What are Bones made of?
Bones are made up of four different layers and each of them play a different role in the bone structure. They are called periosteum, compact bone, spongy bone, and bone marrow.
|
| Image Source: https://elliottelford.com/tag/bone-health/ |
- The first outermost layer is called Periosteum. It's a thin but dense tissue that contains the nerves and blood vessels that provide nourishment to the bone.
- The next layer inside the periosteum is called the compact or cortical bone. It has a smooth texture and it is white and solid. Due to its solid nature, it protects our organs and maintains our body structure. It also helps our bodies to store and release essential nutrients like calcium and phosphorus.
- The third inner layer is called the spongy or cancellous bone. It is a spongy tissue which is less dense compared to compact bone but it has more flexibility. It is normally found at the ends of long bones, near joints and inside the vertebrae.
- The innermost layer of our bone is called the Bone Marrow. It contains two types of marrow, red bone marrow and yellow bone marrow.
- Red bone marrow is where the bones generate our red blood cells, white blood cells, and platelets.
- Yellow bone marrow is one of the places where new bone cells, cartilage cells, and fat cells are created for bone maintenance.
Joints between our bones
Bones provide the structure for our body so it can move in different directions. Not all bones can move relative to each other in all directions. The type of joint connecting the bones determines the direction and extent to which a bone can move and turn.
There are mainly three types of joints that are present in our bodies - fibrous joints, cartilaginous joints, and synovial joints.
- Fibrous joints are connected through a fibrous connective tissue, that connect bones which mostly have no relative movement against each other. The bones in our skull are an example of this type of joint.
- Cartilaginous joints consist of a fibrous cartilage, which connect bones which have only limited movement and therefore are only slightly moveable joints. The vertebrae of the spine are an example of this type of joint.
- Synovial joints are freely moveable joints which connect bones and enable them to move against each other freely. These joints are surrounded by a fluid-filled cavity (called synovial fluid). The bone parts that are within this cavity are covered with smooth cartilage, which lets the bones move smoothly against each other. Synovial joints are the most common joints in our bodies. The knees, elbows, and shoulders are some examples of this type of joint.
Synovial joints are further divided into six types based on their movements:
- Ball and socket joint has a rounded head of one bone sitting in the cup of another bone. This allows movement of bones in all directions. Shoulder joints and hip joints are an example of this type of joint.
- Hinge joint has a door hinge like movement in a single plane. Elbow joint and knee joint are an example of this type of joint.
- Condyloid/Ellipsoid joints allow movement but no rotation. Wrist joint and jaw are an example of this type of joint.
- Pivot joint has one bone that can swivel in a ring formed by a second bone. The joint between the first vertebrae (C1) and the second vertebrae (C2) in our neck is an example of this type of joint.
- Gliding/Plane joints allow two smooth surfaces to glide against each other. The joints between tarsal bones in our feet and the metacarpal bones in our hands are examples of this type of joints.
- Saddle joints allow movement back and forth, and side to side, but no rotation. The base of our thumb is an example of this type of joint.
|
| Image Source: https://open.oregonstate.education/aandp/chapter/9-4-synovial-joints/ |
Tendons and ligaments
To stabilise the connection of bones in our bodies, some of the bones in our bodies are connected to other bones, and others are connected to muscles. These connections are made using tissues called tendons and ligaments.
|
| Image Source: https://medlineplus.gov/ency/imagepages/19089.htm |
Tendons are connective tissues that attach muscles to bones. Every muscle at each end transforms into tendon tissue and connects to bones. Tendons often cross over a joint, which helps to stabilise the joints.
Ligaments are short bands of tough, flexible tissue that connect one bone to another. They stabilise the joint by holding the bones together and resisting abnormal or excess joint movements. The most commonly known ligaments are in our knees, ankles and shoulders, but they exist in every part of our body where bones connect to other bones.
In summary, bones and joints play a key role in keeping our body's structure, and provide a foundation for the muscles to move our body and perform all functions. I'll talk more about bones and their health in my upcoming blogposts.
Stay healthy and enjoy finding joy in health!