The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus.
Digestion is necessary for absorbing nutrients from food and occurs through two processes: mechanical and chemical digestion.
The organs of the digestive system can be divided into upper and lower digestive tracts. The upper digestive tract consists of the esophagus, stomach, and the small intestine; the lower tract includes all of the large intestine, the rectum, and anus.
The enteric nervous system (ENS) is a subdivision of the autonomic nervous system (ANS) that directly controls the gastrointestinal system.
The digestive system functions via a system of long reflexes, short reflexes, and extrinsic reflexes from gastrointestinal (GI) peptides that work together.
The peritoneum, the serous membrane that forms the lining of the abdominal cavity, covers most of the intra-abdominal organs.
The mouth receives and mechanically breaks down food, produces saliva, and is the first portion of the alimentary canal.
The pharynx is part of the digestive and respiratory systems and consists of three main parts: the nasopharynx, oropharynx, and laryngopharynx.
The esophagus is a muscular tube that moves food from the pharynx to the stomach via peristalsis.
The mucosa, composed of simple epithelium cells, is the innermost layer of the gastrointestinal (GI) tract. It is the absorptive and secretory layer of the GI tract.
The submucosa is a dense, irregular layer of connective tissue with large blood vessels, lymphatics, and nerves that supports the mucosa.
The muscularis is responsible for the segmental contractions and peristaltic movements in the gastrointestinal (GI) tract.
Serosa consists of a secretory epithelial layer and a thin connective tissue layer that reduce the friction from muscle movements.
The stomach is divided into four sections, each of which has different cells and functions.
The layers of the stomach produce mucus to protect itself, enyzmes to break down the food for digestion, and muscles to churn the food.
The movement and flow of chemicals into the stomach is controlled by the autonomic nervous system and various digestive system hormones.
The liver makes bile, which is essential for the digestion of fats.
The liver is located in the abdomen and has four lobes.
Hepatocytes are the main tissue cells of the liver. The gallbladder contains the mucosa, muscularis, perimuscular, and serosa layers.
In the hepatic portal system, the liver receives a dual blood supply from the hepatic portal vein and the hepatic arteries.
The liver is thought to be responsible for up to 500 separate functions.
Bile is a fluid produced by the liver that aids the process of digestion and the absorption of lipids in the small intestine.
The gallbladder stores bile produced by the liver.
The gallbladder, a hollow organ that stores bile, is located under the liver.
The pancreas is a gland organ in the digestive and endocrine systems.
The pancreas lies in the epigastrium or upper central region of the abdomen and can vary in shape.
The pancreas serves digestive and endocrine functions, and it is composed of two types of tissue: islets of Langerhans and acini.
Pancreatic fluid contains digestive enzymes that help to further break down the carbohydrates, proteins, and lipids in the chyme.
The small intestine is the part of the gastrointestinal tract where much of the digestion and absorption of food takes place.
The small intestine wall has four layers: the outermost serosa, muscularis, submucosa, and innermost mucosa.
The small intestine uses different enzymes and processes to digest proteins, lipids, and carbohydrates.
The large intestine absorbs water from the remaining indigestible food matter and compacts feces prior to defecation.
The large intestine has taeniae coli and invaginations (the intestinal glands), unlike the small intestines.
The largest bacteria ecosystem in the human body is in the large intestine, where it plays a variety of important roles.
In the large intestine, a host of microorganisms known as gut flora help digest the remaining food matter and create vitamins.
The large intestine absorbs water from the chyme and stores feces until they can be defecated.
Defecation is a combination of voluntary and involuntary processes that create enough force to remove waste material from the digestive system.
Chemical digestion is the enzyme-mediated, hydrolysis process that breaks down large macronutrients into smaller molecules.
The chemical breakdown of the macromolecules contained in food is completed by various enzymes produced in the digestive system.
The absorption of nutrients occurs partially by diffusion through the wall of the small intestine.
Glucose, amino acids, fats, and vitamins are absorbed in the small intestine via the action of hormones and electrolytes.
The cephalic phase of gastric secretion occurs before food enters the stomach due to neurological signals.
The gastric phase is a period in which swallowed food activates gastric activity in the stomach.
The intestinal phase occurs in the duodenum as a response to the arriving chyme, and it moderates gastric activity via hormones and nervous reflexes.
There are five main hormones that aid and regulate the digestive system in mammals.