The Skeletal System
The Human Skeleton
Composed of the body’s
• Bones
• Ligaments (bone-bone)
• Tendons (bone-muscle)
• Cartilage
The Human Skeleton
• Infants have more than
300 bones at birth
• Bones fuse as babies
develop
• 206 bones in the adult
human body
Functions of the Skeletal System
1. Structure and Support
• Leg bones, pelvis, and vertebrae
support the body’s weight
2. Protection
• Skull protects the
brain
• Ribs and sternum
(breastbone) protect
the lungs and heart
Functions of the Skeletal System
3. Movement
• Muscles attach to bones and use
them as levers to move the body
4. Storage
• Calcium and fat (stored E)
5. Blood Cell Production
• Bone marrow produces
millions of red blood cells per
second
Bone Classification
Each bone belongs to one of
two major groups:
Axial skeleton
• Skull, vertebral column, and
rib cage
• Involved in protection,
support, and carrying other
body parts
Appendicular skeleton
• Bones of upper & lower limbs
• Involved in locomotion
Bone Classification
Types of bones:
1. Long Bones
• Longer than they are wide
• All limb bones except the
patella (kneecap) and the
bones of the wrist and
ankle
2. Short Bones
• Roughly cube shaped
• Bones of the wrist and the
ankle
Bone Classification
3. Flat Bones
• Thin, flattened, and usually a
bit curved.
• Scapula (shoulder blade),
sternum (breast bone), ribs,
and most bones of the skull.
4. Irregular Bones
• Have weird shapes that fit none
of the 3 previous classes.
• Vertebrae, hip bones, 2 skull
bones – mandible and maxilla.
Bone Structure
All bones consist of a
dense, solid outer
layer known as
compact bone and an
inner layer of spongy
bone.
Cross Section of a Long Bone
Long Bone
Structure
• Periosteum: Hard outer covering
• Epiphysis: Ends of the bone.
• Diaphysis: The shaft of the bone
• Articular Cartilage: Cushions the
ends of the bones and allows for
smooth movement.
• Epiphyseal Plate: Areas made of
cartilage allowing for the growth of
the bone. Growth plate
Compact Bone Structure
In compact bone, osteocytes (bone cells) are
arranged in rings around Central Canals,
passageways for blood vessels and nerves.
R
Compact Bone Structure
Bone tissue is a type of connective tissue, so it must consist
of cells plus an extracellular matrix.
collagen (protein) – provides strength and resilience
and
calcium – provides hardness and resistance to crushing
Compact Bone 400x
Osteocyte (basic
bone cell)
Haversian Canal
(opening)
Extracellular Matrix
(collagen and Ca)
Spongy Bone Structure
•
Composed of irregular and interconnected
channels, creating lots of space.
•
Absorbs shock/stress on skeleton
•
Space makes bone lighter
•
Space is filled with
bone marrow:
red – blood cell production
yellow – fat storage
Three Types of Bone Cells
1. Osteocytes – mature bone cells , suspended in
matrix [cytes = basic cells]
2. Osteoblasts – build new bone by adding
collagen and calcium to matrix
[blasts = build]
3. Osteoclasts – break down matrix to release
stored calcium; can also clean up unhealthy or
unwanted bone
[clasts = cleave]
Low Ca
in body
Osteoclasts
break down
matrix
Ca released
from bone
Ca enters blood,
travels to muscle
tissue, etc.
High Ca in
Body
Ca from
blood
enters bone
Osteoblasts
store Ca by
making new
matrix
Ca Level
Stable
Osteoblast
activity =
osteoclast
activity
Remodeling
maintains
bone health
Bone Features
• Projections that are sites of tendon and
ligament attachment
• Projections that help to form joints
• Depressions and openings allowing blood
vessels and nerves to pass
Sites of tendon and ligament
attachment
• Tuberosity: large
rounded projection
• Tubercle: small rounded
projection
• Process: any bony
prominence
• Trochanter: very large,
blunt, irregularly shaped
process on femur
Projections that help form joints
• Condyle: rounded
articular projection
Depressions and openings allowing blood
vessels and nerves to pass
• Meatus: canal-like
passageway
• Sinus: cavity within
a bone, filled with
air and lined with
mucous membrane
• Fossa: shallow
depression in a bone
Features that allow blood vessels
and nerves to pass
• Suture (fissure):
narrow, slitlike
opening
• Foramen: round
or oval opening
through a bone