Bone and Calcium Homeostasis Lecture Notes

Functions of Bone

• Storage of Calcium: Bone serves as a storage source of calcium.
  • Calcium homeostasis involves the flow of calcium between the bloodstream and bone under hormonal control.

Osteoclast and Osteoblast Activity

• Osteoclasts: Increase liberation of calcium and phosphate from bone into the bloodstream.
  • "Osteoclasts cause bones to crash."
• Osteoblasts: Move calcium and phosphate from the bloodstream into bone.
  • Activity increases bone formation.

Hormones Involved in Calcium Homeostasis

Main Hormones

1. Parathyroid Hormone (PTH):
   • Increases calcium and phosphate in the blood.
   • Decreases osteoblast activity.
2. Calcitonin:
   • Decreases calcium and phosphate in the blood.
   • Increases osteoblast activity.
   • "Calcitonin tones down calcium in blood."
3. Calcitriol (Active form of Vitamin D):
   • Increases calcium and phosphate in the blood.
   • Decreases osteoblast activity.

Hormonal Effects on Calcium

• Calcium Increase: Concurrent increase of phosphate in blood; decrease in bones.
• Calcium Decrease: Concurrent decrease of phosphate in blood; increase in bones.

Effects of Hormones on Cellular Activity

• Osteoblast Activity:
  • Decreased by PTH and Calcitriol.
  • Increased by Calcitonin.
• Osteoclast Activity:
  • Increased by PTH and Calcitriol.
  • Decreased by Calcitonin.
• Intestinal and Renal Calcium Absorption:
  • Increased by PTH and Calcitriol.
  • Decreased by Calcitonin.

Importance of Calcium Ion Concentration

• Physiological Effects:
  • High calcium leads to hypoexcitable cell membranes, lethargy, fatigue, memory loss.
  • Low calcium causes muscle cramps, convulsions.
• Role of Endocrine System:
  • Critical in calcium homeostasis through bone remodeling and calcium absorption mechanisms.