13+Digestion

Digestion Chapter 18 __**Content Summary **__ //Digestion is a process that occurs on a daily basis for all living organisms. The digestion of the things that we eat greatly involves the ability to break them down into the simplest form so that our bodies can use it for energy, or whatever purpose that it may serve us. Digestion of food is largely accepted to happen in the stomach, at least when we were all young and clueless. The path that the food molecules take through the body is much more intricate than that. Digestion starts when the food enters the mouth, and essentially is being worked on throughout the entire process until the body disposes of it. The three most interesting points that stuck out to me throughout the Digestion System chapter were mainly in the organs that help with this process. The small intestine and the large intestine fascinate me, along with the digestion and absorption of carbohydrates, lipids, and proteins. //

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//The small intestine is vital to the process of digestion, and it could not happen without it. The small intestine can be broken down into three separate parts starting with the duodenum, jejunum, and the ileum. The duodenum is where the pancreatic and common bile ducts empty into the small intestine. Villi are a fingerlike structure that extends out into the intestinal lumen, and at the base of these villi is where the crypts of Lieberkuhn are created. These crypts serve a very unique purpose, as this is where the new intestinal epithelial cells are formed. These new intestinal epithelial cells are then folded to form the structures known as the microvilli. This then as a unit forms the brush border of the mucosa, and the microvilli effectively increase the surface area. Contained in the membranes of the microvilli are specialized enzymes known as brush border enzymes. Along with the other organs that are included in the digestive system, they have to have a way to move the food on to the next organ. The small intestine has two major ways to move that food, and those are the segmentation and the peristalsis. //

//The large intestine, much like the small intestine, can be divided into subunits. These subunits include the cecum, colon, rectum, and the anal canal. The cecum also has another unique part, and that is the appendix that is attached to the inferior medial margin of the cecum. The colon can also be subdivided into sections that include the ascending, transverse, descending, and the sigmoid portions. The associated bulges in the intestine wall are known as the haustra. The entire process of digestion relies on the processes of the bacteria that are in the large intestine. The commensal bacteria are the most numerous in the large intestine. These bacteria are considered to be very helpful to the body, and perform many needed physiological functions. These bacteria are located in the intestinal microbiota. The intestinal microbiota are vital in their production of small fatty chain acids, vitamin K, and some B vitamins. The bacteria of the microbiota help protect the inner linings of the intestine from whatever pathogenic bacteria that may be present. The large intestine also plays a large role in the absorption of water and electrolytes. //

//Although some may believe that the digestion does not begin until the food reaches the depths of the stomach or intestines, the digestion of some things such as starches begins when the food is still in the mouth. Salivary amylase begins this process well before the food has even been swallowed. The digestion of proteins however, does not start until they reach the stomach. This is where the pancreatic juices that contain the protein-digesting enzymes can go to work. These protein-digesting enzymes include both trypsin and chymotrypsin. Lipids are not digested until they reach the small intestine because they bile salt are what emulsifies them. The bile salts create something known as the micelles, which allow fatty acids and monoglycerides to enter. After they enter the micelles, they are either absorbed as they are currently or they are absorbed as free molecules. The epithelial cells are the structures that do this absorbing, and once the substances enter these cells they are used to resynthesize triglycerides. These same triglycerides then combine with proteins to form chylomicrons while they are still in the epithelial cells. These chylomicrons are then secreted into the villi. These are then escorted by the lymph to the thoracic duct, where they can enter the blood. //  Source (Physiology Book)

[|__Digestive System Activity__]

__**Application **__ //Knowing now that I am going to become a nurse, and then a go on to be a nurse anesthetist, the digestive system comes into play in small areas. The digestive system is an important system of the body to know a lot about because we need it to be able to function. The energy that we use and need on a daily basis is created by the digestive system. This particular system takes what you eat, and turns it into the energy you need to do anything, and without it you would no longer be living. As far as being a nurse, the ability to just know how things are broken down and synthesized in the body could help with a variety of things. For example, it is important when it comes to administering drugs to patients. When a patient receives a drug it has to be digested by the body in order for it to take affect. Therefore, it is important to know how the body digestive system works, so you know what side effects to expect after giving the drug. //

__**Essential Questions **__ //The liver’s structure plays a large role, and is a very helpful tool in the processes that take place there. The liver is unique in the fact that it is the largest internal organ, between 3.5 and 4 pounds in an adult, but yet it is no more than one to two cells thick at any given point. The cells in the liver, also known as hepatocytes, form hepatic plates that are only one or two cells thick. These plates have small gaps between them known as the sinusoids. These sinusoids are lined with flattened epithelial cells. The hepatic sinusoids lack a basement membrane or a diaphragm, thus making them much more permeable than any ordinary cell. This unique structure makes the liver able to bring in molecules that normally would not be able to enter through a basement membrane, and enter the blood via the plasma. //

//Another organ where the overall structure makes it easier to do its job would be the stomach. The stomach is made up of multiple layers of muscle that make it easier to contract and break down the food that are contained here. The three layers of muscle include the longitudinal muscle, the oblique muscle, and the circular muscle. Inside these muscles deep in the stomach are folds that contain gastric pits. These pits secrete various products into the stomach in order to help the breakdown of food as well. //

//The digestion of carbohydrates, which are mostly ingested as starches, starts in the mouth with the salivary amylase, but the majority of the digestion takes place in the duodenum as a result of pancreatic amylase. These processes break the starches into one of three molecules, either the maltose, the maltriose, or the oligosaccharides. These three are hydrolyzed in the brush border enzymes located in the microvilli of epithelial cells in the small intestine. //

//The digestion of proteins begins in the stomach with the reaction of pepsin, but the majority of protein digestion occurs in the duodenum and jujenum. Within these two the enzymes of trypsin, chymotrypsin, and elastase are what causes the digestion to occur. The end results are free amino acids, dipeptides, and tripeptides. The free amino acids are ready to move into the blood, but the dipeptides and the tripeptides need a little more work first. These must be transported into the cell cytoplasm where they can be broken down further into free amino acids and then they to are ready to be moved into the blood. //

//<span style="color: #000080; font-family: Verdana,Geneva,sans-serif; font-size: 18pt;">The process of digestion that occurs to fats, or lipids, starts with a process known as emulsification. With emulsification bile salt micelles are secreted into the duodenum. These act as a seperator to disperse the drops of fat into emulsification droplets. From here the emulsification droplets are digested separately by the enzyme pancreatic lipase. The breaks two of the three fatty acids off of the triglycerides and you are left with two free fatty acids and one monoglyceride. The fatty acids and the monoglyceride then move on to the intestinal epithelium where absorption occurs. // <span style="color: #008000; font-family: Verdana,Geneva,sans-serif; font-size: 130%;">Source (Physiology Book)