Final answer:
The visceral layer of the serous membrane covers the outer surface of organs within the body's cavities, providing protection and reducing friction through the secretion of lubricating fluid.
Step-by-step explanation:
The portion of the serous membrane that covers the outer surface of organs is called the visceral layer. The serous membranes are divided into parietal and visceral layers. The parietal layer lines the cavity walls, while the visceral layer covers the organs themselves, also referred to as the viscera.
These layers are separated by a serous cavity, which is filled with lubricating serous fluid to reduce friction. Serous membranes include the pleura in the thoracic cavity, pericardium for the heart, and peritoneum in the abdominal cavity. They are vital in providing a frictionless environment that enables organs to move smoothly against one another.