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The Skeletal System
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Functions Bones
1. Support2. Movement: muscles attach by tendons and use bones as
levers to move body3. Protection
1. Skull brain2. Vertebrae spinal cord3. Rib cage thoracic organs
4. Mineral storage
1. Calcium and phosphorus2. Released as ions into blood as needed
5. Blood cell formation and energy storage1. Bone marrow: red makes blood, yellow stores fat
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Bones of the Human Body
The skeleton has 206 bones
Two basic types of bone tissue
Compact bone
HomogeneousSpongy bone
Small needle-likepieces of bone
Many open spaces
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Microscopic Anatomy of Bone
Osteon (Haversian System) A unit of bone
Central (Haversian) canal Opening in the center of an osteon Carries blood vessels and nerves
Perforating ( Volkmans ) canal Canal perpendicular to the central canal Carries blood vessels and nerves
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Microscopic Anatomy of Bone
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Nutrients diffuse from vessels in central canal Alternating direction of collagen fibers increasesresistance to twisting forces
Isolated osteon:
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Microscopic Anatomy of Bone
Canaliculi Tiny canals Radiate from the
central canal tolacunae
Form a transport
system
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Chemical Composition of bones
Cells, matrix of collagen fibers and groundsubstance (organic: 35%)
Contribute to the flexibility and tensile strength Mineral crystals/salts (inorganic: 65%)
Primarily calcium phosphate Lie in and around the collagen fibrils in
extracellular matrix Contribute to bone hardness
Small amount of water
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Terms (examples)
chondro refers to cartilage chondrocyte endochondral perichondrium
osteo refers to bone osteogenesis osteocyte periostium
blast refers to precursor cell or one that producessomething
osteoblast cyte refers to cell
osteocyte
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Classification of bones by shape
Long bones Short bones Flat bones Irregular bones Pneumatized
bones Sesamoid bones
(Short bones include sesmoid bones)
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Gross anatomy of bones
Compact bone Spongy (trabecular) bone Blood vessels
Medullary cavity Membranes
Periosteum
Endosteum
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Long Bones
Contain mostly compact bone Examples: Femur, humerus
Tubular diaphysis or shaft (yellow marrow in adult)
Epiphyses at the ends: covered with articular (=joint) cartilage Epiphyseal line in adults Kids: epiphyseal growth plate (disc of hyaline cartilage that grows to
lengthen the bone) Blood vessels
Nutrient arteries and veins through nutrient foramen
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Short bones
Generally cube-shape
Contain mostly spongy bone
Examples: Carpals, tarsals
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Irregular bones
Do not fit into otherbone classificationcategories
Example: Vertebraeand hip Have spongy bone
and it is called diploewhen its in flat bones
Have bone marrowbut no marrow cavity
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Flat bones
Thin and flattened Usually curved
Thin layers of compact bone around a layer of spongy bone Examples: Skull, ribs, sternum
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Gross Anatomy of a Long Bone
Diaphysis Shaft Composed of compact
bone Epiphysis
Ends of the bone Composed mostly of
spongy bone
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Structures of a Long Bone Periosteum
Outside covering of thediaphysis
Fibrous connective tissuemembrane
Sharpeys fibers Secure periosteum to
underlying bone Arteries
Supply bone cells withnutrients
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Structures of a Long Bone
Articular cartilage Covers the external surface
of the epiphyses Made of hyaline cartilage Decreases friction at joint
surfaces
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Structures of a Long Bone
Medullary cavity Cavity of the shaft Contains yellow marrow
(mostly fat) in adults Contains red marrow (for
blood cell formation) in
infants
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Membranes
Periosteum Connective tissue membrane Covers entire outer surface of bone except at epiphyses Two sublayers
1. Outer fibrous layer of dense irregular connective tissue
2. Inner (deep) cellular osteogenic layer on the compact bonecontaining osteoprogenitor cells (stem cells that give rise toosteoblasts)
Osteoblasts : bone depositing cells (germinating bone) Also osteoclasts : bone destroying cells (from the white blood cell line)
Secured to bone by perforating fibers ( Sharpeys fibers)
Endosteum Covers the internal bone surfaces Is also osteogenic
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Bone markings Surface features of bones Sites of attachments for muscles, tendons, and
ligaments Passages for nerves and blood vessels Categories of bone markings
Projections and processes grow out from the bonesurface
Depressions or cavities indentations
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Bone markings reflect the stresses
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Changes in the Human Skeleton
In embryos, the skeleton is primarily hyalinecartilage
During development, much of this cartilage isreplaced by bone
Cartilage remains in isolated areas Bridge of the nose Parts of ribs Joints
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Bone Growth
Epiphyseal plates allow for growth of longbone during childhood
New cartilage is continuously formed Older cartilage becomes ossified
Cartilage is broken down Bone replaces cartilage
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Bone Growth
Bones are remodeled and lengthened untilgrowth stops
Bones change shape somewhat Bones grow in width
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Bone Development
Osteogenesis : formation of bone From osteoblasts Bone tissue first appears in week 8 (embryo)
Ossification: to turn into bone
Intramembranous ossification (also called dermal since occursdeep in dermis): forms directly from mesenchyme (not modeledfirst in cartilage)
Most skull bones except a few at base Clavicles (collar bones) Sesamoid bones (like the patella)
Endochondral ossification: modeled in hyaline cartilage thenreplaced by bone tissue
All the rest of the bones
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Intramembranous ossification
(osteoid is the organic part)
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Endochondral ossification Modeled in hyaline cartilage, called cartilage model Gradually replaced by bone: begins late in second month
of development Perichondrium is invaded by vessels and becomes
periosteum Osteoblasts in periosteum lay down collar of bone
around diaphysis Calcification in center of diaphysis Primary ossification centers
Secondary ossification in epiphyses Epiphyseal growth plates close at end of adolescence Diaphysis and epiphysis fuse No more bone lengthening
See next slide
E d h d l ifi i
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Endochondral ossification
Stages 1-3 during fetal week 9 through 9 th month
Stage 4 is just before birth
Stage 5 is process of long bone growthduring childhood &adolescence
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Long Bone Formation and Growth
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Organization of cartilage withinthe epiphysealplate of agrowing longbone
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Epiphyseal growth plates in child, left,
and lines in adult, right (see arrows)
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Bone remodeling
Osteoclasts Bone resorption
Osteoblasts Bone deposition
Triggers Hormonal: parathyroid hormone Mechanical stress
Osteocytes are transformed osteoblasts
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Bone Fractures
A break in a bone Types of bone fractures
Closed (simple) fracture break that does not
penetrate the skin Open (compound) fracture broken bone
penetrates through the skin Bone fractures are treated by reduction and
immobilization Realignment of the bone
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Common type of Fractures
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Repair of bone fractures (breaks)
Hematoma (blood-filled swelling) is formed Break is splinted by fibrocartilage to form a
callus Fibrocartilage callus is replaced by a bony
callus Bony callus is remodeled to form a permanent
patch
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Stages in the Healing of a BoneFracture
Simple and compound fractures Closed and open reduction
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Factors regulating bone growth
Vitamin D: increases calcium from gut Parathyroid hormone (PTH): increases blood
calcium (some of this comes out of bone) Calcitonin: decreases blood calcium (opposes
PTH) Growth hormone & thyroid hormone:
modulate bone growth Sex hormones: growth spurt at adolescense
and closure of epiphyses
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Disorders of cartilage and bone Defective collagen
Numerous genetic disorders eg. Osteogenesis imperfecta (brittle bones) AD
(autosomal dominant)
eg. Ehlers-Danlos (rubber man) Defective endochondral ossification
eg. Achondroplasia (short limb dwarfism) - AD Inadequate calcification (requires calcium and
vitamin D) Osteomalacia (soft bones) in adults Rickets in children
Note: AD here means autosomal
dominant inheritance
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(continued)
Pagets disease excessive turnover, abnormalbone
Osteosarcoma bone cancer, affecting
children primarily Osteoporosis usually age related, esp.
females
Low bone mass and increased fractures Resorption outpaces bone deposition
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Normal bone
Osteoporotic bone
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Skeletal Cartilage
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Skeletal Cartilage
Embryo More prevalent than in
adult Skeleton initially mostly
cartilage Bone replaces cartilage in
fetal and childhood periods
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Location of cartilage in adults
External ear Nose Articular cartilage covering
the ends of most bones andmovable joints
Costal cartilage connecting
ribs to sternum Larynx - voice box
(refer diagram in textbook)
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Epiglottis flap keeping foodout of lungs
Cartilaginous rings holdingopen the air tubes of therespiratory system (tracheaand bronchi)
Intervertebral discs Pubic symphysis Articular discs such as
meniscus in knee joint
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Remember the four basic types of tissue
Epithelium Connective tissue
Connective tissue proper Cartilage Bone Blood
Muscle tissue Nervous tissue
No nerves or bloodvessels
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Cartilage
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Cartilage is Connective Tissue
Cells called chondrocytes Abundant extracellular
matrix
Fibers: collagen & elastin Jellylike ground substance of
complex sugar molecules 60-80% water (responsible for
the resilience) No nerves or vessels
(hyaline cartilage)
Types of cartilage: 3
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Types of cartilage: 3
1. Hyaline cartilage: flexible and resilient Chondrocytes appear spherical
Lacuna cavity in matrix holding chondrocyte Collagen the only fiber Refer textbook for location of HC
2. Elastic cartilage: highly bendable Matrix with elastic as well as collagen fibers Epiglottis, larynx and outer ear
3. Fibrocartilage: resists compression andtension
Rows of thick collagen fibers alternating with rowsof chondrocytes (in matrix)
Knee menisci and annunulus fibrosis of intervertebral discs
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Hyaline Cartilage
Elastic Cartilage
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Elastic Cartilage
Fibrocartilage
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Fibrocartilage
L i f h diff ki d f il
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Locations of the different kinds of cartilage
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Growth of cartilage
Appositional Growth from outside Chrondroblasts in perichondrium (external covering of
cartilage) secrete matrix Interstitial
Growth from within Chondrocytes within divide and secrete new matrix
Cartilage stops growing in late teens (chrondrocytesstop dividing)
Regenerates poorly in adults
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Joints
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Joints
Articulations of bones Functions of joints
Hold bones together Allow for mobility
Ways joints are classified Functionally Structurally
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Functional Classification of Joints
Synarthroses immovable joints Amphiarthroses slightly moveable joints Diarthroses freely moveable joints
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Structural Classification of Joints
Fibrous joints Generally immovable
Cartilaginous joints Immovable or slightly moveable
Synovial joints Freely moveable
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1-Fibrous Structural Joints
Fibrous joints where the bonesare held together byfibrous connective tissue;they lack a synovial cavity.
There are 2 types of fibrous joints:1) Sutures2) Syndesmosis
-slight movement with a fibrousband- Allows more movement thansutures- Example: distal end of tibiaand fibula
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Fibrous Structural Joints: Sutures
Occur between skull bones only The junction filled with minimal connective tissue fibers
continuous with periosteum Bones tightly bind together but able to grow Fibrous tissue ossifies and skull bones fuse into single unit
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Fibrous Structural Joints: Syndesmoses
Bones connected by ligament/fibrous tissue that preventdislocation of the joint
Amount of movement allowed depend on the length of connecting fibers
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2-Cartilaginous joints
Cartilaginous joints in which the bones are heldtogether by cartilage; they lack a synovialcavity (A space between the two bones of a synovial joint,filled with synovial fluid.)
E.g Pubicsymphysis, Intervertebral joints
There are 2 types.
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Cartilaginous joints
a) Synchondrosis - chondro = cartilage, in which theconnecting material is hyaline cartilage. Ex. jointbetween 1st rib and manubrium of the sternum
b) Symphysis is a cartilaginous joint in which the endsof the articulating bones are covered with hyalinecartilage and connected by a broad, flat disc of fibrocartilage.
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Cartilaginous Joints: Synchondroses
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Cartilaginous Joints: Symphyses
Figure 8.2c
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3-Synovial joints Synovial joints - the bones forming the joint have a
synovial cavity and are united by the denseirregular connective tissue of an articular capsule.
Types of synovial joints:a- Plane (gliding) intercarpal & intertarsal jointsb- Hinge elbow
c- Pivot C1 C2d- Condyloid knucklese- Saddle thumb metacarpalf- Ball and socket
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Features of Synovial Joints
Articular cartilage (hyaline cartilage) coversthe ends of bones
Joint surfaces are enclosed by a fibrousarticular capsule
Have a joint cavity filled with synovial fluid Ligaments reinforce the joint
Structures Associated with the
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Structures Associated with theSynovial Joint
Bursae flattened fibrous sacs Lined with synovial membranes
Filled with synovial fluid Not actually part of the joint
Tendon sheath
Elongated bursa that wraps around a tendon
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The Synovial Joint
Synovial Joints: General Structure
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y
Types of Synovial Joints Based on
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Types of Synovial Joints Based onShape
Types of Synovial Joints Based on
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Types of Synovial Joints Based onShape
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Types of Synovial Joints
Plane or Gliding Joints Articular surfaces are
essentially flat
Allow only slipping orgliding movements Only examples of
nonaxial joints
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Movable Joints of the Skeletal System
Gliding Joints Allows one bone to
slide over another. Example: wrist and
ankle
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Hinge Synovial Joints
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Movable Joints of the Skeletal System
Hinge Joints Allows forward and
backward motion Example: knee and
elbow
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Pivot Joints
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Movable Joints of the Skeletal System
Pivot Joints Allows one
bones to rotatearound another.
Example: neck
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Condyloid, or Ellipsoidal, Joints
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Saddle Joints
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Ball-and-Socket Joints
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Movable Joints of the Skeletal System
Ball and Socket Joints Allows fullest range of
motion Examples: shoulder and hip
f h k l l
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Joints of the Skeletal System
Bones in movable joints are heldtogether by strong connective tissuecalled ligaments.
Ligaments are likethe tape thatholds bonestogether.
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Movement Allowed by Synovial
Joints
A l M
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Angular Movement
A l M
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Angular Movement
Angular Movement
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Angular Movement
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(a)Dorsi flexion
(b)Extension
(c)Plantar flexion
R i
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Rotation
The turning of a bonearound its own long axis
Examples Between first two
vertebrae Hip and shoulder
joints
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Abductionof the limbs
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Adductionof the limbs
idli $
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Abductionof thefingers
Midline $
Midli $
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Adduction
of thefingers
Midline $
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Special Movements
Only occur at a few joints
Pronation S pination
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Pronation - Supination
Inversion Eversion
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Inversion - Eversion
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Inversion
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Eversion
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Please refer text book for Protraction and retraction Elevation and depression Opposition Rotational
Circumductional