Serous

Serous is an adjective used in medicine and anatomy to denote relation to serum or to a thin, watery secretion that resembles serum. In anatomy and physiology, the term is most closely associated with serous membranes and serous fluids that lubricate body cavities and organs.

Serous membranes, or serosa, line closed body cavities and cover the surfaces of visceral organs. They secrete serous fluid, a clear, low-protein liquid that reduces friction between moving surfaces. The main serous membranes are the pleura, which surrounds the lungs; the pericardium, which encloses the heart; and the peritoneum, which lines the abdominal cavity and covers abdominal organs. Each membrane consists of a parietal layer lining the cavity and a visceral layer covering the organ, separated by the serous fluid.

Serous fluid is typically derived from plasma filtrate and serves as a lubricant rather than a nutritive fluid. It is distinct from mucus and is usually clear and pale yellow. Serous secretions occur from serous cells and serous acini in certain glands, notably the parotid gland, which produce a watery, enzyme-rich secretion that is important for digestion and lubrication. In contrast, mucous secretions are thicker and produced by mucous cells.

In pathology, serous describes tumors that resemble serous epithelium, such as serous cystadenomas and serous cystadenocarcinomas of the ovary. Serous tumors often exhibit tubal-type epithelium with papillary structures; high-grade serous carcinoma is a common and aggressive form of ovarian cancer.

The term is also used in clinical contexts to describe serous effusions or exudates—clear, serous fluids that accumulate in body cavities due to inflammation, congestive states, or other disease processes.