Jejunum

Your body has a long tube inside. This part is in the middle. It sits between two other parts. It helps take food from your meals.

The inside has tiny finger shapes. These shapes help grab good things. They take nutrients from the food. This helps your body stay strong.

Smooth muscles help move the food. The muscles push the food along. This keeps everything moving well.

This part is often quite wide. It is also very long. It is a very busy part!

The jejunum is the middle part of the small intestine. It sits between the duodenum and the ileum. In humans, it makes up about two-fifths of the small intestine. This part is very busy. It helps your body take in nutrients from food.

Inside the jejunum, there are many large circular folds. These are called plicae circulares. These folds help make more space for food to touch the walls. The walls also have tiny finger-like shapes called villi. These villi are longer here than in other parts. The villi help grab small pieces of food.

Special cells called enterocytes take these nutrients in. Some things, like sugar, move in a simple way. Other things, like vitamins, use a way called active transport. This means the cells use power to move them. Once inside, the nutrients go to the liver through a vein.

Smooth muscles in the walls help move food along. This set of steps is called peristalsis. A thin tissue called mesentery holds the tube in place. This lets the bowel move around inside your belly. The name comes from a Latin word for fasting.

The jejunum is a very important part of the body. It is the second part of the small intestine. Most higher vertebrates have one, including birds, reptiles, and mammals. It sits between the duodenum and the ileum. In adult humans, it is quite long. It makes up about two-fifths of the small intestine.

This part of the body has a big job. It absorbs small nutrient molecules from the food you eat. First, enzymes in the duodenum digest the food. Then, special cells called enterocytes grab the nutrients. Some things like sugar move in a simple way. Other things like vitamins use active transport. This means the cells use energy to move them.

The name of this part comes from history. It comes from the Latin word jējūnus. This word means "fasting." People named it this because it was often empty. After death, this part often had no food in it. This happened because of its intense peristalsis. Peristalsis is how muscles move food along.

There are many specific details about its structure. The inside has large circular folds called plicae circulares. These folds increase the surface area for absorption. There are also finger-like projections called villi. These villi are much longer here than elsewhere. The jejunum is usually wider than the ileum. It also has less fat in its mesentery.

You can think of it like a busy hallway. The folds and villi make the hallway very wide. This gives more room for people to pass through. The mesentery acts like a flexible rope. It holds the bowel but lets it move. Smooth muscles act like waves to push food. This helps everything flow to the liver.

The jejunum is the second part of the small intestine. It is found in humans and most higher vertebrates. This group includes mammals, reptiles, and birds. The jejunum plays a vital role in the digestive system. It sits between the duodenum and the ileum. Its main job is to absorb nutrients from food. This process is essential for keeping the body healthy.

To understand how it works, we must look at the process of absorption. First, enzymes in the duodenum digest food into small molecules. These molecules then enter the jejunum. The lining of the jejunum is made of specialized cells called enterocytes. These cells grab the small nutrient particles. Some nutrients, like the sugar fructose, move through passive transport. Other nutrients, such as vitamins and glucose, use active transport. Active transport means the cells use energy to move these molecules. Once absorbed, most nutrients enter the enterohepatic circulation. They then travel to the liver via the hepatic portal vein.

The structure of the jejunum is built specifically for this work. The interior surface is covered in many tiny projections called villi. These villi look like small, finger-like growths. They greatly increase the surface area available for absorption. The cells on these villi also have even smaller microvilli. Additionally, the submucosa contains large circular folds called plicae circulares. These folds are best developed in the jejunum. By having many folds and villi, the jejunum can absorb much more than a smooth tube could.

There are several ways to distinguish the jejunum from other parts of the intestine. While there is no clear anatomical line between the jejunum and the ileum, there are subtle differences. The jejunum typically has a larger diameter than the ileum. It also has less fat inside its mesentery. The villi in the jejunum are much longer than those in the duodenum or the ileum. Furthermore, the jejunum contains very few Brunner's glands or Peyer's patches. Peyer's patches are lymphoid nodules found mostly in the ileum. However, the jejunum does have some lymph nodes in its mesentery.

The history of the name "jejunum" is quite interesting. It comes from the Latin word jējūnus, which means "fasting." Early observers noticed this part of the intestine was often empty. This was frequently seen in bodies following death. The area was void of food because of its intense activity. This movement is called peristalsis. Peristalsis is a process where circular and longitudinal smooth muscles contract. These muscles work together to push food along the tract. Because the jejunum is so active, it often clears itself quickly.

In terms of scale, the jejunum is a significant portion of the digestive tract. In adult humans, the small intestine is quite long. The jejunum makes up about two-fifths of that total length. The environment inside the jejunum is also very specific. The pH level usually stays between 7 and 8. This means the environment is neutral or slightly alkaline. To keep the bowel mobile within the abdomen, it is suspended by the mesentery. This tissue allows the intestine to move freely while staying in place.

While the term "jejunum" is standard for higher vertebrates, other animals use different names. In fish, the divisions of the small intestine are not as clear. Scientists may use the terms "middle intestine" or "mid-gut" instead. This shows how different biological systems adapt to their environments. Regardless of the name, the function of absorbing nutrients remains a core part of life. The jejunum serves as a highly specialized bridge in the complex system of digestion.