Digestion. The digestive system is made up of a complex series of organs and glands that together process the food that enters the body.

The Ways of Digestion

The digestive system is made up of a complex series of organs and glands that together process the food that enters the body. In order to use the food that is eaten, it has to be broken down into smaller molecules it can process; it also has to excrete the waste.

The digestive process begins in the mouth, where the food is broken down by mastication. Mastication and saliva secretion work together: chewing increases the surface area of foods, which helps to accelerate the breakdown of starch molecules. Mastication causes exocrine glands under the tongue to produce saliva. The starch is broken down into glucose by a production of salivary amylase, an enzyme from the salivary glands. It moistens and compacts the food that has been chewed so that your tongue can roll it into a ball, called the bolus, and push it to the back of your mouth so that you can swallow and have an easy passage down through the pharynx and esophagus. The esophagus is a muscular tube whose muscular contractions propel food to the stomach.

The food reaches the pharynx when the bolus has been produced. The bolus triggers an involuntary swallowing reflex that prevents food from entering the lungs, and directs the bolus into the esophagus. When the food has been chewed and swallowed, it enters the esophagus. The esophagus is a long tube that leads food from the mouth to the stomach. The esophagus uses rhythmic, wave-like muscle movements called peristalsis, to force the bolus from the throat down through the gastroesophogeal sphincter and into the stomach.

During a meal the stomach fills to the capacity of 1 liter, where it ...

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During a meal the stomach fills to the capacity of 1 liter, where it starts off with an empty capacity of 50 to 100 milliliters. The stomach can hold 2 liters or more but at the price of discomfort. On the inner surface of the stomach epithelial cells are lined. They secrete about 2 liters of gastric juices per day. Gastric juice contains of hydrochloric acid, pepsinogen and mucus, which are all important ingredients to digestion. Secretions are controlled by nervous and endocrine signals. The stomach secretes hydrochloric acid and pepsin; the hydrochloric acid lowers the pH of the stomach causing the pepsin to activate. Pepsin is an enzyme that controls the hydrolysis of proteins into peptides. The stomach also churns the food. The mixture of food and acid known as chyme, then leaves the stomach and enters the small intestine.

The epithelial cells have a protective barrier between the cells and the stomach acids. The epithelial cells secreting mucus create this barrier. When the pepsin contacts the mucus, it becomes inactive. Bicarbonate reduces the acidity near the cells lining the stomach. Tight bonds link the epithelial stomach lining cells further preventing stomach acids from passing.

After being in the stomach, food enters the duodenum, the beginning of the small intestine. It then enters the jejunum and then the ileum, which is the end of the small intestine. The small intestine is where the final digestion and the absorption occur. Absorption requires cellular energy because it is an active transport. The small intestine is over 3 meters long but is coiled up. All the coils, the folding and the villi gives this 3meter long tube a surface area of 500 to 600 meters tube. In the small intestine, bile, -which is produced in the liver and the gall bladder- pancreatic enzymes, and other digestive enzymes produced by the inner wall of the small intestine help in the breakdown of food. Villi have cells that produce intestinal enzymes, which finalize the digestion of peptides and sugars. When the food enters the small intestines, it has been broken down into small enough particles so that it can fit in the small intestine. Amino acids and sugars enter the bloodstream by travelling via the capillaries in each villus. Glycerol and fatty acids go into the lymphatic system.

When having passed through the small intestine, the food enters the large intestine. In the large intestine, electrolytes and some of the water is removed from the food. Microbes like bacteria also help the digestion process in the large intestine. The beginning of the large intestine is called the cecum, which is also connected to the appendix. Food travels upward in the ascending colon and then travels across the abdomen in the transverse colon, goes back down the other side of the body in the descending colon, and then through the sigmoid colon.

When the food has passed all these organs in the digestion system the solid waste is stored in the rectum until it is excreted via the anus. That is the end of the digestive system.

Kezia Kristine Krog 10 Palm

Peer Reviews

Here's what a star student thought of this essay

pictureperfect

30th of Jul 2012

Quality of writing

This essay is very well written for this level of qualification, though I disprove of the use of bullet points as this detracts from the essay and it is much more appropriate to write in continual prose. That said, the candidate uses appropriate scientific terms throughout their work which demonstrates a good subject knowledge. In addition to this there are no grammatical or spelling errors with the exception of the word ‘gastroesophogeal’ which should be spelt ‘gastroesophageal’.

Level of analysis

The candidates discussion is well detailed, the information provided is scientifically correct and they have used the advanced names for parts of the digestive system, which is not expected at this level of qualification. It is therefore clear that the candidate has taken the time to do additional research. This demonstrates an ability to work independently and indicates that the candidate is interested in this particular subject. Furthermore, the additional information makes the essay more enjoyable to read. However if you take the time to do any research, it is essential that you state the resources you use, this is important because as well as showing the steps you have taken to prepare for your essay, this can prevent accusations of plagiarism. There is one final area that needs improvement and that is the fact the candidate has not written a conclusion. You must provide a conclusion for your essay as this allow you to bring the essay to close and leave the reader with a good impression of your work. Your conclusion needs to summarise key points from within your essay with reference to why these are important as these help to tie together any lose ends. You should also write a personal response relating to your topic, this could be a discussion of what you have learnt from writing your essay.

Response to question

The candidates introductory paragraph is fairly short and though they have described the digestive system, there is room for improvement here. Firstly, It is obvious from the title and introduction what this essay is going to be about but you should specifically state what you are planning to discuss, this is so that the purpose of your essay is clear from the offset. Furthermore, this is your chance to engage the reader therefore you want to try and make your introduction interesting, you can go about this in several ways, you could state a relevant fact or quote that is interesting or you could mention current scientific ideas/theories. Overall the candidates response is very good, they go into a suitable amount of detail, their essay is easy to follow and is coherent.

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