Dr. Podolin's Endocrine Exam Essay # 4

Discuss how a person maintains calcium balance (hormones, target tissues).  Now explain what happens when that person experiences chronic hypocalcemia.

Calcium plasma level is a very tightly controlled area - Controlled by PTH and Vitamin D.

• Parathyroid Hormone (PTH) - Secreted by parathyroid glands.
  • Target tissues = Bone & Kidney
  • Major overall effect = Increase Ca²⁺ plasma levels
• Bone
  • Fast Exchange - PTH activates membrane bound Ca²⁺ pumps which pump Ca²⁺ out.
  • Slow exchange - Activates osteoclasts to dissolve bone Ca²⁺ for use in plasma
• Kidney
  • Causes Ca²⁺ reabsorption
  • Activates Vitamin D to absorb Ca²⁺ in the GI tract
• Vitamin D - Ingested.  Made in skin with help from ultraviolet light.
  • Activated by PTH
    • Causes the absorption in GI tract
    • This is where all outside Ca²⁺ comes from
  • Lack of Vitamin D
    • Rickets in children
    • Osteomalatia

• Chronic Hypocalcemia
  • Increased PTH released
    • Causes pumping and dissolving of Ca²⁺  from bone
    • Causes the kidneys to reabsorb more Ca²⁺ instead of excreting it.
    • Activates Vitamin D
      • Vitamin D absorbs Ca²⁺ from the GI tract

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