Adult skeleton: Contains 206 bones

Bone marrow: Red marrow makes blood cells. Yellow marrow stores fat

Two types of bone: Dense compact bone and lightweight spongy bone
Alive
Your bones are strong enough to support your weight, but light enough to allow movement. They protect your delicate internal organs and act as a storehouse for minerals, such as calcium. Despite appearing dry and lifeless, your bones are a hive of activity.
Bone structure
Your bones contain blood vessels, nerve cells and living bone cells known as osteocytes. These are held together by a framework of hard, non-living material containing calcium and phosphorous. A thin membrane called the periosteum covers the surface of your bones.
Running along the centre of long bones, such as your femur (thigh bone), is a cavity filled with bone marrow. Red bone marrow is a soft tissue that produces blood cells and yellow bone marrow is a store for fat.
Bone can either be spongy or compact. Spongy bone is lightweight and made up of a mesh of needle-like pieces of bone with large spaces between them. Compact bone is dense and forms the outer layer of all your bones.
Bone shapes
An adult skeleton is made up of 206 bones, which come in several different shapes and sizes. The shape of a bone reflects its role within your body:
• Long bones, like in your arms and legs, are mostly made of compact bone
• Short bones, like the bones in your wrists and ankles, are mainly made of spongy bone
• Flat bones, like your rib and skull bones, are made of a layer of spongy bone sandwiched between two thin layers of compact bone
• Irregular bones, such as your butterfly-shaped vertebrae, are unusual shaped bones that don't fit into the other three groups (1)

There are a number of different causes of fractures. The main ones are listed below.
• The most common cause of a fracture is severe force on your bone. This can happen during a fall or in an accident.
• Bone conditions, such as osteoporosis, can cause fractures. This is because your bones become fragile and brittle and this makes them more likely to break.
• Your bones can fracture because of repeated stress on them. Stress fractures can develop in your lower legs, for example, after repeated exercise, such as running. (2)

The most common causes of fractures are:
• Trauma. A fall, a motor vehicle accident, or a tackle during a football game can all result in fractures.
• Osteoporosis. This disorder weakens bones and makes them more likely to break.
• Overuse. Repetitive motion can tire muscles and place more force on bone. This can result in stress fractures. Stress fractures are more common in athletes. (3)
Causes of bone fractures can include:
• Traumatic incidents such as sporting injuries, vehicle accidents and falls
• Conditions such as osteoporosis and some types of cancer that cause bones to fracture more easily, meaning even minor trauma and falls can become serious. (4)

The function of long bones:-

Long bones are hard, dense bones that provide strength, structure, and mobility. The femur (thigh bone) is a long bone. A long bone has a shaft and two ends.
There are also bones in the fingers that are classified as "long bones," even though they are short in length. This is due to the shape of the bones, not the actual size.
Long bones contain yellow bone marrow and red bone marrow, which produces blood cells.(5)

Long bones have four main