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Gastrointestinal tract
Stomach colon rectum diagram-en.svg
Diagram of stomach, intestines and rectum in the average human
Latin Tractus digestorius (mouth to anus),
canalis alimentarius (esophagus to large intestine),
canalis gastrointestinales (stomach to large intestine)
System Digestive system

The gastrointestinal system is the body system that eats and digests food; it is also called a digestive system.

By breaking down food into simple chemicals that can be absorbed by other parts of the body so the chemicals can be used for energy and building the body, it also gets rid of waste after digestion. The gastrointestinal system starts at the lips and ends at the anus. Animals like worms, insects, mammals, birds, fish, and people all have digestive systems.

The gastrointestinal tract is the gut and other organs that help us digest food.

The gut is the round tubes that food goes through and is digested. The parts of the human, and some other animals, gut system are:

Other organs that are part of the gastrointestinal system but are not part of the gut are:

Food does not go through these organs. But they help the gut digest the food. They also have other work. For example, the pancreas, thyroid, liver, and parathyroids are also endocrine glands that make hormones like insulin.

There are many diseases that affect the gastrointestinal system. Doctors who study the gastrointestinal tract are called gastroenterologists.

Human gastrointestinal tract

Structure

Blausen 0432 GastroIntestinalSystem
Illustration of human gastrointestinal tract

The structure and function can be described both as gross anatomy and as microscopic anatomy or histology. The tract itself is divided into upper and lower tracts, and the intestines small and large parts.

Upper gastrointestinal tract

The upper gastrointestinal tract consists of the mouth, pharynx, esophagus, stomach, and duodenum. The exact demarcation between the upper and lower tracts is the suspensory muscle of the duodenum. This differentiates the embryonic borders between the foregut and midgut, and is also the division commonly used by clinicians to describe gastrointestinal bleeding as being of either "upper" or "lower" origin. Upon dissection, the duodenum may appear to be a unified organ, but it is divided into four segments based upon function, location, and internal anatomy. The four segments of the duodenum are as follows (starting at the stomach, and moving toward the jejunum): bulb, descending, horizontal, and ascending. The suspensory muscle attaches the superior border of the ascending duodenum to the diaphragm.

The suspensory muscle is an important anatomical landmark which shows the formal division between the duodenum and the jejunum, the first and second parts of the small intestine, respectively. This is a thin muscle which is derived from the embryonic mesoderm.

Lower gastrointestinal tract

The lower gastrointestinal tract includes most of the small intestine and all of the large intestine. In human anatomy, the intestine (bowel, or gut. Greek: éntera) is the segment of the gastrointestinal tract extending from the pyloric sphincter of the stomach to the anus and, as in other mammals, consists of two segments, the small intestine and the large intestine. In humans, the small intestine is further subdivided into the duodenum, jejunum and ileum while the large intestine is subdivided into the cecum, ascending, transverse, descending and sigmoid colon, rectum, and anal canal.

Small intestine

The small intestine begins at the duodenum and is a tubular structure, usually between 6 and 7 m long. Its mucosal area in an adult human is about 30 m2 (320 sq ft). The combination of the circular folds, the villi, and the microvilli increases the absorptive area of the mucosa about 600-fold, making a total area of about 250 square meters for the entire small intestine. Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the bloodstream. There are three major divisions:

  1. Duodenum: A short structure (about 20–25 cm long) which receives chyme from the stomach, together with pancreatic juice containing digestive enzymes and bile from the gall bladder. The digestive enzymes break down proteins, and bile emulsifies fats into micelles. The duodenum contains Brunner's glands which produce a mucus-rich alkaline secretion containing bicarbonate. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in the chyme.
  2. Jejunum: This is the midsection of the small intestine, connecting the duodenum to the ileum. It is about 2.5 m long, and contains the circular folds also known as plicae circulares, and villi that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here.
  3. Ileum: The final section of the small intestine. It is about 3 m long, and contains villi similar to the jejunum. It absorbs mainly vitamin B12 and bile acids, as well as any other remaining nutrients.
Large intestine

The large intestine also called the colon, consists of the cecum, rectum, and anal canal. It also includes the appendix, which is attached to the cecum. The colon is further divided into:

  1. Cecum (first portion of the colon) and appendix
  2. Ascending colon (ascending in the back wall of the abdomen)
  3. Right colic flexure (flexed portion of the ascending and transverse colon apparent to the liver)
  4. Transverse colon (passing below the diaphragm)
  5. Left colic flexure (flexed portion of the transverse and descending colon apparent to the spleen)
  6. Descending colon (descending down the left side of the abdomen)
  7. Sigmoid colon (a loop of the colon closest to the rectum)
  8. Rectum
  9. Anus

The main function of the large intestine is to absorb water. The area of the large intestinal mucosa of an adult human is about 2 m2 (22 sq ft).


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