Fundamentals of Human Nutrition/Gastrointestinal system

< Fundamentals of Human Nutrition

Please use this HELP:EDITING link for information about contributing and editing the book.

3.1 Gastrointestinal SystemEdit

The gastrointestinal tract consists, put simply, of a hollow tube passing through the body. It is an external part of the body, responsible for processing and filtering ingested material. It includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus.

3.1.1 StructuresEdit

The mouth is where the process of digestion all begins. When you put food into your mouth you chemically and mechanically process the food. Chemically your mouth secretes saliva which contains salivary amylase, a main enzyme that is able to catalyze the hydrolysis of starch and make them into sugars. The mouth also mechanically processes your food with your teeth to grind up the food and make it easier to swallow to enter the esophagus. The mouth also contains your tongue which helps to propel the food down your throat to continue with digestion.

Once your food is grinded up by the mouth, it goes through the pharynx which is mainly just a passageway allowing your food to move out of the mouth and into the esophagus. According to Whitney/Rolfes (3.1a) the pharynx shares its functions with both the digestive system and the respiratory system. Since the pharynx is involved with both of these systems, it contains a flap of skin called the epiglottis so it can separate these two systems and to make sure that air gets in one and that food gets in the other one.

Once the food hits the esophagus it becomes a bolus and the food is then moved and able to enter the esophagus through sphincters that open and close in order for the food to get through. There are two sphincters in the esophagus, one is the upper esophageal sphincter to allow the food in the esophagus and then once it is finished it goes through the lower esophageal sphincter or also called the cardiac sphincter because it goes near the heart and through the diaphragm and then is able to enter the stomach. An interesting fact about the esophagus is that it also prevents the stomach contents from refluxing upward according to Mayo Clinic and Oxford Medicine.

Once the bolus enters the stomach it remains in the upper portion and it churns. The stomach adds juice in it in order for it to become more liquid and then it becomes chyme. Not only does it provide lubrication to the food, it also releases enzymes like pepsin as well as a protein to denature proteins with hydrochloric acid. Once the chyme is made, the stomach keeps moving the food through the stomach by ways of peristalsis according to Dr. Gillaspy a professor at the University of Phoenix. Peristalsis is a way that the muscles of the stomach move in order to move and churn the food in the stomach. It is able to churn the food because it contains an extra layer of muscle which is diagonal. The stomach’s main action is to move food not to absorb nutrients, yet. Once the chyme is ready to go into the small intestine, it moves through the pyloric sphincter and out of the stomach it goes.

Small intestine
The small Intestine is the main organ for digestion, it is here that all of the food is digested and absorbed into the body in order to access the nutrients from your food. There are three parts of the small intestine, the duodenum, the jejunum, and the ileum. According to “Understanding Nutrition” by Whitney/Rolfes, the small intestine…” is almost 10 feet of tubing coiled within the abdomen.” (3.1a) The small intestine is very large and folded around the center of your stomach, this is because it needs to have a maximal amount of surface area in order for the food and nutrients to be absorbed optimally. The way the small intestine increases its surface area is by ways of microvilli. There are also juices present in the small intestine that are secreted from the pancreas and the gall bladder that allow the chyme to break down and into attainable nutrients.

Large intestine
After the small intestine absorbs all of the nutrients out of the food you ate, it travels into the large intestine or colon by ways of the ileocecal valve. The large intestine surrounds your body by an ascending colon, transverse colon, descending colon, and lastly the sigmoid colon. The large intestine is also responsible for breaking down fibers into fatty acids and breaking down vitamins. The way that the large intestine achieves this is by having a lot of microflora which are good bacteria. The appendix is also attached to the large intestine. The large intestine ends at the rectum and is then finished at the anus.

The anus is the end of digestion where your food will now be excreted. The muscles at the rectum are under voluntary contractions so that you are able to control it yourself, so once your muscles relax then there are 2 sphincters on the anus that then excrete the waste out of your body.

3.1.2 Accessory organsEdit

Salivary Glands The salivary glands produce saliva, which contains a starch-digesting enzyme.
Liver The liver makes bile, which aids in digestion and absorption of fat.
Pancreas The pancreas releases bicarbonate to neutralize intestinal contents; produce enzymes that digest carbohydrates.
Gallbladder The gallbladder stores bile and releases it into the small intestine when needed.