Human Digestive System

Nutrition is the comprehensive biological process by which organisms ingest, digest, absorb, and assimilate food to provide energy and maintain bodily functions.

Fibre is undigestible and moves through the digestive tract without being broken down by enzymes. Many foods contain both soluble and insoluble fiber. Soluble fibre dissolves easily in water and takes on a soft, gel-like texture in the intestines. Insoluble fibre, on the other hand, passes essentially unchanged through the intestines.

All the  hormones control digestion .

Protease and bromelain are the two enzymes, along with the gastric acid contained in the stomach, responsible for the breakdown of protein. The protein found in meat products is very difficult to breakdown and takes the digestive system a long time to perform the task. When protein is sufficiently broken down into its smaller molecules called amino acids, the body can then utilize them to rebuild soft tissue.

Amylase is an enzyme that catalyses the breakdown of starch into sugar. Amylase is present in human saliva, where it begins the chemical process of digestion. Foods that contain much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns some of their starch into sugar in the mouth.

Taking food into the mouth is called ingestion. We use lips, tongue and teeth. The tongue is also important in tasting food, to tell  whether it is good to eat; if not it will be ejected from the mouth rather than swallowed.

Papain is the enzyme found in papaya that is valuable for increased immune system function and has a soothing effect on the stomach by aiding in protein digestion. It can also help alleviate gas, bloating, diarrhea and cramps associated with incomplete digestion

Rugae are the extensive folds in the stomach lining. These folds can stretch to accommodate an increase in stomach volume during consumption of a big meal.

The Suspensory muscle of duodenum or Ligament of Treitz (named after Vلclav Treitz) connects the duodenum of the small intestines to the diaphragm. It contains a slender band of skeletal muscle from the diaphragm and a fibromuscular band of smooth muscle from the horizontal and ascending parts of the duodenum.

All of the above control the digestive process.

Amino-acids are absorbed into the villus cells by active transport and pass out of the opposite side by diffusion. In a fetus a newly born baby , some entire undigested proteins can be absorbed by pinocytosis. This is how babies are able to absorb some of their mother's antibodies from the milk. This can also happen to a small extent in adults.

The gall bladder stores and concentrates bile which emulsifies fats making them easier to break down by the pancreatic juices.

The inner layer of the stomach wall, the mucosa, is specialized to produce large quantities of gastric juice, up to 2 dm each day. Gastric juice contains protease and lipase, as well as hydrochloric acid (HCL).To protect the cells in the wall from damage by the acid and proteases, they are covered with a slimy coat of mucus containing hydrogen carbonate ions which neutralize the acid.

Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material (feces) from the digestive tract via the anus.

The stomach lies below the diaphragm and to the left of the liver. It is the widest part of the alimentary canal and acts as a reservoir for the food where it may remain for between 2 and 6 hours. Here the food is churned over and mixed with various hormones, enzymes including pepsinogen which begins the digestion of protein, hydrochloric acid, and other chemicals; all of which are also secreted further down the digestive tract.