Skeletal System Physiology

Chapter 07: The Skeletal System

7.1 Overview of the Skeletal System

• Main Functions of the Skeletal System

  • Composed of multiple tissues: bone, cartilage, dense connective tissues, blood, and nervous tissue.

  • Multifunctional Aspects:

    • Support and protect softer tissues

    • Facilitates movement

    • Enables blood cell formation through bone marrow

    • Mineral storage (e.g. calcium, phosphorus)

• Divisions of the Skeletal System:

  • Axial Skeleton

  • Appendicular Skeleton

7.2 Bone Shape and Structure

• Variability in Bones:

  • Different sizes and shapes

• Common Features Among Bones:

  • Similar structure, development, and function

7.3 Parts of a Long Bone

• Key Components:

  • Epiphysis: Expanded end, articulates with other bones

  • Diaphysis: Shaft of the bone

  • Metaphysis: Region between epiphysis and diaphysis

  • Articular Cartilage: Covers the epiphysis

  • Periosteum: Dense connective tissue enclosing the bone

  • Compact Bone: Forms the wall of the diaphysis

  • Spongy Bone: Located in the epiphysis, contains trabeculae

  • Medullary Cavity: Hollow chamber within the diaphysis, contains marrow

  • Endosteum: Lining the medullary cavity

  • Bone Marrow: Red (produces blood cells) or yellow (stores fat)

7.4 Microscopic Structure of Bone

• Types of Bone Cells:

  • Osteocytes: Mature bone cells

  • Lacunae: Small chambers housing osteocytes

  • Canaliculi: Tiny passageways connecting lacunae and facilitating nutrient exchange

• Extracellular Matrix:

  • Composed primarily of collagen fibers and inorganic salts:

    • Collagen provides resilience

    • Inorganic salts give hardness

7.5 Hematopoiesis (Blood Cell Formation)

• Process:

  • Takes place in red bone marrow

  • Produces red blood cells, white blood cells, and platelets

• Red vs. Yellow Bone Marrow:

  • Yellow marrow stores fat, does not produce cells.

  • Adult red marrow is found in the skull, ribs, sternum, clavicles, vertebrae, and hip bones.

7.6 Inorganic Salt Storage

• Majority of bone matrix (about 70%) consists of inorganic mineral salts

• Key Minerals:

  • Hydroxyapatite (Calcium Phosphate) is the main component

  • Other minerals: magnesium ions, sodium ions, potassium ions, and carbonate ions

• Osteoporosis: Condition resulting from decreased bone mineralization, increases fracture risk

7.7 Bone Development, Growth, and Repair

• Prenatal Development: Bones begin to develop within weeks after conception

• Types of Bone Formation:

  • Intramembranous Bones: Develop from sheets of connective tissue

  • Endochondral Bones: Develop from hyaline cartilage models

7.8 Intramembranous Bones

• Characteristics:

  • Broad, flat bones such as the skull bones, clavicles, and sternum

• Process of Ossification:

  • Mesenchymal cells change into osteoblasts and form bone matrix

  • When osteoblasts become encased, they turn into osteocytes

7.9 Endochondral Bones

• Characteristics:

  • Begin as masses of hyaline cartilage

  • Include most long bones (e.g., femur, humerus)

• Ossification Process:

  • Chondrocytes enlarge, and matrix breaks down

  • Osteoblasts invade and replace cartilage with bone

7.10 Growth at the Epiphyseal Plate

• Epiphyseal Plate Zones:

  • Zone of Resting Cartilage: Anchors epiphyseal plate to epiphysis

  • Zone of Proliferating Cartilage: Rapidly dividing cells

  • Zone of Hypertrophic Cartilage: Older cells, thickening the plate

  • Zone of Calcified Cartilage: Calcified and dead cells

7.11 Factors Affecting Bone Health

• Nutritional Factors:

  • Vitamin D: Essential for calcium absorption

  • Vitamin C: Necessary for collagen synthesis

• Hormonal Factors:

  • Growth Hormone: Stimulates growth; insufficient amounts can hinder development

  • Sex Hormones: Promote ossification and bone density

• Physical Activity:

  • Regular exercise promotes bone growth and maintenance

7.12 Clinical Applications: Fractures and Repair

• Types of Fractures:

  • Traumatic: Result from an injury

  • Pathologic: Due to disease

  • Simple vs. Compound: Refers to whether the skin is intact or broken

• Fracture Repair Steps:

  • Formation of hematoma immediately post-fracture

  • Development of a cartilaginous callus followed by a bony callus

  • Remodeling restores the bone to its original shape

7.13 Life-Span Changes in Bone

• Age-Related Changes:

  • Decreased height begins around age 30

  • Bone density decreases, leading to brittleness and a higher risk of fractures

  • Osteoclast activity may outpace osteoblast activity, especially in post-menopausal women