The most basic characteristic of epithelial tissue is that it covers the surfaces of the body, whether external or internal. It acts as a protective covering or boundary for such surfaces including the outer layer of the skin, as well as the inner surface of "hollow" organs like the stomach, colon, and blood vessels. Beyond this, epithelial tissue is typically identified as having six characteristics. Some of the common characteristics are that it is made almost entirely of cells, contains cells joined by specialized contacts, and has distinct upper and lower surfaces. Other features are that it is not supported by blood cells, it retains the ability to regenerate, and is supported by connective tissue.
All epithelial tissues share a feature that is sometimes referred to as cellularity. Cellularity simply means that the tissue is made almost completely of cells, with very little space in between them. In other tissues, particularly connective tissues, more of an area of nonliving matter, called the extracelluar matrix, exists between cells. Another characteristic is that epithelial cells share special points of contact. These contacts are made by possible by special proteins called integral membrane proteins.
Another shared characteristic of epithelial tissue is that its upper cells are different from its lower cells. This feature is known as polarity, and the upper and lower surfaces are called apical and basal, respectively. The apical cells are "free" in the sense that they are not attached to other cells, except for neighboring epithelial cells. The basal cells are attached to what is called a basement membrane; the basement membrane is necessary to attach epithelial tissue to nearby connective tissue. All epithelial tissues are supported by connective tissue, another common feature among them.
Epithelial tissue contains no blood vessels, and is therefore said to be avascular. It is instead supported by capillaries in connective tissues, which supply the epithelial tissue with nutrients through a process called diffusion. Although epithelial tissue contains no blood vessels, it does contain nerve endings.
The cells of epithelial tissue are capable of rapid division, which is the process that creates new cells. Many epithelial cells, in different parts of the body, are lost due to friction or exposure to harmful substances. The skin, for instance, constantly produces new cells to replace the dead cells closest to the skin's outer surface. The cells of tissues lining the digestive tract, including those of the esophagus, stomach, and intestines, also undergo continuous division.
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bivie
Post 3 |
@lighth0se33 - You're right, I remember another one: Pseudostratified. It gives the appearance of the stratified, but it's not -- it's an imposter. (The things that stick in my brain...) However, it redeems itself by having an interesting characteristic: It has cilia. Cilia is like little hairs. The lungs have cilia in them to clear out mucus and such. Smokers beware: Some authorities say that smoking wears down these hairs and they no longer function properly. It's the same as walking across a section of grass so often that it wears down and eventually just goes away. |
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wavy58
Post 2 |
@lighth0se33 - We are studying these cells in class now. There are many types of epithelial cells, so I will list just a few.
Squamous cells are thin and flat and line the heart, lungs, mouth, and blood vessels. They also make up the skin’s outer layers.
Cuboidal cells are square-shaped and line gland ducts and kidney tubules. They also make up the germinal epithelium, which is where egg cells and sperm cells are made.
Columnar cells are elongated and shaped like columns. They line the intestines and stomach. Some have special sensory receptors and are found in the ears, nose, and taste buds. Goblet cells are in the duodenum. |
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lighth0se33
Post 1 |
Aren’t there many different types of epithelial cells? It seems like I vaguely remember learning this in high school biology. |
