 The Skeletal System
 Chapter 6-9
 Individual bones:
 Tissues
 Bone
 Cartilage
 Epithelial tissue
 Fibrous connective tissue
 Blood
 Nervous tissue
 Bone Structure
 Long bone
 External structure
 Epiphysis, the portion of the bone that interacts with other bones
 Articular cartilage, protective layer of hyaline cartilage coating the epiphysis
 Hyaline cartilage, most common type of cartilage, looks like “milky
glass”
 Diaphysis, long narrow portion between epiphyses, AKA: shaft
 Periosteum, any part of the bone not covered by articular cartilage is protected
by this tough fibrous membrane. It is a vascular tissue, functions in bone repair.
 Internal structure
 Tissue types:
 Compact bone, dense strong and resistant to bending
 Spongy bone, branching bony plates that create irregular spaces, strong
and durable because they allow for some compression.
 Tissue location
 Compact bone makes up the wall of the diaphysis
 Spongy bone makes up the bulk of the epiphysis especially in regions
that are subject to compression, (weight bearing joints)
 Description: the diaphysis is a semi-rigid hollow structure
 Medullary cavity, hollow tube runs from end to end in the open
space of the diaphysis
 Endosteum, lines the cavity
 Marrow, specialized, highly functional, soft CT, inside the cavity
 Microscopic Structure:
 Osteocyte, individual compact bone cell, located in…
 Lacunae, chambers arranged in concentric circles around…
 Osteonic canal, pathway for arteries, veins, and nerves through the bone
 Canaliculus, smaller canals running perpendicular to the osteonic canal,
connecting lacunae
 Haversian System: (aka Osteon) the whole system of concentric circles and the
canals associated with them
 Volkmann’s canals, contain larger vessels and nerves allowing for
communication of entire Haversian systems, the medullary canal, and the bone
surface.
 Spongy bone avoids this whole process, thin bony plates allow for nourishment by
diffusion.
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Two means of bone formation:
1. Intramembranous bone formation
2. Endochondral bone formation
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Intramembranous Bone
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Broad, flat bones of the skull
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Formation
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Osteoblasts become active and spongy bone is formed throughout existing
membrane.
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Left over membrane becomes periosteum.
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Endochondral Bone
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Most long bones
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Formation:
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Masses of hyaline cartilage develop rapidly giving even the young fetus a
“human” structure.
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Ossification is a gradual process
The center of the medullary cavity serves as the primary ossification
center.
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Ossification occurs from the inside out.
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The secondary ossification center is formed later in the open space of
the epiphysis.
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This ossification also occurs in an outward direction.
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Between the two ossification centers there is an epiphyseal disc (AKA growth
plate)
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Bone formation, lengthening continues until the two ossified areas meet.
Bone Demolition
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Osteoclasts break down bone tissue
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–
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Remodeling
Osteoblasts form new bone tissue for replacement and remodeling.
Gross Function
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Provide shape
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Aid in body movement
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Support
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Blood cell formation
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Protection
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Movement
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Provide structure
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Gross movement
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Serve as storage units
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4 Parts of a Lever
1. Rod (bar)
2. Fulcrum (pivot)
3. Resistance ( weight being moved.
4. Force (energy supplying movement)
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Example
1. Rod: radius and ulna
2. Fulcrum: elbow joint
3. Resistance: hand and object
4. Force: biceps brachii
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What is the reverse?
5. Rod: radius and ulna
6. Fulcrum: elbow joint
7. Resistance: hand and object
8. Force: triceps brachii
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What is happening?
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Blood Cell Formation
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Hematopoiesis
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Once upon a time…
in the yolk sac hematopoiesis began for the embryo. Throughout life hematopoiesis continues in
the …
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Liver
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Spleen
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Bone marrow
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Red marrow
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(Yellow marrow)
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Red Marrow
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Functions in the formation of:
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RBC
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WBC
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platelets
Why is it red?
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Hemoglobin carried in RBC, changes the pigmentation of the marrow.
Yellow Marrow
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Functions in fat storage.
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Inactive in hematopoiesis.
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Replaces much of the red marrow as a human ages.
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Why is it yellow?
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Fat in the body is yellow. Gooey, gross, and yellow.
While most of the red marrow is replaced by yellow marrow, red marrow for hematopoiesis does
remain in the spongy bone of the…
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Thorax
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Vertebra
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Humerus
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Pelvis
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Femur
Epiphysis of the
Bone as a Storage Unit
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Bone is used to store inorganic salts. (No Carbon)
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Primarily stores Ca+
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[Ca+] control
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If [Ca+] in blood is too low
osteoclasts are stimulated to breakdown bone tissue to release Ca+.
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If [Ca+] in blood is too high, osteoblasts are stimulated to form bone tissue, trapping the
Ca+.