Skeletal System Lecture
Lesson3:Bones and Bone Growth
Function of the Skeletal System
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Provides shape and form
Support
Protection
Allows bodily motion
Produces blood
Stores minerals
Bones
• Over 300 when you are born
• 206 in the adult skeleton
• Half are in the feet and hands
– 52 in the feet
– 54 in the hands
Basic structure of a Long Bone
Epiphysis: ends of bone containing compact bone enclosing
spongy bone.
Epiphyseal Growth Plate
Diaphysis: shaft containing compact bone surrounding a
medullar cavity.
In addition, long bones possess:
Periosteum: connective tissue membrane on diaphysis.
Articular cartilage: glassy, hyaline cartilage allows
smooth movement of joints at epiphyses.
articular cartilage
periosteum
Bone is Living Tissue!
Bone is like a labyrinth with passageways that contain vessels
and nerves (known as bone matrix).
Bone is living, growing tissue. It is continually being changed
and replaced (known as bone remodeling).
Bone is mostly made of collagen (protein) and calcium
phosphate. Calcium phosphate is a mineral compound that adds
strength and hardens the framework.
Bone Growth and Remodeling
Bone formation begins in embryo. It starts as hyaline cartilage
which serves as the “model” or basis for bone structure.
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In the fetus, hyaline cartilage is covered with bone matrix
by osteoblasts (temporarily giving bones a flexible interior with hard
outer shell).
•Next, ossification occurs. This involves the hyaline
cartilage being digested away leaving a medullary
cavity within the newly formed bone.
ossification
•By birth, most (but not all) cartilage has been converted
to bone except in two areas:
1)articular cartilage at ends of long bones
2)epiphyseal plates (place where diaphysis and epiphysis meet).
Epiphyseal plate: site of bone growth, to allow us to grow taller.
(this area has not ossified until late puberty thus on an x-ray of a femur, the
epiphyseal plate appears black.)
Epiphyseal line: appears when growth has stopped.
(this line occurs due to ossification when growth no longer occurring.
On an x-ray, one can see a faint white line between diaphysis and epiphysis).
epiphyseal plate
epiphyseal line
o When we grow, our bones also increase in diameter (known as
appositional growth).
o Osteoblasts in periosteum add bone tissue to the outside of the
diaphysis. This allows our bones to grow larger and stronger to
support more muscle mass.
Appositional Growth
Bone Remodeling is occurring continuously & is affected by:
1) Pull of gravity & pull of muscles on skeleton (due to physical
activity).
Bone remodeling
Martial arts bone remodeling training
Bone lengthening (external fixator)
Bone lengthening (magnets)
Knee replacement surgery
2) Calcium levels in blood (remember osteoblasts and osteoclasts
will constantly paste calcium on bones and eat away at calcium on
bones to maintain homeostasis).
Classification of Bones
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Long Bones
Short Bones
Flat Bones
Irregular Bones
Long Bone
• longer than wide
• bones of limbs &
digits
Short Bones
• cube-like
• bones of wrist and
ankle
Sesamoid Bone
• Small irregularly
shaped bone
embedded in tendon
• Patella, plantar side of
the big toe
Flat Bones
• thin, flattened slightly
curved
• Sternum and cranial
bones
Irregular Bones
• odd-shaped
• vertebral, hip bones