The digestive system provides our body with the necessary substances. We get nutrients from food. Food products cannot be absorbed by cells unchanged. Proteins, fats and carbohydrates that come from food are first broken down to simple substances: starch breaks down to glucose, proteins to amino acids, fats to glycerol and fatty acids. Cleavage products are absorbed into the bloodstream and delivered to the tissues. Then, in the cells, the formation of carbohydrates, proteins and fats, necessary for the human body, occurs.
Digestion is a set of processes of mechanical processing of food, the breakdown of nutrients and the absorption of the resulting products.
These processes take place in the digestive organs. The digestive organs include: the oral cavity, pharynx, esophagus, stomach, small and large intestines, anus. This is the digestive tract.
The walls of all organs of the digestive tract are three-layered. The outer layer is formed by the connective tissue membrane, the middle one consists of smooth muscles, and the inner layer is made of epithelial tissue containing a large number of glands (it is a mucous membrane).
The glands also belong to the digestive system. Two large glands (liver and pancreas) are connected by ducts to the small intestine. The salivary glands open into the mouth. Many small glands are located in the lining of the stomach and small intestine. The secretions of the glands contain digestive enzymes that hydrolyze nutrients.
In the digestive tract, there is a gradual breakdown of proteins, fats and carbohydrates contained in food products, the absorption of the formed products into the bloodstream and the removal of undigested residues from the body.