the digestive system is responsible for the breakdown the digestion and absorption of food the digestive tract also known as the elementary Canal is the pathway where food travels through after being ingested the digestive tract consists of the mouth es esophagus stomach small intestine large intestine also known as the colon and the rectum therefore we can refer to the digestive tract as a long tube that runs from the mouth to the rectum food enters the mouth and leaves through the rectum but there are also other organs called accessory organs that play fundamental roles in digestion these organs include the salivary glands tongue teeth the liver galbladder and the pancreas without the proper function of these accessory organs food will not be digested properly and consequently will not be absorbed resulting in gastrointestinal diseases such as malnutrition so looking at a general overview of the digestive system food can be grouped into three main categories carbohydrates such as bread proteins such as meat and lipids such as oil these foods are ingested by the human the food will be digested by the digestive system and then absorbed into the bloodstream where it will be then delivered to body tissues as energy or for storage finally waste is excreted another fundamental point to take in is that the digestive tract All Share three similar anatomical properties here I'm drawing a diagrammatical cross-section representation of the digestive tract the digestive tract have three main layers the Lumen is the inside Space of the digestive tract the first layer is um is mucus and we find it around the Lumen mucus lubricates the food and also protects the lining of the digestive tract then you have the epithelial cells the lining of the digestive tract that forms the tract itself some of these cells are are what produce and secrete mucus the third layer is the smooth muscle layer the outer layer which is important in contraction through contraction the smooth muscle allows the food to move through the digestive tract after being ingested now that we have a better feel for the digestive system let us look at each of the organs of the digestive system and what they do in relation to Foods being consumed so food enters the oral cavity the process called mastication occurs which is essentially chewing food will be broken down mechanically by the mouth teeth playing a key role the tongue plays a role in tasting the food as well as mixing the food around while the salivary glands within the oral cavity secrete saliva which lubricates the food there are three salivary glands the sublingual meaning below the tongue parotid and sub mandibula which means below the mandible the salivary glands also secrete an enzyme called amas which will initiate carbohydrate digestion once the food leaves the oral cavity in a partially digested form it is swallowed a term called deguen the food is actually now referred to as a bolus the bolus which means bow in Latin is a mass of food that has been chewed up the bolus will travel through the esophagus thanks uh thanks to peristalsis now peristalsis is the involuntary contraction of the smooth muscles that line the digestive tract peristalsis allows the movement of food through the digestive tract essentially and so the Bolis will eventually enter the stomach the stomach will temporarily store and churn the Bolas the stomach is able to churn the Bolis because it has three layers of muscle the stomach cells also secrete chemicals and enzymes such as hydrochloric acid that helps break down the food kill bacteria and stimulate enzyme secretions the stomach cells also secrete mucus that helps protect the lining of the stomach as well as pepsin that begins protein digestion the vigorous contraction of stomach muscles and the stomach secretions results in the liquefication of the food which is then slowly released into the small intestine the pylorus sphin is the barrier between the stomach and the small intestine during digestion the Pyar sphin opens in in phases allowing the liquefied food now referred to as Kim to enter the small intestine now Kim is the term used to describe a semifluid mass of partially digested food so essentially before the stomach the food was referred to as Bolis after the stomach it is K the small intestine runs from the pylorus to the ilocal valve which where it joins to the large intestine the small intestine is divided into three segments the duodenum the Jenum and ilium the ilium connects to the starch of the large intestine here the small intestine is very important because it is where most of the digestion and absorption of food takes place however it cannot do this without the help of the accessory organs the liver the galbladder and the pancreas so let us learn a bit more about these accessory organs and learn about their role in digestion so here we are zooming into the liver and the galbladder the liver produces bile which has a critical role in lipid digestion the galbladder stores the B and when needed the galbladder will contract and release the B into the small intestine so B will enter the small intestine through the bile duct so to see where the food is the Kim the Kim is actually coming from the stomach and is here within the small intestine now so the other important accessory organ that has to be mentioned here is the pancreas the pancreas is an important endocrine and exocrine gland during digestion the pancreas secretes many enzymes these pancreatic digestive enzymes will be secreted into the small intestine as well through the pancreatic duct the pancreatic duct actually connects with the bile duct and um and consequently to the small intestine the main enzymes secreted by the pancreas for digestion are lipases for lipid digestion pancreatic amase for carbohydrate digestion and protease that helps in protein digestion so the Kim will en counter all these enzymes and will be digested further the small intestine itself have some enzymes called brush water enzymes that are actually found on the cell membranes these brush B enzymes include molas lactase sucrase and peptidase the brush butter enzymes are sort of the final step of food digestion the Kim will encounter all these enzymes and chemicals which will further digest um it into smaller molecules these smaller molecules are the monosaccharides amino acids fatty acids and glycerol which are the building blocks of carbohydrates proteins and fats and it is only in this form that the body can absorb them so the monosaccharides and amino acids are able to be absorbed by the small intestine into the bloodstream where it will then travel to specific areas in the body the fatty acids are absorbed by the small intestine into the lymphatics with the help of bile so from all this we can see how the small intestine is the major place for the digestion and absorption of food therefore it is important that we understand more about the hystology of this organ if we zoom into the small intestine we can find the lining of the intestine with its rich blood supply the small intestine is composed of finger-like projections called Villi and crypts now below the crypts are stem cells that keep dividing renewing the cells above the Villi is important in food digestion and absorption because it increases surface area the small intestine also have um has a thin layer of mucus Now we move on to the large intestine also referred to as the colon the main function of the large intestine is to absorb water and ions as well as storing and transporting waste that will be expelled by the body but there are other things that happen within the large intestine because what happens is that foods that are not digested and absorbed in the small intestine these foods will reach the colon and so we will soon see what will happen to these non-digestible foods but first we need to learn a bit more about the anatomy of the large intestine the large intestine is divided into a few sections the seeum the ascending colon transverse colon the descending colon the zigm colon and the rectum there is also the anus region this pointy bit here is known as the appendix it has a role in the immune system what people what most people may not know about the large intestine in particular particular the proximal area of the large intestine so I'm talking about the seeum is that a lot of these non-digested Foods undergo fermentation by the trillions of bacteria that live here so let's have a look at what happens so here we are zooming into this area here we have the colon cells and we can find mucus above the colon cells and so here is the Lumen residing within the Lumen are many types of bacteria that can digest these uh foods that have escaped digestion in the small intestine so foods that are not digested and absorbed in the small intestine can undergo fermentation by bacteria in the colon through fermentation the bacteria can produce many substances that the human body can use such as short chain fatty acids finally it is important to compare the hystology between the small intestine and the large intestine so let's take a section of the large intestine it also has a rich blood supply to the lining the large intestine has Crypts where stem cells uh keep dividing renewing the cells above however the large intestine do not have villi and to add further to this the large intestine has a very thick mucous layer compared to the small intestine with an additional thinner mucus layer on top the difference in mucus thickness is thought to be because of the denser population of bacteria that reside in the large intestine and of course substances foods and contents that are not digested and absorbed will be excreted by the body as feces and that is where I finish thank you for watching