Chapter 7

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc.

Chapter 7Chapter 7

The Skeletal System

Mosby items and derived items © 2010, 2006, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc.2

ObjectivesObjectives

• List and discuss the generalized functions of the skeletal system

• Identify the major anatomical structures found in a typical long bone

• Discuss the microscopic structure of bone and cartilage, including the identification of specific cell types and structural features

• Explain how bones are formed, how they grow, and how they are remodeled


ObjectivesObjectives

• Identify the two major subdivisions of the skeleton and list the bones found in each

• List and compare the major types of joints in the body and give an example of each

• Name and describe major disorders of bones and joints


Functions of Skeletal SystemFunctions of Skeletal System

• Provides internal framework that supports the body

• Protects internal organs and helps fight disease by producing white blood cells

• Makes movement possible by working in concert with muscle contraction and relaxation

• Stores calcium, a vital resource • Forms blood cells—process is called

hematopoiesis


Types of BonesTypes of Bones

• Four major types, according to overall shape of the bone – Long—example: humerus (upper arm)– Short—example: carpals (wrist)– Flat—example: frontal (skull)– Irregular—example: vertebrae (spinal bones)– Some also recognize a sesamoid (round)

bone category—example: patella (kneecap)



• Structure of long bones – Diaphysis, or shaft—hollow tube of hard compact bone– Medullary cavity—hollow space inside the diaphysis that

contains yellow marrow– Epiphyses, or ends, of the bone—made of spongy bone that

contains red bone marrow– Articular cartilage—thin layer that covers each epiphysis;

provides a cushion– Periosteum—strong, fibrous membrane covering bone

everywhere except at joint surfaces– Endosteum—thin membrane that lines medullary cavity




• Structure of flat bones – Thin layer of compact bone surrounding

cancellous (spongy or diploe) bone– Open spaces within spongy bone are

surrounded by boney trabeculae



Microscopic Structure of Bone and CartilageMicroscopic Structure of Bone and Cartilage

• Two major types of connective tissue: bone and cartilage

• Bone types – Spongy

• Texture from needlelike threads of bone called trabeculae surrounded by network of open spaces

• Found in epiphyses of bones• Spaces contain red bone marrow




• Bone types– Compact

• Structural unit is an osteon-calcified matrix arranged in multiple layers or rings called concentric lamella

• Bone cells, called osteocytes, are found inside spaces called lacunae, which are connected by tiny tubes called canaliculi

• Covered by periosteum



• Structural unit called osteon or Haversian system composed of:– Concentric lamella—circular layers of calcified

matrix– Lacunae—spaces in matrix between lamella

containing osteocytes– Canaliculi—canals/passageways that connect

lacunae and all nutrients to reach osteocytes– Central canal of osteon contains blood vessel



• Structural unit called osteon or Haversian system composed of:– Spongy bone

• Found in epiphyses of bones • Appears “porous” to naked eye with many open

spaces in matrix• Spaces contain red bone marrow• Texture results from needlelike threads of bone

called trabeculae




• Cartilage – Cell type called chondrocytes located in

lacunae– Matrix is flexible gel-like substance and

lacks blood vessels


Bone Formation and Growth Bone Formation and Growth

• New bone-forming cells are called osteoblasts and bone resorbing cells are called osteoclasts

• The ability of bone to ossify, grow, change shape, heal after injury, and respond to stress occurs because of continuous “sculpting” by osteoblasts and osteoclasts


Bone Formation and GrowthBone Formation and Growth

• Bone is formed by two processes– Most bones develop from a process called

endochondral ossification– Some flat bones (e.g., skull bones) form in

connective tissue membranes by another process



• Endochondral bone formation – Bones develop from cartilage models – Center of ossification first appears in

diaphysis– Centers of ossification then develop in

epiphyses



• Endochondral bone formation– Epiphyseal plate of cartilage between

epiphyses and diaphysis remains until skeletal maturity

– Epiphyseal line (bone) replaces epiphyseal plate (cartilage) when growth ceases



Bone Formation and Growth Bone Formation and Growth

• Early bone development (before birth) consists of cartilage and fibrous structures

• Cartilage models gradually replaced by calcified bone matrix—process called endochondral ossification

• Osteoblasts form new bone, and osteoclasts resorb bone




Divisions of SkeletonDivisions of Skeleton

• Axial skeleton (80 bones)– Skull– Spine, or vertebral column – Thorax

• Appendicular skeleton (126 bones)– Upper extremities, including shoulder

(pectoral) girdle – Lower extremities, including hip (pelvic) girdle



• Skeleton composed of the following divisions and their subdivisions – Spine or vertebral column

• Four normal curves • Three abnormal curves

– Lordosis or “swayback”– Kyphosis or “hunchback”– Scoliosis



• Skeleton composed of the following divisions and their subdivisions– Divisions

• Cervical (7 bones)• Thoracic (12 bones)• Lumbar (5 bones)• Sacrum (1 bone)• Coccyx (1 bone)



• Skeleton composed of the following divisions and their subdivisions– Thorax

• Composed of:– 12 pairs of ribs

– Sternum or breastbone

– Thoracic vertebrae

• Ribs– True ribs—rib pairs 1 through 7

– False ribs—rib pairs 8 through 10

– Floating ribs—rib pairs 11 and 12



• Skeleton composed of the following divisions and their subdivisions– Appendicular skeleton (126 bones)

• Bones in shoulder or pectoral girdle connect bones of upper extremity (arm, forearm, wrist, and hands) to axial skeleton

• Bones in hip or pelvic girdle connect bones of lower extremity (thigh, leg, ankle, and foot) to axial skeleton



• Skeleton composed of the following divisions and their subdivisions– Upper extremity

• Shoulder or pectoral girdle formed by:– Scapula– Clavicle (frequently fractured)

• Arm—humerus• Forearm—radius and ulna• Wrist—8 carpal bones• Hand—5 metacarpal bones• Fingers—14 phalanges or finger bones



• Skeleton composed of the following divisions and their subdivisions– Lower extremity

• Hip or pelvic girdle formed by the two coxal or pelvic bones (one on each side) with sacrum and coccyx behind

– Each coxal bone in infant consists of separate ilium, ischium and pubic bones—bones are fused into a single coxal bone in the adult

– Acetabulum is cup-shaped socket—articulates with head of femur



• Skeleton composed of the following divisions and their subdivisions– Thigh bone—femur

• Patella or kneecap articulates with femur and tibia

• Lower leg—tibia (“shinbone”) and fibula



• Skeleton composed of the following divisions and their subdivisions– Foot

• 5 metatarsal bones• 7 tarsal bones (calcaneus or heel bone is largest

tarsal)• 14 phalanges or toe bones• 3 arches of foot—two longitudinal (medial and

lateral) and a transverse or metatarsal arch—if weakened, result is “flat feet”



Differences Between a Man’s and a Woman’s Skeleton

Differences Between a Man’s and a Woman’s Skeleton

• Size—male skeleton generally larger• Shape of pelvis—male pelvis deep and

narrow; female pelvis broad and shallow• Size of pelvic inlet—female pelvic inlet

generally wider; normally large enough for baby’s head to pass through it

• Pubic angle—angle between pubic bones of female generally wider



Joint (Articulations)Joint (Articulations)

• Every bone except hyoid (which anchors the tongue) connects to at least one other bone

• Joint types classified by degree of movement – Synarthrosis (no movement)—fibrous connective

tissue grows between articulating bones (e.g., sutures of skull)

– Amphiarthrosis (slight movement)—cartilage connects articulating bones (e.g., symphysis pubis)




• Joint types – Diarthrosis (free movement)—most joints belong

to this class• Structures of freely movable joints—joint capsule and

ligaments hold adjoining bones together but permit movement at joint

• Articular cartilage—covers joint ends of bones and absorbs jolts

• Synovial membrane—lines joint capsule and secretes lubricating fluid

• Joint cavity—space between joint ends of bones




• Freely movable joints – Ball-and-socket– Hinge– Pivot– Saddle– Gliding– Condyloid



Skeletal DisordersSkeletal Disorders

• Tumors of bone and cartilage– Osteosarcoma

• Most common and serious malignant bone neoplasm• Frequent sites include distal femur and proximal tibia

and humerus

– Chondrosarcoma • Cancer of skeletal hyaline cartilage• Second most common cancer of skeletal tissues• Frequent sites include medullary cavity of humerus,

femur, ribs, and pelvic bones




• Metabolic bone diseases– Osteoporosis

• Characterized by loss of calcified bone matrix and reduction in number of trabeculae in spongy bone

• Bones fracture easily, especially in wrists, hips, and vertebrae

• Treatment includes drug therapy, exercise, and dietary supplements of calcium and vitamin D




• Metabolic bone diseases– Rickets and osteomalacia—both diseases

characterized by loss of bone minerals related to vitamins

• Rickets – Loss of bone minerals occurs in infants and young

children before skeletal maturity– Lack of bone rigidity causes gross skeletal changes

(bowing of legs)– Treated with vitamin D




• Metabolic bone diseases– Rickets and osteomalacia

• Osteomalacia– Mineral content is lost from bones that have already

matured – Increases susceptibility to fractures– Treated with vitamin D



• Metabolic bone diseases– Paget disease (osteitis deformans)

• Faulty remodeling results in deformed bones that fracture easily

• Cause may be genetic or triggered by viral infections




• Metabolic bone diseases– Osteogenesis imperfecta (also called brittle

bone disease) • Bones are brittle because of lack of organic

matrix• Treatment may include splinting to reduce

fracture and drugs that decrease cell activity




• Bone infection– Osteomyelitis

• General term for bacterial (usually staphylococcal) infection of bone

• Treatment may involve surgery, drainage of pus, and IV antibiotic treatment—often over prolonged periods




• Bone fractures – Open (compound) fractures pierce the skin

and closed (simple) fractures do not– Fracture types include complete and

incomplete, linear, transverse and oblique




• Joint disorders– Noninflammatory joint disorders—do not usually

involve inflammation of the synovial membrane; symptoms tend to be local and not systemic

• Osteoarthritis, or degenerative joint disease (DJD) – Most common noninflammatory disorder of movable joints

—often called “wear and tear” arthritis– Symptoms: joint pain, morning stiffness, Bouchard nodes

(at proximal interphalangeal joints), Heberden nodes (at distal interphalangeal joints) of the fingers

– Most common cause for partial and total hip and knee replacements




• Joint disorders– Noninflammatory joint disorders

• Traumatic injury– Dislocation or subluxation—articular surfaces of

bones in joint are no longer in proper contact– Sprain—acute injury to ligaments around joints (e.g.,

whiplash type injuries)– Strain—acute injury to any part of the

“musculotendinous unit” (muscle, tendon, junction between the two, and attachments to bone)



• Joint disorders– Inflammatory joint disorders

• Arthritis: general name for several inflammatory joint diseases that may be caused by infection, injury, genetic factors, and autoimmunity

• Inflammation of the synovial membrane occurs, often with systemic signs and symptoms



• Joint disorders– Inflammatory joint disorders

• Rheumatoid arthritis – Systemic autoimmune disease—chronic inflammation of

synovial membrane with involvement of other tissues such as blood vessels, eyes, heart, and lungs

– Gouty arthritis—synovial inflammation caused by gout, a condition in which sodium urate crystals form in joints and other tissues

– Infectious arthritis—arthritis resulting from infection by a pathogen, as in Lyme arthritis and ehrlichiosis, caused by two different bacteria that are transmitted to humans by tick bites



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