What Are Microvilli?

The microvilli are extensions or microscopic fingerlike protrusions found on the surface of certain cells of the body, especially if you are in a liquid medium.

These extensions, whose shape and dimensions can vary (although they are generally 0.1 μm in diameter and 1 μm in height), have a portion of cytoplasm and an axis made up of actin filaments.

microvilli seen under a microscope

They also have other proteins such as: fimbrin, vilin, myosin (Myo1A), calmodulin and spectrin (non-erythrocytic). While the core or axis of the microvillus has actin, the brush border or end of the microvillus contains myosin.

An epithelial cell can have up to 1,000 microvilli, and a microvillus has between 30 and 40 stabilizing actin filaments end-to-end, and parallel to the longitudinal axis.

These filaments help to preserve the structure of the microvilli, and normally, they undergo or present rhythmic contractions, thanks to the contractibility that proteins allow.

The latter means that the microvilli have motor activity and this activity is presumed to affect agitation and mixing within the small intestine.

The action of a microvilli develops when water and solutes pass through pores in the superficial epithelium of the mucosa in which they are found, in a volume that depends on the size of those pores that varies according to their location.

The pores at rest are closed while if they are absorbing they dilate. Since those pores are of different sizes, the water absorption rates at each site are also different.

Microvilli in the human body

They are commonly found in the small intestine, on the surface of eggs, and in white blood cells.

Some microvilli are considered specialized parts of the sensory organs (the ear, tongue, and nose).

Microvilli in epithelial cells are classified into:

1- Checkered plate : as their name indicates, they are ridged on the edge. They are found in the epithelium of the small intestine and the gallbladder.

2- Brush border : present in the epithelium that covers the renal tubules, it has an irregular appearance although its composition is similar to the striated plate.

3- Stereocilia : it looks like a bunch of long microvilli with an actin axis and a wide base while they are thin at their ends.

Function of the microvilli

The different types of microvilli have a common characteristic: they allow the cell surface to be enlarged and they offer little resistance to diffusion, making them ideal for the exchange of substances.

This means that by increasing the surface of the cell (up to 600 times its original size), it increases its absorption or secretion (exchange) surface, with its immediate environment.

For example, in the intestine they help absorb more nutrients and increase the quantity and quality of enzymes that process carbohydrates; in the ovules, they help in fertilization because they facilitate the attachment of the sperm to the testicle; and in white blood cells, it also functions as an anchor point.

The microvilli are responsible for secreting disaccharidase and peptidase, which are the enzymes that hydrolyze disaccharides and dipeptides.

Molecular receptors for some specific substances are found in the microvilli of the small intestine, which could explain that certain substances are better absorbed in certain areas; vitamin B12 in the terminal ileum or iron and calcium in the duodenum and upper jejunum.

On the other hand, they intervene in the process of perception of flavors. Receptor cells for the taste of food are produced on the tongue in groups and form a taste bud that, in turn, forms the taste buds that are embedded in the epithelium of the tongue and make contact with the outside through a pore flavor.

These same receptor cells connect with sensory cells at their inner ends to send information to the brain through three nerves: the facial, the glossopharyngeal and the vagus nerve, thus “informing” the taste of the things or food with which it is used. has contact.

These perceptions vary between people because the number of taste buds is also variable and the receptor cells react in different ways to each chemical stimulus, which means that the different flavors are perceived differently within each taste bud and in each part of the taste. language.

Microvillous inclusion disease

Microvillous inclusion disease is a pathology found in the group of so-called orphan or rare diseases that consists of a congenital alteration of the epithelial cells of the intestine.

It is also known as microvillus atrophy and manifests itself during the first days or two months of life as persistent diarrhea that causes metabolic decompensation and dehydration.

Currently, prevalence data are not handled but it is known that it is genetically transmitted by a recessive gene.

This disease has no cure at present and the child who suffers from it and survives, is left suffering from intestinal failure and depending on parenteral nutrition with the consequent involvement of the liver.

In cases of microvillous inclusion, transfer to a pediatric center specializing in gastrointestinal pathologies is recommended for a small intestine transplant to be performed to guarantee a better quality of life for the child.

There are other pathologies in which microvilli are involved, such as intestinal permeability altered by food allergies or irritable bowel syndrome, but they are more common and for them drugs and treatments have been developed that allow rapid relief of symptoms to those who suffer from it. .

References

  1. Medicine (s / f). Plasmatic Membrane. Cell Surface Specializations. Recovered from: medic.ula.ve.
  2. Orpha (s / f). Microvillous inclusion disease. Recovered from: www.orpha.net
  3. Laguna, Alfredo (2015). Microvilli in Applied Anatomy. Recovered from: aalagunas.blogspot.com.
  4. Chapman, Reginal and others (s / f). Taste bud. Human sensory reception: sense of taste (gustatory. Recovered from: britannica.com.
  5. Keeton William and Others (s / f). Human digestive system. Recovered from: britannica.com.

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