The Skeletal System-The Skeletal System-Osseous Tissue & Skeletal Osseous Tissue & Skeletal

StructureStructureChapter 5Chapter 5

The Skeletal System-The Skeletal System-Osseous Tissue & Skeletal Osseous Tissue & Skeletal

StructureStructureChapter 5Chapter 5

The skeletal system includes:BonesCartilageJointsLigamentsOther connective tissues

Functions of the Skeletal System Support against gravity Protection of soft internal organs Movement (Leverage) Storage

Minerals (calcium, phosphorous) – within the matrix of bone tissue

Energy reserve (adipose) – within the yellow marrow of long bones

Blood cell production – within red marrow of spongy bone tissue

The Structure of a Typical Bone

All bones have a combination of spongy (cancellous) & compact (dense) bone tissue

The Histological Features of Spongy Bone Lamellae (layers) of matrix laid down in trabeculae - branching

network of bony tissue Osteocytes located within lacunae Canaliculi branch out from lacunae Many marrow cavities which contain red marrow & small blood

vessels

The Histological Features of Compact Bone

Osteon/Haversian system - basic functional unit of compact bone

Concentric lamellae (layers) of matrix surrounding central (Haversian) canal

Osteocytes located within lacunae

Canaliculi branch out radially from lacunae

Central canals (containing BVs) run vertically down the length of the bone

Perforating (Volkmann’s) canals (containing BVs) run horizontally across the width

Bone Cells In addition to Osteocytes, the mature bone

cells found within the matrix of bone tissue, there are three other cells that are associated with bonesOsteoprogenitor cellsOsteoblastsOsteoclasts

Bone Cells

Osteoprogenitor cells Derived from mesenchymal cells Can undergo mitosis Mature into osteoblasts

Bone Cells

OsteoblastsResponsible for osteogenesis – create bone

tissueMature into osteocytes

Bone Cells

OsteoclastsDerived from embryological WBCsSecrete enzymes for osteolysis –

resorb/break down bone tissueNecessary for calcium homeostasis

Long bones

Short bones

Flat bones

Irregular bones

Sesamoid bones

Sutural bones

Anatomical Classification of Bones

Bones are classified by their basic shape

Structure of a Typical Long Bone

diaphysis (compact bone)

The Structure of a Long Bone

diaphysis

epiphysis (spongy bone)

epiphysis

The Structure of a Long Bone

diaphysis

epiphysis

epiphysis

articular cartilage

articular cartilage

The Structure of a Long Bone

epiphysis

epiphysis

metaphysis – location of

• epiphyseal plate – in children

• epiphyseal line – in adults

diaphysis

metaphysis

articular cartilage

The Structure of a Long Bone

medullary cavity

• filled with yellow marrow in adults

• lined with endosteum

The Structure of a Long Bone

periosteum

Outer fibrous layer of dense irregular CT for attachment of tendons& ligaments; provides route for blood vessels & nerves; separates bone tissue from surrounding tissues

Double layered membrane surrounding bone except at articular cartilage

Inner cellular layer contains osteoprogenitor cells, osteoblasts, osteoclasts; therefore functions in bone growth & repair

Bone Formation and Growth Ossification - Process of converting other

tissues to bone; begins around week 6-8 of embryological development as mesenchymal CT begins to differentiate

Two types of ossification processes occur during embryological formation:

• Intramembranous

•Endochondral

Intramembranous Ossification Forms flat bones of skull, mandible, clavicle Replacement of mesenchymal membrane with osseous tissue Mesenchymal cells differentiate to osteoprogenitor cells, which then

become osteoblasts Osteoblasts create spongy bone tissue, which then remodels into

compact bone where necessary Other mesenchymal cells around the developing bone form the

periosteum

Mesenchymal tissue forms

Osteoblasts begin to secrete osteoid forming spongy bone tissue

Blood vessels infiltrate tissue. Calcium salts deposit in osteoid. Periosteum develops

Endochondral Ossification Most bones formed this way Mesenchyme creates hyaline Cartilage model, which gets

replaced by bone Replacement begins in middle (diaphysis) & follows in ends

(epiphyses)

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.

Cartilagemodel

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Endochondral Ossification

Cartilage model grows in length (interstitial growth) & in width (appositional growth)

Figure 5.7

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

The perichondrium, which surrounded the cartilage model, now must be referred to as the periosteum.

Figure 5.7

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Blood vessels penetrate the dying cartilage. Newly developed osteoblasts form a primary ossification center.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis Marrowcavity

Primaryossificationcenter

Bloodvessel

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure 5.7

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.

Bone tissue continues to replace cartilage of the diaphysis, and & continues toward each epiphysis.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis Marrowcavity

Primaryossificationcenter

Bloodvessel

Marrowcavity

Bloodvessel

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

The medullary cavity begins to hollow out

Blood vessels invade the epiphyses and osteoblasts form secondary centers of ossification.Cartilage remains only at the ends (articular cartilage) & at metaphysis (epiphyseal plate)

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.

The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis Marrowcavity

Primaryossificationcenter

Bloodvessel

Marrowcavity

Bloodvessel

Secondaryossificationcenter

Epiphysealcartilage

Articularcartilage

An Overview of the Skeleton

Skeletal Divisions Axial skeleton (80 bones)

Skull Thoracic cage and sternum Vertebral column

Appendicular skeleton (126 bones) Upper, lower limbs Pectoral girdle Pelvic girdle

There are 206 bones in the adult human body

Bone Markings (Surface Features)

Markings for articulations: head condyle facet

General elevations & projections:

process

ramus

Table 5-1

Bone Markings (Surface Features)Processes for attachment:

trochanter (femur only) tuberosity tubercle epicondyle crest line spinous process (vertebrae

only) transverse process (vertebrae

only)

Spinous process

Transverse process

Bone Markings (Surface Features)

Spinous process

Transverse process

Depressions:

fossa

sulcus

Openings:

foramen (canal)

meatus

fissure

sinus

Bone Markings (Surface Features)