Bones, Bones, & More Bones

Osteology The science that deals with the study of bones. Each bone is an organ that plays a part in how the skeletal system functions. The skeletal system of an adult is made up of 206 bones. This number varies by age, for example, at birth, our bodies consist of about 270 bones. Over the first 3-5 years of our lives, the number actually increases to over 300. At your age the number actually decreases because the bones fuse (connect) together.

Composition of Bones ¼ of the weight is composed of water. 1/3 of the weight is organic material such as the protein, ossein. The rest of the weight is composed of inorganic materials such as calcium, phosphorus, magnesium, and small amounts of iron, potassium, sodium, chlorine, and fluorine.

Layers of Bone (1) The outer surface of the bone is called periosteum. It’s a thin, dense layer that contains nerves and blood vessels to nourish the bone. The next layer is made up of compact bone. This part is smooth and very hard. This is the part you see when you look at a skeleton.

Layers of Bone (2) Within the compact bone are several layers of cancellous bone. This looks a bit like sponge. Not as hard as compact bone, but still very strong. The cancellous bone protects the bone marrow, which is the innermost layer of bone. Sort of like a thick jelly. Produces new blood cells.

How Do Bones Grow? Bones are made of a network of calcium laid down by cells. During childhood, as you are growing, the cartilage grows and is slowly replaced by bone, with help from calcium As kids grow, special cells at the end of bones add new calcium to the network of bone. Children have layers of these cells in the shape of plates at the ends of their bones. These are called “growth plates,” and they close up when kids reach their full adult height.

When Do Bones Stop Growing? There is no exact age for humans to stop growing. Once the epiphysis (the rounded end of a long bone) has fused to the bone and the growth plate is closed, the bone will stop growing. This usually occurs between the ages of 15-25.

Bone Classification Anatomical Position Shape Axial or Appendicular Long, Short, Flat, and Irregular

Axial Bones 80 bones which lie along the central, vertical axis of the body and support and protect the head and torso.

Appendicular Bones 126 which comprise the appendages, including the shoulders, hips, arms, legs, hands, feet, fingers, and toes.

Shapes Long bones: Strong bones, such as the femur, found in the arms and legs. Short bones: Over ½ of which can be found in the hands and feet, are as broad as they are long. Flat bones: Thin, flat bones, such as the ribs and skull, which serve to protect vital body organs. Irregular Bones: Have shapes that do not fit with the other types of bones, such as vertebrae

Functions of Bones There are five main functions of bones: Support Protection Body Movement Production of Blood Cells Mineral Storage

Support One function of the skeleton is to provide support for your body. The skeleton forms the base to which muscles and other soft tissue attach. Without the support of your bones, like your vertebral column, you would not be able to stand up. Did You Know??? A giraffe and a human have the same number of bones in their necks.

Protection The second function of the skeletal system is to provide protection for the soft, delicate parts of your body. For example: your cranium (skull) and spine protect your central nervous system while your ribcage protects your heart. Did You Know??? Your jawbone is actually the hardest bone in your body.

Body Movement (1) In order to move, muscles need to pull on bones. When muscles contract, the bones to which they are attached act as levers and cause different body parts to move. The movement takes place at the connection between bones, which is called a joint.

Bone Movement (2) Cartilage and Ligaments help move the joints. Synovial fluid acts as a lubricant to keep the joints moving smoothly. Joints are classified by their range of movement. Some are immovable (fixed), some are partially movable (such as the ones found in your spine) allow for flexibility but not a wide range of movement, and freely movable joints (hinged, ball-and-socket, gliding, saddle, and pivot).

Body Movement (2) There are different types of joints in your body: A hinged joint, like the one in your knee, allows you to move your leg back and forth just like a door hinge. A fixed joint, like your skull, has very little movement at all. A ball-and-socket joint, like the one in your shoulder or leg, allows you to move your leg or arm 360° like a shower head.

Body Movement (3) A gliding joint, such as the ones in your wrist and foot, allow for limited movement. A saddle joint, such as the one in your thumb, allows for greater movement than either a hinge or a gliding joint. It gives the thumb the ability to cross over the palm. A pivot joint, such as the one between your head and spine, allows one bone to rotate around another.

Production of Blood Cells It is in the hollow center of bones that bone marrow makes new red and white blood cells. The red blood cells ensure that oxygen is distributed to all parts of your body. The white blood cells are responsible for fighting off germs and disease.

Mineral Storage Bones are storage sites for many minerals. These minerals give bones their rigidity (hardness) and much of its weight. Bones contain a lot of calcium. Calcium is important for bone growth and development. It is also important for muscle contractions.