H 3 5 8 Growth Development in Bones

H 3. 5. 8 Growth & Development in Bones Objectives – What you will need to know from this section Ø Explain the role of osteoblasts in bone growth & bone cell replacement. Ø Explain the process of terminating development of adult height. Ø Outline the process of bone renewal & the role of calcium in bone.

Ø Compact bone consists of living cells (osteocytes) embedded in a matrix of calcium salts and protein (called collagen). Ø It is very dense and is found mainly at the outer edge of bones.

Ø Spongy bone consists of a network of thin, bony columns and plates, along with spaces filled with marrow [red or yellow]. Ø It gives moderate strength to bones but makes them lighter. Ø Red marrow makes blood cells (red, white and platelets).

Growth & Development in Bones Ø In humans and other mammals, the skeleton of the embryo is first made of cartilage, and then replaced by bone while we are still in the womb.

Ø These bone‑forming cells, called osteoblasts, invade the cartilage and produce a matrix of hard calcium phosphate and protein in which they become trapped.

Ø Growth occurs at the growth plate, the junction between the head and the shaft of a bone.

Ø When the shaft and head fuse together, growth stops and the skeleton reaches its adult's height. ØBone has collagen fibres [a protein] running through the hard calcium salts. ØThe combination of the two materials gives it greater strength than either material on their own. ØIt is similar to reinforced concrete (concrete with metal rods and wire through it).

Structure of Bone ØIf you burn a bone, it crumbles. ØThe burning removes the living cells and the protein ‘wire’, leaving only the hard calcium salts, which crumble apart easily. ØIf you put a bone in acid for a day, it becomes flexible and you can bend it. ØThe acid removes the hard calcium salts, leaving the flexible protein [collagen] fibres.

LEARNING CHECK • What material is bone first made of? • Distinguish between osteoblasts and osteoclasts? • Name 3 centres of bone formation. • What is a growth plate? • Bone is a composite material. What does this mean? • When is bone growth complete? • How can you help build up strong bones?