Bones: Structure and Function

Bones

• Organs with associated cartilages that form the skeletal system

Bone Supports

• Provides the body's framework
• Supports the viscera (organs within the thoracic and abdominopelvic cavities)
• Offers attachment points for skeletal muscle tendons

Bone Protection

• Protects internal organs from injury

Bone Assistance in Movement

• Skeletal muscles attach to bones
• Skeletal muscle contractions pull on bones, causing movement

Mineral Storage and Release

• Bones store calcium and phosphate

Blood Cell Formation: Hemopoiesis: Hematopoiesis

• Blood cells are produced in red bone marrow

Structure of a Long Bone

• Diaphysis:
  • Long, cylindrical main portion
  • It is the shaft or body of the bone
• Epiphysis:
  • Proximal or distal ends
• Metaphyses
  • The region between the diaphysis and epiphyses
  • Contains the epiphyseal plate (growth plate)
  • Epiphyseal plate

Articular Cartilage

• Hyaline cartilage covers the epiphysis
• Reduces friction and absorbs shock

Periosteum

• The connective tissue sheath
• Composed of two layers: an outer fibrous layer and an inner osteogenic layer
• Sharpey's fibers (perforating fibers) attach the periosteum to the underlying bone

Medullary Cavity: Marrow Cavity

• Hollow, cylindrical space within the diaphysis (shaft)
• Contains yellow bone marrow and blood vessels
• Reduces the dense bony material
• Minimizes weight for faster running

Blood Cells

• Derived from mesenchyme

Endosteum

• Lines the medullary cavity

Blood Vessels

• Carry nutrients and waste

Bone Growth and Development

• Bone formation via ossification starts around the 6th week of embryonic life and continues throughout adulthood
• Ossification occurs via two processes where existing connective tissue is replaced by bone tissue

Intramembranous Ossification

• Occurs within fibrous connective tissue membranes
• Involves ossification centers, calcification, spongy bone formation, and periosteum formation

Endochondral Ossification

• Takes place inside a hyaline cartilage model
• Cartilage grows through interstitial and appositional growth

Primary Ossification Center

• Appears in the diaphysis before birth
• Forms the medullary cavity
• Bones increase in diameter by means of osteogenic periosteum through appositional growth (osteoblasts from the periosteum add new bone to the outer surface)
• Creates articular cartilage and the epiphyseal plate

Secondary Ossification Center

• Occurs in the epiphyses after birth
• Strengthens the epiphyses, allowing for walking
• The growth end of the long bone retains a strip of cartilage called the epiphyseal disc

Triglyceride Storage

• Triglycerides stored in yellow bone marrow (lipids)

Long Bone Characteristics

• Has a shaft and two distinctive ends
• Example: Humerus, radius, ulna

Short Bone Characteristics

• Equal in length, width, and height
• Example: Carpal (wrist) and tarsal (ankle) bones

Flat Bone Characteristics

• Described as curved, thin, and flat
• Example: Sternum, frontal bone

Irregular Bone Characteristics

• Not long, short, or flat
• Example: Hip bone, vertebra, hyoid bone

Sesamoid Bone Characteristics

• Small bones in tendons
• Example: Patella

Bone Tissue Histology

• Osseous tissue contains a matrix containing widely separated cells
• The matrix contains mineral salts (hydroxyapatites and calcium) deposited in a framework of collagen fibers
• Calcification of bone gives bone hardness

Cell Inside Bone

• Osteoblasts:
  • Bone-building cells
  • Produce bone matrix
  • Not fully surrounded by matrix
• Osteocytes:
  • Mature bone cells
  • Maintain osseous tissue
  • Found in lacunae
• Osteoclasts:
  • Monocytes merge to form large osteoclasts
  • Break down osseous tissue

Bone Disorders

• Osteosarcoma:
  • Most common form of bone cancer, primarily in teenagers
  • Occurs during growth spurts
• Osteomyelitis:
  • Bone infection, characterized by high fever, sweating, chills, pain, and nausea
  • Caused by Staphylococcus aureus
• Osteopenia:
  • Reduced bone mass due to various causes
• Osteoporosis:
  • Characterized by low bone mass
  • Bone reabsorption outpaces bone deposition
  • Often occurs in women after menopause
  • Severe example of osteopenia
• Osteoalgia:
  • Pain in a bone
• Bony spur:
  • Abnormal projection on a bone due to bone overgrowth
  • Common in aging bones

Types of Bone Structures

• Outer plates of compact bone cover the inner core of spongy bone

Bone Surface Markings (Osseous Markings)

• Structural features adapting to specific functions
• The two major types:
  • (1) depressions and openings
  • (2) processes
• Examples include: fissure, foramen, fossa, sulcus, meatus, and process