human anatomy and physiology Welcome to our week of lectures on the digestive system this corresponds to chapter 23 in the Open Stacks textbook first I'll briefly show the learning objectives for the digestive system and we'll begin with a basic overview of the structures of the digestive system here in episode one the digestive system includes the organs and accessory structures showing on the screen here the elementary Canal forms a continuous tube that is open to the outside environment at both ends the organs of the elementary 2 or Canal include the mouth ferx esophagus stomach small intestine and large intestine there are additional accessory digestive structures and these include the teeth the tongue the glands which produce saliva the liver pancreas and gallbladder notably the major functions of the digestive system are highlighted on this screen the digestive system will ingest and digest food absorb released nutrients and excr treat food components that are unable to be digested there are six activities involved in this process including ingestion motility mechanical digestion chemical digestion absorption and defecation with the elimination of those excess materials that cannot be digested these processes are regulated both by neural and hormonal mechanisms on the screen here you can see some of these functions highlighted with propulsion allowing for the food and Bolas to move along the uh Elementary Canal there's also uh mechanical and chemical digestion highlighted what you can see is that that mechanical digestion with chewing begins in the mouth there is churning of materials in the stomach and there's also segmentation which helps to move or Propel materials along as well you have chemical digestion as well and you can see that largely in the intestine more specifically the small intestines you also have absorption in the small intestines and water can move to blood vessels in the large intestines let's look at this in a little bit more detail in the next table here you can see these major functions of the digestive tract highlighted again from ingestion and motility to the secretion of substances mechanical and chemical digestion elimination regulation and absorption briefly ingestion occurs when food is taken into the body motility allows for mechanical digestion the mixing of contents with secretions increasing contact with the absorptive surface and propelling food along the gut secretions of certain substances can allow for processes of digestion and absorption to occur you can think about hydrochloric acid that is present in the stomach you can think about certain digestive enzymes that can also Aid in the breakdown and then subsequent absorption of of materials with digestion once again this includes both mechanical and chemical processes to break down nutrients into uh more simple forms such that absorption can occur once again absorption largely occurring in the small intestine elimination once again that is the excretion or that elimination of material that is not digested digested and absorbed regulation uh this really involves the coordination of the various functions of the digestive system and finally absorption allowing for nutrients to move through the GI or gastro gastrointestinal uh mucosa into the internal environment once again taking place largely in the small intestine now this next slide is a schematic diagram really just to summarize the order of the various digestive organs along the digestive tract starting from the mouth and making its way um uh through the digestive tract and all the way to the anus lastly I'd like to highlight there are several valve likee structures and these sphincter muscles consist of circular fibers arranged such that there is an open an opening in the center when relaxed and no opening is present when these muscles are contracted this really controls the movement of the food or the bolus along the uh digestive tract and so um these are highlighted on the screen here both the upper and lower esophageal sphincters will control the movement of uh food and the Bolis as it's make it as it makes its way way to uh the stomach the uh polaric sphincter will then control uh the movement of materials between the stomach and the first segment of the small intestine also known as the duodenum so effectively it is the exit from the stomach and thereby allows for materials to get absorbed once again largely uh those nutrients largely get absorbed in the small intestine we also then as you're moving down the GI track have the ilocal valve which controls the movement of uh materials between the small intestine and the large intestine so the last segment of the small intestine is known as your ilium and the first segment of the large intestine known as your seeum and then finally uh the anal sphincter is located between the rectum and the anus once again all of these muscles are referred to as sphincter muscles and they're essentially like valves because they contain circular fibers arranged to allow uh for the muscles to either relax and allow materials to pass through or contract and thereby prevent materials from making their way down the digestive tract