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Bones
Our skeletal system provides 5 main
functions for our body…
Support:
1.
 “Reinforced Concrete of Body”
 Forms internal framework that supports and anchors all soft organs
 Examples:
Bones of legs act as pillars to support the body trunk when we stand
 Rib cage supports the thoracic wall

Protection:
2.
 Bones protect soft body organs
 Examples
Skull protects brain
 Vertebrae protect spinal chord
 Rib cage protects organs of thorax

3.
Movement:
 Skeletal muscles attached to bones by tendons use the bones as
levers to move the body and its parts!
4.
Storage:
 Fat is stored in the internal cavities of bones
 Bones itself serves as a storehouse for minerals…the most important
being Calcium and Phosphorous (others are stored as well)
A
small amount of calcium in its ion form (Ca2+)
must be present in the blood at all times for
1.
2.
3.
the nervous system to transmit messages
for muscles to contract
for blood to clot
 Most
of the body’s calcium is deposited in the
bones as calcium salts; the bones are a convenient
place to get more calcium ions for the blood as
they are used up.
 Problems occur if there is not enough OR too much
calcium in the blood…hormones control the
movement of calcium to and from the bones and
blood according to the needs of the body.
5.
Hematopoiesis:
 AKA: Blood cell formation
 Occurs within the marrow cavities of certain bones.
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The adult skeleton is composed of
206 bones
There are 2 basic types of bone
tissue or “osseous”
There are 4 shape groups as well
 Compact


Bone
Dense
Looks smooth and
homogenous
 Spongy

Bone
Composed of small
needlelike pieces of
bone and lots of
open space

1. Long bones
Longer than they are wide
 Have a shaft with heads at both ends
 Mostly compact bone
 All the bones of the limbs, except the wrist and ankle
bones are long bones


2. Short bones

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Generally cube-shaped
Contain mostly spongy bone
The bones of the wrist and ankle are short bones
Sesamoid bones (which form within tendons) are a
special type of short bone.
The best known examples is the patella
 3.



Thin, flattened, and usually curved
Have 2 thin layers of compact bone sandwiching
a layer of spongy bone between them
Most bones of the skull, ribs, and the sternum
(breastbone) are flat bones
 4.


Flat bones
Irregular bones
Bones that do not fit the preceding categories
The vertebrae, which make up the spinal
column, and the hip bones fall into this group
Gross and Microscopic Anatomy
 Diaphysis


or Shaft
Makes up most of
the bone’s length
and is composed
of compact bone
Is covered by
periosteum (a
fibrous connective
tissue membrane)

Epiphyses
Ends of the long bone
 Consists of a thin layer of compact
bone enclosing an area filled spongy
bone
 Is covered by articular cartilage
instead of periosteum. Articular
cartilage is a smooth, slippery
surface…friction at joint surfaces is
decreased.
 In adult bones, there is a thin line of
bony tissue spanning the epiphysis
that looks a bit different from the
rest of the bone in that area called
the epiphyseal line which is a
remnant of the epiphyseal plate
which is a flat plate of cartilage seen
in a young, growing bone. Epiphyseal
plates cause the lengthwise growth
of a long bone. By the end of
puberty, when hormones inhibit long
bone growth, epiphyseal plates have
been completely replaced by bone,
leaving only the epiphyseal lines to
mark their previous location!


Medullary Cavity




In adults the cavity of the
shaft is primarily a storage
area for adipose (fat) tissue.
It is called the yellow
marrow or medullary cavity.
However, in infants this area
forms blood cells, and red
marrow is found there.
In adult bones, red marrow
is confined to the cavities of
spongy bone of flat bones
and the epiphyses of some
long bones.

Bone Markings
Bone surfaces are not smooth, but scarred with bumps, holes, and ridges.
 These “bone markings” reveal where muscles, tendons, ligaments were attached
and where blood vessels and nerves passed. See page 134.
 2 types of bone markings



Projections or processes-grow out from bone surface.
Depressions or cavities-indentations in the bone.

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To the naked eye, spongy bone looks open and spiky,
whereas, compact bone looks very dense….
However, when looking at compact bone through a
microscope, one can see that it has a complex structure. It
is riddles with passageways carrying nerves, blood vessels
and the like, which provide the living bones cells with
nutrients and a route for waste disposal.
 Osteocytes:
mature bone cells found in tiny
cavities within the matrix called lacunae.
 The lacunae are arranged in concentric
circles called lamellae around central
“Haversian” canals.
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Each complex consisting of central canal and matrix rings is called an
osteon, or Haversian system.
Central canals run lengthwise through the bony matrix, carrying blood
vessels and nerves to all areas of the bone.
Tiny canals, canaliculi, radiate outward from the central canals to all
lacunae. The canaliculi form a transportation system that connects all
the bone cells to the nutrient supply through the hard bone
matrix…because of this bone cells are well nourished in spite of the
hardness of the matrix, and bone injuries heal quickly and well.
 The
communication pathway from the outside of
the bone to its interior (and the central canals) is
completed by perforating “Volkman’s” canals,
which run into the compact bone at right angles
to the shaft.
Axial and Appendicular
 Axial:

The bones that form
the longitudinal axis
of the body.
 Appendicular:

The bones of the
limbs and girdles.
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Extends from the skull to the pelvis where it
transmits the weight of the body to the
lower limbs.
Formed from 26 irregular bones connected
and reinforced by ligaments in such a way
that a flexible, curved structure results.
Running through the central cavity of the
vertebral column is the delicate spinal cord.
Before birth, the spine consists of 33
separate bones called vertebra, but 9 of
these eventually fuse to form the 2
composite bones, the sacrum and the
coccyx.
Of the 24 single bones, the 7 vertebrae of
the neck are cervical vertebrae, the next 12
are the thoracic vertebrae, and the
remaining 5 supporting the lower back are
lumbar vertebrae.
The single vertebrae are separated by pads
of flexible fibrocartilage-intervertebral
discs-which cushion the vertebrae.
The disks and the S-shaped structure of the
vertebral column work together to prevent
shock to the head when we walk or run.
They also make the body trunk flexible
 AKA
“articulations”
 Give the body flexibility and allow movement
to occur.
 With one exception (the hyoid bone of the
neck), every bone in the body forms a joint
with at least one other bone!
 Joints have 2 functions:


1. They hold the bones together
2. Give the rigid skeleton mobility

Focuses on the
amount of movement
allowed by the joint
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Synarthroses:
immovable joints
Amphiarthroses: slightly
movable joints
Diarthroses: freely
movable joints
Functional Classification

Based on whether fibrous
tissue, cartilage, or a joint
cavity separates the bony
regions at the joint
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Fibrous: bones united by fibrous
tissue, Example- Skull sutures
Cartilaginous: bone ends are
connected by cartilage,
Example-pubic symphysis of
pelvis and intervertebral joints
of spinal column
Synovial: those in which the
bone ends are separated by a
joint cavity containing synovial
fluid, account for ALL joints of
the limbs, examples and more
to follow….
Structural Classification

Plane joint:

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Hinge joint:
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“knuckle-like”, the egg shaped articular surface of one bone fits into an oval
concavity in another…these joints allow the moving bone to travel from side to
side and back and forth but it cannot rotate around its long axis.
Saddle joint:

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the rounded end of one bone fits into a sleeve or ring of bone…the rotating bone
can turn only around its long axis.
Condyloid joint:
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the cylindrical end of one bone fits into a trough-shaped surface on another
bone…angular movement is allowed in just one plane (like a door hinge).
Pivot joint:
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articular surfaces are flat and only short slipping or gliding movements are
allowed.
each articular surface has both convex and concave areas, like a saddle…these
joints allow essentially the same movement as the condyloid joint.
Ball & Socket joint:

the spherical head of one bone fits into a round socket in another…these
multiaxial joints allow movements in all axes, including rotation! They are the
most freely moving joints.
 Read
page 168 starting at “development
aspects of the skeleton” through page 169
stopping before “prove it yourself”.
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When a baby is born, its skeleton is still
unfinished. In a newborn, the skull has
fibrous regions that have yet to be
converted to bone.
These fibrous membranes are called
fontanels or you may have heard them
called “soft spots”. The rhythm of the
baby’s pulse can be felt in these areas.
The fontanels allows compression
during the birthing process and give
room for growth during the later part
of pregnancy and infancy.
The fontanels are gradually converted
to bone during the early part of infancy
and can no longer be felt by 22-24
months after birth.
There are 4 fontanels:
Anterior-largest on top of head (one you
may know of)
 Posterior
 Mastoid
 Sphenoid

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Mandible-lower jaw bone…is the
largest and strongest bone of the
face.
Hyoid bone-closely related to the
mandible, but not really a part of
the skull…is unique because it is the
only bone of the body that does not
articulate directly with any other
bone…it is suspended in the midneck region, held in place by
ligaments!
Phalanges-each hand contains 14
phalanges…there are three in each
finger (proximal, middle, and
distal) except in the thumb, which
only has two (no middle).
Male and Female Skeletons are
different…the pelvic girdle…Record the
differences listed on page 159 in your text,
then refer to your handout.
Scoliosis
Fractures
Arthritis
Gout
Osteoporosis
 Disorders
of the spine may be congenital
(present at birth) or result from disease,
poor posture, or unequal muscle pull on the
spine. There are 3 main types of abnormal
spinal curvatures:
1. Scoliosis
2. Kyphosis
3. Lordosis

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For their relatively low mass, bones are
amazingly strong. Despite their remarkable
strength, bones are susceptible to fractures,
or breaks, all through life.
A fracture is treated by reduction (which is
the realignment of the broken bone ends.)
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Closed reduction: bone ends are coaxed back
into their normal position by the physician’s
hands.
Open reduction: surgery is performed and the
bone ends are secured together with pins or
wires.
After the broken bone is reduced, it is
immobilized by a cast or traction to allow the
healing process to begin. The healing process
is 6-8 weeks, but it is much longer for large
bones and for the bones of elderly people
(because of their poorer circulation).
 Describes
over 100 different inflammatory or
degenerative diseases that damage the
joints.
 In all its forms, arthritis is the most
widespread, crippling disease in the US… 1
out of 7 Americans suffer its ravages.
 All forms of arthritis have the same initial
symptoms: pain, stiffness, and swelling of
the joint. Then, depending on the specific
form, certain changes in the joint structure
occur.

Osteoarthritis (OA)
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Rheumatoid arthritis (RA)
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Most common form, typically affects the aged, also called “wear & tear arthritis”
Over time, there is a softening, fraying, and eventual breakdown of the cartilage…as the
disease progresses, the bone thickens and extra bone tissue, called “bone spurs” grows
around the eroded cartilage and restricts joint movement
Usually slow and irreversible, but is rarely crippling…symptoms are typically controllable.
Onset usually occurs between the ages of 40-50, but may occur at any age. Affects 3 times
as many women as men.
The course of RA is marked by remissions and flare-ups
Autoimmune disease-a disorder in which the body’s immune system attempts to destroy its
own tissue.
Current therapy for RA involves many different kinds of drugs and exercise is
recommended…replacement joints or bone removal is a last resort for severely crippled RA
patients.
Gouty arthritis “gout”
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A disease in which uric acid (a normal waste product of nucleic acid metabolism)
accumulates in the blood and may be deposited as needle-shaped crystals in the soft tissues
of joints which leads to an agonizingly painful attack that typically affects a single joint,
often in the great toe!
Gout is most common in males and rarely appears before the age of thirty…it tends to run in
families, so genetic factors are definitely implicated.
Untreated gout can be very destructive; the bone ends fuse and the joint becomes
immobilized…fortunately, several drugs are successful in preventing gout attacks.
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A bone thinning disease that afflicts half of women
over 65 and some 20% of men over the age of 70.
Makes the bones so fragile that even a hug or a
sneeze can cause bones to fracture.
The bones of the spine and the neck of the femur
are particularly susceptible…vertebral collapse
frequently results in a hunched over posture
(kyphosis) also known as “dowager’s hump”
Estrogen helps to maintain the health and normal
density of a woman’s skeleton, and the estrogen
deficiency that occurs after menopause is strongly
implicated as a cause of osteoporosis
Other factors may include diet poor in calcium and
protein, lack of vitamin D, smoking, and insufficient
weight-bearing exercise to stress bones.