The digestive system
• the gastrointestinal (GI) tract—also called the digestive tract—and
• the liver,
• pancreas, and
• gallbladder.
The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. The hollow organs that make up the GI tract are:
• the mouth,
• esophagus,
• stomach,
• small intestine,
• large intestine—which includes the rectum—and anus.
Food enters the mouth and passes to the anus through the hollow organs of the GI tract. The liver, pancreas, and gallbladder are the solid organs of the digestive system. The digestive system helps the body digest food.
Bacteria in the GI tract, also called gut flora or microbiome, help with digestion. Parts of the nervous and circulatory systems also play roles in the digestive process. Together, a combination of nerves, hormones, bacteria, blood, and the organs of the digestive system completes the complex task of digesting the foods and liquids a person consumes each day.
Food begins its journey through the digestive system in the mouth where it is chopped into small pieces and moistened by saliva before the tongue and other muscles push it into the pharynx.
The food moves through the GI tract by a process called Peristalsis which looks like an ocean wave travelling through the muscle as it contracts and relaxes.
The pharynx is a funnel -shopped tube that connects the posterior end of the month to the esophagus.
The esophagus is a muscular tube connecting the pharynx to the stomach.
In the stomach the food is mixed with digestive juices causing large molecules of food to break down into smaller molecules. The body then absorbs these smaller molecules through the walls of the small intestine into the bloodstream which delivers then to the rest of the body.
The small intestine absorbs most digestive food molecules as well as water and minerals and passes then to the other parts of the body for storage or further chemical change.
When the food arrives in the large intestine, most of its nutrients have already been absorbed through the GI tract and there it is fermented by the gut flora, the remaining water is absorbed and the indigestible substances form the faeces which are removed in a process known as defecation so that they do not accumulate inside the gut.