L4.4.4: Bone Remodeling

• Two Factors of Bone Remodeling

  [1] Calcium Ion Level in the Blood

  ○ Determines WHEN the bone matrix is to be broken down or formed.

  [2] Pull of Gravity and Muscles on the Skeleton

  ○ Determines WHERE the bone matrix is to be broken down or formed.
• CALCIUM ION REGULATION

  ● Calcium is an important component of muscle contraction and clotting process of blood
• CALCIUM ION REGULATION

  ● Parathyroid Hormone (PTH) — LOW

  ○ Secreted by parathyroid glands (in the throat).

  ○ Released when calcium ion levels in blood are low.

  ○ The glands are stimulated when the calcium is low to release parathyroid hormone (PTH) into the blood.

  ○ Activates osteoclasts, giant bone-destroying cells in bones, to break down bone and release calcium ions stored in the matrix into the blood.
• CALCIUM ION REGULATION

  ● Calcitonin — HIGH (Hypercalcemia)

  ○ Secreted by thyroid glands sequester the excess calcium in the blood.

  ○ The excess calcium is deposited in the bone matrix as hard calcium salts by osteoblasts.
• CALCIUM ION REGULATION HYPERCALCEMIA

  (HIGH BLOOD CALCIUM LEVELS)

  ● Prompts calcium storage to bones by osteoblasts