In most vertebrates, the digestive system consists of the digestive tract and digestive glands.
The digestive system begins with the oral cavity, followed by the pharynx, then the esophagus and, finally, the basis of the digestive system – the gastrointestinal tract.
The oral cavity is the first section of the digestive system, so the entire subsequent digestion process depends on how well and correctly all the processes of the initial processing of food proceed in it. It is in the oral cavity that the taste of food is determined, here it is chewed and moistened with saliva.
The pharynx follows the oral cavity and is a funnel-shaped channel lined with mucous membranes. The respiratory and digestive tract cross in it, the activity of which should be clearly regulated by the body.
The esophagus is a cylindrical tube located between the pharynx and stomach. On it, food enters the stomach. The esophagus, like the pharynx, is lined with a mucous membrane, in which there are special glands that produce a secret that moisturizes food during its passage through the esophagus into the stomach.
The stomach is one of the main components of the digestive tract. It performs a number of important functions, which include: directly digestive, protective, excretory. In addition, processes associated with the formation of hemoglobin occur in the stomach. It is lined with a mucous membrane, in which the mass of digestive glands secreting gastric juice is concentrated. Here, the food mass is impregnated with gastric juice and crushed, more precisely, the intensive process of its digestion begins.
The main components of gastric juice are: enzymes, hydrochloric acid and mucus. The components of gastric juice chemically treat the food that enters the stomach, turning it into a partially digested semi-liquid mass, which then enters the duodenum.
The duodenum is the upper, or first, part of the small intestine. It directly connects to the stomach. Here, in the duodenum, gall from the gall bladder and pancreatic juice enter.