In the esophagus
The food moves along the esophagus by peristalsis. This is the rhythmic, involuntary contraction of the gut wall in a curvy manner, propelling its content along it.
The gut wall comprises of smooth (involuntary) muscles, some of which are arranged longitudinally while others are circular.
In the Stomach
It is found in the left upper part of the abdominal cavity, just below the diaphragm. Its wall, unlike that of the other parts of the gut, comprises of three layers of smooth muscles, which all help to churn(mix) the food in it. The muscles are: the outer longitudinal, the middle circular and the inner oblique(angular) muscles.
The functions of the stomach are to store and digest it. It lining possess three types of gastric glands, producing three types of secretions:
The oxyntic or parietal cells secrete hydrochloric acid
The mucus-secreting cells secrete mucus
These secretions together constitute gastric juice, and are produced from gastric glands, many of which make up the stomach lining.
- Pepsinogen: this is the inactive form of the enzyme pepsin which hydrolyses proteins, digesting them into shorter polypeptides it also converts more pepsinogens into pepsin, a process known as autocatalysis. This enzyme is produced in an active form so as to prevent self digestion of the stomach .
- Hydrochloric acid: its functions are as follows
- It provides the acidic medium(pH=1-2.5) needed for pepsin to act
- It kills many bacteria that came in with food
- It loosens fibrous and cellular components of tissues in food
- It provides pepsinogen into pepsin
- In children’s stomachs, it converts protein (inactive enzyme) to renin (active form). Renin coagukates the soluble protein milk caseinogen in to casin, which if insoluble. Pepsin then acts on casein.
- It begins the hydrolysis of sucrose into glucose and fructose
- HCL renders Ca and Fe salts suitable for absorption in the intestines
- It splits nucleoproteins into nucleic acids and proteins.
In addition to the secretion of HCL, the oxyntic cells also produce a module called the intrinsic gastric factor. It helps for the absorption of molecules of the vitamin B12 complex.
- Mucus: it provides a barrier between the stomach mucosa and gastric juice, thereby preventing self-digestion of the stomach.
- The churning thoroughly mixes the stomach contents producing a semi liquid called Chyme. Churning is an aspect of physical digestion. The main aspect of chemical digestion that occurs in the stomach is the hydrolysis of proteins into polypeptides.
Gradually, the stomach empties its contents into the duodenum. The first part of the small intestines. This occurs through the pyloric sphincter.