The intestinal epithelium is the epithelium

Epithelium

Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...

 that covers the small

Small intestine

The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...

 and large intestine

Large intestine

The large intestine is the third-to-last part of the digestive system — — in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass useless waste material from the body...

. It is simple columnar and nonciliated.

They primarily take part in the digestive system. However, they also express TLR 4

TLR 4

Toll-like receptor 4 is a protein that in humans is encoded by the TLR4 gene. TLR 4 is a toll-like receptor. It detects lipopolysaccharide from Gram-negative bacteria and is thus important in the activation of the innate immune system...

 receptors, and are thus a part of the immune system

Immune system

An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

, both as a barrier and as a first-line pathogen recognition system. The mammalian intestine is covered by a single layer of epithelial cells that is renewed every 4–5 days.

Epithelial cells in the small intestine are a type of brush border cell

Brush border

A brush border is the name for the microvilli-covered surface of simple cuboidal epithelium and simple columnar epithelium cells found in certain locations of the body. Microvilli are approximately 100 nanometers in diameter and their length varies from approximately 100 to 2,000 nanometers in...

 that are joined together by tight junction

Tight junction

Tight junctions, or zonula occludens, are the closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid. It is a type of junctional complex present only in vertebrates...

s to form a polymer impermeable membrane. These cells have a brush border surface to increase their absorptive surface area, thus making them more efficient.

Genes important for the formation of intestinal epithelium are listed in this table

Intestinal epithelial differentiation genes

Table of genes implicated in development and differentiation of the intestinal epithelium The table listed below is a running comprehensive list of all intestinal differential genes that have been reported in the literature. The PMID is the pubmed identification number of the papers that support...

.