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Unveiling the structure of microvilli: the surprising science behind them!
Microvilli are tiny cell membrane protrusions that have extremely important biological functions. These structures not only increase the surface area of cells, but also effectively promote the diffusion of materials and reduce the increase in volume. Microvilli are not only involved in the processes of absorption and secretion, but also play key roles in cell adhesion and mechanosensing. This article will delve into the structure, location, function and clinical significance of microvilli, revealing their surprising role in biology.
Structure
Microvilli are covered by cell membrane, and inside are cytoplasm and microfilaments. Although these are extensions of cells, microvilli contain few organelles. Each microvilli has a dense bundle of cross-linked actin fibers, which is the structural core of the microvilli.
The core of each microvilli is composed of 20 to 30 tightly bundled actin fibers that are cross-linked by bundle proteins such as fimbrin, villin, and espin.
In the microvilli of intestinal epithelial cells, a structural core is attached to the cell membrane along its entire length, with side arms composed of actin and calcium-binding proteins such as calmodulin. This structural design makes microvilli very effective at maintaining shape and function.
Location of microvilli
The structure composed of thousands of microvilli is called a brush border, which is mainly found on the top surface of some epithelial cells, such as those in the small intestine. In addition, microvilli also appear on the surface of egg cells to help fix penetrating sperm cells.
The presence of microvilli increases the absorption surface area and facilitates the absorption process.
In addition, the microvilli on the surface of white blood cells also play an important role, helping the migration and activity of white blood cells.
The relationship between microvilli and cells
Microvilli are cellular structures extending from the surface of the cell membrane. The content of actin fibers in the cytoplasm is highest near the cell surface. These fibers play a decisive role in cell shape and movement. When cells face external stimuli, actin fibers nucleate, helping the cell change shape as needed.
This nucleation process usually keeps the length and diameter of microvilli consistent, while microvilli in the same tissue in different organisms may vary slightly.
For example, the microvilli in the small and large intestines of mice differ slightly in length and thickness of their surface coating.
Function
Microvilli are the primary surface for nutrient absorption in the intestine. These microvilli contain numerous enzymes that help break down complex nutrients into simpler compounds for absorption. For example, enzymes that digest carbohydrates are present in high concentrations on the surface of enterocyte microvilli.
Thus, microvilli not only increase the absorptive surface area of the cell but also enhance the number of digestive enzymes that can be present on the cell surface.
In addition, microvilli also have important functions in immune cells, allowing them to sense surface features of pathogens and other antigen-presenting cells.
Glycocalyx
The surface of microvilli is covered with a glycocalyx layer, which is mainly composed of peripheral glycoproteins that can be connected to the cell membrane through transmembrane proteins. This glycocalyx may serve to aid in the adhesion of substances, absorption of needed nutrients, or as protection against harmful elements. There may also be localization of multiple functional enzymes on the glycocalyx.
Clinical significance
Disruption of microvilli may occur in certain diseases and is often caused by a rearrangement of the cytoskeleton in the host cell. For example, disruption of microvilli is seen in infections caused by enteropathogenic Escherichia coli (EPEC), celiac disease, and microvilli inclusion disease.
The loss of microvilli may be beneficial in certain circumstances, such as in autoimmune diseases.
However, congenital microvilli deficiency leads to intestinal microvilli atrophy, a rare and often fatal neonatal disease. Understanding the structure and function of microvilli will not only help biological research, but may also have a profound impact on future medical technology.
How many mysteries and possibilities of life are hidden under the seemingly tiny structures of microvilli?
