Describe the categories of bone and give examples of each
There are several different categories of bone, often classified based on shape. Flat bones are flat (!)- examples include the sternum and the bones of the skull. Long bones are long (!!) and include bones such as the femur and humerus. Short bones are short (!!!!!!!!!!!!!!!!!!!), and by that I mean they are about as wide as they are long, and include the carpals and tarsals. Irregular bones have weird, irregular shapes (!?!?!?!?!??!!!!!) and include the vertebrae. Finally, there are sesamoid bones, which are bones that are found within tendons. An example of a sesamoid bone is the patella.
Describe the general features of a long bone and a flat bone
Long and flat bones have several features in common. Both bones are made out of several types of bone cells as well as non-cellular components, such as collagen and ground substance. The basic building block of bone is the osteone, or Haversian canal, which is made up of concentric rings of bone around a central canal containing an artery. Osteocytes (mature bone cells) can be found in lacunae, which are little spaces between the concentric rings of the osteone. Cells can communicate with each other via small passages known as canaliculi.
Both long and flat bones have two main regions: cortical bone and cancellous (spongy) bone. In cortical bone, the osteones make up a solid sheet. In cancellous bone, the osteones are arranged in web-like structures called spicules. Cancellous bone also contains the bone marrow, which comes in two flavours: red (blood-forming) and yellow (contains a higher number of fat cells). When we are young, we have more red marrow, but we get more yellow marrow as we get older.
The outer surface of bones is lined by a thin layer of connective tissue called periosteum. Long bones also have a medullary cavity within them. This cavity is lined by a thin layer of tissue called the endosteum.
Describe the four cell types in bone tissue; their function,
origins, and locations in the tissue
The main cell types in bone tissue are osteogenic cells, osteoblasts, osteocytes, and osteoclasts.
Osteogenic cells are found in the inner layer of the periosteum, as well as in the endosteum. Osteogenic cells are stem cells that are able to divide to produce osteoblasts.
Osteoblasts are bone cells that primarily function to build up bone in a process known as osteogenesis. They are found in a single layer of bone underneath the endosteum.
Osteocytes are bone cells that are found in the lacunae of Haversian canals, as mentioned earlier. They contribute to maintaining bone. Osteocytes are formed from osteoblasts that are trapped in the matrix of bone.
Osteoclasts are found in pits called resorption bays. They have the opposite function to osteoblasts: osteoclasts function to break down bone. Osteoclasts are quite large and have multiple nuclei. As opposed to osteoblasts and osteocytes, osteoclasts do not arise from osteogenic cells. Instead, osteoclasts arise from monocytes and macrophages.
Describe the two mechanisms of bone formation
There are two main methods of bone formation: intramembranous ossification and endochondral ossification.
Intramembranous ossification can occur in areas where bones are not subjected to stress. In intramembranous ossification, bone forms within membranes. Bones of the cranium are formed in this way.
Endochondral ossification occurs in bones that are under load or stress during development. In endochondral ossification, there is a cartilaginous growth plate to absorb some of the stress. Over time, the cartilage becomes replaced by bone. Note that bone does not grow from cartilage- it simply replaces it!
Describe bone growth and remodelling
I don't think we need to know too much about this for now, other than that bone is continually being broken down by osteoclasts and built up again by osteoblasts. Bone growth and remodelling takes place according to where stresses are placed on bones.
Describe the structural and functional classification of joints
No comments:
Post a Comment