Bone Structure and Function

Bone Structure and Function

• Bones play five key roles in homeostasis: support, protection, movement, mineral storage, and blood cell formation.
• The adult human skeleton comprises 206 bones.
• Two basic types of bone tissue are compact and spongy bone.
• Bone shapes include long (e.g., femur), short (e.g., carpal), flat (e.g., skull), irregular (e.g., vertebra), and sesamoid (e.g., patella). Different bone shapes are composed of different types of bone tissue.

Bone Structure

• Diaphysis: The shaft of a long bone.
• Epiphyses: The ends of a long bone.
• Periosteum: A dense, fibrous membrane covering the outer surface of the bone.
• Perforating (Sharpey's) fibers: Fibers that secure the periosteum to the underlying bone.
• Epiphyseal line: The remnant of the epiphyseal plate (growth plate) in adults.
• Yellow marrow: Marrow that primarily consists of adipose tissue; found in the diaphysis of long bones.

Compact Bone Structure

• Osteocytes: Mature bone cells.
• Lacunae: Small spaces that house osteocytes.
• Lamellae: Concentric rings of bone matrix surrounding central canals.
• Osteon: The basic functional unit of compact bone.
• Canaliculi: Tiny canals that connect lacunae to each other and the central canal.
• Central (Haversian) canal: Contains blood vessels and nerves.
• Volkmann's (perforating) canals: Canals that connect central canals to each other.

Ossification (Bone Formation)

• Osteoblasts: Bone-forming cells
• Osteoclasts: Bone-resorbing cells.
• Bone formation (ossification) is a dynamic process.
• Appositional growth is an increase in bone thickness/width.

Bone Remodeling

• Bones are constantly remodeled in response to changes in mechanical stress and calcium levels in the blood.
• Parathyroid Hormone (PTH): Released when blood calcium levels are low; stimulates osteoclast activity to release calcium from bone.

Hypercalcemia

• Hypercalcemia is a higher-than-normal level of calcium in the blood.

Fractures

• Closed (simple) fracture: Fracture that does not break the skin.
• Open (compound) fracture: Fracture that breaks the skin.
• Fracture treatment focuses on restoring the bone's alignment.

Fracture Repair

• The Four Major Events in fracture repair are:
  • Formation of hematoma
  • Fibrocartilaginous callus formation
  • Bony callus formation
  • Bone remodeling

Axial Skeleton

• Skull bones, vertebral column, and rib cage.

Appendicular Skeleton

• Bones of the limbs and girdles.

Fetal Skull

• Characteristics of the fetal skull.

Vertebral Column

• Five major regions (cervical, thoracic, lumbar, sacrum, coccyx)
• Abnormal spine curvatures (scoliosis, kyphosis, lordosis).

Sternum

• The sternum is a fusion of three bones: the manubrium, body, and xiphoid process.
• Sternal puncture: A procedure to obtain bone marrow samples.

Ribs

• True ribs, false ribs, and floating ribs.

Joints

• Joints are classified functionally (synarthrotic, amphiarthrotic, diarthrotic) and structurally (fibrous, cartilaginous, synovial).

Synovial Joints

Distinguishing features of synovial joints:

• Articular cartilage
• Joint cavity
• Articular capsule
• Synovial fluid
• Reinforcing ligaments
• Additional stabilizing structures