About the Types of Bones in the Body

Two hundred six bones form the human skeleton, but not all bones fit in the same anatomical groups. Bones originate from either connective membrane or a cartilage model. All bones consist of both compact and spongy bone tissue. People have four types of bones by shape: long, short, flat and irregular. Regardless of their grouping, bones are necessary for our movement and support, the protection of vital organs and the production of red and white blood cells.

Bone Origin

• A human fetus forms bones using two different processes. Intramembranous ossification creates membrane bones in the skull from connective tissue. Connective tissue originates from stem cells that become osteoblasts. Osteoblasts then produce the organic material used for bone tissue. The second process, endochrondral ossification, makes bones from a cartilage model. The model grows long bones to the desired length through cell division. The typical, collagen-based bone tissue later replaces cartilage bones (See Reference 2).

Compact Bones

• Bone tissue functions as either compact or spongy bone depending on the arrangement of the connective tissue's microstructure. Individual bones contain the harder shell of the compact bone and the spongy bone underneath. Compact bones, or cortical bones, have a denser composition within the calcified matrix because they are filled with both organic and inorganic substances (See Reference 1).

Spongy Bones

• Spongy bones, also called cancellous bones, are porous because of their arrangement of tissue. They largely live within the epiphysis, or rounded end, of long bones and just inside the compact bone on other bone shapes. A substantial portion of spongy bone is vascular, and blood cells form in areas of red bone marrow. Although this osseous tissue has a softer consistency, it provides much of a bone's strength (See Reference 1).

Long Bones

• Long bones are characterized as having a greater length than width. This allows them to function as a lever primarily for movement and articulation with other bones. Arms and legs have long bones such as the humerus and femur, but long bones also exist in the smaller fingers and toes. They have a rounded end covered in cartilage called the epiphysis that moves against joints (See Reference 1).

Short Bones

• Short bones are of similar length and width because they work as stabilizers in areas of necessary strength. Typical short bones include the carpals and tarsals found in wrists and ankles. Sesamoid bones, located where tendons pass over joints, are often considered short bones (See Reference 1).

Flat Bones

• Flat bones act like a hard surface to shield and protect organs from harm. They also attach to muscles in the chest or skull. The scapula, or shoulder blade, is a flat bone. Much of an adult's red blood cell count is formed within the bone marrow of flat bones (See Reference 1).

Irregular Bones

• Irregular bones are those that do not fit any of the former three shape categories. Vertebrae bones are irregular and have the specific function of protecting nervous tissue while contributing to balance and support (See Reference 1).