The Skeletal System
Department of Biology
Mission Hills High School
Bones:
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The human body is born with over 300 bones but
quickly begins to reduce in number as bones fuse.
By the time the child becomes an adult, the number
of bones is 206
½ of these bones are in the hands and feet.
Age of a young skeleton can be determined by the
number of bones fused using x-ray of hands.
Functions of bone:
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Forms the framework for the human body (the
skeleton)
Bases for attachment of muscles and tendons
Provides minerals (calcium and phosphates)
Protection for vital organs:
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Brain: cranium
Heart and Lungs: ribcage and sternum
Produces blood elements (RBC’s and WBC’s): Red
bone marrow – center of bone
Composition of bone:
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Bone is primarily composed of calcium
and phosphate
Both give bone a very hard
consistency to perform its job as the
framework for the body
Bone is hard and strong, yet very light.
Classification of bones is by
shape:
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Short bones (wrist and ankles)
Long bones (arms, fingers, legs and toes)
Flat bones (skull)
Irregular bones (hip,vertebrae, sacrum and
maxilla )
Sesmoid – no direct articulation with other
bones (knee cap)
Short bones
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Short bones are "short":
cubelike.
They do not have any cavity
similar to the medullary cavity of
the long bones.
Short bones are made mostly of
spongy bone tissue, but their
outer parts are made of a thin
crust of compact bone tissue.
Long Bones
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Long bones are "long": their
length is superior to their width.
Long bone consist of a shaft
(diaphysis) and two expanded
ends (epiphysis, plural:
epiphyses)
Flat bones
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Flat bones are "flat", platelike.
They are thin and do not have any
cavity similar to the medullary cavity of
the long bones.
The outer part of a flat bone is made of
a layer of spongy bone tissue
sandwiched between two layers of
compact bone tissue.
Irregular bones
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Irregular bones are all the weird-shaped
bones that do not belong in any other
category.
They do not have any cavity similar to
the medullary cavity of the long bones.
They are made mostly of spongy bone
tissue enclosed by a thin crust of
compact bone tissue.
Parts of long bones:
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Diaphysis (shaft)
Epiphysis (ends)
Neck (region between diaphysis and
epiphysis)
Structure of Bone Tissue
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Periosteum: Connective tissue which contains
nerves, blood vessels, gives rise to new bone and
repairs fractures.
Compact bone: Hardest part of the bone, contains
Haversian systems where bone cells are located.
Spongy (Cancellous) bone:
Marrow:
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Red marrow – forms blood tissue.
Yellow Marrow- With increasing age parts become inactive in
blood formation and function as fat storage. It then appears
yellow and is called yellow marrow
End Part 1
Anatomy of The Human
Skeleton
The Human skeleton’s 206 bones
are divided into two sections:
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Axial skeleton (74 bones)
Appendicular skeleton (126 bones)
Ear ossicles are the smallest bones
found in the cranium – 6 bones)
Total is 206 bones!
Axial
Skeleton
Appendicular
Skeleton
Axial Skeleton
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Skull (Cranium and face): 22 bones
Vertebral column: 26 bones
Ribs:24(12 pairs) bones
Sternum: 2 bones
Appendicular Skeleton
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Shoulder girdle: 2 pairs
(4 bones)
Arms and hands: 62 bones
Pelvic Girdle: 2 bones each
fused from three bones.
Legs and feet: 60 bones
Putting it all together:
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Bones are held together by a connective
tissue called ligament.
A joint (articulation) is formed where two
bones meet.
Some joints are immovable, others glide,
some pivot, some are hinge and some are
ball-socket type. This forms the basis of
joint types.
End Part 2