Bone Growth Development Types of Bone Cells Osteocyte

Bone Growth & Development

Types of Bone Cells Osteocyte – mature bone cell, enclosed in lacuna n Osteoblast – bone-forming cell; secretes ECM of bone tissue (collagen fibers & calcium salts) n Osteoclast – bone-destroying cell; breaks down ECM to release calcium into the bloodstream n

Fetal Bone Growth n “Bones” of hyaline cartilage n ECM is mostly collagen fibers n Chondrocytes (in lacunae) n Chondroblasts n Chondroclasts

Ossification n Cartilage is covered by bone & internal hyaline cartilage is broken down

Epiphyseal Plates n At birth, epiphyseal plates still made of cartilage n (Also articular cartilage!)

Bone Growth Through Adolescence Controlled by growth hormone, and after puberty, sex hormones n Longitudinal growth – occurs at epiphyseal plates n n Completely ossified by end of adolescence

Continued… n Bones also grow in diameter along length of diaphysis n Medullary n Animation cavity gets bigger

Bone Remodeling Constant osteoblast & osteoclast activity throughout life n Causes: n n Ca+2 levels in blood n If too low, parathyroid hormone activates osteoclasts n If higher than needed, calcitonin (a hormone) activates osteoblasts n Pull of gravity & muscles n Activates osteoblasts n If not active, activates osteoclasts - atrophy

n Positive or negative feedback? ? ? n Ah, yes, it’s NEGATIVE!

Fractures Reduction – realignment of bone ends n Remember granulation tissue? During which step does it occur? n n New capillaries, phagocytes

Common Types of Fractures

Review 1. 2. 3. 4. 5. 6. 7. Which cell type forms new bone? Which cell type destroys bone? Which cell type is a mature bone cell? What is the name of the “bubble” that a mature bone cell is enclosed within? What kind of tissue are fetal bones made of? What is ossification? What is the site of longitudinal bone growth called?

8. 9. 10. 11. 12. Which hormones control bone growth through adolescence? Which hormones control bone remodeling? What does each one do? Distinguish between the three types of fractures. If a doctor reduces a fracture, what is she doing? Describe the four steps of bone repair after a fracture.