notes on Epithelia PDF

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Goblet Cells: Goblet cells found in several locations of the human body and they are modified columnar epithelial cells. In respiratory epithelium goblet cells occur with pseudostratified columnar ciliated epithelium. Here the cells secrete mucinogen to help clearance of the bronchial tree. Located from the bronchi to trachea. Also found in the small and large intestines. Function to produce mucin to prevent bacteria adhering to the epithelium. Sialomucins produced in the small intestine and sulfomucins produced in the large intestine. In the pancreas and salivary glands, goblet cells also exist to secrete mucin. Main functions are hydration, lubrication and protection of the cell surfaces (mechanical and immunological). Goblet cells in small intestine with “brush border” (microvillia)

Goblet cells found in the large intestine (G – white bubble like structures in the epithelium)

Columnar or cuboidal:

Simple cuboidal epithelium provides protection, forms conduits for gland ducts, and may be specialized for active secretion and absorption. Simple columnar epithelium is mainly found in sites engaged in protection of wet surfaces, nutrient absorption, and secretion. It forms major ducts of glands, convoluted tubules of the kidney, and inner lining of the stomach, small and large intestines, gallbladder, small bronchi of the lungs, and parts of the male and female (oviducts and uterus) reproductive tracts. Both simple cuboidal and columnar often have microvilli on apical surfaces. Stratified cuboidal and stratified columnar epithelia have limited distribution in the adult; they are more common in the embryo and foetus. Both contain two or more layers of cells, and because they are stratified, they are mainly protective and better suited than simple epithelia to withstand wear and tear. Stratified cuboidal epithelium, usually two layers of cells, lines ducts of sweat glands and other exocrine glands. Stratified columnar epithelium is in the pharynx and larynx, conjunctiva of the eyelids, major ducts of exocrine glands, and parts of the male urethra.

Keratin and cell turnover:

Keratin is produced by keratinocytes. Only found in the skin epithelia. These cells migrate (along with the epithelial cells) from the stratum basale through the superficial layers becoming more flattened (now called corneocytes bound together by corneodesmosomes) as they reach the most superficial layer, the stratum corneum, which is composed of keratin. As the cells migrate they also loose the cell membrane, nucleus and organelles (what is left is called keratin). The keratin (keratinocytes/corneocytes) remain in the stratum corneum for 2 weeks before being shed (desquamation), occurs by degradation of the corneodesmosomes by proteases....