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The skeleton system

What is the skeletal system?

The skeletal system in your body is made up of 206 bones, as well as a network of joints, tendons, ligaments and cartilage that hold them all together. You actually have about 300 bones when you're born but some of them fuse together as you grow and develop. Bones come in all shapes and sizes, from long, thigh bones to flat, wide shoulder blades. They fit together like a jigsaw forming the human skeleton. Calcium and other minerals make bones strong, but also flexible, so your bones are strong enough to support you, but light enough to allow easy movement.

The skeletal system diagram

How bones work

Your bones are living, changing organisms, containing blood vessels (nutrient arteries) and nerve and bone cells. The skeletal system works together with your circulatory and nervous system to constantly regenerate itself, replacing old cells with new ones. Inside bones, specialist cells called osteoclasts break down worn-out bone tissue and cells called osteoblasts rebuild them. This is why a bone repairs itself if it's broken.

Structure of the skeletal system

The structure of the skeletal system is divided into two main components, known as the appendicular and axial skeletons.

Appendicular skeleton: this term refers to your arms and legs that are attached, or 'append' to the main structure of your body. These large bones have a wide range of movement and are essential for movement.

Axial skeleton: this term refers to 80 bones all contained in your upper body. They fall into three groups and their key role is to protect vital areas of your body:

  • Skull – comprised of 22 facial, cranial and ear bones that protect your brain
  • Thorax – includes the sternum and 12 ribs that protect vital organs like your heart and lungs
  • Vertebra – consist of 5 sections with 26 flexible bones that protect your spine and spinal cord

Structure of men and women's skeletons

The main differences between a man and woman's skeletal system are the variations required for childbirth. Women have flatter pelvises that are more tilted. They're also proportionately larger, compared to men. The sacrum at the base of a woman's spine is wider and rounder to allow for a baby to pass through. This bigger hip width in women also affects the position of the thigh bones (femurs), so that women typically have an X shape, compared to the Y shape of men.

Generally, a woman's skeletal frame is smaller than a man's and smoother with more gentle hollows, such as the lumbar curve in the back. This can give women a more sway-backed appearance than that of men. Shoulder width is proportionately similar to men but bigger muscle development in men tends to makes a man's shoulders appear larger.

WebMD Medical Reference

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