The **skeletal system** acts as the body’s framework. It is composed of bones, cartilage, tendons, and ligaments that function to support and give shape to the body. All in all, there are 206 bones found in the adult individuals.

Other than being a support system, the skeletal system also functions in the following.

1. Protection of the internal organs
2. Provides muscle attachment and supports the movement of the body.
3. Serves as a mineral and nutrients reservoir.
4. Serves as a site for blood cell formation (bone marrow).

Bones are composed of solid living tissues and protein fibers and calcium salt deposits. The tough outer layer is called periosteum. Just below the periosteum is the compact bone which contains a network of tubes called Haversian canals. Inside these canals are the blood vessels that deliver oxygen and nutrients to the bone. On the outer layer of the compact bone, a spongy bone is found. This spongy layer is usually found in the ends of a long bone. In flat bones, the spongy layer is in located in the middle.

**Joints** are the place in which bones meet or attach to another bone. These structures enable the bone to move without damaging it. The different types of joints are dependent on their type of movement.

Types of joints:

1. **Immovable joint** – These are the joints that are also referred to as *fixed joints*. They are the joints that allow no movement, and they usually interlocked the bones holding them tightly together. Example: joints in the skull

2. **Slightly moveable joints** – These are joints that permit *a small amount* of movement.

3. **Freely moveable joints** – These are joints that enable a wide array of movements, thus they permit one or more directions of movements. Some examples of freely moveable joints are ball-and-socket joints, pivot joints, and saddle joints.

The compact bone forms the outer layer of bones. It is made up of osteons and it is more dense when compared to a spongy bone. On the other hand, the spongy bone forms the inner layer of the bones. It is made up of trabeculae, which look like a latticework.

**Cartilage** is a type of connective tissue present during the embryonic stage. This connective tissue is replaced by bone structures through the process of **ossification**. However, many long bones including those found in the arms and legs contain *growth plates* at the end of each side of the bone. These growth plates are the site in which cartilage grows, therefore, enabling the bones to also grow, and develop stronger

However, when an individual reached late adolescence or early adulthood, these growth plates are replaced by bone tissues, hence, they will be completely ossified. Until then, the person now *stops growing*.