The Skeletal System Overview

The Skeletal System

• The skeletal system provides support and protection for the body's structures.
• It acts as a framework, composed of bones, joints, and supporting connective tissues.
• Muscles work with bones to produce movement at the joints.

Skeletal Cartilage

• Skeletal cartilage is made of highly resilient, molded cartilage tissue, primarily composed of water.
• Contains no blood vessels or nerves.
• Surrounded by a layer of dense connective tissue called the perichondrium, which provides support and contains blood vessels for nutrient delivery.
• Cartilage cells, known as chondrocytes, are housed in small cavities called lacunae within the extracellular matrix.

Types of Cartilage

• Hyaline Cartilage: The most abundant type, providing support, flexibility, and resilience. Contains only collagen fibers. Found in articular joints, ribs, respiratory structures, and the nose tip.
• Elastic Cartilage: Similar to hyaline cartilage but contains elastic fibers, making it the most flexible type. Found in the external ear and epiglottis.
• Fibrocartilage: Contains thick collagen fibers, providing great tensile strength and the least flexibility. Found in the menisci of the knee and vertebral discs.

Bone Markings

• Projections: Indicate sites of muscle, ligament, and tendon attachment, or areas involved in joint formation. Examples include head, process, condyle, epicondyle, and crest.
• Depressions or Holes: Serve as conduits for blood vessels and nerves. Examples include foramen, fissure, sinus, fossa, and meatus (canal).

Compact Bone

• Consists of:
  • Osteon (Haversian system): Basic functional unit of compact bone, containing lamellae, a central canal, and canaliculi.
  • Canals and canaliculi: Channels that house blood vessels and nerves.
  • Interstitial and circumferential lamellae: Layers of bone matrix surrounding osteons.
• Perforating (Volkmann’s) canals: Run perpendicular to central canals, connecting the blood vessels and nerves of the periosteum, medullary cavity, and central canal.

Bone Composition

• Organic Components:
  • Osteoblasts, osteoclasts, and osteocytes - cells responsible for bone formation, resorption, and maintenance.
  • Collagen fibers - contribute to bone's tensile strength and flexibility.
• Inorganic Components:
  • Hydroxyapatites (mineral salts): Make up 65% of bone by mass.
  • Primarily consist of calcium phosphate crystals, responsible for bone's hardness and resistance to compression.

Ossification (Osteogenesis): Bone Formation

• The process of bone tissue formation.
• Begins in month 2 of embryonic development.
• Postnatal bone growth continues until early adulthood.
• Bone remodeling and repair occur throughout life.
• New cartilage grows at epiphyseal plates, where ossification replaces cartilage with bone.
• When all cartilage is ossified, bone growth ceases, leaving an epiphyseal line.

Bone Remodeling

• Bone mass is constantly recycled, with spongy bone replaced every 3-4 years and compact bone every 10 years.
• Involves both bone deposit and bone resorption.
• Remodeling units, containing osteoblasts and osteoclasts, coordinate the process at periosteal and endosteal surfaces.
• Osteoclast activation is influenced by parathyroid hormone (PTH) and immune T cell proteins.

Calcium Homeostasis

• Bone acts as a reservoir for calcium, which plays crucial roles in nerve transmission, muscle contraction, blood coagulation, and other essential processes.
• Parathyroid hormone(PTH): Released in response to low blood calcium levels, stimulates osteoclasts to resorb bone, releasing calcium into the bloodstream.
• Calcitonin: Released from the thyroid gland in response to high blood calcium levels.

Types of Bone Fractures

• Closed fracture: A simple fracture with no open wound.
• Open fracture: A broken bone protrudes through the skin or an external wound leads to a broken bone.
• Greenstick fracture: One side of the bone is broken while the other is bent, common in children.
• Impacted fracture: The broken ends of the bone are jammed into each other.
• Comminuted fracture: Multiple fracture lines with splintering or crushing of the bone.
• Spiral fracture: The bone is twisted apart, common in skiing accidents.
• Transverse fracture: The fracture goes straight across the bone.
• Oblique fracture: The break occurs at an angle across the bone.

Fracture Repair

• A series of steps involving:
  • Blood clot formation.
  • Blood vessels grow into the clot, bringing connective tissue.
  • Fibroblasts and chondroblasts convert the clot into a soft callus.
  • Macrophages clear debris, while osteoclasts resorb dead bone tissue.
  • Osteoblasts transform the soft callus into a hard callus of spongy bone.
  • Osteoclasts and osteoblasts remodel the hard callus into compact bone.

Explore the intricacies of the skeletal system, its components, and functions. This quiz covers the types of skeletal cartilage and their unique characteristics. Test your knowledge on how the skeletal system supports and enables movement in the human body.