Flat+Bone

=Flat Bone=

Other types of bone include long bone, short bone, and irregular bone.

Location
Flat bones include [|the skull], [|the pelvis], and [|rib cage].

Structure
Broad and smooth, flat bones are thin like plate bones due to only consisting of one to two layers. Flat bones can either be made of a single, thin layer of compact bone or be comprised of two layers of intervening spongy bones and [|red bone marrow.]

[[image:472523242_40d90d39fb.jpg width="604" height="443" caption="The Human Skull" link="http://flickr.com/photos/sammygrimes/472523242/"]]
Instead of being straight as per the name, flat bones are usually bent or curved as in the skull or ribs.

[[image:skelet1.jpg width="331" height="225" align="right" caption="The Pelvis/Hip Bone" link="http://www.millwood.ednet.ns.ca/biology/Bio12/imagesBio/skelet1.jpg"]]Function
With the thin layer of spongy tissue, flat bones contain vast amounts of red bone marrow that work to form red blood cells. Flat bones with their large size and plate structure cover vital organs such as the brain to provide extensive protection. While the cranium contains several bones, most of these are flat bones.

=Ossification= [|Ossification] is started by the formation of two connective tissue membranes that hold the spot where the flat bone is to come. On a baby, those spots are known as fontanelles. The fontanelles contain connective tissue stem cells, which form into osteoblasts, or bone cells which secrete calcium phosphate into a matrix of canals.This contributes to the ossification of bone in infants. They form a ring in between the membranes, and begin to expand outwards. As they expand they make a bony matrix. This hardened matrix forms the body of the bone. Since flat bones are usually thinner than long bones, they only have red bone marrow, rather than both red and yellow bone marrow. The bone marrow fills the space in the ring of [|osteoblasts], and eventually fills the bony matrix. After the bone is completely ossified, the osteoblasts retract their calcium phosphate secreting tendrils, leaving tiny canals in the bony matrix, known as canaliculi. These canaliculi provide the nutrients needed for the newly transformed osteoblasts, which are now called osteocytes. These cells are responsible for the general maintenance of the bone. A third type of bone cell found in flat bones is called an osteoclast, which destroys the bone using enzymes. There are three reasons that osteoclasts are normally used: the first is for the reparation of bones after a break. They destroy sections of bone that protrude or make reformation difficult. They are also used to obtain necessary calcium from the bones. When a person's blood calcium is low, the osteoclasts take calcium from the bone and put it into the blood for necessary things such as nerve and muscle action. The last reason that osteoclasts are used is for growing. As the bone grows, the shape of the bone also changes. The [|osteoclasts] dissolve the part of the bone that needs to be changed.