The intestinal villi, in anatomy and physiology, are those extensions of the wall of the small intestine in which the absorption of food occurs. These are special structures in which the nutrients that complement the function of the intestinal folds are assimilated.
In fact, they are found within them and function as transverse projections of the deepest cell layers of the mucosa that reach up to 1 millimeter in length.
Much smaller than the intestinal villi are the microvilli, which are also structures dedicated to the assimilation of nutrients.
characteristics
Microvilli are microscopic filaments that emerge from mucosal cells. Thanks to them and the intestinal villi, the absorption of food that is concentrated in the walls of the mucosa, multiplies thousands of times, since its surface is used to the maximum.
Thus, the intestinal villi are extensions that cover the mucosa or lining that is in the small intestine. These are themselves very tiny epithelial tubes that have a large number of capillaries and that in turn flow into a lymphatic vessel.
In its lower part, or base, the crypts of Lieberkühn are observed, which are glandular depressions that are in charge of secreting the enzymes that participate in the digestion of the intestines.
The absorption process is carried out when the nutrients to be digested, which are in the form of carbohydrates and proteins, go to the portal vein through the capillaries that have the intestinal villi to later pass to the liver.
For their part, the lymphatic vessels are responsible for absorbing the fats that have been digested, so they do not go to the liver but to the bloodstream. In this cycle, the hormone secretin makes an appearance by the action of the mucosa of the small intestine.
In terms of their anatomical and physiological environment, these villi are respectively in the small intestine and in the later stages of digestion.
As a curiosity, the villi are reminiscent of sea sponges, which sometimes act as fingers in which there are absorption cells, capillaries and lymphatic vessels. Therefore, this entire structure is what allows these extensions to fulfill their functions within the digestive system.
Anatomical-physiological context
After a food or drink is ingested, the food bolus is reduced in the stomach and passes through the small intestine.
The action of enzymes is responsible for its chemical decomposition. Then it passes through the intestinal tract, where the absorption of the nutrients that the body requires to grow, stay active and energetic actually takes place.
In this line, the obtaining of nutrients occurs when some elements found in the small intestine have their share in the functions of the digestive system.
This intestine has two muscles (one circular and the other longitudinal) and a membrane on which the intestinal villi are attached, which share space with the microvilli and the folds of the intestines.
The organic fluids constantly run in their cavities and these contain diverse chemical substances although only those that are not useful go to the large intestine, where they are transformed into feces.
Thus, the intestinal villi form a microscopic structure that is inside a much larger structure, which extends for about six meters in length in the abdominal region.
For their part, in their physiological aspects, these villi are located in the final stages of digestion.
Structure and morphology
The intestinal villi, as has been said, can be up to 1 millimeter in length, although this is not usually the norm because since the size tends to be much smaller.
Its shape is similar to that of tiny projections that envelop and cover the mucosa of the small intestine, where most of the digestion takes place.
In this way, the coating covers a large area due to its rolled design and especially due to the existence of these villi.
Following space criteria, intestinal villi are tiny but numerous, which is why they are distributed throughout the small intestine.
This means that these villi have a passive role in digestion, since they do not move but are constantly irrigated by the flow of nutrients that pass through the intestinal tract.
The food that has been consumed is moved by the rhythmic contractions made by the muscular walls of the small intestine, although it receives a chemical shower of secretions, enzymes and bile.
However, the nutrients could not reach the liver or the other parts of the body without the contribution of the intestinal villi, which, due to their great distribution in its mucosa, allows its maximum use, since it touches them on its way.
In fact, intestinal villi can reach up to 25,000 per square inch, which is equivalent to about 40 per square millimeter.
Their number is greater at the beginning of the small intestine and decreases more and more as it progresses in its journey, so their quantity is much lower when they reach the borders that adjoin the large intestine. Observed from afar, the villi give the impression of being velvet.
On the other hand, in its outermost layer, the intestinal villi have absorption cells where the capillaries and the lymphatic vessel are that absorb fats.
Finally, above the villi is a membrane layer, which has cells of various kinds in which the absorption of nutrients can go either to the blood or to the lymphatic system, with goblet cells that secrete a secretion in the intestinal cavity. mucous substance.
Additionally, microvilli can add up to 600 per epithelial cell, which explains why the small intestine has a powerful capacity to take the food that passes through it.
Importance
Based on the above, the intestinal villi are highly relevant in the human body since without them there would be no proper nutrition. Therefore, the person would be excreting what should serve him to live well.
In this vein, intestinal villi do more than behave like sea sponges in the digestive system. They are the extensions that guarantee the entry of the elements that boost the vitality of the body.
Diseases
It is not always possible for the intestinal villi to do their job well. Sometimes these can fail for causes that can be easy or difficult to determine, depending on the pathology that is being discussed.
Whatever the case, the truth is that there are circumstances in which these extensions have clinical problems that can be diagnosed by the doctor; problems that have as a common denominator a poor functioning of the digestive tract.
In this way, the malabsorption of nutrients means that the small intestine is damaged, which suggests that its villi are not in good condition and that therefore they do not absorb the nutrients that come with food properly.
An example is celiac disease, in which the lining of the small intestine has a condition in which there is no tolerance to gluten. In this link you can find the main gluten-free foods for celiacs.
References
- Abbas, B. and Hayes, TL (1989). Internal structure of the intestinal villus: morphological and morphometric observations at different levels of the mouse villus. Journal of Anatomy, 162, pp. 263–273.
- Abrahams, Peter H; Spratt, Jonathan D. et al (2013). McMinn and Abrahams' Clinical Atlas of Human Anatomy, 7th edition. Amsterdam: Elsevier Health Sciences.
- Ball, Jane W., Stewart, Rosalin W. et al (2011). Mosby's Guide to Physical Examination, 7th edition. Missouri: Mosby.
- Drake, Richard; Wayne Vogl, A. and Mitchell, Adam WM (2009). Gray's Anatomy for Students, 2nd edition. Amsterdam: Elsevier.
- Encyclopaedia Britannica (2016). Villus. London, UK: Encyclopædia Britannica, Inc. Retrieved from britannica.com.
- Hall, John E. (2015). Guyton and Hall Textbook of Medical Physiology, 13th edition. Amsterdam: Elsevier Health Sciences.
- Hansen, John T. (2014). Netter's Clinical Anatomy, 3rd edition. Amsterdam: Elsevier Health Sciences.
- Palay, Sanford L. and Karlin, Leonard J. (1959). An Electron Microscopic Study of the Intestinal Villus. Journal of Cell Biology, 5 (3), pp. 363–371.