The ventral portion of the body is divided by the diaphragm. Above the diaphragm is the thoracic cavity and below the diaphragm is the abdominopelvic cavity. The major organs located inside the thoracic cavity are the lungs, aorta, vena cava, heart, and thymus gland. This cavity is protected by the bony coverings of the ribs and the sternum. The abdominopelvic cavity is the largest cavity and has the greatest number of organs compared to the other cavities. On both sides of the diaphragm is a membrane. The membrane has different names depending on the side you examine. The area above the diaphragm is a pleural membrane due to its association with the respiratory system. The pleural membrane is a type of serous membrane. Use your textbook to define a serous membrane.

A **serous membrane** is a smooth, slippery membrane that lines certain internal cavities of the body and covers the organs within these cavities. Specifically, serous membranes consist of two layers: 1. **Parietal Layer**: This outer layer lines the walls of the body cavity. 2. **Visceral Layer**: This inner layer covers the organs contained within the cavity. Between these two layers is a thin space called the **serous cavity**, which contains a small amount of serous fluid. This fluid acts as a lubricant, reducing friction from muscle movements and allowing the organs to move smoothly against each other and the cavity walls. **Functions of Serous Membranes:** - **Protection**: They protect organs by providing a cushioning barrier. - **Lubrication**: The serous fluid minimizes friction between moving structures, facilitating efficient movement within the body. - **Support**: They help hold organs in their proper places within the cavities. **Examples of Serous Membranes Include:** - **Pleura**: Surrounds the lungs within the thoracic cavity. - **Pericardium**: Encloses the heart within the thoracic cavity. - **Peritoneum**: Lines the abdominal and pelvic cavities and covers most of the abdominal organs. These membranes are essential for maintaining the proper functioning and coordination of the body's internal organs by ensuring smooth and frictionless movements.