Thyroid & Adrenals

• Adrenals are the supplier of corticosteroids
• Adrenal corticosteroids knock down the immune systems
• Blood supply of the adrenals

  • Superior adrenal (suprarenal) artery
  • Middle adrenal (suprarenal) artery
  • Inferior adrenal (suprarenal) artery
• There are 2 layers plus a capsule

  • Cortex
  • Medulla
• The adrenal cortex has 3 zones, all of which make steroids

  1. Zona glomerulosa
  2. Zona fasciculata
  3. Zona reticularis
• Zona Glomerulosa

  • Secretes aldosterone
• Aldosterone is a mineralocorticoid (it changes mineral concentration & cortical steroid) that causes uptake of sodium in the kidney
• Because water follows the minerals, more aldosterone means more sodium and thus more blood in circulation and leads to higher blood pressure
• If you retain a lot of sodium you retain a lot of water, which is retained in blood, then increases blood pressure
• When you pick up sodium, you kick out potassium

  • If you mess with your kidney, your sodium and potassium levels get skewed
• Angiotensin II, Aldosterone and Filtration pathway

  1. Decrease in blood pressure + sympathetic nervous system stimulation
  2. Kidney (controls blood pressure)
  3. When blood gets too low, angiotensinogen (circulating in blood)
  4. Renin
  5. Angiotensin 1
  6. ACE converts angiotensin 1 to angiotensin 2
  7. Aldosterone is released
  8. Increase in Na+ and Cl- reabsorption by the kidney (h2O follows)
  9. Increase in blood volume + pressure
• Zona Fasciculata

  •  secretes cortisol
• Cortisol is a glucocorticoid (it changes glucose concentration and is a cortical steroid
• Cortisol causes gluconeogenesis from lipolysis and protein catabolism, so blood glucose levels increase

  • The immune system is also inhibited
• Cortisol helps the sympathetic nervous system by knocking down your immune system for a bit
• About 90% of the hormones produced by the adrenal cortex is cortisol
• The control of corticosteroids

  1. Corticotropin-Releasing Hormone (CRH) turns on the adrenal cortex to make cortisol and causes lover to release glucose
  2. Adrenal Corticotropic Hormone (ACTH, a tropic hormone)
  3. Cortisol production in adrenal cortex
  4. Glucose genesis from protein and fat catabolism
  5. Hepatic glucose secretion
  6. Immunosuppression
• Zona Reticularis

  • Secretes androgens
  • Important for making testosterone and estrogen
• The main androgen secreted by the zona reticularis is dehydroepiandrosterone (DHEA)
• DHEA promotes growth and development, it also contributes more to male sexual development
• DHEA can be a performance enhancing drug
• DHEA is critical for making other adrenal steroids
• Adrenal medulla 

  • Sympathetic ganglion that secretes catecholamines into the bloodstream
• The main catecholamines are epinephrine and some norepinephrine
• Epinephrine and norepinephrine stimulate sympathetic nervous system responses (fight, flight, fright)
• Stress and the Adrenal

  1. Sympathetic neural stimulus epinephrine and norepinephrine are released by the adrenal medulla
  2. Stimulation by ACTH cortisol and other similar hormones are released from the adrenal cortex
• Stress is a normal response to situational pressures or demands, especially if they are perceived as threatening or dangerous
• Stressors can be

  • Physical: pain, hemorrhage etc.
  • Mental: imminent test, unsafe living conditions etc.
• Stress is good to a point but too much stress leads to a chronic stress response and cognitive, emotional and physical symptoms
• The hormones released by the hypothalamus

  • CRH = corticotropin RH
  • GHRH = growth hormone RH
  • TRH = thyroid RH
• The anterior pituitary hormones

  • ACTH = adrenocorticotropic H
  • hGH = human growth hormone
  • TSH = thyroid stimulating H
• Thyroid

  • Ant. pituitary H: TSH thyroid stimulating hormone
  • Releases: thyroid hormones
  • Function: increased use of glucose and ATP production
• Liver

  • Ant. pituitary hormone: hGH human growth hormone
  • Releases: IGFs
  • Function: glycogenolysis and lipolysis
• Adrenal Cortex

  • Ant. pituitary hormone: ACTH adrenocorticotrophic H 
  • Releases: cortisol, epinephrine, norepinephrine
  • Function: lipolysis. Protein catabolism, gluconeogenesis, reduced inflammation
• Sympathetic Effects

  • inotropic and chronotropic effects
  • Decreased blood flow to viscera and skin
  • Increased blood flow to muscles, brain, heart…all the sympathetic effects
• Adrenal diseases

  • These are all due to over or underproduction of the various adrenal hormones
  • The production of all adrenal cortical hormone is related so that when one is messed up, they are often all messed up
• Adrenal steroid synthesis starts with cholesterol
• Hypercortisolemia (Cushing Syndrome)

  • cortisol and its synthetic analogs
  • Cortical steroids increase the rate of:
  • Gluconeogenesis
  • Glucose secretion by liver
  • Breakdown of fate and protein = this is to supply material for gluconeogenesis
  • Decreased glucose uptake and use by peripheral tissues
  • With extremely high amounts of cortisol, or synthetic cortical steroid, lack of tissue repair can lead to striae
  • Tissue torn apart cannot be repaired because of high cortisol
• Hypercortisolemia II (Cushing Syndrome)

  • Stimulate glucose production but inhibit glucose uptake
  • Large doses of cortical steroids cause hyperglycemia and the breakdown of muscle
  • What happens with the extra fat?
  • The fat gets redistributed so that it ends up on:
  • The abdomen and chest but not the legs (truncal or central obesity)
  • The posterior neck causing supraclavicular fat pads or a “buffalo hump”
• Most of cushing syndrome is due to taking high doses of cortical steroids