Chapter6astudents

Bones and Skeletal Tissue Overview

• Part of the skeletal system includes:

  • Bones: 206 total

  • Joints

  • Cartilages

  • Ligaments

• Divided into two divisions:

  • Axial skeleton

  • Appendicular skeleton

Axial and Appendicular Skeleton

Axial Skeleton (80 bones)

• Skull: 8 cranial, 14 facial

• Auditory Ossicles: 6

• Hyoid: 1

• Vertebrae: 26

• Thoracic Cage: 24 ribs + sternum

Appendicular Skeleton (126 bones)

• Pectoral Girdle: 4

• Upper Extremity: 60

• Pelvic Girdle: 2

• Lower Extremity: 60

Skeletal Cartilages

• Lack blood vessels or nerves

• Perichondrium (dense connective tissue) supplies cartilage with nutrients

Types of Cartilage

Hyaline Cartilage

• Most abundant; supports, flexible, resilient

• Found in:

  • Articular: covers long bone ends

  • Costal: connects ribs to sternum

  • Respiratory: larynx and airway reinforcement

  • Nasal: supports nose

Elastic Cartilage

• Similar to hyaline but contains elastic fibers

• Found in external ear, epiglottis

Fibrocartilage

• Compressed with high tensile strength

• Found in menisci of knees, intervertebral discs

Growth of Cartilage

• Appositional Growth: Matrix secretion against external face

• Interstitial Growth: Chondrocytes divide, expanding from within

• Calcification: Occurs during normal bone growth and old age

Classification of Bones

By Location

• Axial skeleton: skull, vertebral column, rib cage

• Appendicular skeleton: limbs, shoulder, hip

By Shape

• Long bones: Longer than wide

• Short bones: Cube-shaped (wrist and ankle)

• Sesamoid bones: Within tendons (e.g. patella)

• Flat bones: Thin, flat, slightly curved

• Irregular bones: Complicated shapes

Functions of Bones

• Support: Framework for body, protects organs

• Protection: Encloses brain, spinal cord, vital organs

• Movement: Serves as levers for muscles

• Mineral Storage: Reservoir for calcium, phosphorus

• Blood Cell Formation: Hematopoiesis in red marrow

• Triglyceride Storage: Energy in bone cavities

Bone Markings

Projections

• Assignments for muscles, ligaments, and tendons

  • Tuberosity: rounded projection

  • Crest: prominent ridge

  • Trochanter: large blunt surface

  • Epicondyle: above a condyle

  • Spine: sharp projection

Depressions and Openings

• Meatus: canal-like passageway

• Sinus: cavity within a bone

• Fossa: basinlike depression

• Foramen: round or oval opening

Bone Texture

• Compact Bone: Dense outer layer, cells in osteons

• Spongy Bone: Honeycomb structure, filled with red marrow

Membranes of Bone

Periosteum

• Outer fibrous layer, inner osteogenic layer (osteoblasts, osteoclasts)

• Contains nerve fibers and blood vessels

Endosteum

• Delicate membrane on internal bone surfaces

Hematopoietic Tissue Location

• Adults: Red marrow in trabecular cavities of femur and humerus

• Newborns: Red marrow in medullary cavities and spongy bone

Histology of Bone

Cell Types

• Osteogenic Cells: Stem cells for osteoblasts

• Osteoblasts: Bone-forming cells

• Osteocytes: Mature bone cells

• Osteoclasts: Cells that resorb bone matrix

Chemical Composition

• Organic: Osteogenic cells, collagen fibers, ground substance

• Inorganic: Hydroxyapatites (mineral salts), mainly calcium phosphate, hardness and compression resistance