Epithelial cells

Epithelium is one of the four primary tissues ( Epithelium, connective, muscle, nervous) found in the human organism. This tissue is characterized by little or no intercellular matrix, the latter being responsible for its compacted aspect. Epithelium is subdivided into two types: the first is called a lining epithelium, the second a glandular epithelium. The lining epithelium has a sheet-like structure laid over a basement membrane. This membrane separates the epithelium from the underlaying connective tissue. The lining epithelium is further divided into two types: the first type is said simple, since it is formed of a single layer of cells; the second type is called stratified. This type has a multiple layers of cells, from 3 to 7 in the urinary tract.

The surface cells of a simple or stratified epithelium can be squamous, cuboidal or columnar. The squamous cells are flat, with an irregular border. The cuboidal cells have a polygonal aspect, with a width to height ratio of around one. Columnar cells have a tall aspect with the nucleus often at one end. The renal tubular cells found in the collector tubes are cuboidal while the proximal tubular cells are columnar.

The stratified epithelium can also be squamous, cuboidal, columnar or transitional. Transitional epithelium (urothelial epithelium) forms the lining of the urinary tract from the pelvis to the bladder. In the urothelial lining's stratification, the bottom cells are rather cylindrical while the intermediate cells have a variable aspect. The surface cells are rounded, with some having characteristic shapes like: kite cells, umbrella cells... This urothelium is seven layer thick in the bladder, 4 to 5 layers in the urethra, and 2 to 3 in the pelvis.

Exfoliation is the elimination of a cell or a group of cells (paired cells is frequent) through a secretion (urine). A normal exfoliation is the result of the renewal of the epithelium. An abundant exfoliation can be the result of a disease, increasing the cellular mortality rate or lowering the linkage of the cells with the basement membrane.

The aspect of cells found in urine, can be quite different from its original tissue-bonded aspect. Because of the lost tissue constraint, the cells adopt a more rounded shape. Because the dying cells cannot resist osmotic attack of urine, all kinds of degenerating transformations occur. These transformations will be more pronounced in cases where there is urinary stasis. The course is long for proximal tubular cells. Normally, well-preserved cells are from the lower urinary tract.

Positive identification of urinary cells is possible with the use of monoclonal antibodies. Segathosy has proposed the use of the URO series monoclonal antibodies to count the different renal cells.

For the routine urinalysis, the cell name used must be sufficiently large to include a great variety of cells (different shapes but of related origin). The names suggested are: renal tubular cells, urothelial or transitional cells, and squamous cells.