What does the intestines do in the digestive system

Your small intestine is the longest part of the human digestive system. It's 20 feet long. After food leaves your stomach, it passes into your small intestine. This is where most of the digestive process takes place.

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Parts of the small intestine
Moving on through
Common disorders of the small intestine
Small Intestine
Large Intestine
Rectum and Anus
What are the three main functions of the intestines?
What does the intestines do in simple terms?
Which intestine is responsible for digestion?

Parts of the small intestine

The upper part of your small intestine is the duodenum. It's the widest part of your small intestine and also the shortest. It's about 10 inches long. When food moves into your duodenum, it mixes with digestive enzymes that your pancreas secretes. These enzymes break down the largest molecules of food, such as proteins and starches. They also neutralize stomach acid. Bile is a substance that breaks down the fats in foods. It also empties into your duodenum by the common bile duct. Some minerals are absorbed here, such as iron and folate.

The middle part of your small intestine is the jejunum. The jejunum absorbs most of your nutrients: carbohydrates, fats, minerals, proteins, and vitamins.

The lowest part of your small intestine is the ileum. This is where the final parts of digestive absorption take place. The ileum absorbs bile acids, fluid, and vitamin B-12. Finger-shaped structures called villi line the entire small intestine. They help absorb nutrients.

Moving on through

Contractions move food through your small intestine. After you eat a meal, your small intestine contracts in a random, unsynchronized manner. Food moves back and forth and mixes with digestive juices. Then stronger, wave-like contractions push the food farther down your digestive system. These movements are known as peristalsis. Your enteric nervous system controls the movements in your small intestine. This is a network of nerves that runs from your esophagus to your anus.

After food leaves your small intestine, contractions push any food that remains in your digestive tract into your large intestine. Water, minerals, and any nutrients are then absorbed from your food. The leftover waste is formed into a bowel movement.

Common disorders of the small intestine

Many conditions can damage or impair your small intestine. Among them are:

Irritable bowel syndrome (IBS). This is a gastrointestinal (GI) disorder. It has many symptoms, including belly pain and cramps, diarrhea or constipation, and bloating. These symptoms generally occur without any visible signs of damage or disease to your digestive tract.
Celiac disease. This is an allergy to gluten, a protein found in wheat, barley, and rye. When your body digests gluten, your immune system attacks the villi lining your small intestine. Without treatment, your body won't be able to absorb nutrients correctly and you may become malnourished.
Crohn’s disease. This is a chronic disease that causes inflammation and irritation in your digestive tract. This can cause ulcers and injury to the intestines. Crohn’s disease most often affects the ileum, a part of your small intestine but it can occur anywhere in the GI tract.
Small bowel obstruction. This is a narrowing of your intestine that prevents food from getting through. It most often affects the small intestine. Small bowel obstruction is often caused by hernias. It is also caused by bands of tissue (adhesions) that can twist or pull your intestine or tumors. A complete bowel obstruction is an emergency. It means that the intestine is completely blocked. It needs medical care right away.

Small Intestine

The small intestine extends from the pyloric sphincter to the ileocecal valve, where it empties into the large intestine. The small intestine finishes the process of digestion, absorbs the nutrients, and passes the residue on to the large intestine. The liver, gallbladder, and pancreas are accessory organs of the digestive system that are closely associated with the small intestine.

The small intestine is divided into the duodenum, jejunum, and ileum. The small intestine follows the general structure of the digestive tract in that the wall has a mucosa with simple columnar epithelium, submucosa, smooth muscle with inner circular and outer longitudinal layers, and serosa. The absorptive surface area of the small intestine is increased by plicae circulares, villi, and microvilli.

Exocrine cells in the mucosa of the small intestine secrete mucus, peptidase, sucrase, maltase, lactase, lipase, and enterokinase. Endocrine cells secrete cholecystokinin and secretin.

The most important factor for regulating secretions in the small intestine is the presence of chyme. This is largely a local reflex action in response to chemical and mechanical irritation from the chyme and in response to distention of the intestinal wall. This is a direct reflex action, thus the greater the amount of chyme, the greater the secretion.

Large Intestine

The large intestine is larger in diameter than the small intestine. It begins at the ileocecal junction, where the ileum enters the large intestine, and ends at the anus. The large intestine consists of the colon, rectum, and anal canal.

The wall of the large intestine has the same types of tissue that are found in other parts of the digestive tract but there are some distinguishing characteristics. The mucosa has a large number of goblet cells but does not have any villi. The longitudinal muscle layer, although present, is incomplete. The longitudinal muscle is limited to three distinct bands, called teniae coli, that run the entire length of the colon. Contraction of the teniae coli exerts pressure on the wall and creates a series of pouches, called haustra, along the colon. Epiploic appendages, pieces of fat-filled connective tissue, are attached to the outer surface of the colon.

Unlike the small intestine, the large intestine produces no digestive enzymes. Chemical digestion is completed in the small intestine before the chyme reaches the large intestine. Functions of the large intestine include the absorption of water and electrolytes and the elimination of feces.

Rectum and Anus

The rectum continues from the sigmoid colon to the anal canal and has a thick muscular layer. It follows the curvature of the sacrum and is firmly attached to it by connective tissue. The rectum ends about 5 cm below the tip of the coccyx, at the beginning of the anal canal.

The last 2 to 3 cm of the digestive tract is the anal canal, which continues from the rectum and opens to the outside at the anus. The mucosa of the rectum is folded to form longitudinal anal columns. The smooth muscle layer is thick and forms the internal anal sphincter at the superior end of the anal canal. This sphincter is under involuntary control. There is an external anal sphincter at the inferior end of the anal canal. This sphincter is composed of skeletal muscle and is under voluntary control.

What are the three main functions of the intestines?

The large intestine has 3 primary functions: absorbing water and electrolytes, producing and absorbing vitamins, and forming and propelling feces toward the rectum for elimination.

What does the intestines do in simple terms?

It helps to further digest food coming from the stomach. It absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water from food so they can be used by the body. The small intestine is part of the digestive system.

Which intestine is responsible for digestion?

Small Intestine (Small Bowel): Almost 20 feet long, the small intestine is the workhorse of the digestive system. It will continue to break down food with enzymes released by the pancreas and bile released from the liver.