Structure and function ALL ABOUT BONES Structure and function

Bones Bones are made of both living and non-living tissue. They can grow in length and width and repair themselves when damaged.

The parts of a bone Periosteum – the tough outer cover (membrane) of the bone. It contains blood vessels. Compact bone – The dense, hard outer layer of the bone we see. It forms the diaphysis (bone shaft). Cartilage - The pearly white layer at the ends of bones that allow smooth movement of the joint.

Parts of a bone continued Spongy bone – lighter and less dense than compact bone, but is still strong. The spaces are filled with fat or marrow. It occurs beneath the compact bone at the bone head (epiphysis) where bones meet. Marrow – two types: Red: produces red blood cells, white blood cells and platelets for clotting. Yellow: fat storage.

Bone growth and repair Bone cells (osteocytes) are arranged in circles around Haversian canals which contain blood vessels and nerves. Between bone cells are calcium carbonate and calcium phosphate compounds and fibers of collagen for strength and flexibility.

Bone growth The bones of a fetus are made of cartilage which hardens as the baby develops. This is called ossification and is when calcium compounds are deposited between the bone cells.

Growth continued When a person grows, their bones increase in length and width. The cartilage near the ends of the bones slowly ossifies, making the bone longer until roughly 20 years of age. Then cartilage production and bone lengthening stop. New bone cells are made on the outer surface of bones so they get wider as a person ages.

Builders and changers When a bone is broken, cartilage is made to hold the pieces together until “bone builders” osteoblasts, form and harden. Osteoclasts are “bone changers” as they can break down bone and change it’s shape.

Bones are held together by ligaments Ligaments Link bones. They are connective tissue made of collagen fibres. When ligaments are damaged, such as from sport, the joint becomes more mobile which can lead to pain.