Download Skeletal System Notes-Part 2

Skeletal System Notes-Part 2
Bone Formation
 Ossification – The process of bone formation.
Bones at Birth
 By birth or shortly after, most hyaline cartilage
models have been converted to bone except for two
regions:
1.
The articular cartilages that cover the bone ends.

2.
These persist for life, reducing friction at joint surfaces.
The epiphyseal plates.

Provide for longitudinal growth of the long bones during
childhood.
Hyaline Cartilage Remodeling
 “New” cartilage is formed continuously on the
external face of the articular cartilage and on the
epiphyseal plate surface that is farther away from the
medullary cavity.
 At the same time, the “old” cartilage abutting the
internal face of the articular cartilage and medullary
cavity is broken down and replaced by bony matrix.
Widening of Bones
 Growing bones must also widen as they lengthen.
 Osteoblasts in the periosteum add bone tissue to the external
face of the diaphysis.
 Osteoclasts in the endosteum remove bone form the inner face
of the diaphysis wall.
 Since these two processes occur at about the same rate, the
circumference of the long bone expands and the bone widens.
Widening of Bones
 Appositional Growth – The process by which bones
increase in diameter.
 The growth of long bones is:


Controlled by hormones (growth and sex hormones).
Ends when the epiphyseal plates are converted to bone (during
adolescence).
 Bone Remodeling is essential if bones are to retain
normal proportions and strength during long-bone
growth as the body increases in size and weight.
Bone Tissue
 Bone is a dynamic and active tissue.
 Bones are remodeled continually in response to changes in
two factors:
1.
2.
Calcium levels in the blood.

When blood calcium levels drop, osteoclasts break
down the bone matrix and release calcium ions into the
blood.

When blood calcium levels are too high, calcium is
deposited in bone matrix as hard calcium salts.
The pull of gravity and muscles on the skeleton.

Bedridden or physically inactive people tend to lose
bone mass and to atrophy because they are not
subjected to stress.

Bones become thicker and form large projections to
increase their strength in areas where bulky muscles
are attached.
Rickets
 Rickets – A disease of children
in which the bones fail to calcify.



As a result, the bones soften and a
definite bowing of the weight-bearing
bones of the legs occur.
Usually due to a lack of calcium or vitamin D in the diet.
Not seen very often in the US.


Foods are fortified with vitamin D and most children drink enough
calcium-rich milk.
It remains a problem in other parts of the world.
Bone Fractures
 Fractures – Breaks of the bone.
 Two types of fractures:
1.
2.
Closed (Simple) Fracture – A fracture in which the bone
breaks cleanly and does not penetrate the skin.
Open (Compound) Fracture – A fracture in which the bone
ends penetrate through the skin.
Treatment of Fractures
 A fracture is treated by reduction,
which is the realignment of the
broken bone ends.


In closed reduction, the bone ends are
coaxed back into their normal position
by the physician’s hands.
In open reductions, surgery is
performed and the bone ends are
secured together with pins or wires.
Treatment of Fractures
 After the broken bone is reduced,
it is immobilized by a cast or
traction to allow the healing
process to begin.

Healing time for a simple fracture is 68 weeks, but is much longer for large
bones and for the bones of elderly
people.
The repair of bone fractures involves four major
events:
1.
A hematoma is formed.
Blood vessels are ruptured when the bone breaks.
 As a result, a blood-filled swelling called a hematoma occurs.
 Bone cells deprived of nutrition die.

2. The break is splinted by a fibrocartilage callus.

CT cells of various types form a mass of repair tissue called the
fibrocartilage callus.
• Contains some cartilage matrix, some bony matrix, and collagen
fibers.
• Acts to “splint” the broken bone, closing the gap.
Repair of Bone
3. The bony callus is formed.
 More osteoblasts and osteoclasts migrate into the area and
multiply.
 Fibrocartilage is gradually replaced by a callus made of spongy
bone, called the bony callus.
4. Over the next few months, the bony callus is
remodeled.

It is remodeled in response to the mechanical stresses placed
on it, so that it forms a strong permanent “patch” at the
fracture site.
Axial Skeleton
 The axial skeleton forms the longitudinal axis of the
body.

It can be divided into three parts:
1.
2.
3.
The skull
The vertebral column
The bony thorax
The Skull
 The skull is formed by two
sets of bones:

The cranium


Protects the fragile brain tissue.
The facial bones

Hold the eyes in an anterior
position and allow the facial
muscles to show our feelings
through smiles or frowns.
The Skull
 All but one of the bones of the skull are joined
together by sutures.

Sutures – Interlocking, immoveable joints.
 Only the mandible (jawbone) is attached to the rest
of the skull by a freely moveable joint.
Normal Open Sutures in Infant Skull
Cranium
 The boxlike cranium is
composed of 8 large, flat
bones.
 Except for two paired
bones (the parietal and
temporal), they are all
single bones.
The Eight Cranial Bones
1.
Frontal Bone – Forms the
forehead, the bony
projections under the
eyebrows, and the superior
part of each eye’s orbit.
2.
& 3.
Parietal Bones – The paired
parietal bones form most of
the superior and lateral
walls of the cranium.

The Eight Cranial Bones
4. & 5.

Temporal Bones – Lie inferior to the parietal bones
The Eight Cranial Bones
6. Occipital Bone – Most posterior bone of the
cranium.

Forms the floor and back wall of the skull.
The Eight Cranial Bones
7. Sphenoid Bone – Butterfly-
shaped; Spans the width of
the skull and forms part of
the floor of the cranial
cavity.


The central part of the
sphenoid bone is riddled with
air cavities, the sphenoid
sinuses.
Part of the sphenoid can be
seen exteriorly forming part of
the eye orbits and the lateral
part of the skull.
The Eight Cranial Bones
8. Ethmoid Bone – Very irregularly shaped; lies
anterior to sphenoid.

Forms the roof of the nasal cavity and part of the medial walls
of the orbits.