Answer:
Bones provide the structure for our bodies. The adult human skeleton is made up of 206 bones. These include the bones of the skull, spine (vertebrae), ribs, arms and legs. Bones are made of connective tissue reinforced with calcium and specialised bone cells. Most bones also contain bone marrow, where blood cells are made.
Bones work with muscles and joints to hold our body together and support freedom of movement. This is called the musculoskeletal system. The skeleton supports and shapes the body and protects delicate internal organs such as the brain, heart and lungs.
Bones contain most of our body’s calcium supply. The body is constantly building up and breaking down bone tissue as required. Healthy bone needs a balanced diet, regular weight-bearing exercise and the right levels of various hormones.
The skeleton
The human skeleton is made up of 206 bones, including bones of the:
Skull – including the jaw bone
Spine – cervical, thoracic and lumbar vertebrae, sacrum and tailbone (coccyx)
Chest – ribs and breastbone (sternum)
Arms – shoulder blade (scapula), collar bone (clavicle), humerus, radius and ulna
Hands – wrist bones (carpals), metacarpals and phalanges
Pelvis – hip bones
Legs – thigh bone (femur), kneecap (patella), shin bone (tibia) and fibula
Feet – tarsals, metatarsals and phalanges.
Bone types
There are four different types of bone in the human body:
Long bone – has a long, thin shape. Examples include the bones of the arms and legs (excluding the wrists, ankles and kneecaps). With the help of muscles, long bones work as levers to permit movement.
Short bone – has a squat, cubed shape. Examples include the bones that make up the wrists and the ankles.
Flat bone – has a flattened, broad surface. Examples include ribs, shoulder blades, breast bone and skull bones.
Irregular bone – has a shape that does not conform to the above three types. Examples include the bones of the spine (vertebrae).
Bone tissue
The different layers of bone tissue include:
Periosteum – the dense, tough outer shell that contains blood vessels and nerves
Compact or dense tissue – the hard, smooth layer that protects the tissue within
Spongy or cancellous tissue – the porous, honeycombed material found inside most bones, which allows the bone to be strong yet lightweight
Bone marrow – the jelly-like substance found inside the cavities of some bones (including the pelvis) that produces blood cells.
Bone marrow
Bone marrow is where blood cells are made. The three different types of blood cell made by bone marrow include:
Red blood cells – carry oxygen around the body.
White blood cells – make up the body’s immune system.
Platelets – are used for clotting.
Bone cells
Our body is constantly remodelling its skeleton by building up and breaking down bone tissue as required. As a result, each bone is rebuilt from scratch about every decade. The bone cells involved in this process include:
Osteoblasts – the cells that build bone tissue
Osteocytes – the cells that maintain bone tissue by controlling the mineral and calcium content
Osteoclasts – the cells that break down old bone tissue.
Bone density
Many factors work together to ensure the strength and health of bones. Bone density relies on:
A steady supply of dietary calcium
Adequate vitamin D from sunshine and food
A healthy diet with plenty of vitamins and minerals
Various hormones including parathyroid hormone, growth hormone, calcitonin, oestrogen and testosterone
Regular weight-bearing exercise.
Bone conditions
Some conditions of bone include:
Fractures – broken bones of various types
Osteoporosis – loss of bone density and strength
Osteomyelitis – infection of the bone
Osteitis – bone inflammation, for example, Paget’s disease of the bone
Acromegaly – overgrowth of bones in the face, hands and feet
Fibrous dysplasia – abnormal growth or swelling of bone
Rickets – a child’s growing bones fail to develop due to a lack of vitamin D
Multiple myeloma – cancer of the plasma cells in bone marrow
Bone cancer – primary bone cancers include osteosarcomas and chondrosarcomas. However, most cancers found in bone have spread from other organs such as the breast, prostate, lung or kidney
Explanation:
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