hi so this should be the last part of my lecture on the digestive system um so i'm just gonna pop my screen here um and so when i finished last time i wanted to uh cover the concept of what digestion was and how we really digested the macromolecules so we have these basic macromolecules carbohydrates lipids proteins and nucleic acids which are our sources for energy and um essentially that's what we need for everything everything takes energy even sleeping in class and sleeping to my videos but anyway that energy powers every chemical reaction and in addition to that we use varying monomers from these macromolecules as building blocks in our cells so um so i wanted to start by looking at um what happens with carbohydrates so carbohydrate digestion actually starts in the mouth as we said already and that happens because of salivary amylase so starch is an example of a carbohydrate equally um you know uh glycogen which is a storage polysaccharide that we find around muscles and liver and many other things in our diet you know are complex forms so salivary amylase starts the digestive process so the longer you do it in the mouth your food in the mouth the more you can break these things up um however the minute you swallow it that enzyme so library amylase encounters the low ph of the stomach so it stops working um and so you know as carbohydrate digestion is not going to get continued until the material is in the small intestine here we have the duodenum and at which point we have pancreatic amylase being released into the duodenum so you know if you appreciate then that you'd start off with some large complex um polysaccharides so multiple sugars making up your macromolecule as you start to break these down in your mouth then maybe you've broken off one or two so polysaccharide means many sugars and oligosaccharide is an intermediate thing um it just refers to several and then we have my diagram is showing you oligosaccharides so we have several units combined together here and then sometimes we have two going together so two monosaccharides will give us a disaccharide so the action of pancreatic amylase then is very important because by the time the carbohydrate gets into the small intestine it could be a mixture of polysaccharides or oligosaccharides or disaccharides but certainly um you know the action of pancreatic amylase is going to keep going until we end up with disaccharides now a disaccharide actually is too large to actually be absorbed um so this would be the point for you to look back in your textbook um at all the ways things cross our plasma membranes and you will realize that something that's big of disaccharide is too big to get across so it has to be in the form of a monosaccharide something like glucose something like fructose something like galactose there are many different kinds of monosaccharides out there only when a carbohydrate is in the form of a monosaccharide can it be absorbed however we've really only mentioned two enzymes salivary amylase and pancreatic amylase and the thing to notice at this point is a disaccharide can be a it's going to be a unique mixture it might be two glucose molecules joined together it might be a glucose and a fructose but my point is these are very very diverse so it takes enzymes from the british border cells okay remember these are the microvilli on the villi it takes these enzymes um that are being released from the british border cells to make that final cut and it is only when we have a monosaccharide can we have absorption taking place so um absorption then from the lumen of the small intestine is only going to occur when we have a monosaccharide and there are multiple different ways things can cross into the brush border cells so we can have you know these standard methods like diffusion you know you can have diffusion of glucose for a glucose channel or fructose channel sometimes you can have solvent drag and the monosaccharide is dragged into a cell with water sometimes you can have um facilitated diffusion which would be a specific molecule that would move it so i summarized that on this slide here so carbohydrate digestion starts with salivary amylase you may get your polysaccharides becoming oligosaccharides there is no carbohydrate glycogen in the stomach but there is carbohydrate digestion in the small intestine so it takes though the bridge border cells to make that final cut and then there are multiple multiple ways that the monomers can get into the membranes um across the membranes and into the cell ranging from passive methods such as diffusion this is a high concentration gradient or using energy to transport that sugar in maybe a glucose um and of course once that monosaccharide is within the british border cell it is going to diffuse in to the blood vessel in the villus and it is going to get transported to the liver and then the liver is going to process it as appropriate so that's carbohydrate digestion um so protein digestion again you're going to start off with a complex protein which is made up of amino acids sometimes we call these peptides so we can call these proteins polypeptides or polyamines but there is no digestion of proteins that happens in the mouth digestion of proteins occurs in the stomach in the very first place so the stomach is the first place and it is here that the acid from the stomach can activate pepsinogen remember synogen is a zymogen so when that is activated it becomes peptide so pepsin is the active enzyme that is going to break these bonds uh in the polypeptide chain so again depending on how long the pepsin is exposed to the peptide you can have maybe a mixture of oligopeptides sometimes dipeptics but mainly a mixture of oligopeptides of varying lengths from the um stomach the kind the um oligopeptides in chyme have to be finished uh when they enter the small intestine so there are multiple enzymes that are secreted there so the pancreas secretes zymogens again remember inactive proteases or protein digesting enzymes that are inactive are called zymogens so there are three zymogens that are released from the pancreas into the small intestines and these are going to continue their action on the sequential digestion of proteins so they're going to act on the oligopeptide and ultimately you're going to end up with dipeptides amino acids joined together and this slide here is really showing you um where these enzymes work so we have trypsin and chymotrypsin up here um and they break the polypeptide chain or the polyamine gene train into oligoamines um and then carboxypeptidase is named for its action so it actually breaks the amino acid next to the cap the carboxyl group remember your chemistry again i'm not concerned with you remembering your chemistry here i just need you to know the names of these protein-digesting enzymes to know where they're produced and to know um that they were zymogens in the first ones so once again then we are going to end up with dye diamino diamines and these diamines then um are going to be broken down into single amino acids so there are about 20 amino acids as you again should recall those 20 amino acids can be joined to any other 20 so these are complex enzymes that are needed to fit that specific site and to make that final breakdown so once again those enzymes that are required to break a diamine or a dipeptide into single amino acids they are secreted by the british border cells so again we don't need to know all the names of those i thought we just need to know the main protein digesting enzymes and that the final cut of the two amino acids is carried out by brush border enzymes and so once this happens then the single amino acids can be absorbed so that absorption is only going to take place then into the brush border cells um after that final pattern again i've summarized it here for you and as we've said before the way that your amino acid is going to enter the brush boiler cells and be absorbed is by diffusion facilitated diffusion active transport solvent drag et cetera all these basic mechanisms and once the amino acid is in the brush border cell it is going to enter the blood vessels in the villi and travel to the liver where it is further processed so it's pretty straightforward for the way that carbohydrates and and proteins are broken down the tricky one is with facts so fats they have to be emulsified so a fat globule if you think about what it's like when you have um you know oil or butter in a saucepan of water that you've got your bastard in you know there are big globs of fat that are floating around in the water and this is exactly how fat really is uh inside volume of our small intestine so there are big droplets and these are impossible to digest without bile so bile here actually coats the surface of the fat globule and that actually breaks it up um a bit like adding detergent to the greasy water in your swordsman you know it breaks it up from from big blocks of grease into smaller droplets so we call these emulsification droplets now these emulsification droplets then create a larger surface area and that large surface area enables pancreatic lipase to enter in to the droplet so this droplet then is sufficient for the enzyme to enter and when the enzyme enters it encounters so when creating lipase encounters all sorts of different fats probably fats are the most diverse things in our diet i mean if you think about it we have cholesterol we have fat soluble vitamins we have you know triglycerides we have all these different components so these are all there in those fat droplets so the end result of the enzymatic activity is to produce a great variety of different types of lipids surrounded with parts of oil on the top of them if you look at my picture and to have a diverse core so they're very very diverse so we we call them mycelies um you know because they're so downwards some might have some cholesterol in some might have you know a monoglyceride some a fatty acid another one may be a fat vitamin so they're very very diverse but what's interesting about fats is they are hydrophobic and something that's hydrophobic is not very soluble in water but it's very soluble in fat and the plasma membrane of our cells and of those british border cells is phospholipids so it's fat material so something that's fatty like a myceli can cross those brush border cells and the membranes very very readily and get into the core of the cell and so this is what happens so they pass very readily across the bridge border and once they're in the cell the cell has to treat it a little bit differently because it's a little bit insoluble and to help increase the solubility it is coated now with some proteins so the british border cells add protein to the mycelies and we form another product now called apollo micro it's the column micron and that column micron then is able to leave the brush border cell and it goes not into the blood this is the exception this one goes directly in to the lacteals that are in the branches of the lymphatic system that are in um in the villi as well as the blood vessel and from there they are going to travel to the liver for further processing so i summarize this here so pancreatic lipase in the small intestines is really the first place fats begin to be significantly digested and that would not happen without bile so somebody that's had their gallbladder removed then i really has a problem digesting fats so mycelies become micro coli microns polymicrons enter the lacteals and travel to the liver for further processing now the only other things that we have to think about how they are digested and absorbed are these things here so nucleic acids vitamins and minerals so nucleases okay there were enzymes nucleases ribonuclease deoxyribonuclease that were produced by the pancreas these hydrolyze dna and rna into their single nucleotides and again now they are further processed by the british border cells and absorbed as phosphate ions whichever that was present than the nitrogenous base vitamins are absorbed and changed for the fat soluble vitamins a d e and k they are going to enter um with fats so they're going to be processed in the mycelies and the column microns with fats however water-soluble vitamins that are present in our food they can enter very easily by simple diffusion and of course as i said already b12 can only be absorbed bound to the intrinsic factor produced by the cells of the gastric glands far as minerals go minerals because they are small like sodium and chloride iron and calcium they are just absorbed directly all the way along the small intestine so effectively then all digestion and absorption is complete um in the small intestine effectively and um i'm sure you've heard the rumor out there that water is mainly absorbed by the large intestine this is not correct because there is a lot of water that is going to follow the movement of the vitamins the sugars and the amino acids into your small intestine simply by osmosis so the majority of water is absorbed by the small intestine and only a very small proportion in the large intestine so i would like to just turn my attention now to the anatomy of the large intestine so we have finished with the mouth the uh stomach and the small intestine so this leaves a large intestine as we're thinking about digestion there really is not very much left here to be that we can make um use of so looking at this slide here you can see that the large intestine is so cool because it's much larger it's much wider um the first portion is this so material from the small intestine passes through the ileocecal valve in to the seeker then we have the ascending colon then we have the transverse colon this is the descending colon here it goes into the sigmoid colon and then into the rectum and then into the anus so there's a sphincter that makes up the ileocecal valve there's a sphincter here external anal sphincter there's also an internal one as well so material moves along compartment by compartment also point out to you here's the appendix the appendix as a member of the new culture associated lymphatic tissue um is believed to have immunological functions and to be possibly latest research suggests a storage area for bacteria so somebody that has their appendix removed um you know often experiences in later life possible some you know there's a correlation with the digestive um dysfunction possibly because the bacteria that are living in this appendix are healthy ones so they will repopulate the gut um when um you know um when the bacteria there have been lost and helped restore balance it's an interesting angle for research so as i said here um the gross anatomy of the large intestine um begins as the c common appendix in the right corner it frames the small intestine in terms of length that is 5 feet long and 2.5 inches in diameter so it's shorter than the small intestine but wider this is in essence because there's no absorption and digestion taken the structure is simple columnar epithelium with um no circular foals no villi it does not need an increased surface area only making mucus to help move that material along and it is in fact very muscular to move the material along as well so mucus for friction free movement and muscle to move the waste product so it's a storage area present within it then as i was alluding to there's a bacterial population in general these are good bacteria they populate the large intestine having managed to evade um uh from in the digestive process while having entered from the anus and once they're present in the gut they can populate the large intestine some of them ferment cellulose meaning they can use it as an energy source whereas we don't have the enzyme to break it down ordinarily the enzyme that breaks down cellulose is cellulase um so they can deal with those hardy plant materials and in doing so as a consequence they can make vitamins b and k through our digestive process when we digest carbohydrates and we make atp our end products in addition to that are carbon dioxide and water now carbon dioxide we can breathe out however in the case of bacteria because they're working in the under conditions in the gut with very little air around um the end product is not carbon dioxide if vitamins b and k and sometimes products that often contain methane or hydrogen sulfide so this is what contributes to gas production so finally in terms of material moving through the large intestine transit time one uh one day maybe half a day any material that's left there is just experiencing um reabsorption from water that might be left the rest of it consists of undigested fiber it consists of epithelial cells it consists of some fat that could not be reabsorbed there are some bacterial cells that are in there a lot of mucus as well so feces then is actually a living material because it contains bacteria and it's something that we like to study because we can tell by the bacteria that's present how healthy an individual is we can look at the fiber content and know how their diet is working and we can look at the color to determine if the liver is functioning correctly or not so many useful um medical indicators can be determined by that somebody that has liver disease may actually have a stool sample that is white rather than a brown or you know or a like green color and babies have you know a species that is yellow and mustard uh in shade so so my last slide here is showing you the anatomy of the anal canal and if you look at the anus here um you can see that the important thing to notice are these blood vessels that are on the side these blood vessels here are hemorrhoidal things um so these hemorrhoidal veins are often very useful in patients because this is an area of good blood supply so that sometimes you know a patient that receives um a suppository is actually having medication that's absorbed in these veins so they can actually get a very good supply of drug through that mechanism simply because from this point from the hemorrhoidal veins the blood supply is going to the heart and then getting pumped up to the lungs as opposed to an oral antibiotic which i was saying to you earlier if it goes into the stomach it's being done is being it travels by the portal vein to the liver and so it's immediately getting broken down so this is often used in medicine for that reason here is a colonoscopy image and this is a very healthy colon on the top here this is a very good way to study problems with the digestive system or to look for colon cancer and so the uh the intestines are emptied when you put the fiber optic cable in through the anus you can see that the healthy wall here um is pink and you can see these blood vessels down here i have a very healthy colon as well but the only thing i wanted to point out was this this is actually a hemorrhoid which is a swollen vein now on the inside in this in individual it's individual um uh probably developed that because they were overweight and sedentary it's very common this is the internal uh an internal hemorrhoid and so my final slide here is the slide on defecation so this is a process whereby the feces are eliminated um stretching the rectum so when the material reaches the rectum it stretches and that triggers you know the need that we have voluntary control over um to go to the bathroom however in some cases um when the rectum is straight um an individual that might be unaware of it because they have maybe um motor neuron disease or they are elderly um are going to still experience bowel movement because it is in fact it can be an involuntary process so it can be an autonomic processor so bear that in mind that when you have to go you have to go and so right now i have now completed my slide set on the digestive system so i have to go as well so um i'm just going to close this slide and when i have closed the slide i am going to go back to my screen and say bye and check on the website for more information later thank you