Which is the longest bone in the human body?

The femur, or thigh bone, is the longest, heaviest and strongest bone in the human body. It runs from the hip to the knee. In an adult, it is about one-quarter of the person's height, typically about 45-50 centimetres long. It can support many times the weight of the body.

The upper end of the femur has a rounded head that fits into a cup-shaped socket in the hip bone called the acetabulum, forming the hip joint, which is a ball-and-socket joint. This allows the leg to move in many directions. The lower end of the femur joins the tibia (shin bone) and the patella (kneecap) to form the knee joint, which is a hinge joint, allowing movement mainly in one plane.

Like other long bones, the femur has a central shaft with a hollow cavity containing bone marrow. Red bone marrow, found especially in the ends of long bones and in flat bones, produces blood cells (red blood cells, white blood cells and platelets). This process is called haematopoiesis.

Some facts about the human skeleton:

An adult human skeleton has 206 bones. A newborn baby has about 270-300 bones, but many fuse together as the child grows.

The skeleton is divided into the axial skeleton (80 bones: skull, vertebral column, ribs and sternum) and the appendicular skeleton (126 bones: the bones of the limbs and the girdles).

The smallest bone is the stapes (stirrup) in the middle ear.

The strongest bone of the face is the mandible (lower jaw), which is also the only movable bone of the skull.

The vertebral column has 33 vertebrae in a child, which become 26 in adults after some fuse together.

Bones are made mostly of calcium phosphate and the protein collagen.

Why not the other options?

• ✗The tibia (shin bone) is the second-longest bone in the body.
• ✗The humerus is the longest bone of the upper arm.
• ✗The fibula is the thin bone beside the tibia in the lower leg.