It directs the food down the correct road as shown below. The epiglottis covers larynx to prevent food and drink from entering the lungs3įortunately, our body was designed in such a way that a small tissue, called the epiglottis, covers the opening to the trachea. This is definitely not where you want your food or drink going, as this is the pathway for the air you breathe. The other road, through the larynx, leads to the trachea and ultimately the lungs. The esophagus road leads to the stomach this is the direction that food should go. It will move down the pharynx where it reaches a “fork in the road”, with the larynx as one road and the esophagus as the other. Now that the food has been thoroughly chewed and formed into a bolus, it can proceed down the throat to the next stop in digestion. Lingual lipase has a small role in digestion in adults, but may be important for infants to help break down triglycerides in breast milk2. Although it is released in the mouth, it is most active in the stomach where it preferentially cleaves short-chain fatty acids in the sn-3 position. Another enzyme, lingual lipase, is also released in the mouth. Lysozyme helps break down bacteria cell walls to prevent a possible infection. The yellow arrows point to the alpha 1-6 glycosidic bonds that cannot be cleaved Purple arrows point to alpha 1-4 glycosidic bonds that can be cleaved. Figure 3.22 Enzymatic action of salivary amylase. Overall this enzyme accounts for a minor amount of carbohydrate digestion. However, salivary amylase cannot cleave the branch points in amylopectin where there are alpha 1-6 glycosidic bonds, as shown in the figure below. Salivary amylase cleaves the alpha 1-4 glycosidic bonds in the starch molecules, amylose and amylopectin. The salivary glands release saliva, mucus, and the enzymes, salivary amylase and lysozyme. Mechanical digestion is called mastication, or the chewing and grinding of food into smaller pieces. We will go through each one in detail, but this table should help give an overview of which enzymes are active at each location of the GI tract.Įnzymes and Digestion – 3.2 Mouth to the Stomachĭigestion begins in the mouth, both mechanically and chemically. There are a number of enzymes that are involved in digestion. The accessory organs do not come directly in contact with food or digestive content. In addition to the GI tract, there are digestion accessory organs (salivary glands, pancreas, gallbladder, and liver) that play an integral role in digestion. Mouth –> Esophagus –> Stomach –> Small Intestine –> Large Intestine –> Rectum –> Anus The journey through the gastrointestinal tract starts in the mouth and ends in the anus as shown below: Figure 3.13 The gastrointestinal or digestive tract2 The organs that form the gastrointestinal tract (mouth, esophagus, stomach, small intestine, large intestine (aka colon), rectum, and anus) come into direct contact with the food or digestive content. Figure 3.11 The digestive tract, also known as the gastrointestinal tract, is a “tube within a tube”Ī number of organs are involved in digestion, which collectively are referred to as the digestive system. If it’s not absorbed, it will be excreted and never enter the body itself. This is because the contents have to be absorbed into the body. Thus, even though the GI tract is within the body, the actual interior of the tract is technically outside of the body. The gastrointestinal (GI, digestive) tract, the passage through which our food travels, is a “tube within a tube.” The trunk of our body is the outer tube and the GI tract is the interior tube, as shown below. This will require higher levels of thinking, but will prove to be well worth it in the end.ĭigestion is the process of breaking down food to be absorbed or excreted. The desired end result for the learner will be an integrated understanding of the process. This section will describe in depth how what you eat is digested. You probably do not think too much about what actually happens to the food you eat.
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