Lecture Notes: Serous Membranes and Lungs

Serous Membranes

• Definition: A system of membranes that separates organs from muscular and skeletal walls, allowing organs to glide without friction.
• Function: Separates organs (e.g., lungs, heart) from the chest wall, facilitates smooth movement.
• Location: Thoracic cavity, pericardial cavity, and abdominal cavity (peritoneal cavity).
• Structure:
  • Membrane wraps around the organ and the chest wall.
  • Continuity of membranes with the parietal part attached to the body wall and the visceral part to the organ.
  • Inside, epithelial cells secrete serous fluid to reduce friction.

Pleura and Intrapleural Pressure

• Pleura: Specific serous membrane around the lungs.
  • Parietal pleura: Attaches to chest wall.
  • Visceral pleura: Attaches to lungs.
• Intrapleural Pressure:
  • Greater suction inside than atmospheric pressure, allowing lung attachment to chest wall.
  • Function in Breathing: As the chest wall moves, it pulls the lungs to expand and contract.
• Complication: Pneumothorax occurs when air enters the intrapleural space, causing lung collapse.

Lung Anatomy

• Position: Each lung is situated on the side of the mediastinum, bound by the diaphragm below.
• Lobes:
  • Right Lung: 3 lobes - superior, middle, and inferior (separated by horizontal and oblique fissures).
  • Left Lung: 2 lobes - upper and lower (separated by an oblique fissure).
• Pulmonary Segments: Important for radiology and surgical procedures.
• Hilus: Entry/exit for blood vessels, nerves, bronchi.

Alveoli

• Function: Site of gas exchange (external respiration) between air and blood.
• Pulmonary Artery/Veins:
  • Arteries carry oxygen-poor blood to alveoli.
  • Veins carry oxygen-rich blood to the heart.
• Lymphatic Network: Separate system for lung drainage and nutrition.

Ventilation

• Mechanism of Breathing:
  • Inhalation: Lungs follow thoracic movement; diaphragm and intercostal muscles increase chest volume.
  • Exhalation: Generally passive via recoil of diaphragm and chest wall, can be forced by additional muscles.
• Pressure Dynamics:
  • Intrapulmonary pressure refers to pressure within the lungs.
  • Air moves from higher to lower pressure zones, facilitating breathing.

Additional Notes

• Muscles Involved in Breathing:
  • Diaphragm (primary muscle).
  • External intercostals (assist elevation of thorax).
  • Additional muscles for forced breathing (e.g., neck muscles, internal intercostals).