What Are Stratified Columnar Cells?
Stratified columnar cells form a distinct type of epithelial tissue characterized by multiple layers of cells. The cells at the surface layer are columnar, meaning they are taller than they are wide. Deeper layers, closer to the underlying tissue, consist of cells that may be more irregular, cuboidal, or polygonal in shape. This multi-layered arrangement distinguishes them from simple epithelia, which have only a single cell layer.
This tissue type is rare in the human body. The cells in the basal layer are the only ones directly attached to the basement membrane, and they continuously divide to replace older cells that are shed from the surface. This continuous regeneration helps maintain the integrity of the tissue.
Key Locations in the Body
Stratified columnar epithelium is found in several specific anatomical locations throughout the body. A notable site is the male urethra, where it lines various segments, transitioning from other epithelial types. It is present in the membranous and penile (spongy) parts of the urethra. In the eye, this tissue lines parts of the conjunctiva, which is the mucous membrane covering the inner surface of the eyelids and the white part of the eyeball.
Additionally, stratified columnar cells are found in the large excretory ducts of certain glands, such as the salivary glands. The main excretory ducts of the parotid gland exhibit this type of epithelium. Parts of the pharynx, a region of the throat, also contain stratified columnar epithelium. This tissue is also identified in a small area of the mucosal membrane of the anus, particularly in the anal crypt and sinus regions.
The Role of Stratified Columnar Cells
The multi-layered structure of stratified columnar cells provides significant protective capabilities for the underlying tissues. In areas like the male urethra, this layering offers a barrier against mechanical stress and helps prevent the entry of pathogens into the urinary tract. The multiple cell layers allow for continuous cell replacement, which is beneficial in regions exposed to friction or potential damage.
Beyond protection, these cells also contribute to secretion. In the conjunctiva of the eye, for example, they secrete mucus, which helps keep the eyes moist and clean. In the large ducts of glands, this tissue aids in the transport and secretion of substances, functioning as a conduit for glandular products. This combination of protective layering and secretory function highlights the specialized role of stratified columnar epithelium in maintaining the integrity and operation of the specific body parts where it resides.