OsteologyOsteologyOsteology

Dr. Carmen E. RexachAnatomy 35

Mt San Antonio College

Functions of the Skeletal System:

• Support• Movement• Protection• Hemopoiesis• Electrolyte balance (Ca++/PO4

-3)• Acid-base balance• Storage of heavy metals

General Classification of Individual Bones

• By shape– Long– Short– Flat– irregular

• Long bones– longer than

wide– have a marrow

cavity– Ex: femur,

humerus

• Short bones– Cube shaped– Carpals and tarsal

• Flat bones– Broad surfaces for

muscle attachment– Enclose and protect

soft organs – Ex: roofing bones of

skull, scapula, clavicle

• Irregular bones– Varied shapes– Prominent surfaces – Ex: vertebrae,

sphenoid bone

General Classification of Individual Bonesby developmental location

• Sesamoid• intramembranous

development within a tendon

• Ex: patella

• Sutural (Wormian)• intramembranous

development within a suture

Composition of Long and Flat Bone

• Composition– Compact (dense) outside– Spongy (cancellous) inside

• Flat bones = diploë• Long bones = trabeculae

Regions of long bone• Diaphysis• Epiphysis• Medullary cavity• Epiphyseal plate vs.

epiphyseal line• Periosteum

• Fibrous layer• Osteogenic layer• Sharpey’s fibers

• Nutrient foramina• Endosteum• Articular cartilage

General anatomy of long and flat bone

Surface features:articular

• Facet– smooth flat articulating

surface

• Condyle– smooth rounded

articulating knob

• Head– prominent condyle on a

neck• Anatomical neck• Surgical neck

anatomical

surgical

Surface features:non-articular (prominences)

• Crest or line– narrow ridge

• Tuberosity– large roughened surface

• Epicondyle– a roughened projection

next to a condyle

• Tubercle– small rounded rough

process• Trochanter

– massive roughened process (femur only)

• Process– any marked bony

prominence• Spine

– a long slender process

• Fossa– a flattened shallow

depression• Sulcus

– narrow, long groove• Alveolus

– a socket (teeth)• Sinus

– a cavity

• Meatus– blind ended canal (temporal

bone)• Fissure

– a wide slit in bone• Foramen (foramina)

– any opening in bone• Canal

– long foramen

Surface features:depressions/openings

Surface Features

Surface Features

Histology of Osseous Tissue• Connective Tissue

– Matrix• Non-living ground substance, stuff• Composition

– 85% Hydroxyapatite crystals» Ca10(PO4)6(OH)2

– 10% CaCO3

– Other minerals » Mg, Na, K, Fl, etc.

– collagen– Cells

Rickets and Osteomalacia

Cells– Osteogenic

• line the inner periosteum• produce new bone cells

through mitosis– Osteoblasts

• secrete matrix• high metabolic rate• Osteoblasts trapped in

lacunae– Osteocytes

• highly branched• surrounded by matrix• low metabolic rate

– Osteoclasts• fixed macrophage• Break down old bone

cells– bone lining cells

• line the surface of bones

• regulate calcium and phosphate passage

Multinucleated<150μm in diameter

On bone surface

Use HCl to dissolve bone minerals

Bone structure• Compact bone

– Solid bone tissue– Haversian system = osteon

• Concentric lamellae and central canal• Lacunae, canaliculi

• Spongy (cancellous) bone – First bone tissue to be laid down– trabeculae = lattice of thin plates– Spicules = rods and spines that fuse together to

form trabeculae– Porous, filled with bone marrow– Arranged in lamellae, but few osteons– Light weight + strength to bone

Bone marrow• Red

– Myeloid tissue– Distribution in child vs. adult– hematopoietic

• Yellow– Fatty marrow replaces red bone marrow

in adults– Not hematopoietic, except in severe or

chronic anemia• Can revert back to red bone marrow

Development of Bones• Ossification = osteogenesis

– deposition of bone tissue– begins at approx 4 weeks gestation– apparent at approx 10 weeks– bone tissue arises as connective tissue

from embryonic mesenchyme– Two types

• Endochondral• intramembraneous

Endochondral

• built on a hyaline cartilage model (perichondrium)

• ossification results in spongy bone first then an outer layer of compact bone

• 1o in diaphysis, 2o in epiphysis

Increasing the Diameter of Developing (Endochondral) Bone

• appositional growth on the outer surface• osteogenic cells differentiate into

osteoblasts• matrix, blood vessels added to outer

(periosteal) surface• osteoclasts remove matrix at the endosteal

surface• marrow cavity enlarges as bone diameter

enlarges

Intramembranous Bone Development (dermal ossification)

• roofing bones of the skull, mandible, clavicle

• proceeds without a hyaline cartilage model• bone tissue deposited “between sheets” of

fibrous connective tissue• spongy bone then outer layers of compact

bone• Diploe = spongy bone between 2 layers of

compact bone

Organization of the Skeleton (Major Divisions)

• Axial– bones that form the axis of the body– support and protect the organs of the

head, neck and trunk• Appendicular

– the bones of the upper and lower extremities + 2 bony girdles that attach the extremities to the axial skeleton

Number of bones: axial skeleton

80±187±1Total2525Rib cage26±133±1Vertebral column11Hyoid66Auditory ossicles1414Facial88CranialAdultFetusStructure

Number of bones: appendicular skeleton

206217Total skeleton126130 Total6060Lower extremities26Pelvic girdle6060Upper extremities44Pectoral girdle

AdultFetusStructure