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The skeletal system

Functions of the skeletal system

  1. Supports the soft tissues as a framework
  2. Protection for internal organs and brain
  3. Assists in movement
  4. Storage of minerals such as calcium and phosphorus
  5. Production of blood cells from the bone marrow

 

The skeleton is composed of 206 bones divided into two areas: the axial and appendicular bones.

The axial skeleton consists of bones that form the axis of the body and support and protect the organs of the head, neck and trunk:

  • The skull, which has 22 bones consisting of 8 cranial and 14 facial bones
  • 1 atlas bone and 1 axis bone (1st and 2nd vertebra)
  • The thorax consists of 12 pairs of ribs and 1 sternum bone
  • The vertebral column which has 33 bones – 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4 coccyx

The appendicular skeleton is composed of bones that anchor the appendages to the axial skeleton:

  • The upper extremities consist of 2 humerus, 2 ulna and 2 radial bones plus 8 carpals, 5 metacarpals and 14 phalanges
  • The lower extremities 2 femur, 2 patellas, 2 fibula, 2 tibia, 7 tarsals, 5 metatarsals and 14 phalanges
  • The shoulder girdle consists of 2 clavicle bones and 2 scapula bones
  • The pelvic girdle is fused to the sacrum at the sacro-iliac joint at the base of the spine or vertebral column

 

Bone formation

The process of bone formation is called ossification. Specialised cells called osteoblasts make bone tissue which secretes collagen to form a strong framework. Minerals such as calcium and salts are deposited within the bone where it hardens and becomes calcified. The osteoblasts become trapped in the bone tissue and become osteocytes. The osteoblasts continue to make new bone tissue to replace the old as it is broken down.

 

Types of bones

  • Long bones: found in the arms and legs
  • Short bones: found in the wrist and ankles
  • Flat bones: plate like, protect the brain
  • Irregular bones: found in the spine

 

Composition of bone

Compact or dense bone is hard and forms the outer part of bones. Spongy or Cancellous bone lies inside the compact bone and is porous with tiny holes.

bones presentation