Functions of Bone (Osseous Tissue) • Structural Support: • Protection: • Storage: 1) minerals and 2) lipids • Blood Cell Production: • Body Movement: • Detoxification:
Constituents of Bone Organic (~1/3) Calcium Hydroxyappitite Ca3(PO4)2.(OH)2 80% Collagen Inorganic (~2/3) Specialized Bone Cells Calcuim Carbonate CaCO3 15% Glycosaminoglycans (GAGs) Other Minerals: Mg, SO4, Na, K 5% Flexibility! Rigidity!
Hormonal Control of Bone Tissue Human Growth Hormone (hGH): (Pituitary gland) Thyroxine: (Thyroid gland) Stimulate Osteoblasts Sex Hormones: (estrogen, progesterone, testosterone) (Ovaries and Testes) Calcitonin: Inhibits Osteoclasts (Thyroid gland) Parathyroid Hormone: (Parathyroid gland) Stimulates Osteoclasts Increases Ca2+ absorption from intestine, ↓ Ca2+ in urine. Calcitriol: (Skin and kidneys)
2 Types of Ossification 1. Intramembranous Ossification mesoderm Mesenchymal cells Osteoprogenitor cells osteoblast Osteocytes in bone tissue
2. ENDOCHONRAL OSSIFICATION starts as a cartilage model of bone
Appositional Bone Growth Bone Remodeling: Depositing and removing bone tissue!
Fractures Simple (Closed): Compound (Open):
Disorders of Bone Tissue • Osteopenia: A reduction in bone mass with age. • Osteomalacia (‘rickets’ in children): Defective mineralization of bone, resulting in too much flexibility, bone cannot bear weight sufficiently. • Osteoma: Cancer of bone tissue (uncontrolled bone growth, a malignant tumor = cancer).
Osteoporosis: A significant reduction in bone mass that impairs function. From too little mineralization of bones for these reasons: • Decrease in hormone levels, e.g., loss of estrogen at menopause – decreases efficiency of calcium absorption. 2) deficiency of minerals in youth, thus too little to begin with. 3) imbalance of activity of osteoblasts and osteoclasts.