Villus, singular villi, can be observed as thin, slender, vascular projections in anatomy that are responsible for increasing a membrane's surface area. The placenta and the mucous membrane lining of the small intestine are major villous membranes. The small intestine villi projects into the intestinal cavity, substantially expanding the area of the surface for absorption of food and adding digestive secretions.
Villi in the human body are around 10 to 40 per square millimetre of tissue (6,000 to 25,000 per square inch). At the beginning of the small intestine, they are most abundant and diminish in number by the end of the tract. They range from approximately 0.5 to 1 mm in length (about 0.02 to 0.04 inch).
Structure of Villi
The excessive percentage of villi gives a velvety appearance to the internal intestinal wall. Each villus carries a central core which is further made up of one vein, one artery, a muscle strand, a lymphatic capillary (lacteal) which is located centrally, and connective tissue that provides structures with support.
It is assumed that the blood vessels carry proteins and carbohydrates ingested by the villi cells, while the lymphatic capillary eliminates droplets of emulsified fat (chyle). The muscle strand helps the villi to contract and expand; these contractions are assumed to empty the lacteal material into larger lymphatic vessels.
It is believed that the blood vessels carry proteins and carbohydrates ingested by the villi cells, while the lymphatic capillary is responsible for eliminating droplets of coagulated fat (chyle). The muscle strand causes the villi to contract and expand; these contractions are thought to empty the lacteal material into larger lymphatic vessels.
Below given picture is the villi diagram:
[Image will be uploaded soon]
Role of Villi
The role of villi or villi function are stated below:
The villi along with the microvilli support in increasing the intestinal adsorbent surface area by approximately 30-fold and 600-fold, respectively. This, therefore, provides extraordinarily effective nutrient absorption in the lumen.
For digestion, there are also enzymes (enterocyte digestive enzymes) on the surface. Amino acids and simple sugars are taken up by the villi and are collected by Villus capillaries into the bloodstream.
As they have a very thin wall, single-cell thick, which makes a shorter diffusion path, Villi are adapted for the process of absorption in the small intestine. They have a wide surface area, so the absorption of fatty acids and glycerol into the bloodstream would be more effective. To sustain a concentration gradient, they have a rich blood supply.
Villi function Can also be Studied in Terms of Clinical Significance:
Villous atrophy- The villi may become flattened in small intestinal diseases due to the effects of inflammation, and the villi can often disappear. This deterioration is referred to as villous atrophy, and is often a coeliac disease characteristic.
Absorption of Nutrients and Elimination of Waste:
Food eaten is chewed, consumed, and passed through the stomach via the esophagus where it is digested and broken down into a liquid termed as chyme. Chyme moves on to the duodenum from the stomach. There, it combines with pancreatic and bile juices that disintegrate nutrients further. Finger-like projections called villi line the small intestine's inner wall and collect much of the nutrients.
The Villi digestive system is responsible for the absorption of the Nutrients: Nutrients are absorbed into capillaries of the circulatory system and into lacteals of the lymphatic system by villi, that line the walls of the small intestine. Villi are observed to carry both lymphatic vessels, called lacteals, and capillary beds. Fatty acids which are absorbed by broken-down chyme are then passed down to the lacteals.
The process of absorption and waste compaction completes at Large Intestine: Chyme flows into the large intestine's cecum from the small intestine via an ileocecal valve. As peristaltic waves transfer the Chyme into the ascending and transverse colons, some residual nutrients and some water are absorbed. Combined with peristaltic waves, this dehydration helps in compression of the Chyme. The solid waste that is produced is called feces.
Defecation helps in the elimination of the waste from the body: the body removes wastes material, via the rectum and anus, that was produced during the digestion. This process of removal of waste is called as defecation, and it is carried out by rectal muscle contraction, internal anal sphincter relaxation, and an initial contraction of the external anal sphincter's skeletal muscle. Under the direction of the autonomic nervous system, the defecation reflex is often involuntary.