Anatomy

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Osseous Tissue Objectives • Describe the functions of the skeletal system. • Classify bones and identify the major markings. • Identify cell types in bone and list their functions. • Compare spongy and compact bone. • Compare intramembranous and endochondral ossification. • Discuss the effects of nutrition, hormones, exercise, and aging on the bones. • Describe the types of fractures and certain skeletal system disorders.

The skeletal system includes • Bones of the skeleton • Cartilages, ligaments, and other connective tissues that stabilize and connect

Functions of the skeletal system • Support and movement • Storage of minerals and lipids/energy • Blood cell production - hematopoiesis • Protection • Leverage

A Classification of Bones

Bone shapes • Long bones – femur, humerus • Short bones - carpals • Flat bones - parietal, sternum • Irregular bones – vertebra, pelvis • Sesamoid bones– develop in tendon – patella and other variable bones of joints • Sutural bones– variable skull bones

Bone structure = two types of bone • Compact bone (dense) • Spongy bone (cancellous)

A typical long bone includes • Diaphysis - shaft • Epiphyses - ends • Metaphysis – union of above two • Articular cartilage- hyaline cartilage covering of articulating end of bone • Marrow cavity or medullary cavity– hollow center

• Filled with red or yellow marrow

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• Covered by periosteum • Lined by endosteum at medullary cavity

Bone Histology

Osseous tissue • Supporting tissue with a solid matrix • Minerals deposited in lamellae • Covered by periosteum • Cells are widely scattered in a matrix of protein fibers (collagen) and a ground

substance of calcium salts

Cells in bone: • Osteocytes = mature bone cells

• In lacunae • Connected by canaliculi

• Osteoblasts synthesize new matrix = immature bone cells • Osteogenesis

• Osteoclasts dissolve bone matrix • Osteoprogenitor cells differentiate into osteoblasts

• Basic unit of compact bone is an Osteon or Haversian System • Concentric lamellae around a central (Havesian) canal • Canals contain blood vessels • Perforating canals extend between adjacent osteons • Interstitial lamellae fill-in space between osteons • Circumferential lamellae cover bone • Periosteum covers bone – two layers: outer fibrous and inner cellular

• Spongy bone contains trabeculae, an irregular lattice-work of ununited lamellae • Compact bone located where stresses are limited in direction • Spongy bone located where stresses are weaker or multi-directional

Bone Development and Growth • Ossification = converting other tissue to bone • Calcification = depositing calcium salts within tissues Two major processes: Endochondral Ossification and Intramembranous Ossification

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Endochondral ossification • Hyaline cartilage model replaced by bone – See Figure in text • Begins at Primary Ossification Center • Chondrocytes hypertrophy and die, leaving spaces in diaphysis • Blood vessels grow around perichondrium, osteoblasts develop, and lay down bone on

surface • Blood vessels penetrate into central region, medullary cavity forms • Repeats at Secondary Ossification Center(s) in epiphysis • All hyaline cartilage replaced except for articular cartilage, and epiphyseal/growth

plate • Continues to regulate bone length • Timing of epiphyseal closure/ossification differs by site and gender • Appositional growth increases bone diameter by laying down bone on surface

Intramembranous ossification Bone forms directly without a hyaline cartilage model Few bones - skull, clavicles

Bone is continually changing • Remodeling from stress and exercise This is the process of replacement of old bone tissue by new.

25% replaced annually Distal femur replaced every 4 months Other bones (face) may never be fully replaced

• Hormone levels also influence bone remodeling • Growth hormone and thyroxine increase bone mass • Calcitonin (from thyroid gland) and PTH (from parathyroid glands) control blood

calcium levels

Calcitonin (CT) as blood Ca++ increases Increases osteoblast activity Increases bone Ca++

Decreases blood Ca++

Parathyroid Hormone (PTH) as blood Ca++ decreases Increases osteoclast activity Decreases bone Ca++

Increases blood Ca++

The skeleton is a calcium reserve • 99 percent body’s calcium in the skeleton • Calcium ion concentration maintained by bones, GI tract, and kidneys • Calcitonin and PTH regulate blood calcium levels

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Fracture repair • Fracture hematoma • External callus • Internal callus

Bone Markings (Surface Features)

• Are characteristic for each bone and each individual • Markings include

• Elevations • Projections • Depressions • Grooves and tunnels

See table in text for terminology examples

Aging and Disorders of the Skeletal System

Effects of aging include • Osteopenia – normal loss of bone • Osteoporosis – severe loss of bone resulting in loss of function

• Risk factors include: age, sex, race, genetics, poor diet, lack of exercise

Other Skeletal Disorders Kyphosis or hunchback

Exaggerated thoracic curve – age, diet, rickets, genetics, posture, polio Lordosis or swayback

Exaggerated lumbar curve - age, diet, genetics, poor posture Scolosis

Abnormal lateral curve – genetic, polio Spina bifida

Lamina of vertebra fail to unite at midline, mild to severe Herniated disc

Nucleus pulposus bulges through annulus fribosus, compressing nerves Compression fracture of vertebrae

Vertebral body height is compressed, requires decompression