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The Skeletal System
•Parts of the skeletal system
•Bones (skeleton)
•Joints
•Cartilages
•Ligaments
•Two subdivisions of the skeleton
•Axial skeleton  bones that form the
longitudinal axis of the body
•Appendicular skeleton  bones of the limbs
and girdles
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Functions of Bones
• Support the body
• Protect soft organs
• Skull and vertebrae for brain and spinal cord
• Rib cage for thoracic cavity organs
• Allow movement due to attached skeletal muscles
• Store minerals and fats
• Calcium and phosphorus
• Fat in the internal marrow cavity
• Hematopoiesis  blood cell formation
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Bones of the Human Body
•The adult skeleton has 206 bones
•Two basic types of bone tissue
•Compact bone
•Dense; looks smooth and homogeneous
•Spongy bone
•Small needle-like pieces of bone
•Many open spaces
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Classification of Bones on the Basis of
Shape
•Bones are classified as:
•Long
•Short
•Flat
•Irregular
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Classification of Bones
•Long bones
• Typically longer than they are wide
• Shaft with heads situated at both ends
• Contain mostly compact bone
• All of the bones of the limbs (except wrist,
ankle, and kneecap bones)
• Example:
• Femur
• Humerus
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Classification of Bones
•Short bones
•Generally cube-shaped
•Contain mostly spongy bone
•Includes bones of the wrist and ankle
•Sesamoid bones are a type of short bone
which form within tendons (patella)
•Example:
•Carpals
•Tarsals
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Classification of Bones
•Flat bones
•Thin, flattened, and usually curved
•Two thin layers of compact bone surround a
layer of spongy bone
•Example:
•Skull
•Ribs
•Sternum
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Classification of Bones
•Irregular bones
•Irregular shape
•Do not fit into other bone classification
categories
•Example:
•Vertebrae
•Hip bones
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Anatomy of a Long Bone
•Diaphysis
•Shaft
•Composed of compact bone
•Epiphysis
•Ends of the bone
•Composed mostly of spongy bone
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Anatomy of a Long Bone
•Epiphyseal plate (Growth plate)
•Flat plate of hyaline cartilage seen in young,
growing bone
•Cause the lengthwise growth of long bone
•Completely replaced by bone at the end of
puberty (no more vertical growth)
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Anatomy of a Long Bone
•Marrow (medullary) cavity
•Cavity inside of the shaft
•Contains yellow marrow (mostly fat) in
adults
•Contains red marrow for blood cell formation
in infants
•In adults, red marrow is situated in cavities of
spongy bone and epiphyses of some long
bones
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Formation of the Human Skeleton
•In embryos, the skeleton is primarily hyaline
cartilage
•During development, much of this cartilage is
replaced by bone
•Cartilage remains in isolated areas
•Bridge of the nose
•Parts of ribs
•Joints
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Types of Bone Cells
•Osteocytes  mature bone cells
•Osteoblasts  bone-forming cells
•Osteoclasts  giant bone-destroying cells
•Break down bone matrix for remodeling and
release of calcium in response to
parathyroid hormone
•Bone remodeling is performed by both
osteoblasts and osteoclasts
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Rickets
A disease of children in which the
bones fail to calcify. As a result, the bones
soften, and the weight-bearing bones of the
legs show a definite bowing.
Usually due to a lack of calcium in the
diet or a lack of Vitamin D
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Bone Fractures
•Fracture  break in a bone
•Types of bone fractures
•Closed (simple) fracture—break that does
not penetrate the skin
•Open (compound) fracture—broken bone
penetrates through the skin
•Bone fractures are treated by:
• Reduction  the realignment of the broken
bone ends
•Immobilization  cast or traction
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Common Types of Fractures
•Comminuted  bone breaks into many
fragments
•Compression  bone is crushed
•Depressed  broken bone portion is pressed
inward
•Impacted  broken bone ends are forced into
each other
•Spiral  ragged break occurs when excessive
twisting forces are applied to a bone
•Greenstick  bone breaks incompletely
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The Axial Skeleton
•Forms the longitudinal axis of the body
•Divided into three parts
•Skull
•Vertebral column
•Bony thorax
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The Skull
•Two sets of bones
•Cranium  encloses and protects the fragile
brain tissue
•Facial bones  hold the eyes in an anterior
position and allow facial muscles to show
feelings
•Bones are joined by sutures
•Only the mandible is attached by a freely
movable joint
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Paranasal Sinuses
•Hollow portions of bones surrounding the
nasal cavity
•Functions of paranasal sinuses
•Lighten the skull
•Give resonance and amplification to voice
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The Hyoid Bone
•The only bone that does not articulate with
another bone
•Serves as a moveable base for the tongue
•Aids in swallowing and speech
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The Vertebral Column
•Each vertebrae is given a name according to
its location
•There are 24 single vertebral bones
separated by intervertebral discs
•Cervical vertebrae  7 in the neck
•Thoracic vertebrae  12 in the chest
region
•Lumbar vertebrae  5 associated with the
lower back
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Sacrum and Coccyx
•Sacrum
•Formed by the fusion of five vertebrae
•Coccyx
•Formed from the fusion of three to five
vertebrae
•“Tailbone,” or remnant of a tail that other
vertebrates have
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The Vertebral Column Problems
•Herniated (“slipped”) Disc
•Can occur in two ways:
•Drying of the discs, along with a
weakening of the surrounding ligaments
•Exceptional twisting forces on the spine
•If the disc presses on the spinal cord or
spinal nerves it can cause numbness in the
legs and excruciating pain
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The Vertebral Column Problems
•Scoliosis  abnormal curvature of the spine
where the spine is curve side to side in an “sshape”
•Kyphosis  curving of the spine that causes a
bowing of the spine that results in a hunchback
•Lordosis  an inward curvature of a portion of
the lumbar spine
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