Structure of Human Bones

Human bones are living tissue that are nourished by blood vessels, and constantly growing and repairing themselves. They protect and support the body, provide levers for muscles to pull, maintain chemical balance in the blood and produce blood cells through bone marrow.

Shapes

• There are five shapes of bones. Flat bones include the scapula (shoulder blade), sternum and the outer bones of the cranium (skull). Long bones are longer than they are wide, and include the femur (thigh), humerus (upper arm) and phalanges, the bones of the fingers. (Even though they are short in size, these are considered long bones.) Short bones are nearly equal in length and width. These are the carpals (wrist bones) and tarsals (ankle bones). Sesamoid bones form in cartilage, and can often form at the base of fingers. The patella, or kneecap, is an example of a sesamoid bone. Finally, elaborately shaped bones are called irregular bones. These include the vertebrae and some skull bones, such as the sphenoid.

Bone growth

• Bones grow in childhood at the epiphyseal plate, which is at the end of long bones. In adulthood, the cartilage in this plate dissolves and shows as a faint epiphyseal line. Growth here determines a person's height, Achondroplastic dwarfism is caused when the long bones of the limbs stop growing in childhood. People with this disorder have a proportionate head and trunk, but the arms, legs and fingers are stunted.

Fractures

• A fracture is a broken bone. Fractures can be closed (skin is not broken) or open (skin is broken and the bone sticks out). Some special types of bone fractures are spiral (caused by twisting the arm), Colles (broken wrist) or Pott's (broken ankle).

Marrow

• Bones contain red and yellow marrow. Red bone marrow produces red blood cells. In adults, most red marrow changes to yellow bone marrow, which contains fat, like the center of a ham bone. Red marrow in adults is usually found in the trunk of the body: the bones of the skull, the ribs, the vertebrae and the hips. Therefore, if it's necessary to extract bone marrow for a transplant, it is usually done from the hip, the most accessible of those places.

Fun Fact

• A broken hip does not involve the hip bone; it is actually a break near the surgical neck of the femur (thigh bone).