Compact bones are located in all areas of the body, as compact tissue forms the hard outer shell of bones. There are five main types of compact bones: long, short, flat, irregular, and sesamoid. These types of bones have their own function in the skeletal system depending on where they are located.
The outer tissue of bones is very hard and solid compared to the other main type of bone tissue in the body, cancellous tissue, which is located underneath the compact bone tissue. Long bones are a type of compact bones, and are named because their length is greater than their width. These bones are curved for strength and grow from their ends, known as extremities. Examples of long bones include the femur, tibia, and ulna. Short bones are smaller and cube-shaped, which provides them with strength in certain areas of the body that have a lot of pressure and wear, such as the wrists and ankles.
Flat bones are thinner than long or short bones and are made for protection and to provide surface area for muscles to attach to. Cranial, rib, and sternum are examples of flat bones. Irregular bones are made of various shapes and sizes that can not easily be categorized and include the vertebrae and some facial bones. Sesamoid bones develop in areas where there is a lot of movement, and therefore friction, such as the kneecaps, or patellae, and in hands and feet. All of these types are compact bones because they are covered with compact tissue for protection.
Major functions of compact bones within the body include support and protection because the tissue is so hard. In general, the skeletal system also stores minerals, produces blood cells, and stores chemical energy. Animals have compact bones located within their bodies as well, though the structure of their skeletal system and the number of bones are often different.
Compact bone tissue is denser than other types of tissue because most of the area is composed of ground organic substances and inorganic salts, leaving only small spaces in between for bone cells. In humans, compact bones make up a majority of the bone tissue in the skeletal system, which is up to 80 percent of all bone tissue. As humans grow from childhood, the compact bone tissue grows stronger and becomes multilayer, which ends in late adolescence when the bones become fully developed.