  • —EXCESS of aldosterone : HYPOKALEMIA
  • —TOO LITTLE of aldosterone: HYPERKALEMIA
  • Results in conservation of Na+ in extracellular fluid & enhanced urinary K+ excretion
  • ↑ Na+ reabsorption leads to ↑ water reabsorption
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11
Q

Signaling Mechanism for Aldosteron

A
  • High lipophilicity of aldosterone allows ready diffusion into cell
  • Activation of the mineralocorticoid receptor (MR) by aldosterone can be antagonized with spironolactone, a MR antagonist.
  • —ENaC - epithelial sodium channel proteins
  • ¢help maintain Na-K homeostasis together with Na-K pump
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12
Q

Regulation of Aldosterone Secretion

A

Renin Angiotensin: Angiotensin II causes marked ↑ in aldosterone secretion

Potassium: High levels of K+ induces marked ↑ in aldosterone secretion

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13
Q

Major glucocorticoid:

A

Cortisol, known also as hydrocortisone.

Small but significant amount of glucocorticoid activity is provided by corticosterone.

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14
Q

Effects of CORTISOL on Carbohydrate Metabolism

A

-STIMULATION OF GLUCONEOGENESIS IN LIVER

  • —Increased expression of enzymes for gluconeogenesis plays major role
  • —Mobilization of amino acids from extrahepatic tissues

DECREASED GLUCOSE UTILIZATION BY CELLS

  • —Results in ↑ blood glucose & secretion of insulin
  • —May cause “adrenal diabetes” due to impaired action of insulin
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15
Q

Effects of cortisol on protein metabolism

A

¢Cortisol ↓ protein synthesis & ↑ protein catabolism in muscle & many tissues EXCEPT IN LIVER

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16
Q

Effects of cortisol on fat metabolism

A

-Cortisol ↑ mobilization of fatty acids from adipocytes

—Fatty acids used in preference to glucose as energy source

17
Q

Cortisol plays key role in resisting

A

stress & inflammation

¢Stress triggers ↑ ACTH secretion by pituitary & ↑ cortisolsecretion by adrenals

¢Multiple mechanisms contribute to cortisol’s ability to suppress inflammation

  • —Stabilization of lysosomal membranes in inflammatory cells
  • —↓ permeability of blood capillaries
  • —↓ chemotaxis of leukocytes into inflamed area & ↓ phagocytosis
  • ¢Mediated by ↓ production of prostaglandins & leukotrienes
  • —Suppression of immune system & ↓ expansion of T lymphocyte clones
  • —Suppression of fever & ↓ vasodilaton

¢Cortisol may also enhance repair & healing of damaged tissues

18
Q

Regulation of Cortisol Secretion

A

ACTH acts on GPCR to stimulate of adenylyl cyclase; ↑ cAMP stimulates conversion of cholesterol to pregnenolone; pregnenolone → cortisol

19
Q

Pathophysiology of Adrenal Medulla

A

Pheochromocytoma

¢Neoplasms of the chromaffin cells of the adrenal medulla

¢These tumors secrete excessive amounts of epinephrine, norepinephrine, or both

¢Most common presenting feature of pheochromocytoma is hypertension

20
Q

Pathophysiology of Adrenal Cortex
Hyperadrenalism

A
  • Characterized by excess cortisol secretion, also known as Cushing’s syndrome
  • Primary cause is usually excess ACTH secretion from anterior pituitary
  • —Can arise from tumor in adrenal cortex, ectopic tumor or excess CRH secretion
  • Major symptoms of Cushing’s syndrome due to changes in fat & protein metabolism
21
Q

Cushing’s Syndrome

A

¢Symptoms

  • —Extra fat deposition in upper abdomen & thorax (“buffalo torso”)
  • —Edematous appearance of face (“moon face”)
  • —Gradual weight gain
  • —Severe muscle weakness
  • —Osteoporosis
  • ¢↓ osteoblast function and Ca2+ absorption; ↑ bone resorption
  • —Suppressed immune function
  • Surgery & pharmacological antagonism (drugs that inhibit steroidogenesis) provide treatment options
  • Ketoconozole and Mitotane can both block cortisol biosynthesis and are indicated for Cushing’s syndrome
22
Q

Pathophysiology of Adrenal Cortex
Hypoadrenalism

A
  • Also known as Addison’s disease
  • Atrophy or injury of adrenal cortices leads to adrenal insufficiency
  • Autoimmune process responsible in most cases (-80%)
  • Can occasionally arise secondary to impaired function of anterior pituitary
  • Disease characterized by reduced production of aldosterone & cortisol
  • —Symptoms characterized by these deficiencies
  • —Most patients also show excessive melanin pigmentation (due to excess ACTH – absence of negative inhibition)
23
Q

Diagnosis of Addison’s Disease

A

-ACTH Stimulation test

—Administration of 250 μg of synthetic ACTH (cosyntropin) intravenously or intramuscularly and monitor elevation of cortisol level

—No elevation in cortisol is a positive indicator of Addison’s disease

24
Q

Hyperaldosteronism
Conn’s Syndrome

A
  • Tumor in zona glomerulosa
  • The most important effects are hypokalemia, hypertension, mild metabolic alkalosis, slight ↑ in ECF volume and blood volume
  • Occasional periods of muscle paralysis caused by the hypokalemia
  • Treatment options include surgical removal of tumor or pharmacological antagonism (for mineralocorticoid receptor with spironolactone
25
Q

Hypoaldosteronism causes

A
  • Causes: destruction of adrenocortical tissue, defects in the synthesis of aldosterone or inadequate stimulation of aldosterone secretion
  • Characterized by Na+ loss (hyponatremia), hypovolemia, hypotension, hyperkalemia and metabolic acidosis
  • Mineralocorticoid replacement therapy
26
Q

Adrenogenital Syndrome

A

¢Excessive quantities of androgens → intense masculinizing effects

¢Females: development of male secondary sexual characteristics

¢Rapid development of male sexual organs in prepubertalmales (pseudopuberty) but little effect in mature males

27
Q
A

Anatomy?Physio (11 decks)

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