W4 - The Skeletal System&Joints

8/2/2019 W4 - The Skeletal System&Joints

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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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Nutrients diffuse from vessels in central canal Alternating direction of collagen fibers increasesresistance to twisting forces

Isolated osteon:


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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

l l


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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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Hinge Joints Allows forward and

backward motion Example: knee and

elbow


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Pivot Joints


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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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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

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