The Skeletal System

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The Skeletal System

• Department of Biology
• Mission Hills High School

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Bones

• 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.

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Functions of bone

• 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
• Brain cranium
• Heart and Lungs ribcage and sternum
• Produces blood elements (RBCs and WBCs) Red
  bone marrow center of bone

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Composition of bone

• 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.

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Classification of bones is by shape

• 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)

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Short bones

• 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.

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Long Bones

• 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)

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Flat bones

• 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.

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Irregular bones

• 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.

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Parts of long bones

• Diaphysis (shaft)
• Epiphysis (ends)
• Neck (region between diaphysis and epiphysis)

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Structure of Bone Tissue

• 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
• 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

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End Part 1
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Anatomy of The Human Skeleton
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The Human skeletons 206 bones are divided into
two sections

• Axial skeleton (74 bones)
• Appendicular skeleton (126 bones)
• Ear ossicles are the smallest bones found in the
  cranium 6 bones)
• Total is 206 bones!

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Axial Skeleton
Appendicular Skeleton
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Axial Skeleton

• Skull (Cranium and face) 22 bones
• Vertebral column 26 bones
• Ribs24(12 pairs) bones
• Sternum 2 bones

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Appendicular Skeleton

• 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

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Putting it all together

• 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.

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End Part 2