Bones
© 2006 Pearson Publishing Tel 01223 350555
The skeleton
•
The skeleton forms the framework of the
human body
•
It has five main functions:
– Support — it gives the body a structure
(to which muscles attach)
– Protection — it protects the vital organs
(eg the brain) from injury
– Movement — it enables movement where two
bones come together at the joints
– Shape — it makes the body tall, short, broad
or narrow
– Contains bone marrow — which produces blood
cells and stores mineral salts
How bones grow
• The skeletal system of an
embryo starts off as
cartilage — a firm but
elastic material
• As the embryo grows,
cartilage gradually
changes to bone — this is
called ossification
• This process continues
throughout childhood
• Ossification replaces
and repairs bones
throughout life
The skeleton
Names of bones
You must learn these:
• Cranium
• Tibia
• Sternum
• Fibula
• Ribs
• Scapula
• Ilium
• Clavicle
• Humerus
• Tarsals
• Ulna
• Metatarsals
• Radius
• Carpals
• Femur
• Metacarpals
• Patella
• Phalanges
Classification of bones
There are four types of bones:
• Long bones — strong and light
bones, used as levers for movement,
eg femur, humerus, tibia, fibula
• Short bones — very strong bones,
used for grip, balance and fine
movements, eg carpals, tarsals
• Flat bones — used for protection
and muscle attachment,
eg cranium, pelvis, scapula, ribs
• Irregular bones —
eg vertebrae, facial
Characteristics of a bone
• Periosteum
— hard outer
covering
• Red marrow at
ends — produces
red blood cells
• Yellow marrow in
shaft — produces
white blood cells
• Articular cartilage
— prevents bone
erosion at joints
The vertebral column (spine)
• Keeps the body upright
• Helps posture and movement
• Acts as a shock absorber
• Protects the spinal cord
A typical vertebra
Five regions of the spine
• Cervical — neck region, seven
vertebrae, top two = atlas, axis
• Thoracic — chest region, 12
vertebrae, ribs attached to it
• Lumbar — lower back region,
five vertebrae, largest vertebrae,
allows back flexibility
• Sacrum — base region, five
vertebrae fused together,
attached to the pelvis, allows
weight transfer to hips/legs
• Coccyx — ‘tail’ region, four
vertebrae fused together
Strength of bones
• Two factors determine the strength of bones:
– The thickness of the bone
– Bone density (sometimes called bone mineral
density or BMD)
• Stronger bones mean increased strength and less
risk of injury, so enhanced sporting performance
• Bone density can be increased by aerobic exercise
and strength training
Bones and weight
• In adults, putting on weight increases bone density
and makes the bones stronger (although gaining too
much weight causes other problems)
• Being too thin causes bones to weaken and increases
the risk of fractures
• Younger people who are overweight because of a
lack of exercise are less likely to have strong bones,
but it is still important to avoid being underweight
Factors affecting bones
Age
• Bones reach their peak strength in adulthood, then
tend to get weaker as we become elderly
• This may be due to lower activity levels rather than
the ageing process itself
Gender
• Girls and women tend to have slightly thinner bones
• Older women (post-menopausal) are particularly at
risk of weakening bones
• Weakening bones can lead to the medical condition
osteoporosis, so it is important to keep exercising as
you get older, particularly for women