Body Systems: The Skeletal System

The backbone, or vertebral column is the center of the skeleton. The backbone is made up of 26 small bones, or vertebrae (singular vertebra). If your backbone were just one bone, you would not be able to bend or twist.

The bones of your skeleton are both strong and lightweight. Bones are hard because they are made up of two minerals--phosphorus and calcium. New bone tissue forms continually throughout your life.

Many bones have the same basic structure. A thick, tough membrane covers all of a bone except the ends. Blood vessels and nerves enter and leave the bone through the membrane. Beneath the membrane is a layer of compact bone, which is hard and dense, but not solid.

Small canals run through the compact bone, carrying blood vessels and nerves from the bone's surface to the living cells within the bone. Just inside the compact bone is a layer of spongy bone, which has many small spaces within it.

Spongy bone is also found at the ends of the bone. The spaces in bone contain a soft connective tissue called marrow. There are two types of marrow--red and yellow. Red bone marrow produces blood cells. Yellow marrow stores fat that serves as an energy reserve.

Cartilage is a connective tissue that is more flexible than bone. When you were an infant, much of your skeleton was cartilage. By the time you stop growing, most of the cartilage will have been replaced with hard bone tissue.

A joint is a place in the body where two bones come together. Joints allow bones to move in different ways. Immovable joints connect bones in a way that allows little or no movement.

Movable joints allow the body to make a wide range of movements. Movable joints include ball-and-socket joints, pivot joints, and gliding joints. The bones in movable joints are held together by a strong connective tissue called a ligament.

A combination of a balanced diet and regular exercise can start you on the way to a lifetime of healthy bones. As people become older, their bones begin to lose some minerals.

Mineral loss can lead to osteoporosis, a condition in which the body's bones become weak and break easily. Regular exercise and a diet rich in calcium can help prevent osteoporosis.