Essentials of Anatomy and Physiology

234 The Endocrine System

Bones

Ca+^2 is retained in bone matrix

Accelerates calcium

absorption by bones

Hypercalcemia (high blood calcium)

Thyroid

Calcitonin Inhibits

Bones

Small intestine

Reabsorb Ca+^2 to the blood

Hypocalcemia (low blood calcium)

Parathyroids

PTH

Kidneys

(vitamin D activated)

Figure 10–6. Calcitonin and parathyroid hormone (PTH) and their functions related to

the maintenance of the blood calcium level.

QUESTION:Which hormone helps keep calcium in bones? What vitamin does PTH help

activate, and where?

Table 10–4 HORMONE OF THE PARATHYROID GLANDS

Regulation

Hormone Functions of Secretion

Parathyroid hormone

(PTH)

• Increases the reabsorption of calcium and phosphate
  from bone to blood


• Increases absorption of calcium and phosphate by
  the small intestine


• Increases the reabsorption of calcium and the excre-
  tion of phosphate by the kidneys; activates vitamin D

Hypocalcemia stimulates secre-

tion. Hypercalcemia inhibits

secretion.