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Bone Remodeling Physiology

Bone Remodeling: Physiology Glucocorticoids ↓ Osteoblast (bone building cells) activity, ↑ osteoclast (bone cells that break down bone) activity Hyperparathyroidism ↓ Blood Ca2+ ↑ Parathyroid hormone (serum Ca2+ concentration increasing hormone) Trauma Osteoblasts detect breach in matrix integrity Hyperthyroidism ↑ Triiodothyronine (T3) ↑ Bone turnover Puberty ↑ Growth hormone ↑ Blood calcium (Ca2+) ↑ Calcitonin (reduces serum Ca2+ by ↓ renal Ca2+ reabsorption & ↑ osteoclast activity) Net bone resorption process (bone tissue released from bones) Surveillance osteoblasts produce receptor activator of nuclear activator kappa beta (RANKL; osteoclast stimulating protein) Monocytes fuse into osteoclasts (cells for bone breakdown) Osteoclast actions Secrete HCl to dissolve hydroxyapatite (bone matrix forming inorganic mineral) Serum markers of bone resorption: C-Telopeptide (CTX) P-Telopeptide (PTX) Net bone formation process Hormones activate osteoblast Osteoblast actions Secrete osteoprotegerin that binds RANKL Secrete osteoid seam (a new layer of unmineralized organic bone matrix) Osteoblasts deposit hydroxyapatite on seam Phagocytose osteocytes within bone matrix Authors: Andrew Wu, Jason Kreutz Reviewers:Mizuki Lopez, Gurreet Bhandal, Luiza Radu *Samuel Fineblit * MD at time of publication Secrete collagenase enzyme to help digest collagen ↓ Osteoclast activity Osteoblasts become osteocytes (mature cells) within bone Serum markers of bone formation: ↑ Alkaline phosphatase (ALP) ↑ Bone-specific alkaline phosphatase (BSAP; an enzyme produced by osteoblasts during mineralization of bone) Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published Oct 4, 2024 on www.thecalgaryguide.com