we take in food and the digestive system is largely a disassembly system and then an absorption system so the disassembly is requires mixing with digestive fluids and then you know breaking up of the food particles and then eventually chemical reactions to snip the macro molecules into um much smaller absorbable units so that's a lot of what happens now something as simple as a person ingesting a dairy product with lactose in it and not having the enzyme lactase so a single enzyme uh is is no longer being produced um that can cause pretty significant GI distress okay uh so if you've got a great food source for microbes and we don't digest it and use it by our digestive system then you know that will lead to discomfort and possibly biohazard in the bathroom or wherever it happens um along the elementary Canal along that tube that is the disassembly line there are accessory organs and the accessory organs basically connect in the mouth and at the beginning of the small intestine that's pretty much the the pattern of them so there are really only two major places where the accessory organs all connect in um and so oral cavity and and then the dadum which is the beginning of the small intestine that's pretty much where they're at you might say that the appendix could also be considered an accessory organ it's a little dead end off of the end of the large intestine and so it is really continuous with the elementary Canal or the digestive tract uh but you may see you may sort of view it as off the beaten path so to speak um this is what I think of as an anatomically correct view of the digestive system which means that different things are in different you know they're in approximately their actual place in 3D um in order in order to study the digestive system for function it's actually pretty helpful to sort of stretch it out at least in our mind or in our drawing and follow the tube be able to follow exactly where the tube goes because right here we can see the oral cavity the esophagus the stomach and then the dadum but then after that we lose track of where everything is you know where where the next bit of tubing is um so just be aware of that in lab one of the things that we'll I'll have you do is draw an actual track that you can follow um and label the different parts and we'll talk a little bit about what happens we'll also be doing dissection okay so here I have the layout of the major named organs um there's a lot more detail than this but these are just the major landmarks and so if we show where the accessory organs connect in it's just like I was saying the teeth the tongue the salivary glands um they're associated with the mouth the gallbladder the liver the pancreas they all secret into the small intestine in particular the beginning of the small intestine let's see so then so the foods processed a lot of that processing is breaking it down molecular disassembly and then the extracting nutrients from it is absorption and then there is you know a variety of things that we don't absorb and that includes the microbes that live in our gut it includes fibers it includes a variety of of other things um bacteria especially bacteria that can digest us or could cause an infection in us are inherently gross and so that's part of why poo is gross is because there are lots of microbes uh associated with that thank goodness for plumbing okay so the breakdown is mechanical and chemical uh so the mechanical includes you know the chewing of the mouth um any of you heard of phases in in US history and probably elsewhere in the world as as well where you needed to chew your food a certain amount of time times Etc and there have been a variety of different ideas and there's actually in healthy people you could gulp your food I mean the most of these systems are efficient enough that they have excess capacity I'm not saying you should gulp your food and not chew it but you know dogs seem to think it's a great way to go um they do stuff that we probably shouldn't do for a variety of reasons but uh my point is that yes the mechanical disassembly the mechanical breakdown is going to occur chew it enough for you know hopefully good taste and so that you're not worried about choking and all that but there's no reason why you need to bite you know chew each bite of food 50 times or anything like that unless you have some sort of a digestive issue and um mechanically breaking it up improves your digestion which is not an issue for most people um so ingestion uh that term is the selective intake of food this is complicated um my uncle gave me a book that he found in a discount Book Bin called nutrition and neurotransmitters it's small it's thin it's kicked my ass for years trying to read the various studies because it gets into a lot of detail about nutrition receptors and ways that the body can detect nutrient levels and then neural Pathways primarily in the brain that seem to impact not only food selection but also Behavior so there's a whole chapter on salty behavior that talks about the type of um neurologically based behavior that people have who crave salt and a lot of it's actually based on uh Rat studies with some human studies to support it but ingestion is actually complicated um it's you know it ties in a lot with um learned behaviors as well as subconscious desires for certain things to try and regulate the nutrients that we bring in okay so then digestion occurs from the mouth all the way you know down through the large intestine um and actually what I just said may not be the correct view because for at least at least probably over a million years our ancestors so way before our ancestors were considered humans um food has been ground food has been cut so with sharp sharp blades primarily from stone ground with stone cooked and all of those processes all also do the beginnings of mechanical and some chemical digestion there's some evidence that humans are quite dependent on that if you ever really and use this wisely I realized that food selection and eating and caloric intake and all of that uh is something that um all of us in one way or another can have Hang-Ups with at some point in our life but if you ever want to really regulate the amount of of calories that you can bring in just eating relatively raw food hopefully microbially safe raw food um we're not super deficient at breaking down uncooked unprocessed food so as a nutritionist when I hear people go off on rants about you know stay away from processed foods it's like well at some level compared to a foraging animal almost all of the food that we eat is processed in some way or another and um you may say well what about an apple well apples didn't used to have so much carbohydrates they didn't used to be in the form that they're in we've selectively bred them so that they produce a fruit that's very different from sort of the wild uh non-domesticated form um anyways we have really shaped um the food intake uh that we have by all of our cooking and all of our foods that are available to us okay most nutrients seem to be absorbed once the Macro Molecule once the protein gets broken down into individual amino acids once the carbohydrate gets broken down into single monosaccharides once the lipids are what's called emulsified and the triglycerides start getting broken down into monoglycerides um and individual fatty acids so requires a fair bit of chemical digestion before absorption can occur um we'll talk about water and water regulation the main thing that people usually pick up early in looking at graphs and all that regarding water is that the large intestine is really important in water reabsorption to keep us from getting dehydrated and for allowing the food stuff that we don't absor absorb to turn into feces and to not um not have us lose a whole bunch of water um that view of the large intestine being extremely important with water management is important and correct but a lot of times people willum to the wrong conclusion that water absorption primarily occurs in the large intestine almost all absorption of all nutrients with very few exceptions primarily occur in the small intestine so most of the water is reabsorbed in the small intestine it's just one of the few things that the large intestine can do other than house microbes which is really important is absorb the remaining water even though that's not the majority of it okay water reabsorption is more important than I think probably the average person would think there's a type of bacterial infection called a chera infection and CH is a bacteria that lives in the gut and it blocks the absorption of nutrients and that causes and it releases irritating substances that causes someone to have such bad diarrhea that they could have access to as much water as they want and they could still die of dehydration like they could drink literally gallons of water a day and they still get dehydrated and could potentially die from from it if all they drink is water so they had to develop um and I'm not sure I can't remember the doctors who developed it but it's one of the world health organizations and other groups uh treatments to manage um Cher is called oral rehydration therapy and so having additional salt and some carbohydrate mixed in with the water helps the body more effectively absorb it and hold on to the water so that the person won't die of dehydration and of course the major group of people that we worry about are infants um but I mean you it's a horrific thought of here you've got this baby with really bad diarrhea and you just see them sort of shrivel up and dehydrate right in front of your your eyes over hours to days and so what's that yeah um so anyways my point is that a properly functioning um small intestine and large intestine to reabsorb that water is actually essential for survival and there are some things that can mess that up up and then of course have to get rid of um the feces get rid of what's left over um which is something that most people have feel some awkwardness about that for a variety of reasons and uh hence the book it's a children's book I think Everybody Poops which um I don't know if any of you have hung out around uh longdistance hikers but the first two weeks or so on the Pacific Crest terel people will talk about uh their gear and who they are and all that but for most of the rest of their hike they talk about how their poops are going and how they're eating their food is going real basic stuff sometimes they'll talk about campsites and all that um so Everybody poops and finding a good place to do that we take for granted but uh if you're on a trail it can be a big deal any of you hiked into like a national park where you had to have a WG bag where you had to poop in the bag and haul it on out okay there's some areas Zion where you have to do that and just when there's high traffic lots of people that you there aren't enough places to bury it um and so it's a requirement that you pack it out okay so the elementary Canal is a long tube which is somewhat vague even though we've got some measurement here there isn't any one length for it it's sort of like there isn't any one length to rubber band if you don't specify how much tension is on it okay so the elementary Canal has longitudinal smooth muscle that can either be contracted or relaxed so it's somewhat variable in length um but what we do know is that the length of the digestive tract for modern humans is rather short compared to other organisms of about the same size size okay so we we don't have a particularly long digestive tract there's a hypothesis called the expensive Oregon hypothesis and the idea is that the brain is very expensive it has high nutrient needs and glucose the digestive tract when activated is actually very expensive it takes a lot of blood flow it takes a lot of oxygen you have to make a lot of ATP and so the expensive organ hypothesis which I might have mentioned before I can't remember is that in order to have our brains be as big as they are the digestive tract had to actually shrink and become less expensive and that's part of why me talking about food being prepared or processed is sort of a big deal it's thought that by by many actually um uh in particular paleoanthropologists um but even people who do comparative anatomy and physiology that humans would not have been able to achieve large brains unless we processed food unless we cooked it unless we ground it up you said size change like what would cause that well in order to move food um it does something called peristalsis and so the smooth muscle in different regions is actually pinching down and then shortening and then relaxing and that's how the food gets moved along and so if you were to you know don't actually do this but if you were to put electrodes at both ends and run electricity through all of it you'd get some significant contraction and everything would shorten up um if you were to give someone a whole bunch of magnesium don't do that either um it would cause smooth muscles to relax and it would effectively somewhat lengthen so it changes size long yeah and so it's it's difficult to actually talk about how long is this digestive tract it it depends on the tenic sort of like saying how long is the biceps brachi ey muscle well is it is the elbow completely extended or is it Flex it's two different lengths at the two different extremes same thing for the digestive tract probably most of us have had situations where our GI tract was all wound up and not only did things get sphincteric you know the sphincters got a little Twitchy but the length of the digestive tract may have shortened um in doing that shortening pretty high pressure can be developed there there are measured pressures of up near 100 PSI now that's pounds per square inch how does that compare to like the pressure on the tires of your vehicle yeah 35 is really common okay uh so when someone has a diverticulitis or d That's the inflammatory portion of it or diverticulosis of the large intestine either their connective tissue of their large intestine is been broken down significantly over time or there's some really high pressures that are developing so so don't piss them off they could explode anyways I shouldn't make jokes like that um so mechanical digestion that's a physical mixing but it's also cutting and grinding of the teeth um you know of course being around people with various dentition the main thing with the cutting and grinding of the teeth is just certain foods can't they're going to avoid certain foods if they don't have effective teeth because you can't get it into chunks that you're willing to try and uh ingest because of the worry of choking uh so that's part of it as well as the mechanical digestion stomach does a lot of churning it's actually really set up to be a churning chamber I don't know if you thought about it that way but it there's some acid there's some digestive enzymes but the actual physical um shape of it the overall structure is to set up this churning and to be able to sort of pound on some of the bits in the food and break it up um in order and you have a water bottle on you I just think of an enclosed one this I'll use this hand sanitizer because it's more enclosed in order for Effective churning or mixing to occur I need to have not only liquid but what else you have to have air and we're going to see that there's actually some anatomy of the stomach that helps ensure that there's always an air pock ET so that you can get effective mixing um let's see just since I'm thinking of it right now in one of the two practices that I practiced in uh not only did I and the senior doctor specialize in nutrition but we did some pretty Advanced testing direct testing of digestive function not just sending out uh stool samples but also you know a variety of other testing including having Electronics be swallowed in direct measurement of um the digestive tract and I'll probably talk about that a little bit later on because some of the general Notions that people have including medical professionals about the digestive tract what we found in a lot of patients was actually pretty different from the the general belief of how the digestive system doesn't work in particular acid is considered bad and sometimes people may not have enough acid uh is one of the the major themes that came out of about a year and a half of practice in in that uh Clinic okay so figuring out how digestive enzymes work is going to be a important part of our activity and they have to be formed inactive because digestive enzymes can break down basically anything that our body is made out of and so if they were just formed and they were fully active they would start digesting the very cells that made them and so the concept of a zymogen starting with a z there uh zymogen is an inactive form of a an enzyme and then it there's a whole activation process sort of like nuclear launch codes so you only actually activate it in the location and at the time where it's where it's needed so with the time that we have left I'm wanting to just hit an overview of the digestion of various um molecules and some of you feel free to yell at me because one of our plicker questions you're like why didn't you just go through this before we asked the plicker question so starch you know you got a potato or rice or some pasta and you ingest it it's a Macro Molecule and in order to break down that starch there are a group of enzymes that are all called amales that will break starch down so there is salivary amales which most of us don't really notice these days so you know a long time ago someone puts a starchy food in their mouth and it will taste sweet to them uh there's some evidence that since the 19 late 1980s 1990s the high use of high fructose corn syrup and the ability to change starch into fructose has reset a lot of people's idea of what sweet is fructose is about a 100 times sweeter by volume than sucrose and so when starch which is primarily GL um glucose polymer gets broken down into glucose a lot of people don't even really know notice it as sweet but throughout most of human history things that were sweet would have been noticed because of that salivary amalay so that that salivary amales may not be as important for digestion as it was for tasting the sweetness in food and then selecting it and liking it okay that little bit of of sweetness I think probably most of us can relate to a warm um biscuit or bun or bread you know that just cooling out of the oven and you take a bite and there is sort of that extra sweetness due to the warmth that warmth plus the salivary amas uh there can be a little bit of a little bit of extra sweetness there okay pancreatic amales does most of the work and so the pancreas releases this enzyme uh and scorts it into the small intestine and starts breaking down um the starch into glucose subunits now maltose is two gluc oses and so if you've heard of like a malted beverage or you've heard of uh taking like an onion and cooking it and caramelizing it and you get that little bit of Browning that occurs um that actually takes starch and the heat can break it into maltos and so you can make onions go from their you know pungent odor to a lot more mild and sweet just by cooking them and that's taking the cellulose in the in the onion and uh breaking it down into a digestible form of carbohydrate such as malose so then in the small intestine we have what are called brush border enzymes they're enzymes that are lining the Villi of the small intestine and um they can take little dimers and short sections of carbohydrate and they can break them down into individual building blocks and most most often it's glucose or it will get converted into glucose so like table sugar which is sucrose it's a glucose plus a fructose um the glucose will be absorbed actually fructose is as well fructose is sort of a weird one and then it can just be taken up into cells without the insulin receptor being required glucose requires the insulin receptor um but most other carbohydrates they're going to get converted to glucose um by an enzyme in the cell so most important important organ for digesting carbohydrates is the pancreas and then secondary would be the small intestine and it's it's the small intestine brush border enzymes that lose the production of lactase which will then cause someone to become lactose intolerant which is the normal pattern for mammals it's lactase persistence that's sort of the mutant ability uh that some around half of adult humans on the planet have that they can continue digesting lactose without having GI upset even into adulthood okay so protein digestion um the stomach uh uses both hydrochloric acid to denature the protein it will cause proteins that are clumped up in globular to uh have some coal bonds snipped to have some changes in the electrostatic interaction with the acid in the stomach and the protein will come Unwound the hydrochloric acid which is not shown here also will activate the pepsin so without acid pepsin doesn't get activated okay the Unwound protein which they haven't really shown here um will then be snipped up into smaller bits by pepsin which is in the stomach and then um the little Sac um excuse me the the little peptides uh they will go into the small intestine and the pancreas will produce a variety of other enzymes um even though carbohydrates in the form of starch you know they really just have one major enzyme amas um there are some carboh carbohydrates are complicated I don't want to get the idea that they're they're simple we just can't break down cellulose so cellulose humans don't have the ability to break that down um some bacteria that live in termites do um some fungi do there's some bacteria in SPI basically that can break down cellulose but not a lot else um but for the most part amales is the answer to carbohydrates you know large carbohydrates why is it that there's pepsin Tron kimot Trion carboxy peptid a and a variety of other Pro proteolytic enzymes there's like a whole bunch of them and I just named some of the major ones why do we need so many of them that yeah different amino acids so whereas most carbohydrates at least the standard ones are just a glucose glucose Bond so you just go and snip between glucoses um if you just have a two amino acid little peptide so we've got one and two how many different amino acids can be in the first amino acid spot how many different amino acids are coded for by the genetic code 20 and then in the second there's another 20 which means just to snip that one bond between two amino acids there are actually 400 different combinations so the reason why we need pepsin U Trion um carboxypeptidase and a variety of others uh is because we have you know 400 different bonds that actually need to be snipped when we look at the actual amino acids on either side of the peptide bond so then it actually becomes somewhat surprising that so few major ones uh can do so much and so pepsin maybe it can maybe it can cleave a little over a dozen different peptide bonds okay and what that means is in a large protein you're going to somewhat not randomly but between certain amino acids it will go and and snip them and break them up into sections Tron which the small the small intestine houses the pancreas produces the inactive version of it it will go and snippet other Loc same things for koton something called carboxy peptidase and there are some other related enzymes instead of them being specific about which amino acids they snip between they start on one end of a chain of amino acids and start snipping one at a time which means that they can in theory snip almost any of the 400 bonds they just need to be on the end and not snip in the middle why is it that that the stomach doesn't just use carboxypeptidase and start at an end and start snipping and then we wouldn't need any of the other enzymes yeah I mean we need to break you need more ends you need to you need to have a whole bunch of snips in long chains of protein so then the carboxypeptidase has many different places it can start otherwise it would take too long so it's not fast enough you gave the short elegant answer um and so then some of these peptidases they're going to be in the brush border of the small intestine as well and uh so then they'll deliver individual amino acids now for a long time the standard dietitians and nutritional researchers statement has been that all proteins are completely digested down into individual amino acids and absorbed and that's been sort of the belief there is some pretty good evidence that you don't have to have a leaky gut or some other health problem for a percentage of certain enzymes to actually be absorbed whole and intact and functional it's not super common but there is some evidence that functional enzymes can be absorbed under certain circumstances so just a little heads up there um lipid digestion is quite a bit different from the carbohydrate or the protein digestion and that we're instead of dealing with something that's inherently water soluble we're dealing with something that is inherently not water soluble and so when we eat our french fries in our burger or whatever and it has some fat in that um as we're as our saliva and our stomach acid is starting to mix with everything the lipids that separate on out they separate into fat globules um in order to break that up very similar to the Reas the way that protein needs to be broken up uh to digest it we just talked about that you need something very different and that is bile acids so bile acids they are both Hy hydrophilic on one side and hydrophobic on the other so there's what's called an emulsifying agent that can interact with fat soluble stuff and water soluble stuff and they break up the fat globules into much smaller little particles and in doing that it gives a lot more surface area for lipas to interact with it now in the mouth I don't have this shown here the mouth actually has lingual lipace and it's very likely that that lingual lipas um plays a role sort of more similar to salivary amales and it's more for detection of the nutrients in food for choosing food rather than being a major contributor to digestion but to be honest I don't claim to really understand lingual lipace as far as like why it's there why it's important um so I've sort of glossed over this and a lot of the textbook gloss over it but stomach acid is not just for denaturing protein stomach acid can cleave carbohydrates and start the process of breaking down carbohydrates it can actually um set up fat to be more absorbable even in a water-based environment so the stomach's really important for not just protein digestion which is the classic answer for the importance of the stomach but it's actually pretty important for digesting just about anything um so bile is created by the liver concentrated in the gallbladder and a much larger volume is in the gallbladder the gallbladder can concentrate it about three times what the liver can make and so if someone has their gallbladder taken out because they've had gall stones and had some problems or whatever they're going to just need to limit the amount of fat that they ingest in any one meal um if they or elongate the amount of time that they eat the meal um because they don't have the volume of bile and they don't have the concent ated bile and if they violate that any idea what will happen yeah the microbes have a party any times the microbes are having party in your digestive tract not a fun thing um so uh bile even though it's not an enzyme it is really important for uh fat digestion and then we have pancreatic lipase which is the major in enzyme released Again by the pancreas and it will take the individual primarily triglycerides snip it on up into monoglycerides and fatty acids those can be absorbed then they get reassembled in the intestinal cells and then they a something called a kyom micron which is basically a version of these fat globules will get reassembled and put um put it goes through the lacal remember so the lymphatic system and then it will get into the circulation in the subclavian veins and go to to General circulation and so Lacs after or excuse me uh kyom microns which the Lacs are the lymphatic structures in the small intestine and the kyom microns are the actual little fat globules that are manufactured by epithelial cells in the small intestine um those get put in bloodstream they can be picked up by um cells that need lots of calories because fat is a very efficient way to store and distribute calories so kyom microns are within a class called uh lipoproteins and you've probably C if even if that term doesn't sound familiar you've certainly heard of lipoproteins if you've heard of good cholesterol and bad cholesterol it's actually a reference to lowdensity lipoprotein or LDL which is considered a bad cholesterol it actually is a lipoprotein that has a lot of cholesterol in it versus highdensity lipoprotein or HDL which is considered the good cholesterol it is a lipoprotein that has a low concentration of cholesterol in it cholesterol that we ingest isn't really broken down we don't digest it we just absorb it um it will need to be emulsified by bile so if you have a you know a cow that you eating beef and it's got this plaque of cholesterol in one of its vessels that you also ingest I realize this is a very nice conversation right before lunch um you know the bio will help emulsify that break it up and then it's going to be put into those kyom Micron lipoproteins and distributed throughout the body we do need cholesterol cholesterol is essential for all of our cells so I want to remind you that it's not a bad thing we use it to stabilize cell membranes what else is cholesterol used for yeah so the steroid hormones which include the the adrenal cortex hormones cortisol sterone um and then some of the androgens and then also the estrogens progesterone and testosterones okay so peristalsis is the movement of uh things through the tube there's a pinching action that have you have a area of the um Elementary Canal that's stretched and just behind it you'll have a reflex where it pinches and so it's like having it's like having a golf ball underneath a blanket that you can just sort of push behind it and then you can move the golf ball around um whereas segmentation instead of trying to move things from one location to another the area that is stretched where the food is it's called a bolus of food is the technical term it will pinch there and that's more like whacka moole the food is there and you try and whack it to try and break it up okay and so this is just an overview of U both chemical and mechanical digestion and then also propulsion as things move along this is the sort of diagram that we need to understand the physiology of digestion and absorption and where different things happen