hi everybody and welcome back to miss Angler's biology class I am Miss angler in today's video we're going to be looking at digestion and this is a follow-on video from the small and large intestine we're going to focus in on the processes of chemical and mechanical digestion and we're going to see what are the structures required for these things to happen now if you are new here don't forget to give this video a thumbs up and make sure you are subscribed with your notifications turned on because I post every Tuesday and Thursday for grades 10 to 12 biology and if grade 11 is really getting you down right now because there's just so much to learn you should think about getting a copy of my cheat sheet study guide it makes learning and studying so easy it's literally taking pages and pages and pages of your textbook and putting it into one easy page of study notes so let's talk about why do we go through digestion now when we look at our mouth we often don't think that digestion is actually necessarily happening in our mouth but it is and there are many important processes that begin the digestive system or the digestion process right here in our mouths now ultimately the overall goal for digestion is to make smaller particles okay so keep that in the back of your head when they ask questions like why do you chew why is there enzymes why is there this why is there that the end goal is we want to make smaller particles so we can increase the surface area because if you increase the surface area you can do a lot of digestion a lot quicker and you can access the nutrients a lot faster remember everybody that when you eat like a like a hamburger that carbohydrate of the hamburger bun that doesn't just like go straight into your bloodstream otherwise you would just be made out of Hamburg abandon everything else that you've eaten instead we have to take that very large structure that is insoluble doesn't dissolve in water um it doesn't move through your capillaries we've got to make it really teeny tiny so that it can be absorbed into your tissues now this whole process is in two parts one is mechanical and as we see here in the mouth there are a couple of things that we've already covered when it comes to what's in the mouth we already know that we've got teeth which are responsible for mechanical digestion I don't know if you know this but also the tongue technically counts as a part of the mechanical digestion and moving that around in your mouth and then sitting in the back of your throat and on the top of your mouth which is a little bit invisible in this picture here but you have your salivary glands and they start the chemical digestion so let's get into some more specifics about mechanical digestion beyond the mouth the mouth is where mechanical digestion is going to begin with your teeth and your tongue but a lot of people don't realize that mechanical digestion continues going down the esophagus the technique counts as a part of the mechanical digestion because of the way in which the esophagus moves now what you can see here in this picture over here is you can see a bolus of food making its way down the esophagus and ultimately what happens is the esophagus is a tube of muscle which is slowly squeezing the food or the bolus down to the stomach and I'm sure we are familiar with this term we use the term peristalstas which is the contractular wave movement that squeezes the food from the top of the esophagus down the esophagus to the stomach now speaking of the stomach the stomach itself often we don't think about the stomach being mechanical digestion because we think oh it's all the juices and the liquids so it must be just be you know chemical but that's actually not true we still have mechanical digestion taking place inside the stomach yeah and we can see a lovely cross-section into the stomach first of all let's take note of the fact that the stomach is made out of smooth muscle and smooth muscle everyone remember is involuntary muscle that can contract and relax and instead of Contracting and relaxing which we call churning that is what mixes your food so that it's evenly um digested throughout and that counts as mechanical digestion now we can mechanically digest food up until a certain point but there's a limitation to this right you can chew and chew and chew food and mix it as much as you want but eventually it will become a liquid but it's not small enough for any absorption to happen into the bloodstream and that is where chemical digestion takes place now there are three major places that chemical digestion takes place starting off with the salivary glands now here is a little diagram over here which we did Cover in my introduction to the digestive system which was the sets of our salivary glands which is this one over here and we've actually got uh three sets of glands in our mouth and they secrete out saliva which contains enzymes now this is not the only place that enzymes are secreted but it is where chemical digestion specifically for starch begins now the main attraction for chemical digestion is always going to be the stomach okay what we see here in front of us is we have a liquefied version of the food that we have eaten and that is due to all the substances that we have added to it including most importantly hydrochloric acid as well as of course those enzymes because we do also have enzymes in the stomach now I'm going to elaborate on these enzymes a little bit later but I want you to know that enzymes perform their job best in a environment that suits them so their pH and their temperature and that's why we find enzymes in different locations we have them in our mouth in our stomach and our third and final location which is in the duodenum which is the first section of this small intestine now I want you to know everyone that after the duodenum no more chemical digestion takes place absorption begins and it's important to know that because ultimately the enzymes don't continue doing their process forever and ever and ever and ever there is a limitation to how long this goes on for and so digestion needs to be roughly completed by the time food leaves the duodenum now why are we going through chemical digestion ultimately I want you to think of it like this when you eat food you are eating food that is in a complex structure so we're touching on our grade 10 knowledge and we're thinking of chemistry of life when we look at something like for example a protein a protein if I draw it for you here is made up of amino acids each one of these circular structures represents one amino acid and so if I join enough amino acids together I form a protein now when you eat whole pieces of protein like you eat a piece of meat that piece of meat is not useful to you even if we liquefied it so we make digested it we need to get it to its simplest form its amino acids and so to do that we use enzymes and hydrochloric acid to cut these chemical bonds between the amino acids so that we can get them as individuals because we want them remember the smallest pieces remember that's the goal and we do this with carbohydrates with proteins and with fats but we do them in different ways and in different locations and so that brings me on to a really important part about whether or not a substance is soluble or insoluble now when we speak about chemical digestion we are ultimately taking something that is insoluble in specifically water and we're making it soluble in water and so what that means is that before we did any digesting just like we did earlier when I drew you this diagram down here this would be considered an insoluble substance it's too big it's too complex we want to make it smaller so we just have these individual Parts which are soluble so that they can be absorbed in to the bloodstream so now we need to talk about the star of the chemical digestion which is enzymes now I'm not going to go into all of the basics or enzymes in this video if you can't remember everything from grade 10 then click the link above now the little video card that will take you to my enzyme video go watch that refresh your mind and what enzymes are and how they work and then come back here so we can see how enzymes are used in the digestive system specifically now ultimately when we talk about enzymes in the digestive system we want to know why we use enzymes and the first thing we need to talk about is we use enzymes because without them our metabolic rate would be too slow and so if you were eating food it would take so long to digest food that if you rely just on Hydrochloric acid to digest your food it wouldn't take a few hours it could take days weeks before food is completely digested with the hydrochloric acid and that's just not Optimum you would die before then and so what we also need to remember is how enzymes do their job and remember this is just a refresher on these Basics we need to know but remember enzymes can be catabolic and they can be anabolic catabolic means they break down and anabolic means they can break up and all enzymes can do both depending on how much substance you have if you need more you'll build up if you need less you'll break down and so forth so it just depends on what the body needs at the time now another little refresher that is key to the digestive system is this little cutout that we see inside of enzymes now that little Qatar is called the active site and that is where the chemical reactions take place and I want you to be very aware that the digestive system has certain PHS for their enzymes to work now this is just a summary of some of the ph's that you may need to know depending on your school and your teacher you might need to to know even more than what is in this table but these are the minimum now you will notice if you look at the table that there are specific PHS that certain substances need to be in so for example starch needs to be in a pH of seven protein needs to be in roughly a pH of three and lipids or fats need to be in a pH of eight now if you know the digestive system you will know that the pH changes regularly your mouth begins at a pH of seven your stomach can go all the way down to a pH of two and then your small intestine goes back up again to a pH of eight and so it's really important that the enzymes that exist in the mouth and the stomach and the beginning of the small intestine all have the right pH because if they don't what do we know happens again this is a little bit of revision we know if we have the wrong pH or temperature we end up denaturing or changing the active site remember the basics of Bio if you change the shape you change the function and so we've got to keep that in mind because if we want to be able to digest a substance we have to be able to digest a protein with a protein enzyme and most of the enzymes associated with the digestive system have a name linked to the substance they are digesting so for example the classic three enzymes we generally need to know are amylase and it's known as a carbohydrase enzymes generally end in the word A's or the suffix A's we have trypsin which is a type of protease or protein enzyme and lipasas which are fats we also in exams and tests need to know the origins of these substances these enzymes and so first of all we see amylase coming from your salivary glands and the pancreas protein and trypsin um enzymes are seen in the stomach pancreas and small intestine whereas lipids are exclusively from the pancreas now I can't stress enough to you the importance of knowing your enzyme characteristics and the reason for that and how it links into the digestive system is if you understand their characteristics you will be able to understand their role in the digestive system and how they are affected this is often where a lot of the application questions come in the exam as well so we need to remember that enzymes are reusable often you get asked why do you only need a small amount and that's because they can be used over and over and over again the other thing that's really important to understand is that enzyme Source substrate specific which means in the digestive system if I digest fat I can only digest fat I cannot digest protein I cannot digest carbohydrates so that's why I need to have a environment that allows me to do my job efficiently also what's important as we just covered is that they are pH specific and I'm going to come back to that as we round off this video and last but not least as I mentioned just earlier that we only need a really small amount of enzymes because they're so good at their job that they are reusable and they just do their job over and over and over and over again and they require small amounts because they do their job in their metabolic functions so quickly now one really important thing that I must clarify and that we must get right before the end of this video is the enzyme action location this is the thing that we get wrong time and time again in exams so let's just quickly recap about the PHS of the various enzymes when we're in the mouth the pH is roughly a seven which is fairly neutral the stomach is an acidic pH of two and then the duodenum and the small intestine are both a pH of roughly an eight which makes them alkaline now this is important because it ultimately affects how the enzyme is going to work and where it is allowed to work now when we're reading this diagram it's also important to understand you know what we're looking at here every time you see an arrowhead like this one over here it means that the digestion of that substance is taking place if there is no Arrowhead like we can see over here by Lopez or lipids there's no digestion happening and so we need to keep that in mind as we go through this location of enzyme action now we're going to start off with the carbohydrates narcobohydrates begin their enzyme journey in your mouth and they interact with salivary amylase which loves a pH of seven and they become polysaccharides and disaccharides you will notice in the mouth as well that there is no digestion of lipids or proteins happening you'll see there's no Arrowhead there it's just like a solid color so that means that no digestion is happening in terms of chemical digestion so the only substance being digested in your mouth is a carbohydrate okay and that's because the pH is just right now what happens when we go to the stomach we go into the stomach and the pH dramatically changes okay dramatically you will notice now in carbohydrates nothing is happening in there and that is because amylase cannot perform its Duty in a pH of two yeah neither can the same happen for leopards and so they don't get digested they're either however we notice here that proteins do get digested and they are going to be digested into polypeptides via a enzyme called pepsin and that's just one of the protein enzymes that I've mentioned I did also mention trypsin earlier now that means in the stomach the only so routine so those are the two things that are important and you'll see we're keeping their digestions separate from one another carbohydrates and proteins but now we get down to the small intestine which is where it gets interesting and it gets a little more complicated the pH of the duodenum is eight and you will notice that carbohydrates come back into digestion via pancreatic amylase so not salivary amylase but pancreatic amylase and you'll see there's digestion happening here which forms disaccharides you will also notice that protein is also happening in terms of its digestion and it is becoming peptides with the use of the um enzyme trypsin which I've mentioned earlier again you will still notice no digestion of fats are occurring fats are really tricky to digest everybody and you may or may not remember this but I did mention in my introduction to the digestive system that in order to digest fats we need bile and so bile is really important and bile only comes into play um in the duodenum which we can see here it says bile salts and the enzyme lipase and so we only add them then right they only actually get added then it's once we are in the duodenum with those substances and this is just the beginning part remember of your small intestine now that you've added in everything you are now able to digest protein as we can see here you are able to digest carbs and now finally you are able to digest fats in this final section remember fats need to be emulsified okay they are not soluble in water again going back to the beginning of the video we're taking insoluble substances and we're making them soluble and so fat goes on a much longer digestive Journey because it's not soluble from the very beginning it's insoluble in water in particular and so we've got to add a lot of substances to it and finally right at the very end when we get to the small intestine we can finally digest fats and then of course absorb now as always I like to finish off my videos with a terminology recap you can use these for flashcards they make studying super easy and these are just some of the words that I've used throughout the video that you should know and be able to use in an exam first of all at the very beginning I spoke about the ability to break down foods and chew them and we actually call that mastication it means to chew and it makes food smaller via mechanical digestion we spoke about the enzyme amylase which is the enzyme found in our salivary glands it's where chemical digestion begins for carbohydrates in the mouth we spoke about peristalsis which is the contractual waves of the esophagus as it pushes food down and we spoke about metabolic reactions metabolic reactions being the way in which enzymes do their job now enzymes can be catabolic or anabolic which means they can build up or break down substances depending on how much you need of that thing and speaking of enzymes we spoke about their active sites which is the area that links in with the substance you're trying to break down or the substrate and that specific substrate is specific to the enzyme now if you change the active site you denature it which means that you cannot use it anymore and this is very relevant remember to the digestive system because we often denature with ph and so if it's in the wrong pH the enzyme won't work anymore it'll be denatured and last but not least we spoke about the words insoluble and soluble which if you remember the whole point of this whole journey is to create small particles to increase the surface area so that absorption can take place now if the substance doesn't get small enough it won't be soluble it won't move into water it won't move into the bloodstream and so if something is insoluble it's not absorbable and it won't be able to be used by the body so the point of the digestive system is to make food smaller increasing the surface area so that it can become soluble and be absorbed into the bloodstream now if you like this video don't forget to give it a thumbs up and I will see you all again soon bye