Calcium Pathophysiology and Parathyroid Hormone (PTH)

Overview

• Parathyroid Glands: Four glands located behind the thyroid.
• Cells in Parathyroid Glands: Contain parathyroid hormone (PTH) packaged in vesicles and calcium receptors.

Role of Calcium Receptors

• Function: These receptors are inhibitory.
• High Calcium Levels: Activate receptors, inhibiting PTH release.
• Low Calcium Levels: Receptors are not activated, leading to PTH release.

Functions of PTH

• Target Systems:
  • Bones: Leads to reabsorption, increasing calcium and phosphorus.
  • Kidneys: Causes reabsorption of calcium and excretion of phosphorus.
  • Gastrointestinal System: Indirectly increases absorption of calcium and phosphorus via Vitamin D.

Vitamin D and PTH

• Vitamin D: Produced in kidneys, affects gut absorption, increasing calcium and phosphorus levels.

Kidney's Role

• Dominance: Kidneys regulate calcium and phosphorus levels effectively.
• High PTH: Elevates calcium, reduces phosphorus.
• Low PTH: Opposite effect.

Disorders Affecting PTH and Calcium Levels

• Granulomatous Diseases: e.g., TB, sarcoidosis can cause a pseudo-elevation in Vitamin D.
• Albumin Levels:
  • Calcium is bound to albumin; only 1% is ionized (free) calcium in blood.
  • Inverse Relationship: A decrease in albumin increases calcium level.
  • Calculation: Normal albumin is 4, calcium is 10. For each point decrease in albumin, calcium increases by 0.8.
  • Example: Albumin of 3 and calcium of 9.2 means actual calcium is 10.

Key Takeaways

• Influencers of Calcium Levels: Include albumin levels, granulomatous diseases, and pH-related diseases.
• Next Discussion: Further exploration of the impact of pH and PTH on calcium levels.