The process of digestion in human beings is a complex pathway that involves different types of tissues such as epithelial and muscular tissues (Campbell and Reece, 2004). Human digestion starts in the mouth where the salivary glands are located along the epithelial lining of the mouth. Saliva that is secreted by the salivary glands contains enzymes such as amylase that initiate destruction of the starches that are present in the food introduced into the mouth. The teeth also aid in chewing and biting the food.
Once the food is partially dissociated, the food passes into the esophagus which is a muscular organ that undergoes muscle movements, also known as peristalsis. This rhythmic constriction and relaxation of the esophagus facilitates the transport of the food into the stomach. Once the food reaches the stomach, several gastric acids are introduced to the food that will help in its further dissociation. The environment of the stomach is highly acidic and this helps in further digestion of the food into chyme (Raven et al. , 2004). From the stomach, the chime moves on to the small intestines, which are structurally divided into 3 regions.
The duodenum is the initial one-third of the small intestines, while the jejunum is also known as the middle section of the small intestines and the ileum is that last region. Bile is added to the chime in the small intestines and this secretion aids in emulsifying the fats that are present in the food that was consumed. The bile originates from the liver and is technically stored in the tiny sac called the gall bladder which empties the bile into the intestines whenever necessary. From the small intestines, the chime is transferred to the large intestines when most of the assimilation of nutrients occurs.
This is also where water and electrolytes are reabsorbed by the body. The large intestine is made up of 3 regions, known as the ascending, transverse and descending colon. The portion of the chyme that is not assimilated by the large intestine is compacted as feces, which are stored in the rectum until excretion.
References Campbell NA and Reece JB (2004): Biology, 7th ed. New York: Benjamin Cummings, 1312 pages. Raven PH, Johnson GB, Singer S and Losos J (2004): Biology, 7th ed. San Francisco: McGraw-Hill, 1250 pages.