skeletal system. the skeletal systemthe skeletal system: overview components of the skeletal system ...
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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