In discussing the reproductive system and its problems, the word ‘epithelium’ is often used. So, before going further, I will explain what it means. This and related terms given below are used in Pap-smear reports and to describe other gynaecological conditions; knowing what they mean can remove much of the mystery and anxiety of hearing or seeing them used about your health.
Cells that form layers covering the outside of the body and lining internal cavities that open onto skin are called epithelial cells, and the layer itself is called an epithelium. Epithelial cells can have protective, filtering or secretory (glandular) functions.
Epithelial cells are packed tightly together to form sheets. No blood vessels pass between the cells, so they must obtain their oxygen and nutrients from blood vessels in the connective tissue on which the epithelial cells lie. This connective tissue is an important part of all covering and lining membranes.
Epithelial sheets may be one cell thick, described as ‘simple’, or many cells thick, described as ‘stratified’. Stratified epithelium is found where a tough, protective covering is needed, such as skin and in the mouth and vagina. Simple epithelium performs secretory or filtering functions. Cells from epithelial layers often grow down into the connective tissue beneath to form glands, for instance the glands in the lining of the uterus and the cervix. The epithelial cells of glands that lie beneath the surface become modified so that they can secrete; this happens, for example, in the sebaceous and sweat glands of the skin and the milk-producing glands of the breast.
Epithelial membranes are also described according to the shape of their surface cells: flat cells are ‘squamous’ (from the Latin squama, meaning ‘a flat scale’); taller cells are ‘cuboidal’; tallest cells are ‘columnar’. Thus ‘stratified squamous epithelium’ is many cells thick with flat cells on its surface; ‘simple columnar epithelium’ describes a single layer of tall cells.
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