Adrenal Gland and cortex Of endocrine system

also known as suprarenal glands

Paired, pyramid-shaped organs atop kidneys

Structurally and functionally it is two glands in one

• Adrenal cortex: three layers of glandular tissue that synthesize and secrete several different hormones

• Adrenal medulla: nervous tissue that is part of sympathetic nervous system

This area of adrenal gland produces over 24 different hormones collectively called

corticosteroids

Three layers of cortical cells produce the different corticosteroids

• Zona glomerulosa - Mineralocorticoids

• Zona fasciculata—

  Glucocorticoid

• Zona reticularis—Gonadocorticoids

• Zona glomerulosa—

  • Mineralocorticoids

• Regulate electrolyte concentrations (primarily Na⁺ and K⁺) in ECF

  • Importance of Na⁺: affects ECF volume, blood volume, blood pressure, and levels of other ions (K⁺, H⁺, HCO₃^- and Cl^-)

Aldosterone -most potent mineralocorticoid 

• Stimulates Na⁺ reabsorption by kidneys

  • Results in increased blood volume and blood pressure

• Stimulates K⁺ elimination by kidneys

• Effects of aldosterone are short lived

• Stimulates synthesis and activation of Na⁺-K⁺ ATPase transport pumps

  • Pump exchanges Na⁺ for K⁺ 

Factors that regulate aldosterone secretion: 

• Renin-angiotensin-aldosterone mechanism

• Plasma concentration of K⁺

• ACTH

• Atrial natriuretic peptide

Renin-angiotensin-aldosterone mechanism (RAAS System) -

• Decreased blood pressure stimulates special cells in kidneys

• These cells release renin into blood 

• Renin cleaves off part of plasma protein, angiotensinogen, that triggers enzyme cascade, resulting in conversion to angiotensin II

  • Angiotensin II is a potent stimulator of aldosterone release 

• Decreased blood pressure stimulates special cells in kidneys

• These cells release renin into blood 

• Renin cleaves off part of plasma protein, angiotensinogen, that triggers enzyme cascade, resulting in conversion to angiotensin II

  • Angiotensin II is a potent stimulator of aldosterone release 

Plasma concentration of K⁺

• Mineralocorticoids

• Increased K⁺ directly influences zona glomerulosa cells to release aldosterone

  • Increased K⁺ directly stimulates aldosterone release; low levels inhibit it

ACTH

• Can cause small increases of aldosterone during periods of increased stress

Atrial natriuretic peptide (ANP) 

• Secreted by heart in response to high blood pressure

• Blocks renin and aldosterone secretion to decrease blood pressure

Zona fasciculata—Glucocorticoids

• Influence metabolism of most cells and help us resist stressors

• Keep blood glucose levels relatively constant

• Maintain blood pressure by increasing action of vasoconstrictors

Glucocorticoid hormones include:

• Cortisol (hydrocortisone); only glucocorticoid in significant amounts in humans

• Cortisone

• Corticosterone

Regulation of secretion ;

• Cortisol is released in response to ACTH

  • ACTH released in response to corticotropin-releasing hormone (CRH)

  • CRH released in response to low cortisol levels

  • Increased cortisol levels inhibit ACTH and CRH through negative feedback

• Cortisol secretion cycles are governed by patterns of eating and activity

• Acute stress (infection, physical or emotional trauma) interrupts cortisol rhythm

• CNS can override cortisol inhibition of ACTH and CRH, leading to more cortisol secretion

Actions or regulation of secretion -

• Cortisol is released in response to ACTH

  • ACTH released in response to corticotropin-releasing hormone (CRH)

  • CRH released in response to low cortisol levels

  • Increased cortisol levels inhibit ACTH and CRH through negative feedback

• Cortisol secretion cycles are governed by patterns of eating and activity

• Acute stress (infection, physical or emotional trauma) interrupts cortisol rhythm

• CNS can override cortisol inhibition of ACTH and CRH, leading to more cortisol secretion

Reglation of secrwtion actions -

• Cortisol causes increase in blood levels of glucose, fatty acids, and amino acids 

• Prime metabolic effect is gluconeogenesis, formation of glucose from fats and proteins

  • Encourages cells to use fatty acids for fuel so glucose is “saved” for brain

• Other function is to enhance vasoconstriction

  • Causes rise in blood pressure to quickly distribute nutrients to cells

• Excessive levels of glucocorticoids:

  • Depress cartilage and bone formation

  • Inhibit inflammation by decreasing release of inflammatory chemicals

  • Depress immune system

  • Disrupt normal cardiovascular, neural, and gastrointestinal functions

• Glucocorticoid drugs can control symptoms of many inflammatory diseases (arthritis, allergies) but can also cause undesirable effects

Zona reticularis—Gonadocorticoids (adrenal sex hormone)

• Weak androgens (male sex hormones) converted to testosterone in tissue cells, some to estrogens

• May contribute to:

  • Onset of puberty and appearance of secondary sex characteristics

  • Sex drive in women 

  • Source of estrogens in postmenopausal women