The Skeletal System-Osseous Tissue & Skeletal Structure

The Skeletal System-Osseous Tissue & Skeletal Structure

• The skeletal system includes:– Bones– Cartilage– Joints– Ligaments– Other 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

Bone tissue

• Anatomy of a bone

• Structure of bone tissue

• Formation and growth of bone

• Fracture and repair

• Effects of physiological processes on bone

Long bones

Short bones

Flat bones

Irregular bones

Sesamoid bones

Sutural bones

Anatomical Classification of Bones

Bones are classified by their basic shape

The parts of a long bone

• Diaphysis-shaft• Epiphyses- ends• Come together at

metaphyses• Articular cartilage

protects epiphyses• Periosteum covers bone • Medullary cavity contains

marrow; is lined by endosteum

Bone cells

Organization of bone tissue

compact

spongy

Compact vs. spongy bone

• Compact bone– External layer– Arranged in osteons– Lamellae are found

around periphery and between osteons

– Central canals connected to each other by perforating canals

• Spongy bone– No osteons– Arranged in trabeculae– Major type of tisse in

short, flat, irregular bones

– Much lighter than compact bone

– Supports red bone marrow

Blood and nerve supply to bone

• Abundant supply of blood

• May have several nutrient arteries

• Nerves accompany blood vessels

Ossification (osteogenesis)

• Bone forms within mesenchyme in layers (intramembranous)– Flat bones of skull and

mandible– Osteocytes secrete

calcium– Compact and spongy

bone form

Bone remodeling replaces old tissue

• Resorption by osteoclasts, deposition by osteoblasts

• Strengthens bone

• Repairs damaged bone

The Structure of a Typical Bone

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

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 bones– Osteoprogenitor cells– Osteoblasts– Osteoclasts

Bone Cells

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

Bone Cells

• Osteoblasts– Responsible for osteogenesis – create bone

tissue– Mature into osteocytes

Bone Cells

• Osteoclasts– Derived from embryological WBCs– Secrete enzymes for osteolysis –

resorb/break down bone tissue– Necessary for calcium homeostasis

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

Two types of ossification processes occur during embryological formation:

• Intramembranous

•Endochondral

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

Types of fracture

Stress fracture is not visible;Overuse or degeneration

Process of fracture repair

Bone grows slowly; blood supply may be affected

Life processes and bone formation

• Why is exercise good for bones?• How does aging affect bones?

– Loss of bone mass due to calcium loss– Decreased production of collagen

Treatment of osteoporosis

• Prevention

• Steroid hormone replacement (stimulates osteoblast activity)

• Evista has estrogen-like effects on bone formation

• Fosamax blocks bone resorption

Summary

• Bone is a complex tissue• It is constantly being remodeled• Bones consist of compact and spongy bone, lots

of blood vessels and nerves• Functions of bone:

– Support and protection– Movement– Calcium levels– Blood cell formation– Fat storage