DIGESTIVE SYSTEM AND DIGESTION

The human body needs for its functiong. Our body assimilates proteins, fats, carbohydrates and other nutrients. The digestion of the starchy parts of food begins in the mouth where it is moistered with saliva. In the tongue papillae (ligual papillae) there are taste receptors. Over the mucous membrane of the oral cavity there are many tactive, temperature and pain receptors. The teeth, the gums, the soft and hard palates and the salivary glands are important structures located in the oral cavity. In the oral cavity the food must be well chewed between the teeth, then the food passes through the pharynx (throat) and down through the esophagus (gullet) into the stomach which is a dilated portion of the alimentary truct pyriform in shape. The stomach is composed of a fundus (upper part), a body (middle part) and an antrum (lower, digistal part), the upper opening of the stomach is calld the cardiac sphincter and the lower one - pyloric. The folds in the mucous membrane lining the stomach are called rugae.

In the stomach the components of food are dissolve and hydrolysed by enzymes of saliva gastric juice. Different gastric glands are found in the stomach. They produce hydrochloric acid and pepsin to digested food. The gastric juice secreted by the stomach possesses antibacterisl activiti. Pepsin converts proteins to smaller substances called peptones. But food does not enter the bloodstream through the stomach.

Further digestion and absorbtion of food into the blood takes place in the small intestine. After portions of the stomach contents enter into the duodenum they turn acid, but then the reaction rapidly changes because the hydrochloric acid of the gastric juice is neutralizated by the bile, the juice of the pancreas, the juice of the duodenal glands and intetstinal crypts. The bile comes from the liver and gallbladder by means of special ducts. The pancreatic juice, a colourless clear fluid contains sodium, potassium chlorides and is rich in enzymes which digested proteins, fats and carbohydrates.

Food passes in peristaltic waves from the duodenum to the jejunum and the ileum, which is attached to the large intestine. The entire intestine has many projections called villi. It is in the small intestine where the so - called cavital and membrane hydrolyses of nutrients takes place. The products of digestion are absorbed into the blood and lymph.

The remaining of food (the fluid of digestion) from the small intestine pass into the large intestine which consists of cecum, colon (ascending, transverse, descending), sigmoid colon and rectum. The vermiform appendix hangs from the cecum. The rectum ends in the anus. The process of digestion is completed in the large intestine by the abcorption. The unabsorbed and undigested components of food, the remains of the digesting fluids are evacuated from the body.