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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