Chapter 7
Skeletal System
Subdivision: Micro-anatomy & Physiology
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Functions of the System:
• Protection
• Support
• Allows for body
movement
• Produces blood cells
• Stores minerals
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Introduction to the Skeletal
System
• Components of the Skeletal System= bones,
cartilage, ligaments, and tendons
• Some definitions:
– Cartilage= somewhat rigid, covers the surfaces
of bones in/near joints
– Tendons= band of strong tissue that connects
bones to muscle
– Ligaments= band of strong tissue that connects
bone to bone
– Axial Skeleton=Head to pelvis, main body
– Appendicular Skeleton= Everything else
Introduction to BONE
A. Bones are very active tissues
B. Each bone is made up of
several types of tissues and so is
an organ.
C. Bone functions reflect the
system
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Bone Functions
(the organ)
A. Support and Protection
1. Bones give shape to the head, thorax, and limbs.
2. Bones such as the pelvis and lower limbs provide support for the
body.
3. Bones of the skull protect the brain, ears, and eyes.
B. Body Movement
1. Bones can act as levers.
a. A lever has four components: a rigid bar, a pivot or fulcrum an object
that is moved against resistance, and a force that supplies energy.
C. Blood Cell Formation
1. Blood cells begin to form through hematopoieses in the yolk sac; they
are later
manufactured in bone marrow.
2. Two kinds of marrow occupy the medullary cavities of bone.
a.Red marrow functions in the formation of red blood cells,
white
blood cells, and platelets,and is found in the spongy bone of the skull,
ribs, sternum, clavicles, vertebrae, and pelvis.
b. Yellow marrow, occupying the cavities of most bones, stores fat.
D. Storage of Inorganic Salts
1. The inorganic matrix of bone stores inorganic mineral salts in the
form of calcium phosphate that is important in many metabolic
processes.
2. Calcium in bone is a reservoir for body calcium; when blood levels are
low, osteoclasts release calcium from bone.
3. Calcium is stored in bone under the influence of calcitonin when blood
levels of calcium are high.
4. Bone also stores magnesium, sodium, potassium, and carbonate ions.
5. Bones can also accumulate harmful elements, such as lead, radium,
and strontium.
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General Bone Structure= Types of Bone
Bones differ in size and shape, yet are similar in several ways.
– Long = longer than it is wide
» Epiphysis= end of a long bone; separated from the main part of
the bone from immature cartilage
» Diaphysis= shaft of a long bone
» Medullary Cavity= hollow space running the length of the
diaphysis; has blood, nerves, and marrow
» Epiphyseal Line= “Growth Plate”; Where the cartilage is
converted to bone as it grows in length
Examples: Upper and lower limbs
– Short = same length and width
» Carpals tarsals
– Flat = not wide; flat like a plate
» Ribs, sternum, skull, scapulae
– Irregular = not distinct shape
» Vertebrae, facial
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More Bone Structure..
Long Bone in depth
– Parts
1. Expanded ends of bones that form joints with adjacent
bones are called epiphyses.
2. Articular cartilages (hyaline cartilage) cover the
epiphyses.
3. The shaft of the bone is the diaphysis.
4. A tough layer of vascular connective tissue, called the
periosteum, covers the bone and is continuous with ligaments
and tendons.
5. A bone's shape makes possible its function; bony processes or
grooves indicate places of attachment for muscles.
6. Compact bone makes up the wall of the diaphysis; the epiphyses
are filled with spongy bone to reduce the weight of the
skeleton.
7. The diaphysis contains a hollow medullary cavity that is lined
with endosteum and filled with marrow.
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More Bone Structure..
Flat, Short, Irregular Bones
• Flat bones
– No diaphyses, epiphyses
– Sandwich of cancellous (spongy bone tissue)
between compact bone tissue
• Short and Irregular bone
– Compact bone that surrounds cancellous bone
tissue center
– No diaphyses and not elongated
Microscopic Structure of Bone
Bone matrix (chemical components):
component of bone
Organic: collagen and proteoglycans
Inorganic: Calcium & Phosphate
non-living
Bone Tissue:
Compact bone tissue: dense/hard
Spongy bone tissue: porous ‘like a sponge’
Bone cells= living part of bone
Stem cells or osteoprogenitor cells
Osteoblasts- make new bone; immature bone cell
Osteocyte- mature bone cell; maintains tissue
Osteoclasts- breaks down and re-absorbs of old,
damaged, or diseased tissue bone
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Microscopic Structure of Bone
• Compact bone tissue
– Haversian system—osteons (functional unit of tissue)
– Contain living bone cells
– Delivery of nutrients & removal of waste
•
•
•
•
•
Lamellae
Lacunae
Canaliculi
Haversian canal
Volkmann’s canals
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Microscopic Structure of Bone
Spongy (Cancellous) Bone
– Consists of trabeculae (bony plates)
– Oriented along lines of stress
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Bone Growth & Development
A. Bones form by replacing connective
tissues in the fetus.
B. Some form within sheetlike layers of connective tissue
(intramembranous bones), while others replace masses of
cartilage (endochondral bones).
Intramembranous Bone Development
1.The flat bones of the skull form as intramembranous bones
that develop from layers of connective tissue.
2.Osteoblasts deposit bony tissue around themselves.
3. Once osteoblasts deposit bone are located in lacunae, they
are called osteocytes.
4. Cells of the membranous connective tissue that lie outside
the developing bone give rise to the periosteum.
*Basically it is when matrix gets deposited on the surface of
existing bone, this causes a growth in diameter
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Endochondral Bone Development
1. Most of the bones of the skeleton fall into this category.
2. They first develop as hyaline cartilage models and are then replaced with bone.
3. Cartilage is broken down in the diaphysis and progressively replaced with bone
while the periosteum develops on the outside.
4. Cartilage tissue is invaded by blood vessels and osteoblasts that first form
spongy bone at the primary ossification center in the diaphysis.
5.Osteoblasts beneath the periosteum lay down compact bone outside the spongy
bone.
6.Secondary ossification centers appear later in the epiphyses.
7. A band of hyaline cartilage,the epiphyseal plate,forms between the two
ossification centers.
8.Layers of cartilage cells undergoing mitosis make up the epiphyseal plate.
9.Osteoclasts break down the calcified matrix and are replaced with bone building
osteoblasts that deposit bone in place of calcified cartilage.
10. Epiphyseal plates are responsible for lengthening bones while increases in
thickness are due to intramembranous ossification underneath the periosteum.
11. A medullary cavity forms in the region of the diaphysis due to the activity of
osteoclasts.
* Basically, occurs in the epiphyseal plates, the cartilage is covered to bone as
the cartilage becomes calcified (filled with calcium) causing it to get hard.
The growth occurs from the middle outward to increase length (growth in
height)
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Factors Affecting Bone Growth
• Nutrition
– Vitamin D
• Necessary for absorption of Ca from intestines
• Insufficient causes rickets and osteomalacia
– Vitamin C
• Necessary for collagen synthesis by osteoblasts
• Deficiency results in scurvy
• Hormones
– Growth hormone from anterior pituitary
– Thyroid hormone required for growth of all
tissues
– Sex hormones as estrogen and testosterone18
Homeostasis of Bone
‘Remodeling Bone’
REQUIRES only certain bone cell
Review of Types of Bone Cells:
Osteoclast
Osteoblast
Osteocyte
Process: Osteoclasts tear down and osteoblasts build bone
throughout the lifespan with the processes of resorption and
deposition, with an average of 3% to 5% of bone calcium
exchanged annually.
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How does bone repair from injury?
Bone Repair
Day of Accident
2-3 Days
4 to 6 Weeks
After 6 Weeks
Weeks to Months
Bone Repaired
Broken Bone
A clot forms in the damaged area
Blood Vessels and cells invade the clot and produce
which is a callus
a fibrous network between the broken bones
Osteoblasts enter callus and begin to form spongy bone or cancellous bone
Spongy bone is slowly remodeled to form compact bone
Bone healed stronger around the surrounding area
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