Small intestine

Your body has a long tube inside.

It sits between your stomach and your large intestine. This tube is very long. It folds many times to fit inside you.

It has tiny finger-like parts. These parts catch the good parts of food. They send the food into your blood. This helps your body grow. This tube is also very narrow. It is thinner than your large intestine.

It is a very busy place!

Your small intestine is a very busy organ.

It sits between your stomach and your large intestine. Even though it is called "small," it is actually longer than the large intestine. It is only called small because it is much narrower.

This organ has three main parts. The first part is the duodenum. It is shaped like a C. It receives juices from the liver and pancreas to help break down food. The middle part is the jejunum. This is where most nutrients enter your blood. The last part is the ileum. It absorbs things like vitamin B12.

The inside of the tube is not smooth. It has many folds and tiny finger-like parts. We call these parts villi. These villi help catch nutrients from your food. Each villus has tiny blood vessels near its surface. These vessels carry the nutrients to the rest of your body. This way, your body gets the power it needs to grow.

The small intestine is a very important organ in your body. It sits between your stomach and your large intestine.

Even though it is called "small," it is actually much longer than the large intestine. It gets its name because it is much narrower in diameter. This organ is where most of the nutrients from your food are absorbed. This process allows your body to use food for energy and growth.

This organ works in a very organized way to break down food. First, food moves from the stomach into the duodenum through a muscle called the pyloric sphincter.

The pancreas and liver send juices into the duodenum to help. These juices include enzymes that break down proteins and bile that helps with fats. The duodenum also uses bicarbonate to neutralize strong acids from the stomach. After this, the food moves through the jejunum and finally the ileum.

Scientists have studied how this organ develops before a baby is even born. In the fifth week of life, the ileum grows very fast. It forms a U-shaped fold called the primary intestinal loop. This loop grows so quickly that it actually moves out of the abdomen. By the tenth week, it moves back inside the body. During this time, the intestine also rotates to create its final shape.

There are many specific facts about the size and parts of this organ. The small intestine is divided into the duodenum, the jejunum, and the ileum. The duodenum is the shortest part and is shaped like a "C." The ileum is about 3 meters or 9.8 feet long. In a typical living person, the length can vary quite a bit. The length often depends on how tall a person is.

To catch all the nutrients, the inside of the intestine is not smooth. It has many circular folds and tiny finger-like parts called villi.

These villi have even smaller projections called microvilli. These parts work together to create a huge surface area. This large surface area makes it easier to absorb things like sugars and amino acids. The nutrients then travel through blood vessels to the rest of your body.

The small intestine is a vital organ within the gastrointestinal tract. It is located between the stomach and the large intestine. Its primary purpose is the absorption of nutrients from food. This process provides the body with energy and the building blocks for growth. Although it is called "small," this name refers to its narrow diameter. In reality, the small intestine is much longer than the large intestine.

Digestion in the small intestine is a complex chemical process. It begins when the pyloric sphincter allows food to enter the duodenum. The duodenum is the shortest section and is shaped like a "C." It receives gastric chyme from the stomach. The pancreas and liver also send digestive juices here. The pancreas provides enzymes like trypsin and chymotrypsin to break down proteins. The liver provides bile to help emulsify fats.

To protect the body, the duodenum must neutralize strong stomach acids. Brunner's glands in the duodenum produce a mucus-rich, alkaline secretion. This secretion contains bicarbonate. The pancreas also releases bicarbonate into the duodenum. These two sources work together to neutralize the acid in the chyme. This step is essential for the chemical environment needed for enzymes to function. The hormone secretin helps promote this release of bicarbonate from the pancreas.

The small intestine is divided into three distinct structural regions. The first is the duodenum, which prepares food for absorption. The second is the jejunum, which is the midsection of the organ. The jejunum is about 2.5 meters long and is specialized for nutrient absorption. It uses enterocytes to absorb small particles like sugars and amino acids. The third section is the ileum, which is the final part. The ileum is approximately 3 meters, or 9.8 feet, long. It absorbs vitamin B12, bile salts, and any remaining nutrients.

To maximize absorption, the inner wall of the intestine is not smooth. It features permanent wrinkles called circular folds. From these folds, microscopic finger-like protrusions called villi extend. The individual cells on these villi have even smaller projections called microvilli. These three structures greatly increase the total surface area of the mucosa. The human small intestinal mucosa has an average surface area of 30 to 200 square meters. This massive surface area allows for efficient nutrient uptake. Each villus contains a network of capillaries and lymphatic vessels called lacteals.

Different nutrients follow specific pathways during absorption. Amino acids and carbohydrates enter the bloodstream through the capillaries. Lipids are absorbed into the lacteals. Some nutrients move through the wall via diffusion or active transport. For example, glucose and amino acids use co-transport. Fructose is absorbed through facilitated diffusion. Water is absorbed throughout the intestine via osmosis. Specific items like iron and folate are absorbed primarily in the duodenum. Vitamin B12 requires a protein called intrinsic factor to be absorbed in the ileum.

The development of the small intestine is a remarkable biological event. It begins from the midgut of the primitive gut tube. By the fifth week of life, the ileum grows very rapidly. This growth creates a U-shaped fold called the primary intestinal loop. This loop grows so fast that it protrudes through the umbilicus. By week 10, the loop retracts back into the abdomen. During this time, the intestine rotates anticlockwise and then rotates another 180 degrees. This complex movement creates the necessary twisted shape for the digestive system.