1. Anatomy & Physiology Chapter 7: Skeletal System

2. Introduction to Skeletal System
Human skeleton is initially cartilage and fibrous membranes
By age 25 the skeleton is completely hardened
206 bones make up the adult skeleton (20% of body mass)
80 bones of the axial skeleton
126 bones of the appendicular skeleton
The organs of the skeletal system include the bones and structures that connect bones to other structures including ligaments, tendons, and cartilages.

3. Bone Classification Bone Classification: Long bones ex. femur
Short bones
ex. tarsals
Flat bones
ex. skull
Irregular bones
ex. vertebrae
Sesamoid bones
ex. patella
(b)
(c)
(d)
(a)
(e)

4. Parts of a Long Bone Epiphysis Diaphysis Metaphysis Compact bone
Distal
Proximal
Diaphysis
Metaphysis
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Epiphyseal plates
Articular cartilage
Proximal
Spongy bone
epiphysis
Space containing red marrow
Compact bone
Spongy bone
Endosteum
Compact bone
Medullary cavity
Articular cartilage
Periosteum
Endosteum Y
ellow marrow
Periosteum
Diaphysis
Medullary cavity
Trabeculae
Bone marrow
Red marrow and yellow marrow
Distal
epiphysis
Femur

5. Parts of a Long Bone
Diaphysis = shaft a. consists of central medullary cavity b. surrounded by a thick collar of compact bone Epiphyses = expanded ends a. consist mainly of spongy bone b. surrounded by a thin layer of compact bone c. proximal epiphysis vs. distal epiphysis Epiphyseal line = remnant of epiphyseal disc/plate a. cartilage at the junction of the diaphysis and epiphyses (growth plate)

6. Parts of a Long Bone
Periosteum = outer protective covering of diaphysis a. supplied w/ blood, lymph vessels & nerves (nutrition) b. osteogenic layer contains osteoblasts (bone-forming cells) and osteoclasts (bone-destroying cells) c. serves as insertion for tendons and ligaments Endosteum = inner lining of medullary cavity a. contains layer of osteoblasts/osteoclasts Articular cartilage = pad of hyaline cartilage on the epiphyses where long bones articulate or join a. “shock absorber”

7. Parts of a Flat Bone Flat bones
1. covered by periosteum – covered compact bone
2. surrounding endosteum – covered spongy bone
3. In a flat bone the arrangement looks like a sandwich:
a. spongy bone (meat) sandwiched between
b. two layers of compact bone (bread)
Hematopoetic tissue (red marrow) is located in the spongy bone within the epiphyses of long bones and flat bones

8. Microscopic Structure: Chemical Composition of Bone
Organic components (approx. 35%)
Cells:
osteoprogenitor cells
1. can undergo mitosis and become osteoblasts
osteoblasts
1. form bone matrix by secreting collagen
2. cannot undergo mitosis
osteocytes
1. mature bone cells derived from osteoblasts
2. principle bone cell
3. cannot undergo mitosis
4. maintain daily cellular activities
(ie. exchange of nutrients & wastes with blood)

9. Microscopic Structure: Chemical Composition of Bone
Organic components…cont.
Cells:
Osteoid
1. primarily collagen (90% of bone protein) which gives bone its high tensile strength
2. other bone proteins include osteocalcin, osteonectin, and osteopontin
3. also contains glycolipids and glycoproteins
Inorganic components
Hydroxyapatite (mineral salts) which is primarily
a. calcium phosphate [Ca3(PO4)2(OH)2]
b. gives bone its hardness or rigidity

10. Microscopic Structure: Compact Bone
Compact bone is solid, dense, and smooth
Structural unit = Haversian system or osteon
a. elongated cylinders cemented together to form the long axis of a bone
b. components of Haversian system
osteocytes (spider shaped bone cells in “lacunaea”
that have laid down a…
matrix of collagen and calcium salts in…
concentric lamellae (layers) around a…
central Haversian canal containing…
blood vessels and nerves.
CONTINUED NEXT SLIDE

11. Microscopic Structure: Compact Bone
c. Communicating canals with compact bone -canaliculi connect the lacunae of osteocytes -Perforating (Volkmann’s) canal connect the blood & nerve supply of adjacent Haversian systems together.

12. Compact Bone Osteon Haversian System Central canal Perforating canal
Volkmann’s canal
Osteocytes
Lamellae
Lacunae
Bone matrix
Canaliculi
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Osteon
Compact
bone
Central canal
containing blood
vessels and nerves
Endosteum
Spongy
bone
Periosteum
Nerve
Blood
vessels
Pores
Central
canal
Perforating
canal
Compact
bone
Nerve
Blood
vessels
Nerve
Trabeculae
Bone matrix
Canaliculus
Osteocyte
Lacuna
(space)

13. Microscopic Structure: Spongy Bone
Consists of poorly organized trabeculae
( small needle-like pieces of bone)
with a lot of open space between them
nourished by diffusion from nearby Haversian canals

14. a: © Ed Reschke; b,c: Courtesy of John W. Hole, Jr.
Spongy Bone
Spongy bone is aka cancellous bone
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Spongy
bone
Compact
bone
(a)
Remnant of
epiphyseal plate
Spongy bone
Compact bone
(b)
(c)
Spongy
bone
Compact
bone
a: © Ed Reschke; b,c: Courtesy of John W. Hole, Jr.

15. Bone Development and Growth
Introduction
The “skeleton” of an embryo is composed of fibrous CT membranes ( formed from mesenchyme and hyaline cart) that is loosely shaped like bone.
This skeleton provides supporting structures for ossification to begin.
At about 6-7 wks gestation ossification begins and continues throughout adulthood.

16. Bone Development and Growth
Ossification follows one of two patterns
Intermembranous Ossification
When bone forms on or within a fibrous CT membrane
ex. Flat bones are formed in this manner
Endochondral ossification
Occurs when a bone is formed from a hyaline cartilage model.
a. most bones of the skeleton are formed this way
b. Primary ossification center hardens as fetus or infant
c. Secondary ossification centers develop in child and harden during adolescence and early adulthood
During infancy and childhood long bones lengthen entirely by growth at the epiphyseal plates (longitudinal growth)
Bones grow thicker by “appositional growth”

17. Endochondral Ossification
Hyaline cartilage model
Primary ossification center
Secondary ossification centers
Epiphyseal plate
Osteoblasts vs. osteoclasts
Articular
cartilage
Remnants of
epiphyseal
plates
Secondary
ossification
center
Cartilaginous
model
Developing
periosteum
Compact bone
developing
Spongy
bone
Epiphyseal
plates
Blood
vessel
Medullary
cavity
Medullary
cavity
Medullary
cavity
Compact
bone
Remnant of
epiphyseal
plate
Epiphyseal
plate
Calcified
cartilage
Primary
ossification
center
Secondary
ossification
center
Spongy
bone
Articular
cartilage
(a)
(b)
(c)
(d)
(e)
(f)

18. Growth at the Epiphyseal Plate
The epiphyseal plate allows for bone lengthening until adulthood.
As a child grows…
a. cartilage cells are produced by mitosis on the epiphyseal side of the plate
b. they are then destroyed and replaced by bone on the diaphyseal side of the plate
*therefore the thickness of the plate remains almost constant while the bone on the diaphyseal side increases in length.
c. the cartilage of the epiphyseal plate is replaced by bone forming the epiphyseal line.
d. ossification of most bones is completed by age 25.

19. Bone Thickening: Appositional Growth
Along with increasing in length bones increase in thickness or dia.
1. occurs in osteogenic layer of periosteum
2. Osteoblasts lay down matrix (compact bone) on outer surface
3. This is accompanied by osteoclasts destroying the bone matrix
at the endosteal surface.

20. Homeostasis of Bone Tissue
Once bones are formed, the actions of osteoclasts and osteoblasts
continually remodel them
Bone remodeling occurs throughout life
a. osteoclasts resorb bone
b. osteoblasts replace the bone
c. these opposing processes are highly regulated so that total mass of bone tissue in adult skeleton normally remains constant
even though 3-5% of bone calcium is exchanged each year.

21. Homeostasis of Bone Tissue
Bone Resorption – action of osteoclasts via stimulation from parathyroid hormone (PTH)
Bone Deposition – action of osteoblasts and via stimulation from calcitonin
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Developing medullary
cavity
Osteoclast
© Biophoto Associates/Photo Researchers, Inc.

22. Bone Function Support Bones in legs and pelvis support trunk
The atlas (1st vertebra) supports the skull etc
Protection of underlying organs
The skull protects the brain
The rib cage protects the heart and lungs etc.
Body Movement
a. Skeletal muscles attached to bones by tendons
b. Serve as levers to move bones.
Hematopoiesis
Blood cell formation
a. All blood cells formed in the red marrow of certain bones

23. Divisions of the Skeleton
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Axial Skeleton
Skull
Spine
Rib cage
Cranium
Skull
Face
Hyoid
Clavicle
Scapula
Sternum
Humerus
Ribs
Vertebral column
Vertebral column
Appendicular Skeleton
Upper limbs
Lower limbs
Shoulder girdle
Pelvic girdle
Hip bone
Carpals
Sacrum
Radius
Coccyx
Ulna
Metacarpals
Femur
Phalanges
Patella T
ibia
Fibula T
arsals
Metatarsals
Phalanges
(a)
(b)

24. 7.6: Skull
Is composed of the cranium (brain case) and the facial bones

25. 7.7: Vertebral Column
The vertebral column, or spinal column, consists of many vertebrae separated by cartilaginous intervertebral discs.