Ileum

Your body has a long tube inside. This tube helps you get food. The ileum is the last part of this tube.

It takes good things from your food. It picks up things your body needs. This includes a special vitamin. It also takes in salts.

Inside the tube, there are tiny folds. These folds have small bumps. These bumps help catch the food.

Muscles in the tube push the food. They move it along in waves. This helps move things to the next part.

This part is very important. It keeps your body working well.

The ileum is the last part of the small intestine. It follows two other parts called the duodenum and the jejunum. In humans, it is about 2 to 4 meters long.

The ileum has a very important job. It absorbs things from your food that were not taken up earlier. It picks up bile salts and vitamin B12. To do this, the walls have many tiny bumps. These are called villi. Each villus has even smaller bumps called microvilli. These tiny parts create a very large surface area. This helps the body catch more nutrients.

The walls of the ileum have many layers. One layer has special cells. Some cells make mucin to keep the walls slippery. Other cells make hormones. The ileum also has Peyer's patches. These are groups of cells that help your immune system. They help protect your body from germs.

Muscles in the wall move food along. They use waves of muscle movement called peristalsis. This pushes food toward the large intestine. The ileum ends at a small valve. This valve stops food from flowing backward.

The ileum is the final section of the small intestine. It belongs to most higher vertebrates like birds, reptiles, and mammals. This part follows the duodenum and the jejunum. In humans, the ileum is about 2 to 4 meters long. Its environment is usually neutral or slightly basic. The pH level stays between 7 and 8. The name comes from a Greek word for a medical condition.

This organ has a very important job to do. It absorbs vitamin B12 and bile salts. It also catches any nutrients left over from the jejunum. To do this, the walls have many tiny bumps. These are called villi. Each villus has even smaller bumps called microvilli. These tiny parts create a huge surface area for catching food products.

The walls of the ileum are made of four layers. The innermost layer is a mucous membrane. It has five different types of cells. Enterocytes help digest and absorb nutrients. Goblet cells make mucin to keep the walls slippery. Paneth cells release substances to fight germs. Microfold cells move antigens to immune cells. Enteroendocrine cells release important hormones.

Moving food through the body takes a special way of working. The ileum uses smooth muscle to push food along. This happens through waves of muscle movement called peristalsis. The food is called chyme at this stage. The ileum ends at the ileocecal valve. This valve connects the ileum to the cecum. It stops food from flowing backward into the jejunum.

We can learn a lot about how we grow from the ileum. It starts as part of the midgut in a tiny embryo. By the fifth week, it grows very fast. It forms a U-shaped fold called a primary intestinal loop. This loop can grow so much that it moves outside the abdomen. By week 10, it moves back inside. This helps create the twisted shape of the large intestine.

The ileum is the final section of the small intestine in most higher vertebrates. This includes mammals, reptiles, and birds. It follows the duodenum and the jejunum in the digestive tract. In humans, the ileum is approximately 2 to 4 meters long. The environment inside the ileum is usually neutral or slightly basic. This means the pH level stays between 7 and 8. The name is derived from the Greek word *eileos*. This word refers to a specific medical condition known as ileus.

The primary function of the ileum is to finish the work of nutrient absorption. It absorbs vitamin B12 and bile salts. It also absorbs any products of digestion that the jejunum did not catch. To do this effectively, the ileum uses a massive surface area. The walls are covered in folds. Each fold has many tiny, finger-like projections called villi. The cells lining these villi have even smaller projections called microvilli. This structure allows for the adsorption of enzymes and the absorption of nutrients.

Inside the villi, specialized structures help move nutrients into the body. Large numbers of capillaries carry amino acids and glucose to the liver via the hepatic portal vein. Small lymph vessels called lacteals are also present in the villi. These lacteals absorb fatty acids and glycerol, which are the products of fat digestion. The ileum also uses enzymes to finish breaking down food. Cells in the lining secrete protease and carbohydrase enzymes into the lumen. These enzymes help complete the digestion of proteins and carbohydrates.

The wall of the ileum consists of four distinct layers. The innermost layer is the mucous membrane. This layer contains five specific types of cells. Enterocytes with microvilli digest and absorb nutrients. Goblet cells secrete mucin to lubricate the organ walls. Paneth cells are common in the terminal ileum and release antimicrobial substances like lysozyme. Microfold cells transport antigens to the immune system. Finally, enteroendocrine cells secrete hormones such as gastrin, secretin, and cholecystokinin.

Below the mucosa, the ileum has other complex layers. There is a lamina propria made of loose connective tissue. This area contains Peyer's patches, which are large aggregates of lymphoid tissue. These patches are a distinctive feature of the ileum and help with immunity. Next is the submucosa, which contains large blood vessels and the submucosal plexus. This plexus is part of the enteric nervous system. The outer layers include the muscularis mucosae and an external muscular layer. This muscular layer has two parts: an inner circular layer and an outer longitudinal layer. Between them sits the myenteric plexus.

Movement through the ileum is controlled by muscular contractions. The two layers of smooth muscle create waves called peristalsis. This process pushes the chyme, or partly digested food, along the tract. The ileum ends at the ileocecal junction. Here, the terminal ileum meets the cecum of the large intestine. This connection is managed by the ileocecal valve (ICV). The valve prevents the backflow of ingesta. It also helps manage the pressure between the jejunum and the cecum. In horses, a disturbance in this balance can cause colic.

The development of the ileum is a complex process in the embryo. It begins as part of the midgut in the primitive gut tube. By the fifth week of life, the ileum grows very rapidly. It forms a U-shaped fold called the primary intestinal loop. This loop grows so fast that it actually protrudes through the umbilicus. Between weeks six and ten, the small intestine rotates anticlockwise. By week 10, the loop retracts back into the abdomen. In about 2% to 4% of humans, a connection called the vitelline duct fails to close. This can leave a remnant known as Meckel's diverticulum.