Osseous Tissue and Skeletal Structure

The Skeletal System: An Introduction

The skeletal system includes

• Bones of the skeleton

• Cartilages, ligaments and other connective tissues that stabilize and connect

Functions of the skeletal system

• Support

• Storage of minerals and lipids

• Blood cell production

• Protection

• Leverage

A Classification of Bones

Bone shapes

• Long

• Flat

• Short

• Irregular

• Sesamoid

• Sutural

Bone structure = two types of bone

• Compact bone (dense)

• Spongy bone (cancellous)

A typical long bone includes

• Diaphysis

• Epiphyses

• Metaphysis

• Articular cartilage

• Marrow cavity

• Filled with red or yellow marrow

Bone Histology

Osseous tissue

• Supporting tissue with a solid matrix

• Crystals of hydroxyapatite

• Minerals deposited in lamellae

• Covered by periosteum

Cells in bone:

• Osteocytes = mature bone cells

• In lacunae

• Connected by canaliculi

• Osteoblasts synthesize new matrix

• Osteogenesis

• Osteoclasts dissolve bone matrix

• Osteolysis

• Osteoprogenitor cells differentiate into osteoblasts

Compact bone and spongy bone

• Basic unit of compact bone is an osteon

• Osteocytes arranged around a central canal

• Perforating canals extend between adjacent osteons

• Spongy bone contains trabeculae

Bones and stress

• Compact bone located where stresses are limited in direction

• Spongy bone located where stresses are weaker or multi-directional

Bones are:

• Covered by periosteum

• Lined by endosteum

Bone development and growth

• Ossification = converting other tissue to bone

• Calcification = depositing calcium salts within tissues

Osseous Tissue and Skeletal Structure

Intramembranous ossification

• Begins with osteoblast differentiation

• Dermal bones produced

• Begins at ossification center

Figure 6.7 Intramembranous Ossification

Endochondral ossification

• Cartilage model gradually replaced by bone at metaphysis

• Increasing bone length

• Timing of epiphyseal closure differs

• Appositional growth increases bone diameter

Osseous Tissue and Skeletal Structure

The Dynamic Nature of Bone

continually changing

• Remodeling

• Exercise

• Hormone levels

• Growth hormone and thyroxine increase bone mass

• Calcitonin and PTH control blood calcium levels

The skeleton is a calcium reserve

• 99% body’s calcium in the skeleton

• Calcium ion concentration maintained by bones GI tract and kidneys

• Calcitonin and PTH regulate blood calcium levels

• Calcitonin decreases blood calcium levels

• PTH increases blood calcium levels

Fracture repair

• Fracture hematoma

• External callus

Internal callus

Bone Markings (Surface Features)

Bone markings

• Are characteristic for each bone and each individual

• Markings include

• Elevations

• Projections

• Depressions

• Grooves and tunnels

Aging and the Skeletal System

Effects of aging include

• Osteopenia

• Osteoporosis