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Digestion, Absorption and Metabolism

There three major steps in the digestion process. This includes the ingestion when the food enters the body, digestion where the food is broken down by digestive enzymes and then the body absorbs the nutrients needed from the food. Digestion is important because this is how the body get's its fuel from the food.

The digestive system includes the mouth, esophagus, stomach, small and large intestines. The accessory organs include the teeth, tongue, salivary glands, liver, pancreas and gallbladder.

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Carbohydrate digestion begins in the mouth when the food enters, the teeth begin chewing and saliva is released. In the saliva there are digestive enzymes called amylase that begin to breakdown carbohydrates. Amylase is an enzyme present in the saliva that helps break down starches and help convert it to glucose. Glucose is the body's main fuel source. “That’s why the more you chew bread the sweeter it tastes.” (Crash Course, 2012) This chewed up food is now referred to as the bolus.

Once the bolus has been swallowed, it will travel through the esophagus into the stomach. The stomach has three it must do. First it must store the swallowed food and liquid, next it will mix the food, liquid and digestive juices to produce chyme and lastly, it will release the chyme into the small intestines.  

Protein digestion begins in the stomach. "Cells in the stomach release gastric juice, a mixture of water, enzymes, and hydrochloric acid. This strong acid mixture is needed to activate a protein-digesting enzyme and to initiate digestion of protein—protein digestion is the stomach’s main function. " (Sizer and Whitney, 2017, pg. 85)

In the small intestines is where most of the fat digestion takes place. This is where the bile from the gall bladder emulsifies the fat preparing it for enzyme action."Then fat-digesting enzymes break the fats down into absorbable pieces. The pieces then assemble themselves into balls that remain emulsified by bile." (Sizer and Whitney, 2017, pg, 169)

Once the chyme has been processed through the small intestine it then enters the large intestine via the cecum. "Monoglycerides and fatty acids enter absorptive cells in the small intestine through micelles; they leave micelles adn recombine into chyomicrons, which then enter the bloodstream. Fat-soluble vitamins are absorbed in the same manner as lipids; water-soluble vitamins can be directly absorbed into the bloodstream through the intestine." (Digestion and Absorption, 2017) The job of the large intestine is to take what is left from the small intestine and remove all the water and bile salts before it is exported through the rectum. If it didn't do its job, it would result in constant diarrhea. "The absorption of water by the large intestine not only helps to condense and solidify feces, but also allows the body to retain water to be used in other metabolic processes." (Large Intestine, 2017) This is why when you do have diarrhea it is important to keep your fluids up, you can easily become dehydrated.

References

Digestion and Absorption. (2017). Boundless. Retrieved 27 June 2017, from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-absorption-754-11987/

Large Intestine. (2017). InnerBody. Retrieved 27 June 2017, from http://www.innerbody.com/anatomy/digestive/large-intestine

Sizer, F. & Whitney, E. (2017). Nutrition: Concepts and controversies (14th ed.). Mason, OH: Cengage Learning..