NOTES:
Skeletal
System
(Ch 5, part 1)
Individual bones are the organs of the
skeletal system. A bone contains very
active tissues.
BONE STRUCTURE:
*Bone structure reflects its function.
Parts of a long bone:
• EPIPHYSES:
-enlarged portions at ends of a long bone;
-covered with cartilage;
-articulate (form JOINTS) with other bones.
Parts of a long bone:
• DIAPHYSIS:
-shaft of bone (located between the
epiphyses)
• PERIOSTEUM:
-tough, vascular covering that
encloses the entire bone
except where the articulate
cartilage is
Types of Bone Tissue:
 COMPACT BONE: has a continuous
matrix with no gaps; found in the wall of
the diaphysis
Types of Bone Tissue:
 SPONGY BONE (a.k.a. cancellous
bone): has irregular interconnecting
spaces between bony plates that reduce
the weight of bone.
**both compact and spongy bone are
strong and resist bending
**the center of the
diaphysis is a hollow
chamber (MEDULLARY
CAVITY),
lined with a thin layer of
cells (ENDOSTEUM)
and filled with soft
connective tissue
(MARROW)
Bone Markings
• Bones not smooth but can have bumps,
holes, ridges
– These are called bone markings
• Purpose:
– Muscles, tendon, ligament attachments
– Allow blood vessels and nerves to pass
through
• Two categories of bone markings
– Projections/processes
• Grow out from bone surfaces
• Example trochanter
– Depressions/cavities
• Indentations into bone
• Example fissure
Microscopic Structure of Bone:
• bone cells = OSTEOCYTES; located in
small chambers (LACUNAE) which form
concentric circles around central canals
• intercellular material = mostly COLLAGEN
(gives bone its strength and elasaticity)
and inorganic salts (make bone hard and
resistant to crushing).
Microscopic Structure of Bone:
• compact bone contains OSTEONS
cemented together
• central canals (HAVERSIAN CANALS)
contain blood vessels that nourish the
cells of osteons
• diffusion from the surface of the thin, bony
plates nourishes the cells of spongy bone
Bone Development and Growth
 Intramembranous Bones:
• layers of connective tissue form
membranes at the site of future bones;
• some cells mature and differentiate into
bone-producing cells (OSTEOBLASTS);
• osteoblasts deposit bony matrix around
themselves and SPONGY BONE forms in all
directions within the layers of connective
tissues;
Intramembranous Bones
• osteoblasts completely surrounded by
matrix are mature OSTEOCYTES
• EXAMPLE: the broad, flat bones of the
skull form in this way and fuse together at
sutures.
Bone Development and Growth
 Endochondral Bones:
• most bones in the body develop in this
way
• develop as hyaline cartilage “models”;
later replaced by bone tissue
• primary ossification center appears first
in the diaphysis
• later, secondary ossification center
appears in the epiphyses
Endochondral Bones
• an epiphyseal plate remains between the
primary and secondary ossification centers
• long bones continue to lengthen until the
epiphyseal plate are ossified (hardened)
• a developing long bone thickens as
compact bone is deposited beneath the
periosteum
Endochondral Bones
• in the middle of the diaphysis,
OSTEOCLASTS break down bone tissue and
the resulting space becomes the medullary
cavity, which later fills with marrow
• the bone in the central regions of the
epiphyses and diaphysis remain spongy bone
• the hyaline cartilage on the ends of the
epiphyses persists throughout life as
articular cartilage
**throughout life, osteoclasts continually
break down bone matrix and
osteoblasts replace it; these opposing
processes of resorption and deposition
of calcium help to maintain calcium
levels in the body**
BONE FUNCTION:
 Support and Protection
• bones shape and form body structures
• bones support and protect softer,
underlying tissues
BONE FUNCTION:
 Body Movement
• bones and muscles
function together as
LEVERS
• a lever consists of: a
rod, a pivot (fulcrum), a
resistance, and a force
that supplies the energy
BONE FUNCTION:
 Blood Cell Formation
• depending on stage of life, blood cell
formation occurs in the :
-yolk sac (embryo)
-liver and spleen
-bone marrow
• Marrow can be:
-RED: stores RBCs,
WBCs, and platelets
-YELLOW: stores fat
BONE FUNCTION:
 Storage of Inorganic Salts
• matrix of bone tissue contains large
quantities of calcium phosphate
• blood calcium levels vary; when blood calcium
is:
LOW: osteoclasts break down bone, releasing
calcium salts
HIGH: osteoblasts form bone tissue and store
calcium salts
Storage of Inorganic Salts
• bone also stores small amounts of
magnesium, sodium, potassium, and
carbonate