Calcium Endocrinology (MT3)

Calcium

Important for bone structure, clotting (phospholipids and Ca2+ for clot formation), milk production, and balance of excitable tissues (brain, heart, and muscle)

Come from small intestine, bone, and kidney

Increase plasma calcium

Vit D and PTH

Decrease plasma calcium

Lack of vit D and PTH

Calcitonin

Vitamin D activation

1. D3 from diet or sun

2. Hydroxylation in liver

3. Hydroxylation in kidney

4. Increase in plasma calcium and phosphate (calcium and phosphate absorption from intestine and kidney; increased bone resorption to liberate calcium and phosphate)

5. Bone deposition

Vitamin D3

Requires an increase in plasma calcium AND phosphate

Increases absorption of calcium and phosphate by intestine and kidney

D3 hypovitaminosis

Rickets in children and osteomalacia in adults

Etiologies: Lack of sun, and diet vit D, hepatic diseases, and renal diseases

Parathyroid Hormone (PTH)

Triggered by low plasma calcium, increases plasma calcium for neurons, muscle, etc (decreases phosphate)

Calcium homeostasis

Mechanism of PTH

Net bone resorption (breakdown by osteoclasts) → Kidney reabsorption (calcium reabsorbed and phosphate excreted) → Absorption of calcium from intestines

Primary hyperthyroidism

Hypersecreting adenoma of parathyroid gland

Hormone profile: High PTH and high calcium

Ectopic hyperparathyroidism

Cancer secretes PTH mimic

Hormone profile: High PTH and high calcium

Secondary hyperparathyroidism

Renal failure or vit D hypovitaminosis

Hormone profile: High PTH and high calcium

Hypercalcemia

Caused by primary or ectopic hyperparathyroidism

Signs: Weak bones, kidney stones, intestinal problems, psychiatric overtones (Bones, stones, moans, overtones)

Ocular: Band keratopathy and metastatic calcification

Secondary hyperparathyroidism pathogenesis

1. Vit D deficiency

2. Hypocalcemia

3. Hypersecretion of PTH

4. Not enough calcium to inhibit PTH

Presents as a vitamin D deficiency