villi

Examples of villi in the following topics:

• Chorionic Villi and Placental Development

  • In the placenta, chorionic villi develop to maximize surface area contact with maternal blood for nutrient and gas exchange.
  • During the secondary stage (fifth week), the villi increase in size and ramify, while the mesoderm grows into them, so that at this point the villi contain trophoblast and mesoderm.
  • At this point, the villi contain trophoblast, mesoderm, and blood vessels.
  • Embryonic blood is carried to the villi by the branches of the umbilical arteries.
  • After circulating through the capillaries of the villi, it is returned to the embryo by the umbilical veins.

• Development of the Extraembryonic Coelom

  • It is the fetal aspect of the placenta that gives rise to chorionic villi.
  • Villi emerge from the chorion, which invade the endometrium, destroy the uterine decidua, and allow the transfer of nutrients from maternal blood to fetal blood.
  • Chorionic villi are at first small and nonvascular, and consist of only trophoblast, but they increase in size and branch.
  • Blood is carried to the villi by the paired umbilical arteries, which branch into chorionic arteries and enter the chorionic villi as cotyledon arteries.
  • After circulating through the capillaries of the villi, the blood is returned to the embryo by the umbilical veins.

• Implantation

  • The syncytiotrophoblast then implants the blastocyst into the endometrium of the uterus by forming finger-like projections into the uterine wall called chorionic villi .
  • The chorionic villi grow outwards until they come into contact with the maternal blood supply.
  • The chorionic villi will be the border between maternal and fetal blood during the pregnancy, and the location of gas and nutrient exchange between the fetus and the mother.
  • The creation of chorionic villi is assisted by hydrolytic enzymes that erode the uterine epithelium.
  • During implantation extensions of the trophoblast, the syncytiotrophoblasts, embed within the endometrium and form chorionic villi.

• Histology of the Small Intestine

  • The intestinal villi are part of the mucosa.
  • Intestinal villi (singular: villus) are tiny, finger-like projections that protrude from the epithelial lining of the mucosa .
  • Villi increase the internal surface area of the intestinal walls.
  • Increased absorptive area is useful because digested nutrients (including sugars and amino acids) pass into the villi, which is semi-permeable, through diffusion, which is effective only at short distances.
  • The villi are connected to blood vessels that carry the nutrients away in the circulating blood.

• Anatomy of the Small Intestine

  • The epithelial cells which line these villi possess even larger numbers of microvilli.
  • The villi in the jejunum are much longer than in the duodenum or ileum.
  • The wall itself is made up of folds, each of which has many tiny finger-like projections known as villi on its surface.
  • The villi contain large numbers of capillaries that take the amino acids and glucose produced by digestion to the hepatic portal vein and the liver.
  • Lacteals are the small lymph vessels that are present in villi.

• Absorption in the Small Intestine

  • From the plicae circulares project microscopic finger-like pieces of tissue called villi (Latin for "shaggy hair") .
  • The function of the plicae circulares, the villi and the microvilli is to increase the amount of surface area available for the absorption of nutrients.
  • The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids).

• Mucosa

  • On the mucosa layer, small finger-like projections called villi and microvilli help to increase surface area for nutrient absorption.
  • The small intestine epithelium (particularly the ileum) is specialized for absorption, with villi and microvilli increasing surface area.

• Anatomy of the Digestive System

  • It contains the plicae circulares and villi to increase the surface area of that part of the GI Tract.
  • Ileum: Has villi, where all soluble molecules are absorbed into the blood (capillaries and lacteals).

• Fourth Week of Development

  • The chorion undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo.
  • Until about the end of the second month of pregnancy the villi cover the entire chorion, and are almost uniform in size, but after this they develop unequally.

• Histology of the Large Intestine

  • Instead of having the evaginations of the small intestine (villi), the large intestine has invaginations (the intestinal glands) .
  • The crypts and intestinal villi are covered by epithelium which contains two types of cells, goblet cells (secreting mucus) and enterocytes (secreting water and electrolytes).