Skeletal System

The Skeletal System: Overview Components of the skeletal system

Bones (~ 206 in an adult) Joints Cartilages Ligaments

Two divisions Axial skeleton Appendicular skeleton

Primary Functions of the Skeletal System 1. Structural support – framework for the

attachment of soft tissues and organs 2. Protection of soft organs

Ribs – protect the heart and lungs Skull – protects the brain Vertebrae – shield the spinal cord Pelvis – protects digestive & reproductive

organs

Primary Functions of the Skeletal System 3. Storage – calcium salts (Mineral reserve)

& lipids (energy reserve in the yellow marrow)

Yellow bone marrow

Primary Functions of the Skeletal System 4. Red Blood cell formation – red marrow

Primary Functions of the Skeletal System 5. Leverage for body movements –

delicate to powerful motions

Bone Composition Two types of bone tissue:

Compact bone: Homogeneous, relatively solid & protective outer layer

Spongy bone: Open network of small needle-like pieces of bone

Figure 5.2b

Bones – Composition Mass of a bone attributed to

three components 2/3 calcium deposits 1/3 collagen fibers Osteocytes & other cells ~ 2%

Classification of Bones on the Basis of Shape

Figure 5.1

Classification of Bones 1. Long bones

Have a shaft with heads at both ends Contain mostly compact bone

Examples: Femur, humerus, metacarpals

Classification of Bones 2. Short bones

Generally cube-shape Contain mostly spongy bone

Examples: Carpals, tarsals

Classification of Bones 3. Flat bones

Thin & often curved Thin layers of compact bone around a layer

of spongy bone Examples: Skull, ribs, sternum

Classification of Bones 4. Irregular bones

Odd shapes Do not fit into other categories Example: Vertebrae and pelvis

Gross Anatomy of A Long Bone

Gross Anatomy of a Long Bone Diaphysis Shaft Composed of compact bone

Figure 5.2a

Gross Anatomy of a Long Bone Epiphysis Ends of the bone Composed mostly of spongy bone Covered by articular cartilage Articulates with another bone at a joint

Figure 5.2a

Structures of a Long Bone Periosteum

Outside covering of the diaphysis – isolates bone from surrounding tissues

Fibrous connective tissue membrane – provides passage for blood vessels & nerves

Figure 5.2c

Structures of a Long Bone

Sharpey’s fibers - Secure periosteum to underlying bone

Structures of a Long Bone Articular cartilage

Covers the external surface of the epiphyses Hyaline cartilage Decreases friction at joint surfaces

Structures of a Long Bone Medullary cavity

Cavity of the shaft – lined by the endosteum Contains yellow marrow (mostly fat) in adults Contains red marrow (for blood cell formation)

in infants

Figure 5.2a

Bone Markings Surface features of bones Sites of attachments for muscles,

tendons, and ligaments Passages for nerves and blood vessels ***You are responsible for the bone

markings on your notes page*** What they are and their function

Joints Articulations of bones – exist wherever

two bones meet Functions of joints: strength & mobility

Structural Classification of Joints Fibrous joints - Generally immovable

Cartilaginous joints - Immovable or slightly moveable

Synovial joints - Freely moveable

Functional Classification of Joints Synarthroses – immovable joints

Amphiarthroses – slightly moveable joints Diarthroses – freely moveable joints

Synarthroses Bony edges are close together and may

interlock Suture – bones interlocked and bound together

with dense connective tissue (skull)

Syndesmoses (fibrous) Allows more movement than sutures due to

longer connective fibers The joints have more “give” Distal ends of the tibia and fibula

Amphiarthroses Symphysis (cartilaginous): Bones connected

by cartilage Examples

Pubic symphysis Intervertebral joints

Figure 5.27d–e

Diarthroses (Synovial Joints) Articulating bones are separated by a joint cavity

Typically found at the ends of long bones

Synovial fluid is found in the joint cavity

Figure 5.24f–h

Features of Synovial Joints Joint surfaces are enclosed by a fibrous

articular capsule Ligaments reinforce the joint

Features of Synovial Joints Bursae – small packets of connective tissue

filled with synovial fluid Shock absorber/ friction reducer Found where tendons or ligaments rub against

other tissues

Features of Complex Synovial Joints Meniscus - shock absorbing fibrocartilage pad

Fat pads – protect the articular cartilages & act as “filler”

Types of Synovial Joints Based on Shape

Figure 5.29a–c

Plane/Gliding Joint Articular surfaces are flat Short slipping or gliding

movements Nonaxial - no rotation Carpal and tarsal joints Ends of clavicles

Hinge Joint Cylindrical end of one bone fits into a

trough-shaped surface on the other Uniaxial – movement around one axis Elbow & joints of the phalanges

Pivot Joint Uniaxial joints – rounded end of one bone

fits into a sleeve or ring of bone Proximal radioulnar joint The atlas and dens of the axis

Condyloid (ellipsoidal) Joint Biaxial – can rotate around two different axes

Oval shaped articular surface & concavity Bone may travel from side to side & back and

forth Metacarpophalangeal joints

Saddle Joints Biaxial Joint – articulated surfaces have

convex and concave surfaces Joint of the thumb

Ball-and-Socket Joint Only multiaxial joints – spherical head of

one bone fits into the round socket of another

Provide greatest variation in motion

Inflammatory Conditions Associated with Joints Bursitis – inflammation of a bursa usually

caused by a blow or friction Tendonitis – inflammation of tendon

sheaths

Rheumatism General term describing pain or stiffness

arising in the muscular or skeletal system Several major forms of rheumatism:

Arthritis – inflammatory or degenerative diseases of joints

Also known as degenerative joint disease (DJD) 25% of women and 15 % of men over age 60 show signs of

this disorder Over 100 different types The most widespread crippling disease in the United States

Clinical Forms of Arthritis Osteoarthritis: Most common chronic arthritis

Probably related to normal aging processes – softening, fraying and breakdown of the articular cartilage

Exposed bone thickens into spurs – limits movement

Clinical Forms of Arthritis Rheumatoid arthritis

An autoimmune disease – the immune system attacks the joints

Often leads to deformities in hands and feet

Clinical Forms of Arthritis Gouty Arthritis: Inflammation of joints is

caused by a deposition of urate crystals from the blood Needle like crystals usually accumulate in one joint

– typically the big toe Can usually be controlled with diet

Review- Correctly label the types of joints

Review – Correctly label the four types of bones and give an example of each

Figure 5.1

Review – Label the main structures of a long bone

Microscopic Anatomy of Bone Osteon (Haversian System)

A unit of bone

Microscopic Anatomy of Bone Central (Haversian) canal

Opening in the center of an osteon Carries blood vessels and nerves

Microscopic Anatomy of Bone Perforating (Volkman’s) canal

Canal perpendicular to the central canal Carries blood vessels and nerves

Microscopic Anatomy of Bone Lacunae: Cavities containing bone cells

(osteocytes) Arranged in concentric rings

Detail of Figure 5.3

Microscopic Anatomy of Bone Lamellae: Rings around the central canal

Sites of lacunae

Microscopic Anatomy of Bone Canaliculi: Tiny canals that form a transport

system between individual cells Radiate from the central canal to lacunae

Detail of Figure 5.3

Types of Bone Cells Osteocytes - Mature bone cells

Maintain normal bone structure Recycle calcium salts Assist in bone repair

Types of Bone Cells Osteoblasts: Responsible for osteogenesis

(bone formation) Produce new bone matrix Promote the deposition of calcium salts in the bone

matrix When completely surrounded by calcified matrix it

will differentiate into an osteocyte

Types of Bone Cells Osteoclasts - Bone-destroying cells Produce large amounts of acids and enzymes Osteolysis – as bony matrix dissolves, stored

minerals are released Helps regulate calcium and phosphate levels

Ossification & Bone Growth Skeletal growth begins

about 6 weeks after fertilization All skeletal components

are initially composed of cartilage

Bone growth continues through adolescence Some portions continue

to grow until about age 25

Ossification Process of replacing other tissues with bone

Intramembranous – bone develops within sheets or membranes of connective tissue

Endochondral – bone replaces existing hyaline cartilage Most bones are formed in this way

Long Bone Formation and Growth

Figure 5.4b

Bone Growth and Remodeling Bones are remodeled and lengthened until growth

stops Appositional growth – as the bones lengthen they

also increase in diameter Cells of the periosteum develop into osteoblasts

and produce bone matrix Inner surface eroded by osteoclasts increasing

the diameter of the marrow cavity

Bone Growth and Remodeling Reliable source of minerals needed for growth to

occur – absorbed from mother while developing Mother often loses bone mass during

pregnancy Diet must have adequate amounts of calcium,

phosphates & Vitamin D3

Bone Remodeling Normal process of protein and mineral

composition being removed and replaced About 18% each year in adults Causes bones to change shape May change shape/size in response to stresses such

as fractures, breaks or change in muscle mass Bone mass lost with disuse and age

Bone Health Bones become stronger in response to stress When we are inactive (no exercise) – bones

become weak and fragile

Areas That Do Not Undergo Ossification

Cartilage remains in isolated areas Bridge of the nose Larynx Trachea Parts of ribs Joints

Skeletal Disorders Heterotopic Bones: abnormal development of

osteoblasts in normal connective tissues Fibrodysplasia Ossificans Progressiva: rare genetic

heterotopic disorder Muscles of the back, neck & upper limbs gradually

replaced by bone

Rickets Softening and bending of the bones due to

Vitamin D3 deficiency Children get bowed legs as they bend under

the weight of the body No longer common (in US) due to dietary

supplements

Scurvy Vitamin C deficiency causes reduction in

osteoblast activity Weak and brittle bones Common on ships

Osteopenia Bones become thinner and weaker

with age Reduction in bone mass begins

between ages 30 – 40 Important to build strong bones as

a child/ young adult

Osteopenia Osteoblast activity declines Osteoclast activity remains normal Women lose about 8% and men about 3% of their

bone mass every decade Epiphyses, vertebrae & jaws affected the most

Fragile joints/limbs, height reduction and tooth loss

Osteoporosis Bone-thinning disease that afflicts half of

women over 65 and 20% of men over 70 Bones are brittle and fracture easily Often causes kyphosis due to vertebral

collapse Caused partially by estrogen deficiency after

menopause Other factors include lack of calcium, protein

and vitamin D in the diet, smoking and insufficient weight-bearing exercise

Osteoporosis

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

Treating Bone Fractures Bone fractures are treated by reduction and

immobilization Realignment of broken bone ends

Closed reduction - bone ends coaxed back into place by physician's hands

Open reduction - surgery, bone ends secured together with pins, wires or plates & screws

Types of Bone Fractures Comminuted - bone fragments into many pieces Compression - bone is crushed ( due to porous

bone) Depressed - broken bone is pressed inward (e.g. in

skull) Transverse - break occurs across the long axis of a

bone

Types of Bone Fractures Impacted - broken bone ends are forced into each

other Spiral - ragged break as a result of excessive

twisting of bone Epiphyseal - break occurring along epiphyseal

line/plate Greenstick - bone breaks incompletely

Common Types of Fractures

Table 5.2

Bone Remodeling After a Fracture

Review – label the microscopic anatomy of the bone