Bones are made of calcium, phosphorus, sodium and other minerals as well as protein collagen. An infant’s skeleton has about 350 bones. As they grow up, some of the bones grow while others fuse together to form longer one. Thus a child grows up into an adult who would have about 206 bones. Bones support the shape of the body and protect the organs from injuries. For instance, the skull protects the brain; rib cage protects the heart and lungs, pelvis protects the hip. The smallest bone is the stirrup bone inside the ear and the longest bone is the thigh bone called femur.
One important function of the bones is to help produce blood cells. Flexible tissues in the interior of the bones are called bone marrow that contains the important stem cells. The stem cells produce red blood cells, white blood cells and platelets. Red blood cells carry oxygen and nutrients, white blood cells fight infection and platelets help in clotting blood.
Bones are connected to one another in many ways – as fixed joints, hinged joints, ball-and-socket joints and many more. Though there are around 206 bones, there are about 360 joints. Joints facilitate free movements without bones knocking each other. Fixed joints are immovable joints such as in the skull. Hinged joints allow movements in one direction like in knees and elbows. Ball and socket joints allow movements in a full circle and rotation around their axis. Hips and shoulders have ball and socket joints. The most common diseases that occur especially in old age due to affected joints are arthritis and osteoporosis.
Cartilage is a flexible, rubbery connective tissue found in joints between bones, rib cage, ears, nose and few other parts. It supports bones and protects them where they touch each other.
There are connective tissues which attach bone to bone by long fibrous straps called ligaments. They usually serve to hold structures together and keep them stable. Injuries common among sportsmen during sports activities is the ligament tear. It occurs when ligaments get over stretched.