Unit 7 Reflection

This unit, we dragged the skeleton out of the (supply) closet and learned all about bones! The skeleton is actually an organ system called the skeletal system, and while at first, it may seem like bones are relatively inanimate, bones are actually constantly undergoing change and vital processes.

The different types of bone cells.
Image courtesy of Wikipedia Commons.

Let us first examine the anatomy of a bone on a microscopic level. Within the bone, there are osteogenic cells, and conveniently, "Osteo" means "Bone" in Greek. Obviously, our bones don't stay the same size throughout our entire life, otherwise, we would remain baby-sized forever. We actually undergo a process called ossification, or osteogenesis, in order to remodel and grow our bones. This process takes place from fetal development to around 25 years old, when our bones are completely ossified. This utilizes two types of cells: the osteoblasts and osteoclasts. Osteoblasts are the bone-building cells, and osteoclasts are the bone-destroying cells. Together, they work in harmony to remodel the bone in a constant state of flux. As old bone is destroyed, new bone is formed, keeping our bones nice and fresh. In fact, we create an entirely new skeleton approximately every 7 years! Mature bone cells are called osteocytes, and they conduct the daily processes of bones to maintain homeostasis. Bones have a compact bone exterior that is hard and dense, and a spongy bone interior that is more porous and filled with bone marrow/blood vessels. Through the Haversian Systems, osteons, or cylindrical canals, contain the bone's blood supplies. They are surrounded by lamellae which run perpendicularly to the osteons in order to provide more sturdiness. The lacunae are small spaces in the bone that contain the previously mentioned osteocytes.

Now we will look at bones on a macroscopic level, as well as discuss the different types of classification of bones. Bones can be classified into 4 different groups: long, short, flat, or irregular. Long bones are longer than they are wide, like the femur. Short bones are cuboidal shaped, like the carpals in your hand. Flat bones are, well, flat, like the ribs or the sternum. Lastly, irregular bones are the bones that don't fit into any other category, like the odd-shaped pelvis. In the skeleton, there are also joints that allow for movement in our bodies. Fibrous joints are surrounded by dense connective tissue and are synarthrosis, or immovable. An example would be the sutures of your skull. Cartilaginous joints are surrounded by cartilage and are amphiarthrosis, or allow for little movement. Synovial joints are the joints we typically think of, and they are surrounded by a joint capsule containing synovial fluid. They are diarthrosis, or fully moveable, and include joints like your elbows. To see a fun activity where we examined and classified bones on our own of rodents, refer to the Owl Pellet Lab.