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The gastrointestinal system, also known as the GI tract or digestive tract, is a series of hollow organs that connect to digest and move food through the body. The GI tract includes the mouth, oesophagus, stomach, small intestine, and large intestine. The small intestine is the longest part of the gastrointestinal tract, measuring 22 feet long. The large intestine is the final step in the digestive process, including the colon, rectum, and anus. The GI tract is lined with muscles and nerves that work together to move food through the body. This process is called peristalsis, which involves the contraction and relaxation of muscles to push food through the intestines.
| Characteristics | Values |
|---|---|
| Definition | The gastrointestinal system comprises the gastrointestinal tract (GI tract) and accessory organs. |
| GI Tract | A series of hollow organs joined in a long, twisting tube from the mouth to the anus. |
| Hollow Organs | Mouth, oesophagus, stomach, small intestine, large intestine, and anus. |
| Accessory Organs | Teeth, tongue, and glandular organs such as salivary glands, liver, gallbladder, and pancreas. |
| Function | Ingestion and digestion of food, nutrient absorption, secretion of water and enzymes, and excretion of waste products. |
| Length | Approximately 9 meters (30 feet) long. |
| Muscle Layers | An inner circular layer and a longitudinal outer layer. |
| Muscle Function | The inner circular layer prevents food from travelling backward, and the longitudinal layer shortens the tract. |
| Peristalsis | The automatic wave-like movement of the muscles that line the gastrointestinal tract, propelling food and fluids forward. |
| Segmentation | Circular muscles in the intestines contract to move food back and forth, mixing it with gastric juices to aid digestion. |
| Tonic Contractions | Smooth muscle in the intestinal wall produces tonic contractions that maintain organ dimension against an imposed load. |
| Forceful Contractions | Smooth muscle produces forceful contractions that propel food along the gastrointestinal tract. |
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What You'll Learn
The gastrointestinal tract
The human gastrointestinal (GI) tract, also known as the digestive tract, is a series of hollow organs that connect to digest and move food through the body. The GI tract includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine. The small intestine is the longest part of the gastrointestinal tract, measuring 22 feet long. The large intestine is the final step in the digestive process and includes the colon, rectum, and anus.
The upper gastrointestinal tract consists of the mouth, pharynx, oesophagus, stomach, and duodenum. The demarcation between the upper and lower tracts is the suspensory muscle of the duodenum, which is also the division used by clinicians to describe gastrointestinal bleeding as being of "upper" or "lower" origin. The duodenum is the first part of the small intestine, followed by the jejunum and the ileum.
The lower gastrointestinal tract includes most of the small intestine and all of the large intestine. The large intestine is subdivided into the cecum, ascending, transverse, descending, and sigmoid colons, rectum, and anal canal. The small intestine is a tubular structure around 6 to 7 metres long, while the entire human GI tract is about 9 metres long.
The GI tract is lined with muscles and nerves. Food moves through the GI tract by a process called peristalsis, which is the automatic wave-like movement of the muscles that line the tract. The nerves of the ENS release substances that speed up or delay the movement of food and the production of digestive juices. The nerves also send signals to control the actions of the gut muscles to contract and relax to push food through the intestines. The circular layer of muscle prevents food from travelling backward, while the longitudinal layer shortens the tract.
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The role of smooth muscle
The gastrointestinal (GI) system comprises the GI tract and accessory organs. The GI tract consists of the oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine, and anal canal. The small intestine is the longest part of the gastrointestinal tract, measuring 22 feet long. The large intestine is the final step in the digestive process and includes the colon, rectum, and anus.
The GI tract is a series of hollow organs that connect to digest and move food through the body. The hollow organs that make up the GI tract contain a layer of muscle that enables their walls to move. This layer of muscle is known as smooth muscle. Smooth muscle is derived from the embryonic mesoderm. It is a thin muscle that makes up the muscularis mucosae, a layer of the GI tract that aids the passing of material and enhances the interaction between the epithelial layer and the contents of the lumen by agitation and peristalsis.
The muscular layer of the GI tract consists of an inner circular layer and a longitudinal outer layer. The circular layer prevents food from travelling backward, while the longitudinal layer shortens the tract. The inner circular layer is helical with a steep pitch, and the outer longitudinal layer is helical with a much shallower pitch. The stomach contains an additional inner oblique muscular layer to aid with grinding and mixing food.
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Peristalsis
Problems with peristalsis can be related to the muscles or nervous system and can occur anywhere in the GI tract. Medications, injuries, infections, diseases, hormone fluctuations, and electrolyte imbalances can all affect the muscles or nerves involved in peristalsis. Alterations in peristalsis function have been implicated in motility disorders such as gastroesophageal reflux disease (GERD) and small intestinal bacterial overgrowth (SIBO).
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Gastrointestinal muscle issues
The gastrointestinal (GI) system comprises the GI tract and accessory organs. The GI tract consists of the oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine, and anal canal. The accessory organs include the teeth, tongue, and glandular organs such as salivary glands, liver, gallbladder, and pancreas. The GI tract is a series of hollow organs that connect to digest and move food through the body.
The GI tract contains a layer of muscle that enables its walls to move. The muscle behind the food contracts and squeezes the food forward, while the muscle in front of the food relaxes to allow the food to move. This process is called peristalsis, which is the automatic wave-like movement of the muscles that line the GI tract. Peristalsis moves food through the digestive system, beginning in the throat when swallowing and continuing through the oesophagus, stomach, and intestines during digestion. Peristalsis is a type of involuntary muscle movement. When peristalsis moves backward instead of forward, it is called retroperistalsis, antiperistalsis, or reverse peristalsis, which occurs when the vomiting reflex is triggered.
Problems with peristalsis can be related to muscles or the nervous system, and can occur anywhere in the GI tract. Medications, injuries, infections, diseases, hormone fluctuations, and electrolyte imbalances can all affect the muscles or nerves involved in peristalsis. Gastrointestinal issues such as constipation and diarrhoea can be related to peristalsis problems.
Gastrointestinal involvement is frequently observed in myotonic muscular dystrophy (MD) patients, and digestive complaints may be the first sign of the disease. Dysphagia, heartburn, emesis, regurgitation, coughing while eating, and dyspepsia are the most common complaints involving the upper digestive tract, while abdominal pain and bloating, changes in bowel habits (diarrhoea or constipation), and dyschezia are common signs of impairment of the lower digestive tract. These clinical manifestations have generally been attributed to motility disorders caused by striated and, more rarely, smooth muscle damage.
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Accessory organs
The gastrointestinal (GI) system comprises the GI tract and accessory organs. The GI tract is a series of hollow organs that connect to digest and move food through the body. The accessory organs include the teeth, tongue, and glandular organs such as the salivary glands, liver, gallbladder, and pancreas.
The GI tract is a long tube that runs from the mouth to the anus. It includes the oral cavity, pharynx, oesophagus, stomach, small intestine, and large intestine. The small intestine is the longest part of the gastrointestinal tract, measuring 22 feet long. The large intestine is the final step in the digestive process and includes the colon, rectum, and anus.
The accessory organs of the GI system support the ingestion, digestion, and absorption of food, as well as the secretion of water and enzymes, and the excretion of waste products. The liver, for example, is an accessory organ that supports digestion by delivering bile and enzymes to help the small intestine break down food. The liver is both an organ and a gland, located on the right side of the body under the ribs.
The pancreas is another accessory organ that is located behind the stomach and in front of the spine, also on the right side of the body. It produces digestive fluids that are mixed with food in the small intestine. The gallbladder is tucked below the liver and connected to the bile ducts inside and outside of it. It releases bile to aid in digestion.
The tongue and teeth are also accessory organs of the GI system. They play a role in the mechanical processing of food and sensory analysis of food material before swallowing.
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Frequently asked questions
The gastrointestinal tract, or GI tract, is a series of hollow organs that connect to digest and move food through your body. It includes the mouth, oesophagus, stomach, small intestine, and large intestine.
The gastrointestinal muscle is a layer of muscle that enables the walls of the large, hollow organs of the GI tract to move. The muscle behind the food contracts and relaxes to push food and liquid through the GI tract.
Peristalsis is the automatic wave-like movement of the muscles that line the GI tract. It moves food through the digestive system, beginning in the throat when you swallow, and continuing through the oesophagus, stomach, and intestines.
The muscular layer of the gastrointestinal muscle consists of an inner circular layer and a longitudinal outer layer. The circular layer prevents food from travelling backward, and the longitudinal layer shortens the tract.
Smooth muscle in the intestinal wall produces tonic contractions that maintain organ dimension against an imposed load, such as a bolus of food. Forceful contractions also occur to propel the bolus along the GI tract.
