Epithelial cells are a type of cell that covers the inside and outside of the surfaces of the body. They are tightly packed together to form a thin, continuous, and protective layer of compactly packed cells with little intercellular matrix, known as epithelial tissue. Epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue, and nervous tissue.

Epithelial cells can be different shapes and can be arranged in a single layer or multiple layers depending on where they are in the body and what kind of functions they have. There are many different kinds of epithelial tissue throughout the body, including the outer layer of the skin, the lining of the intestines, the lining of the respiratory tract, the lining of the abdominal cavity, and sweat glands.

Epithelial cells have many functions, including diffusion, filtration, secretion, selective absorption, germination, and transcellular transport. They also play a vital role in providing protection from the outside world, including defense against physical, chemical, or biological damage.

Epithelial cells are found in many parts of the body, including the urinary tract, where they are classified into three types: transitional cells, renal (kidney) tubular cells, and squamous cells. An epithelial cells in urine test looks at a sample of urine under a microscope to count the number of epithelial cells in the urine. A large number of epithelial cells in urine may indicate a urinary tract infection, kidney disease, or other serious medical condition.