Epithelial tissue: guarding the borders

When one talks about this kind of tissue, the skin is first of all recalled, although epithelial tissue is basically a kind of "border guard". She separates organs from each other, she is contained in the mucous membranes. Non-uniform epithelial tissue, the structure and functions of which are interrelated in a special way for each of the species of this tissue. What kind of speech? Read on.

A characteristic common feature of all types - cells that are closely adjacent to each other, often located in layers, which is explained by the barrier function of the epithelial tissue. Also, all types of epithelial tissue are united by the fact that they are always separated from neighboring structures by a connective tissue - this formation is called the basal membrane.

In general, the epithelium is simple (in one layer) and layered (in several). Accordingly, the epithelial tissue structure can have very different.

A simple epithelium can be slightly flattened in shape. This type is called squamous. It lays the lungs, blood vessels, cavities of the heart. Also, such cells are in the upper layers of the skin and the oral mucosa.

It is not difficult to guess about the shape of cells of the cubic epithelium. Such cells are found in glands, ducts of glands and kidney tubules. In addition, they are the rudimentary epithelium in the ovaries of women and men's testicles.

The prismatic epithelium is simple and layered. Cells have the form of oblong stalks. The nuclei in such cells are "hidden" closer to the basal membrane and away from the surface. Well, in the stomach, whose surface they lining, this is very rational - the environment is too aggressive there. Some of these cells are part of sensory organs - smell, taste and hearing.

The pronged prismatic epithelium has outgrowths of a special form, which are able to advance what is next to them by rapid undulating movements. They "live" in the nose and ... in the fallopian tubes of women, which allows them to move the egg to the uterus.

The glandular epithelium is called the prismatic, containing the secreting cells. Sometimes the secreting cells are larger than the columnar cells. Where do cells that can create a secret come from? These are cells of epithelial tissue that have passed the path of specialization. And "experts" they can be very different. They are engaged in the production of enzymes, hormones, milk, mucus, sweat, earwax and saliva. Of course, all these substances are unable to produce unicellular glands, this is the case of glands consisting of many epithelial cells. And unicellular cells are called goblet cells. Initially they were called enterocytes, because most of these cells are in the small intestine. But then it turned out that they are present in the conjunctiva of the eye, in the respiratory system, and in the ducts of the glands.

Where the processes of friction are great and injuries are likely, the body builds a complex epithelium - the very one that always consists of several layers. It's about the skin and the mucous membrane of the mouth. On the surface of the skin are cells in which there is a lot of protein-keratin, in the mouth of keratin in the cells is small, so the skin and mouth mucosa are significantly different in touch.

The epithelial tissue function is very different. The list below is not absolutely complete.

Protective function . Epithelium prevents mechanical damage, chemical burns, puts a barrier against infection and protects the underlying cells from water loss.

Function of sensations : specialized cells of epithelial tissue form sensory organs.

Secretory function : described in detail in the section on glandular epithelium.

Absorptive : in the small intestine through the epithelium, nutrients are absorbed.

Excretion : sweat glands secrete unnecessary substances, and also the epithelium in the kidneys is able to participate in filtration, and in reabsorption too.

Diffusion : through the thin epithelium in the respiratory system into the body and from it penetrate gases.

Purification function : in the respiratory tract, the epithelium cleans the air of dust.

Reduction of friction : the epithelium of the vessels reduces friction between the vessel wall and blood cells.

As you can see, there are many functions, because there are many kinds. More on this you will read in good histology textbooks.