Lecture Notes on Thorax and Thoracic Cavity

Introduction to the Thorax

• Transition from limbs to trunk region.
• Thorax: Upper part of the trunk, houses vital organs (lungs, heart).
• Diaphragm: Musculotendinous partition dividing upper and lower trunk.

Body Cavities

• Silomates: Possess a silabic cavity.
• Development: From bilaminar germ disc to trilaminar, leading to 3D body shape.
• Primitive Body Cavity: Development of pleura, peritoneum, and pericardium.
• Organs invaginate into body cavities during development.

Thoracic Cavity Structure

• Shape: Conical, apex is truncated; kidney shape in cross-section for adults.
• Divisions:
  • Two pleural cavities (lateral).
  • Pericardial cavity (midline).
• Rigid yet flexible wall for organ protection and expansion.
• Thoracic wall: Osteocartilaginous, elastic, fibrous, and muscular.

Rib Cage

• Definition: Composed of ribs, sternum, and thoracic vertebrae.
• Rib Features:
  • 12 thoracic vertebrae (stacked).
  • Intercostal spaces filled with muscles, vessels, and nerves.
  • Ribs articulate with the sternum via costal cartilages.
  • Chondrosternal joints: Primary cartilaginous joints.

Sternum Structure

• Parts: Manubrium, body, zifister.
• Manubrium: Articulates with the first rib and sternoclavicular joints.
• Sternal Angle: Important landmark for rib counting, located at T4.
• Body of Sternum: Articulates with ribs 2-7, related to pleura and heart.

Ribs Overview

• Types of Ribs:
  • True ribs (1-7): Direct sternum articulation.
  • False ribs (8-10): Indirect articulation.
  • Floating ribs (11-12): No anterior connection.
• Typical Rib Structure: Head, neck, tubercle, shaft.
• Atypical Ribs: Variations in facets and structure for ribs 1, 2, 10, 11, and 12.

Thoracic Movements During Respiration

• Inspiration: 3D dimensions of thorax increase.
  • Anterior-Posterior Diameter: Increased by pump handle movement (sternum moves forwards).
  • Transverse Diameter: Increased by bucket handle movement (lower ribs elevate).
  • Vertical Diameter: Increased by diaphragm's piston action.
• Accessory respiratory muscles: Sternocleidomastoid, pectoral muscles, etc.

Clinical Correlation

• Fractured Ribs: Can lead to flail chest (segment moves paradoxically).
• Pigeon Chest & Funnel Chest: Abnormal thoracic shapes affecting respiration.
• Cervical & Lumbar Ribs: May compress nerves/vasculature leading to symptoms.

Conclusion

• Understanding thoracic anatomy is essential for recognizing respiratory movements and clinical implications.
• Lecture concludes with a summary of thoracic structures and functions.