Human Digestive System

The pharynx is part of the gastrointestinal tract, lying between the mouth and the esophagus. The oropharynx is the first region food enters when it is swallowed. The opening from the oral cavity into the oropharynx is called the fauces. Masses of lymphoid tissue - the palatine tonsils - are near the fauces. The lower region, posterior to the larynx, is the laryngopharynx, or hypopharynx. The laryngopharynx opens into both the esophagus and the larynx.

Secretin is produced by cells of the duodenum. Its production is stimulated by acid chyme from stomach. It stimulates the pancreas to produce sodium bicarbonate, which neutralizes the acidic chyme. It also stimulates the liver to secrete bile.

The small intestine is approximately 6 m long. Like the stomach, it contains numerous ridges and furrows. In addition, there are numerous projections called villi that function to increase the surface area of the intestine. Individual villus cells have microvilli which greatly increase absorptive surface area.

Chewing breaks food into smaller particles so that chemical digestion can occur faster. Salivary amylase breaks starch (a polysaccharide) down to maltose (a disaccharide). Bicarbonate ions in saliva act as buffers, maintaining a pH between 6.5 and 7.5. Mucins (mucous) lubricate and help hold chewed food together in a clump called a bolus. The tongue contains chemical receptors in structures called taste buds.

Chyle is a semi -fluid of partly digested food present in the ileum.

Absorption of glycerol, fatty acids and monoglycerides takes place by lymph vessels (lacteal) within villi.

Blood is slightly alkaline, with a normal pH range of approximately 7.35 to 7.45. Therefore, the statement that blood is acidic is false.

Enterokinase is a proteolytic enzyme that is secreted by duodenal mucosa.

 The undigested food in Hydra is expelled from mouth.

The 'Brush Border' of intestines is an example of simple epithelium.

The flexibility of the cell membrane enables the cell to engulf the food.

The human alimentary canal is approximately 9 meters long from the mouth to the anus.

Absorption is the process by which nutrients from digested food are taken up by the intestinal walls into the bloodstream.

Goblet cells of intestinal epithelium secrete mucous.

The assimilation process of digested food in humans is very much complex as the digested food has to be utilized in a very proper way that can help human to live healthy life. The products of the digestion are finally absorbed through the lining of small intestine into the blood stream and become a part of the cell components, this is called assimilation. Blood carries these products to each and every part of the body. On reaching the cells they either take part in the synthesis of carbohydrates, proteins and fats of the human tissue or are metabolized to generate energy in the form of ATP which is used when required.