Human Digestive System

Lipase is an enzyme used in detergent formulation obtained from microbe.

Digestion of carbohydrates begins from the mouth and ends in small intestine.

Amylase is an enzyme,  that breaks starch down into sugar. Amylase is present in human saliva, where it begins the chemical process of digestion.

It is highly acidic in nature with a pH of 0.9 to1.5. The important constituent of gastric juice include HCl, pepsinogen, intrinsic factor, gastric mucin and gastric lipase. HCl is present in gastric juice in high amount and converts pepsinogen into pepsin and stimulates secretion of various hormones from small intestine.

The term bolus applies to this mixture of food and solutions, until they are passed into the stomach. The food that has been chewed and mixed in the mouth with saliva, is known as bolus. Chewing helps to reduce food particles to a size readily swallowed and saliva adds digestive enzymes, water and mucus, that help chemically to reduce food particles, hydrate them for taste and lubricate them, for easy swallowing.

Pepsin, the important gastric enzyme, is most active at a pH of 2.0 to 3.0 and is inactive at a pH above about 5.0. Consequently, for this enzyme to cause digestive action on protein, the stomach juices must be acidic. Pepsin initiates the process of protein digestion, usually providing only 10 to 20 per cent of the total protein digestion to convert the protein to, proteoses, peptones, and a few polypeptides. This splitting of proteins occurs as a result of hydrolysis, at the peptide linkages between amino acids.

Lysosomes carry hydrolytic enzymes.

The esophagus which is also known as the Gullet, is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing food passes from the mouth through the pharynx into the esophagus and travels to the stomach.

Bile is a bitter, alkaline, brownish-yellow or greenish-yellow fluid that is secreted by the liver, stored in the gallbladder, and discharged into the duodenum and aids in the emulsification, digestion, and absorption of fats.

The saliva in the moth, besides helping to masticate the food, carries an enzyme called ptyalin which begins the chemical action of digestion. It initiates the catabolism  of carbohydrates by converting starches into simple sugars.

Rennin, plays an important role in the stomach of the infant. It curdles milk and allows the pepsin to work upon it.

Chyme undergoes chemical changes initiated by gastric juices secreted by the walls of the stomach. These juices include mucus for lubricating the stomach, hydrochloric acid and gastric juice. The enzyme or active principle of the gastric juice is pepsin. This enzyme in combination with hydrochloric acid starts the breakdown of proteins into absorbable amino acids called polypeptides. The gastric juice has no effect upon starches or fats.  

The inner surface of the intestine is made of mucosal folds, or folds covered in mucus, like the stomach. These folds mix food and crimp the intestine to provide large surface area. The surface of these folds are covered with villi, or small hairs that contains cells that will extract nutrients. The surface of villi is covered with epithelial cells, and the surface of these is covered in microvilli. Together, these elements allow the intestine to be capable to ingesting huge amounts of food.

Mastication or chewing is the process by which food is crushed and grinedd by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes.It takes place in the mouth.

From the stomach, the partially digested food passes into the duodenum, the upper part of the small intestine. Food that has been thoroughly digested should have a thin liquid consistency when it leaves the stomach.