Structure of the Bones
Cells that make up the Bone:
- osteoclast: a very large cell formed in bone marrow, its function is to absorb and remove unwanted tissue.
- osteoblast: found within the bone, its function is to form the tissue and minerals that give bone its strength.
- osteocyte: found within the bone, its function is to help maintain bone as living tissue.
3 types of Bone tissue:
- compact tissue - the harder, outer tissue of bones.
- cancellous tissue - the sponge-like tissue inside bones.
- subchondral tissue - the smooth tissue at the ends of bones, which is covered with another type of tissue called cartilage. Cartilage is the specialized, gristly connective tissue that is present in adults, and the tissue from which most bones develop in
Types of Bones
There are 5 main categories of bones
Long Bones
A long bone is made up of a shaft and 2 ends and is longer than it is wide. Long bones have an outside layer of compact bone and an inner cavity containing bone marrow. The ends have spongy bone and an epiphyseal line. The epiphyseal line is a remnant of an area of hyaline cartilage that grew during childhood to help lengthen the bone.
Short Bones
Short bones are usually cube-shaped. This means they are about the same width as they are length. The carpal and tarsal bones are the most obvious of the short bones. They are usually smaller and collectively gathered as a group to work together, or form a larger structure. They are stronger because of their short compact structure, however, they break more easily due to lack of support and bone marrow.
Flat Bones
Flat bones are strong, flat plates of bone. Their main function is providing protection to vital organs and being a structural base for muscles to attach to. An example of a flat bone is the Scapula. Both front and back surfaces are formed of compact bone for strength and protection with the middle of the flat bone contains spongy bone and bone marrow. In adults, the highest number of red blood cells are formed in flat bones.
Irregular Bones
Irregular bones are bones in the body which do not fall into any other category, becasue they are not a regular shape. Good examples of these are the Vertebrae, Sacrum and Mandible . They primarily consist of cancellous bone, with a thin outer layer of compact bone.
Sesamoid bones
Sesamoid bones are short or irregular bones, embedded in a tendon. The most common is the Patella, which splits up the Patella tendon and is in the middle of it. Sesamoid bones are usually in a tendon where the tendon passes over a joint and the sesamoid bone then protects the tendon.