How many bones does an adult human have?

An adult human has 206 named bones; as a normal human being ages, certain bones fuse together. As a result of the fusing, a baby who is born with 300 bones will have about 206 bones by adulthood. Bones largely protect our organs and form a supportive frame for our body. Our red and white blood cells are produced in our bones, and bones also store the important minerals and fats our bodies need.

Bones are made up of three layers. The outer layer is the compact bone, the hardest type of bone in our bodies. It makes up about 80% of our bones and is instrumental in supporting our bodies when we walk or run. In the meantime, 20% of the bones in our body are made of spongy bone (which isn't actually spongy at all). Spongy bone contains marrow and the blood vessels that carry specific nutrients to different sections of our body.

The innermost bone layer is the bone marrow, which consists of yellow and red marrow. Red marrow is found in the center of flat bones such as ribs. Red blood cells, white blood cells, and platelets are made in red marrow. Yellow marrow is predominantly made of fat and is found in long bones such as thigh bones. Incidentally, thigh bones—otherwise known as femurs—are said to be the longest bones in the human body. They usually measure some 20 inches long. Unlike red marrow, yellow marrow does not produce red blood cells, white blood cells, or platelets.

Bones are made up of four kinds of cells: osteocytes, osteoclasts, osteoblasts, and lining cells. Lining cells cover the surfaces of all bones, while osteoblasts are responsible for making new bones and rebuilding broken, existing bones. Osteocytes are old osteoblasts which have stopped making new bone; osteocytes are mostly found in compact bone. Meanwhile, osteoclasts work with osteoblasts to reshape and reabsorb existing bone.

Our bones are part of either the axial skeleton or appendicular skeleton. The axial skeleton supports our main body frame, while the appendicular skeleton supports our extremities (arms and legs). The axial skeleton consists of some 80 bones. It is made up of the cranial bones, facial bones, vertebral column bones, and thorax bones. Meanwhile, the appendicular skeleton is made up of the remaining 126 bones.

As mentioned above, the adult human has 206 named bones. We also have unnamed bones in the adult body, such as the sutural bones. Sutural bones are located within the sutural joints between cranial bones. The exact number of sutural bones differs between individuals.