Gastrointestinal tract

Your body has a long tube inside.

It goes from your mouth to your bottom. This tube helps turn food into energy. It also gets rid of waste.

The tube has many parts. It has a stomach and two kinds of intestines. Small parts in the tube soak up food. Other parts take in water. Tiny living things live in your gut too. This long tube helps you grow.

Your body has a long, continuous tube inside.

It goes from your mouth to your anus. This is called the gastrointestinal tract. It is one of the biggest systems in your body. Its main job is to take food and extract nutrients. Nutrients are the good things your body needs to grow. The tract also absorbs energy from your food.

The tract has many important parts. It starts with the mouth and esophagus. The esophagus is a tube that leads to the stomach. Next are the intestines. The small intestine is very long. It is about 6 to 7 meters long. It uses tiny parts called villi to soak up food. The large intestine is shorter. It helps the body absorb water and salts.

Inside the tube, tiny living things live. We call this the gut microbiota. It has about 4,000 different types of bacteria and viruses. These tiny guests help keep your body healthy.

The walls of the tube have four layers. These layers help move food along in a way called peristalsis. This movement pushes food through the whole tube.

Your body contains a long, continuous passageway called the gastrointestinal tract.

This system is one of the largest in the human body. It runs from your mouth all the way to your anus. Its main job is to digest food to get nutrients. These nutrients provide the energy your body needs to work. The tract also helps remove waste as feces.

This system works through a step-by-step process. First, food enters through the mouth and travels down the esophagus. It then enters the stomach to be broken down. Next, the food moves into the small intestine. In the duodenum, the first part of the small intestine, enzymes and bile help break things down further. The small intestine then absorbs sugars, proteins, and fats into your blood. Finally, the large intestine absorbs water and salts from what is left.

Scientists study how this tract forms during growth. In a developing human embryo, the gut starts as a structure called the endoderm. Around the sixteenth day, the embryo begins to fold. This folding pinches off a piece of the yolk sac to create the primitive gut. This primitive gut eventually grows into three main segments. These segments are called the foregut, midgut, and hindgut. These names reflect where each part comes from during early development.

There are many amazing facts about the scale of this system. The small intestine is a very long tube. It can be about 6 to 7 meters long in an adult. To absorb nutrients better, it uses tiny structures called villi. These increase the surface area by about 600 times. The large intestine is shorter, at about 1.5 meters long. Inside your gut, there are about 4,000 different types of bacteria and viruses. This collection of tiny living things is called the gut microbiota.

The walls of the tract are built with four special layers. These layers include the mucosa, submucosa, muscular layer, and the adventitia.

The muscular layer is very important for movement. It uses a way of working called peristalsis. This is a series of coordinated muscle contractions. These contractions push food through the tube in one direction. This ensures that your food moves steadily through the entire system.

The gastrointestinal tract, often called the GI tract or alimentary canal, is a continuous passageway. It runs from the mouth to the anus. This system is one of the largest in the human body. Its primary purpose is to digest food to extract nutrients and absorb energy. Once nutrients are removed, the remaining waste is expelled as feces.

The tract is divided into the upper and lower gastrointestinal tracts. The upper tract includes the mouth, pharynx, esophagus, stomach, and the duodenum. The duodenum is the first part of the small intestine. A thin muscle called the suspensory muscle of the duodenum marks the boundary. This muscle connects the duodenum to the jejunum, which is the next section. The lower tract consists of the rest of the small intestine and the entire large intestine. This division is important for clinicians when they identify the origin of gastrointestinal bleeding.

The small intestine is a long, tubular structure measuring about 6 to 7 meters in length. It is divided into three parts: the duodenum, the jejunum, and the ileum. The duodenum is roughly 20 to 25 cm long. It receives chyme, which is partially digested food, from the stomach. In this section, pancreatic juice and bile from the gallbladder enter the tract. Enzymes break down proteins, while bile emulsifies fats into micelles. Brunner's glands in the duodenum produce an alkaline mucus. This secretion, along with bicarbonate from the pancreas, neutralizes stomach acids. The jejunum is the midsection where sugars, amino acids, and fatty acids are absorbed. The ileum is the final 3-meter section. It primarily absorbs vitamin B12 and bile acids.

The large intestine is much shorter, measuring about 1.5 meters. It forms an arch starting at the cecum and ending at the rectum. The colon is the longest part of this system. Its main job is to absorb water and salts. The large intestine includes the cecum, the appendix, and several parts of the colon. These parts are the ascending, transverse, descending, and sigmoid colons. The transverse colon runs across the abdomen. The descending colon moves down the left side. Finally, the waste moves through the rectum and the anal canal.

The structure of the gut wall consists of four concentric layers. The innermost layer is the mucosa, which surrounds the lumen, or open space. The mucosa contains the epithelium, which handles absorption and secretion. Below this is the submucosa, a layer of connective tissue containing blood vessels and nerves. The third layer is the muscularis externa, or muscular layer. This layer contains an inner circular layer and an outer longitudinal layer. The circular layer prevents food from moving backward. The longitudinal layer helps shorten the tract. In the stomach, a third oblique muscle layer helps grind food. Between these muscle layers is the myenteric plexus, which helps control movement.

Movement through the tract happens via peristalsis. This is a series of coordinated muscle contractions that propel food forward. These contractions are managed by the enteric nervous system, which is a self-contained nervous system within the gut. Specialized pacemaker cells called myenteric interstitial cells of Cajal initiate this activity. The gut also contains a massive collection of microorganisms called the microbiota. This includes around 4,000 different strains of bacteria, archaea, viruses, and eukaryotes. These organisms play vital roles in metabolism and immune health.

The development of the gut begins in the human embryo. Around the sixteenth day, the embryo folds to create the primitive gut. This structure is derived from the endoderm, a primary layer of cells. The primitive gut eventually patterns into three segments: the foregut, midgut, and hindgut. The foregut gives rise to the esophagus, stomach, and the first parts of the duodenum. The midgut forms the lower duodenum, the jejunum, ileum, cecum, and part of the colon. The hindgut forms the final third of the transverse colon and the descending colon. This embryological origin determines the blood supply for each section through specific arteries.