Pharmacology of Calcium Regulation

Parathyroid and Calcium Regulation

• Location and Structure

  • Four small glands located on the posterior aspect of the thyroid gland.
  • Each gland is about the size of a grain of rice.

• Function of Parathyroid Glands

  • Produce parathyroid hormone (PTH), which regulates calcium levels in the blood.

• Calcium Regulation Mechanism

  1. PTH Release

     • Stimulated by low blood calcium levels (hypocalcemia).

  2. Effects of PTH

     • Bone Resorption
       • Stimulates osteoclasts to break down bone, releasing calcium into the bloodstream.
     • Kidney Function
       • Increases renal tubular reabsorption of calcium and decreases phosphate reabsorption.
       • Stimulates conversion of vitamin D to its active form (calcitriol), enhancing calcium absorption in the intestines.
     • Intestinal Absorption
       • Active vitamin D (calcitriol) increases calcium absorption from dietary sources.

• Calcium Homeostasis

  • Normal blood calcium levels range from 8.5 to 10.2 mg/dL.
  • PTH, along with calcitonin (produced by the thyroid gland), maintains calcium levels:
    • Calcitriol has a synergistic effect with PTH on calcium absorption.

• Pathophysiology

  • Hyperparathyroidism
    • Excessive PTH secretion leading to elevated calcium levels (hypercalcemia), bone loss, and kidney stones.
  • Hypoparathyroidism
    • Insufficient PTH secretion leading to low calcium levels (hypocalcemia), muscle cramps, and potential seizures.

• Clinical Relevance

  • Diagnosis
    • Measured through serum calcium and PTH levels to assess parathyroid function.
  • Treatment
    • Calcium and vitamin D supplementation for hypoparathyroidism.
    • Surgical removal or management of hyperparathyroidism.

Parathyroid Glands

• Small, pea-sized glands located behind the thyroid gland
• Produce parathyroid hormone (PTH)

Calcium Regulation: The Role of PTH

• PTH is released when blood calcium levels are low (hypocalcemia)
• PTH's Actions:
  • Bone: Stimulates bone resorption by osteoclasts, releasing calcium into the blood
  • Kidney: Increases calcium reabsorption and decreases phosphate reabsorption in the kidneys
  • Intestine: Promotes conversion of vitamin D to its active form (calcitriol), enhancing calcium absorption
• Normal blood calcium levels: 8.5 to 10.2 mg/dL

Maintaining Calcium Homeostasis

• PTH and calcitonin (from the thyroid gland) work together to regulate calcium levels
• Calcitriol and PTH synergistically increase calcium absorption

Hyperparathyroidism

• Excess PTH secretion leads to high blood calcium levels (hypercalcemia)
• Symptoms: bone loss, kidney stones

Hypoparathyroidism

• Insufficient PTH production leads to low blood calcium levels (hypocalcemia)
• Symptoms: muscle cramps, seizures

Clinical Relevance

• Diagnosis: Blood tests measure serum calcium and PTH levels
• Treatment:
  • Hypoparathyroidism: Calcium and vitamin D supplementation
  • Hyperparathyroidism: Surgical removal or management of the affected gland(s)