MCQ

• Adrenal gland

  Comprises two endocrine organs, with one surrounding the other

  
• Adrenal gland components

  • Adrenal medulla
  • Adrenal cortex

  
• Adrenal medulla

  Main secretions are the catecholamines: epinephrine, norepinephrine, and dopamine

  
• Adrenal cortex

  Secretes steroid hormones

  
• The adrenal cortex acts as a secondary site for androgen synthesis, releasing sex hormones such as testosterone that influence reproductive function

  
• The adrenal medulla constitutes 28% of the adrenal gland's mass and features two morphologically distinct cell types: one secreting epinephrine and the other secreting norepinephrine

  
• In humans, 90% of these cells secrete epinephrine, while 10% secrete norepinephrine
• Adrenal cortex zones

  • Zona glomerulosa
  • Zona fasciculata
  • Zona reticularis
• All three cortical zones secrete corticosterone, but only the zona glomerulosa has the active enzymatic mechanism for aldosterone biosynthesis

  
• The enzymatic mechanisms for cortisol and sex hormone formation are located in the two inner zones (zona fasciculata and zona reticularis)

  
• Catecholamines


  Norepinephrine, epinephrine, and small amounts of dopamine synthesized in the adrenal medulla

  
• Norepinephrine synthesis


  Hydroxylation and decarboxylation of tyrosine

  
• Epinephrine synthesis

  Methylation of norepinephrine

  
• In plasma, approximately 95% of dopamine and 70% of norepinephrine and epinephrine are conjugated to sulfate, rendering these conjugates inactive

  
• The catecholamines' half-life in circulation is about 2 minutes
• Effects of epinephrine and norepinephrine

  • Promote glycogenolysis in liver and skeletal muscle
  • Mobilization of free fatty acids (FFA)
  • Increased plasma lactate
  • Stimulation of the metabolic rate

  
• Adrenergic receptors

  Mediate the metabolic effects of epinephrine and norepinephrine

  
• Effects of epinephrine and norepinephrine on hormones

  • Increase insulin and glucagon secretion via β-adrenergic mechanisms
  • Inhibit insulin and glucagon secretion through α-adrenergic mechanisms

  
• Effects of norepinephrine and epinephrine on the cardiovascular system

  • Norepinephrine induces vasoconstriction via α1-receptors
  • Epinephrine causes vasodilation in skeletal muscle and liver blood vessels via β2-receptors
  • Both enhance the force and rate of heart contractions via β1-receptors

  
• Dopamine effects

  • Induces renal vasodilation, likely via specific dopaminergic receptors
  • Causes vasoconstriction, presumably by norepinephrine release
  • Exerts a positive inotropic effect on the heart through β1-adrenergic receptors
  • Promotes natriuresis, possibly by inhibiting renal Na, K, ATPase

  
• Regulation of adrenal medullary secretion

  • Drug actions can directly influence adrenal medulla secretion
  • Physiological stimuli primarily affect it through the sympathetic nervous system

  
• Basal catecholamine secretion is low, with further reductions in epinephrine and norepinephrine levels during sleep (low sympathetic nervous system activity)

  
• Increased adrenal medullary secretion

  Triggered by emergency situations (stimulation of sympathetic nervous system), part of the broader sympathetic response described by Cannon as the "emergency function of the sympathoadrenal system," preparing the individual for fight-or-flight scenarios and increasing plasma catecholamines under various conditions

  
• Adrenal cortex hormones

  Derivatives of cholesterol, share the cyclopentanoperhydrophenanthrene nucleus with cholesterol, bile acids, vitamin D, and ovarian and testicular steroids

  
• Physiologically significant steroids secreted by the adrenal cortex

  • Mineralocorticoid: Aldosterone
  • Glucocorticoids: Cortisol and corticosterone
  • Androgens: Dehydroepiandrosterone (DHEA) and androstenedione

  
• Deoxycorticosterone, another mineralocorticoid, is secreted in amounts similar to aldosterone but has only 3% of aldosterone's mineralocorticoid activity
• Steroid biosynthesis

  1. Cholesterol, derived from acetate synthesis or uptake from LDL, is the precursor of all steroids

  2. Cholesterol ester hydrolase catalyzes the formation of free cholesterol, which is transported to mitochondria for conversion to pregnenolone

  3. Pregnenolone moves to the smooth endoplasmic reticulum, converting to progesterone in part

  4. ACTH binding to adrenocortical cell receptors activates adenylyl cyclase via Gs protein (Increase cAMP), increasing pregnenolone formation and its derivatives promptly

  5. Over time, ACTH also boosts the synthesis of P450 enzymes involved in glucocorticoid production
• Glucocorticoid binding

  • Cortisol binds to transcortin or corticosteroid-binding globulin (CBG) in circulation, synthesized in the liver and influenced by estrogen levels
  • CBG levels rise during pregnancy and decrease in conditions like cirrhosis, nephrosis, and multiple myeloma
  • Changes in CBG levels affect free cortisol levels, influencing ACTH secretion and cortisol production
  • Cortisol also binds to albumin, extending its half-life in circulation to 60-90 minutes
  • Bound steroids are inactive, and due to protein binding, little free cortisol and corticosterone are found in urine
  • Bound cortisol serves as a circulating hormone reservoir, ensuring a constant supply of free cortisol to tissues

  
• Metabolism and excretion of glucocorticoids

  1. Cortisol is metabolized in the liver, the main site for glucocorticoid catabolism

  2. It is reduced to dihydrocortisol and then to tetrahydrocortisol, which is conjugated to glucuronic acid

  3. Cortisone, an active glucocorticoid converted to cortisol, is extensively used in medicine but not secreted in significant amounts by the adrenal glands

  4. Cortisone formed in the liver hardly enters the circulation as it is quickly reduced and conjugated to form tetrahydrocortisone glucuronides

  
• Aldosterone

  • Minimally bound to protein and has a short half-life of about 20 minutes
  • Secreted in small amounts compared to cortisol and is converted in the liver to tetrahydroglucuronide derivative, with some converted in the liver and kidneys to an 18-glucuronide

  
• 17-Ketosteroids

  • The major adrenal androgen is dehydroepiandrosterone (DHEA), a 17-ketosteroid, with androstenedione also being secreted
  • The 11-hydroxy derivative of androstenedione and 17-ketosteroids from cortisol and cortisone are formed by side chain cleavage in the liver
  • Testosterone is converted to a 17-ketosteroid, contributing to the daily 17-ketosteroid excretion of 15 mg in men and 10 mg in women, with two-thirds in men being adrenal secreted or formed from cortisol

  
• Adrenal androgens

  • Promoting protein anabolism and growth (anabolic hormone), exert masculinizing effects
  • Testosterone from the testes is the most potent androgen, with adrenal androgens having less than 20% of its activity
  • Adrenal androgen secretion is acutely controlled by ACTH, not gonadotropins, and normally exerts minimal masculinizing effect unless secreted in excess

  
• Adrenal estrogens

  The adrenal androgen androstenedione is converted to testosterone and estrogens in peripheral tissues, serving as a significant estrogen source in men and postmenopausal women

  
• Glycogenolysis

  The process where the body breaks down glycogen into glucose, which is a type of sugar that provides energy. This happens mainly in the liver and skeletal muscles.
• Natriuresis

  The process of excreting sodium in the urine
• Androgens


  A group of hormones that play a role in male traits and reproductive activity. They are sometimes called male hormones, though both men and women produce them. Androgens are important for the development of male sex organs and other male physical characteristics like body hair and muscle mass.

  
• Types of hormones secreted by pancreas


  • Insulin
  • Glucagon
  • Somatostatin
  • Pancreatic polypeptide

  
• Islets of Langerhans


  Collections of cells within the pancreas, categorized into A, B, D, and F types based on staining properties and morphology

  
• Cell types in islets of Langerhans and their secretions


  • A (α) cells secrete glucagon
  • B (β) cells secrete insulin
  • D (δ) cells secrete somatostatin
  • F cells secrete pancreatic polypeptide

  
• In the management of patients with acute pancreatitis, early enteral feeding can be started if there are no signs of peritonism or organ failure.