parathyroid and adrenal

• Parathyroid glands


  • 4 parathyroid glands are found near the posterior aspect of the thyroid gland
  • Small (20-40 mg); bean-shaped
  • 2 cell types: Chief cells (produce PTH) and Oxyphil cells (no established function of significance)
  • Located near thyroid capsule, sometimes within thyroid gland, may also be found outside their normal anatomic site between the hyoid bone in the neck and mediastinum
  • Most have 4 PT glands but some have 8 or 2
  • Smallest endocrine gland in the body
• Parathyroid hormone (PTH)


  • Major function: maintain Ca level
  • Secreted by chief cells
• Specific effects of parathyroid hormone

  1. Mobilizes Ca and Phosphate from bone

  2. Increases phosphate excretion

  3. Decreases Ca excretion

  4. Decreases renal H+ secretion

  5. Enhances renal hydroxylation of Vitamin D3 (cholecalciferol)

  6. Increases calcium absorption from gut

  
• Effects of PTH on calcium and phosphate

  • Bone: Stimulates osteoblast to increase growth and metabolic activity, Stimulates bone resorption to release Ca and phosphate into bloodstream when there is hypocalcemia
  • Kidneys: Increases renal reabsorption of calcium, Decreases renal reabsorption of phosphate
  • Intestine via the Kidney: Enhances the absorption of Ca in the intestine by increasing the production of activated vitamin D

  
• Regulation of serum phosphate

  1. Reduces reabsorption of phosphate from proximal tubule of the kidney

  2. Enhances uptake of phosphate from the intestine and bones into the blood

  3. In the intestine, phosphate absorption is not as dependent on vitamin D as with that of calcium

  4. End result is small net drop in serum concentration of phosphate

  
• Vitamin D synthesis


  PTH increases activity of 1-a-hydroxylase enzyme, converting 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol (active form of vitamin D)

  
• Stimulators of PTH secretion

  • Decreased serum calcium / hypocalcemia
  • Mild decreased in serum magnesium
• Inhibitors of PTH secretion

  • Increased serum calcium
  • Severe decreased in serum magnesium (produces symptoms of hypoparathyroidism such as hypocalcemia)
• Low blood calcium


  PT gland secretes PTH, which stimulates osteoclasts to promote bone resorption and release calcium into the blood

  
• High blood calcium


  PT gland secretes calcitonin, which stimulates osteoblasts to promote bone mineralization and remove calcium from the blood

  
• Relationship between PTH and vitamin D


  Active form of vitamin D promotes increased absorption of calcium and phosphate in the small intestine

  
• Hypoparathyroidism


  • Decreased parathyroid gland function = decreased PTH
  • Causes include removal of parathyroid or thyroid gland, autoimmune parathyroid destruction
  • Results in decreased serum calcium level
• Pseudohypoparathyroidism


  • Genetic condition associated with resistance to the PTH response, due to defect on the PTH receptor adenylate cyclase complex
  • May also be resistant to TSH, glucagon, and gonadotropins
  • Presents with decreased serum calcium and increased phosphate
• Hyperparathyroidism


  • Excess PTH in the bloodstream due to overactivity of one or more of the body's 4 parathyroid glands
  • Causes include parathyroid adenoma (primary hyperparathyroidism), low calcium levels (secondary hyperparathyroidism), or autonomous function of hyperplastic parathyroid glands (tertiary hyperparathyroidism)
• Summary of effects of decreased vs. increased calcium on PTH, vitamin D, calcitonin, and physiological processes

  
• or


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  • as
  • dehydroepiandrosterone
• MINERALOCORTICOIDS


  • Production: (such as aldosterone) happens in the G-zone
  • Primary hormone: aldosterone
  • Most potent electrolyte regulating hormone
  • Secretion is regulated by oligopeptide angiotensin 2 (active form of angiotensin)
• Stimulus (e.g., Low Blood Pressure, Low Blood Volume)

  1. Release of Renin by Juxtaglomerular Cells in Kidneys

  2. Renin Converts Angiotensinogen (from Liver) to Angiotensin I

  3. Angiotensin Converting Enzyme (ACE) Converts Angiotensin I to Angiotensin II

  4. Angiotensin II Acts on: Blood Vessels: Vasoconstriction, Adrenal Cortex: Release of Aldosterone

  5. Aldosterone Acts on Kidneys to: Increase Sodium (Na+) Reabsorption, Increase Water Retention

  6. Increased Blood Volume and Blood Pressure

  7. Negative Feedback: Inhibition of Renin Release, Inhibition of Angiotensin II Production
• PRIMARY MINERALOCORTICOIDS - ALDOSTERONE


  Aldosterone is secreted in response to: ↑ K levels; Na is reabsorbed, ↓ extracellular (plasma) Na levels, ↓ low fluid levels and blood volume

  
• Affects metabolism in different ways

  ↑ urinary excretion of K ions in response to hyperkalemia, ↑ interstitial levels of Na ions in response to low sodium levels, ↑ water retention and blood volume

  
• HYPOALDOSTERONISM

  ↓ aldosterone secretion, Due to destruction of adrenal glands and deficiency of mineralocorticoid, Also associated with enzyme 21-hydroxylase deficiency, Symptoms: Hyperkalemia, Metabolic acidosis

  
• Parathyroid glands


  • 4 parathyroid glands are found near the posterior aspect of the thyroid gland
  • Small (20-40 mg); bean-shaped
  • 2 cell types: Chief cells (produce PTH) and Oxyphil cells (no established function of significance)
  • Located near thyroid capsule, sometimes within thyroid gland, may also be found outside their normal anatomic site between the hyoid bone in the neck and mediastinum
  • Most have 4 PT glands but some have 8 or 2
  • Smallest endocrine gland in the body
• Parathyroid hormone (PTH)


  • Major function: maintain Ca level
  • Secreted by chief cells
• Specific effects of parathyroid hormone

  1. Mobilizes Ca and Phosphate from bone

  2. Increases phosphate excretion

  3. Decreases Ca excretion

  4. Decreases renal H+ secretion

  5. Enhances renal hydroxylation of Vitamin D3 (cholecalciferol)

  6. Increases calcium absorption from gut

  
• Effects of PTH on calcium and phosphate

  • Bone: Stimulates osteoblast to increase growth and metabolic activity, Stimulates bone resorption to release Ca and phosphate into bloodstream when there is hypocalcemia
  • Kidneys: Increases renal reabsorption of calcium, Decreases renal reabsorption of phosphate
  • Intestine via the Kidney: Enhances the absorption of Ca in the intestine by increasing the production of activated vitamin D

  
• Regulation of serum phosphate

  1. Reduces reabsorption of phosphate from proximal tubule of the kidney

  2. Enhances uptake of phosphate from the intestine and bones into the blood

  3. In the intestine, phosphate absorption is not as dependent on vitamin D as with that of calcium

  4. End result is small net drop in serum concentration of phosphate

  
• Vitamin D synthesis


  PTH increases activity of 1-a-hydroxylase enzyme, converting 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol (active form of vitamin D)

  
• Stimulators of PTH secretion

  • Decreased serum calcium / hypocalcemia
  • Mild decreased in serum Mg

  
• Inhibitors of PTH secretion

  • Increased serum calcium
  • Severe decreased in serum Mg (produces symptoms of hypoparathyroidism such as hypocalcemia)

  
• Low blood calcium


  PT gland secretes PTH, which stimulates osteoclasts to promote bone resorption and release calcium into the blood

  
• High blood calcium


  PT gland secretes calcitonin, which stimulates osteoblasts to promote bone mineralization and remove calcium from the blood

  
• Relationship between PTH and vitamin D


  Active form of vitamin D promotes increased absorption of calcium and phosphate in the small intestine

  
• Hypoparathyroidism


  • Decreased parathyroid gland function = decreased PTH
  • Causes include removal of parathyroid or thyroid gland, autoimmune parathyroid destruction
  • Results in decreased serum calcium level

  
• Pseudohypoparathyroidism


  • Genetic condition associated with resistance to the PTH response due to a defect on the PTH receptor adenylate cyclase complex
  • May also be resistant to TSH, glucagon, and gonadotropins
• Hyperparathyroidism


  • Excess PTH in the bloodstream due to overactivity of one or more of the body's 4 parathyroid glands
  • Causes include parathyroid adenoma (primary hyperparathyroidism), low calcium levels (secondary hyperparathyroidism), or autonomous function of hyperplastic parathyroid glands (tertiary hyperparathyroidism)

  
• Adrenal gland is a multifunctional organ able to produce steroid hormones and neuropeptides essential for life
• Adrenal hypofunction


  • Decreased synthesis, secretion, and function of adrenal hormones
  • Treated with exogenous hormone replacement
• Adrenal hyperfunction


  • Increased synthesis, secretion, and function of adrenal hormones
  • Managed with pharmacological suppression or surgery (severe cases)
• Adrenal gland anatomy


  • Also known as suprarenal gland, located on top of the kidney
  • Composed of distinct but conjoined gland with adrenal cortex (yellowish outer region) and adrenal medulla (dark mahogany inner region)
• Adrenal gland functions


  • Chiefly responsible for releasing hormones in response to stress, through the synthesis of corticoids, catecholamines, and epinephrine
  • Affect kidney function through the secretion of aldosterone, which is involved in regulating the osmolality of blood plasma and the reabsorption and secretion of electrolytes