Skeletal System

Define a simple and compound fracture and explain the repair of fractures

A simple fractures is where the break is completely internal and the skin is not punctured. A compound fracture is where the broken bone punctures the skin and projects to the outside. First a haematoma (blood clot) forms at the break. A cartilaginous callus forms at the site of the fracture. Osteoblasts then replace the cartilage with spongy bone and "knit" the broken ends of the bone together. The spongy bone is eventually replaced by compact bone.

Name and describe the functions of the skeletal system

• Support: The skeleton provides a framework for the body by supporting soft tissues and providing points of attachment for skeletal muscles. • Protection: The skeleton protects many internal organs from injury. For example, cranial bones protect the brain, vertebrae protect the spinal cord, and the rib cage protects the heart and the lungs. • Movement/leverage: Skeletal muscles attach to bones by tendons and when they contract they pull on the bones and produce movement. Thus we can walk, pick up objects, dance etc. • Storage of minerals: Bone tissue stores several minerals, the most important of which are calcium and phosphorus. On demand, bone releases minerals into the blood stream to maintain critical mineral levels (homeostasis) and to distribute the minerals to other parts of the body. • Blood cell production : Blood cells (red blood cells, white blood cells ) are produced in the red bone marrow.

Why do bones have bone markings?

• Attachment sites for muscles, ligaments, and tendons • Joint surfaces • Conduits for blood vessels and nerves

Describe the anatomy of a long bone

A typical long bone such as the humerus (upper arm bone) or the femur (thigh bone) consists of the following components: • Epiphysis are the ends of the bone. Thus a long bone has a proximal epiphysis (the end which is closest to the point of attachment to the body—remember proximal and distal from the first practical) and a distal epiphysis. • Diaphysis is the bone's body or the shaft, the long, cylindrical main part of the bone. • Epiphyseal line is between the epiphysis and the diaphysis in the adult. This is a remnant of the epiphyseal plate, a disc of hyaline cartilage that grows during childhood to lengthen the bone. • Articular cartilage is a thin layer of hyaline cartilage covering the epiphysis where the bone forms an articulation (joint) with another bone. The cartilage reduces friction and absorbs shock at freely moveable joints. • Periosteum is a tough, white fibrous membrane that surrounds the bone surface where it is not covered by articular cartilage. The periosteum has a rich supply of blood and lymphatic vessels and nerves, which enter the bone shaft through the nutrient foramen. The internal surface of the periosteum consists of osteoblasts (bone forming cells) and osteoclasts (bone destroying cells). The periosteum is essential for bone growth, repair and nutrition. • Nutrient foramen are small openings in the bone shaft through which blood and lymphatic vessels and nerves enter. The blood vessels bring in nutrients and oxygen and remove waste. • Medullary cavity is the space within the diaphysis that contains fatty yellow bone marrow in the adults. • Endosteum is the connective tissue membrane lining of the medullary cavity. Like the periosteum it contains osteoblasts and osteoclasts.

Discuss the chemical composition of bone and the relative advantages conferred by its organic and its inorganic components

Bone consists of a matrix that is made up of an organic (collagen - fibres) and an inorganic (mineral salts - calcium phosphates) component. There are three main types of cells in bone tissue: osteoblasts (cells that form bone), osteocytes (mature bone cells that maintain bone) and osteoclasts (that break down bone). The calcium phosphate crystals give the bone the hardness whereas collagen gives the bone its flexibility and resistance to shattering.

Describe and compare and contrast the structure of compact and spongy bone

Compact bone (also known as dense bone or hard bone) forms the external layer of all bones in the body and forms the bulk of the body of long bones. Compact bone provides protection and support and helps the long bones resist the stress placed on them by the weight of the body. Spongy bone makes up most of the short, flat, and irregularly shaped bones and the epiphysis of long bones. Spongy bone in the skull, hip bones, ribs, sternum, vertebrae and the ends of some long bones is the only site of red bone marrow and thus the only site where blood cells are formed.

Describe the effects of ageing on the skeletal system.

Osteoblast activity declines (cells that form bones) whilst osteoclast activity (cells that break down bones) remains at the previous levels therefore our bones begin to lose mass and become thinner and weaker. In addition, as we age the proportion of protein (organic) content declines relative to the mineral (inorganic) content, resulting in brittle bones.

Classify bones on the basis of their shape

The 206 bones of the skeleton can be conveniently divided into the: • Axial Skeleton - consists of the bones of the skull, the ribcage and the vertebral column • Appendicular Skeleton - consists of the bones of the shoulder (pectoral) girdle and the upper limbs and the hip (pelvic) girdle and the lower limbs. These 206 bones can be classified according to their shape. • Long bones are those where the bone is longer than it is wide - all the limb bones except the wrist and ankle bones. • Short bones are cube like - bones of the wrist and the ankle • Flat bones are thin and sheet like, often with a slight curvature - bones of the skull, ribs and shoulder blades (scapulae) • Irregular bones: This convenient category includes all bones which don't fit neatly into the above three groups! Irregular bones have complicated shapes. Some examples of irregular bones are vertebrae (which have convoluted protrusions) and the hip bones (os coxae).