Bone and Calcium Homeostasis

May 26, 2024

Mindmap

Bone and Calcium Homeostasis Lecture

Introduction

  • Bone acts as a storage source of calcium.
  • Calcium is essential for forming strong bones.
  • Calcium homeostasis refers to the flow of calcium between the bloodstream and bone.
  • This process is under endocrine or hormonal control.

Hormonal Control in Bone Remodeling

Osteoclasts and Osteoblasts

  • Osteoclasts: Increase calcium and phosphate in the blood by breaking down bone.
    • Remember: "Osteoclasts crash bones."
  • Osteoblasts: Build bone, decreasing calcium and phosphate in the blood by depositing these ions into bone.

Key Hormones

  • Parathyroid Hormone (PTH)
    • Increases calcium and phosphate in the blood.
    • Decreases osteoblast activity.
    • Increases osteoclast activity.
    • Increases calcium absorption from intestines and kidneys.
  • Calcitriol (Active form of Vitamin D)
    • Similar effects as PTH.
    • Increases calcium and phosphate in the blood.
    • Decreases osteoblast activity.
    • Increases osteoclast activity.
    • Increases calcium absorption from intestines and kidneys.
  • Calcitonin
    • Decreases calcium and phosphate in the blood.
    • Increases osteoblast activity.
    • Decreases osteoclast activity.
    • Decreases calcium absorption from intestines and kidneys.
    • Remember: "Calcitonin tones down calcium in blood."

Relationship Between Calcium and Phosphate

  • Calcium and phosphate levels in blood are positively correlated.
  • Increased calcium in blood = decreased calcium in bone, and vice versa.

Table Overview of Hormone Effects

  1. Osteoblast Activity:
    • PTH: Decreases
    • Calcitriol: Decreases
    • Calcitonin: Increases
  2. Osteoclast Activity:
    • PTH: Increases
    • Calcitriol: Increases
    • Calcitonin: Decreases
  3. Calcium Absorption (Intestinal/Renal):
    • PTH: Increases
    • Calcitriol: Increases
    • Calcitonin: Decreases

Importance of Calcium Homeostasis

  • High Blood Calcium: Leads to hypoexcitable cell membranes (lethargy, fatigue, memory loss).
  • Low Blood Calcium: Leads to muscle cramps and convulsions.

Summary

  • The endocrine system critically regulates calcium homeostasis through hormones that affect bone remodeling and calcium absorption.