Ivclinical Considerations

A. Primary hyperparathyroidism (e.g., adenoma, hyperplasia) is characterized by excessive secretion of PTH, leading to hypercalcemia.

B. Malignant tumors (e.g., lung, breast, or ovarian carcinomas) may secrete a PTH-related protein, leading to hypercalcemia.

C. Primary hypoparathyroidism (e.g., surgical removal, DiGeorge syndrome, autoimmune destruction) is characterized by the absence of PTH, leading to hypocalcemia.

D. Pseudohypoparathyroidism is a rare condition characterized by abnormal PTH receptors, leading to hypocalcemia, although there are high PTH levels.

Calcitonin —

Hypocalcemia

Figure 22-1. Calcium homeostasis. In this diagram, blood calcium levels have decreased, such that parathyroid hormone (PTH) is released. PTH and l,25-(OH)2 vitamin D regulate blood calcium levels by acting on the kidney, bone, and intestine. Blood calcium levels can be depicted on a thermometer such that when blood calcium levels are too high, calcitonin is released. When blood calcium levels are too low, PTH is released.

Elevate blood Ca2+ levels

Figure 22-1. Calcium homeostasis. In this diagram, blood calcium levels have decreased, such that parathyroid hormone (PTH) is released. PTH and l,25-(OH)2 vitamin D regulate blood calcium levels by acting on the kidney, bone, and intestine. Blood calcium levels can be depicted on a thermometer such that when blood calcium levels are too high, calcitonin is released. When blood calcium levels are too low, PTH is released.

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