Final answer:
The thorax contains three membranous sacs: the pleura in the pleural cavity for the lungs, the pericardium in the pericardial cavity for the heart, and the peritoneum in the abdominopelvic cavity for abdominal organs. These sacs reduce friction and protect the organs they surround.
Step-by-step explanation:
Membranous Sacs in the Thorax
The thorax, a part of the human body, houses three distinct membranous sacs that serve various functions:
- Pleura: This serous membrane envelops the lungs within the pleural cavity. Its primary function is to reduce friction between the lungs and the thoracic wall as the lungs inflate and deflate during breathing.
- Pericardium: The pericardium is a double-walled sac containing the heart in the pericardial cavity within the mediastinum. It is designed to minimize the friction between the heart and the pericardial wall, allowing for smooth heart movements.
- Peritoneum (though not in the thoracic cavity, it's often discussed together with the other serous membranes): This membrane lines the peritoneal cavity found within the abdominopelvic area and reduces friction among the abdominal and pelvic organs.
The thoracic cage, including the rib cage and the diaphragm, supports and protects these sacs and the organs they enclose. Lungs are cushioned by the pleura in the thoracic cavity, which is bounded inferiorly by the diaphragm, a crucial muscle in the process of breathing.