hi everybody and welcome back today we're going to be looking at the process of absorption that takes place in the small intestine and up until this point we know that we have taken a solid food and we have broken it down into smaller pieces to increase the surface area so that absorption can take place now the next part is we need to absorb the nutrients in the small intestine so if we just have a quick little look at the diagram to familiarize ourselves with the structures that we're going to use they have taken a cross-section through our small intestine as you can see over here and remember that the small intestine is specially structurally suited to do its job in particular it has transverse folds which essentially means that the inside lining is a folded layer sort of like a wave like motion and on those folds we find these structures called a villus and remember it's all about increasing surface area now the key linked to increasing the surface area is that we want to make our small intestine more efficient so that we can absorb our nutrients faster because the turnover rate in humans is so high in our nutrition we need to ensure that there's a constant flow of nutrients into the bloodstream now we're going to look at some very specific structures within the small intestine and we're going to look at how they do their job and how they facilitate the absorption of nutrients we're also going to look at how do fats proteins and carbohydrates enter the bloodstream each having their own obstacles they have to overcome in order to enter the bloodstream so in order for the small intestine to absorb as much as possible in terms of nutrients into the bloodstream the structures that line the inside of the small intestine need to facilitate it as best as possible and there are some adaptations that we need to know that make this more efficient one of them being that the small intestine is lined with columnar epithelium now columnar epithelium is just as the name suggests it is a section of cells that are closely packed together that represent columns as you can see in the diagram above and it lines most of the digestive organs and you will notice found in and amongst the columnar cells in the diagram are these goblet cells and goblet cells are responsible for secreting amongst other things mucus and mucus is a really important role in our absorption as water is the universal solvent and it allows for easy lubrication of food as it moves through the digestive system but also to allow nutrients to be absorbed into the bloodstream you will also notice that the columnar epithelium in this particular picture has cilia and yet again cilia is there to increase the surface area because the greater the surface area the more efficient you are in absorption which ultimately means that columnar epithelium facilitates absorption now if you were to look inside these columnar epithelium you will see a large amount of mitochondria and as we know mitochondria are responsible for cellular respiration now when we speak about cellular respiration remember we are taking glucose and we are converting it into energy now why would we need so many of these mitochondria because they actually exist in very large numbers in the intestines and the main reason for that is active transport active transport which i'm going to explain in the next slide is efficiently moving substances against a concentration membrane that means that you are taking substances from a low concentration and pushing them into a higher concentration which is very difficult to do if you don't have enough mitochondria which luckily these particular columnar epithelium have large amounts of mitochondria within them now in order for us to understand how absorption works we need to have a good grasp of how substances move across a membrane and in particular there are two ways in which a substance can move one of them is what we call passive transport and the other is active transport essentially we're very familiar with passive transport for the following reasons now when we go over the basics of passive transport we need to look at a few things first of all passive transport is when we move from a high concentration of nutrients to a low concentration and remember that requires very little energy none in fact because a lot of membranes simply allow substances to diffuse straight through the membrane or if not they will move through what we call channel proteins which are specialized proteins that allow only certain substances to move through them however this entire type of diffusion is passive which means we don't need any energy to do this on the other hand we have active transport which is what we more commonly find in the intestines now for active transport it's the opposite we now need to move substances from a low concentration to a high concentration and because we are going against the concentration gradient we are going to need large amounts of energy and that's where the mitochondria comes into play and that's why our columnar epithelium that lines the intestinal walls have so many mitochondria as you can see in the diagram we have atp involved which remember is our energy molecule that we need to use to do this and you will also notice that there is a channel protein involved because it needs to regulate what's going in and what is going out in terms of maintaining that concentration gradient now when it comes to absorbing carbohydrates and proteins the process is fairly simple because both of these substances are water soluble so they can move straight into the villi and what we're looking at here in this diagram is we have cut a villi in half and i just want to go through some of the structures you need to be familiar with so first of all you will notice the outer layer has microvilli sitting on the surface of one singular villi you will see something called a lacteal running down the middle which we'll get to later on we have our blood capillary which is a smaller extension of our blood vessels which is our venule and our arterial and then you will notice that the arrows that are leaving our villi are going off to their final destination of where they need to be processed as nutrients before they enter our cells essentially at this point what has happened is that carbohydrates have been digested into their simplest forms into their monomers let's remind ourselves what the monomers are of carbohydrates and proteins so carbohydrates are monosaccharides and proteins are amino acids and remember we want to make these substances as small as possible because look at the space that we have to fit them through we have to fit them in between these cells which means we need them to be as small as possible and not just that we need them to be in their most basic components in their monomer form because we need to be able to incorporate these nutrients into the cells themselves now when we look at these in particular and how they move across our membranes our monosaccharides and our amino acids combined with what we call protein carriers the protein carriers are those protein channels that we see in cellular membranes that allow substances to move into the cell efficiently we then enter the capillary and this is a very straightforward process because remember carbohydrates and proteins are soluble in water which means they can easily dissolve into the blood we then take these nutrients and we transport them to the rest of the body now this starts as passive transport remembering that passive transport is when we have a high concentration on the outside of the cell that we want to then put into the villus itself now it starts off from a high concentration going into a low concentration on the inside but that's only at the very very beginning remember the digestive system wants to absorb as much as possible and so for a very short time it is passive diffusion however very quickly it will become active transport the reason for that is slowly but surely the outside will become a lower concentration and we will have to go against the concentration gradient and force it into the higher concentration on the inside of the villus where we've absorbed a lot of the nutrients already and please take note of that because often there's a technicality that a lot of people don't understand and therefore they get questions wrong surrounding how do substances move from passive and into active transport we can now finally look at the final substance that needs to move into the bloodstream and that is fats now fats are a little bit more complicated because unfortunately fats are not soluble in water so they're not going to be able to pass into the bloodstream immediately instead we need to take our fat droplets we need to make them even smaller so that they can at least move into the villas not necessarily the bloodstream and then we move them into their own specialized structure which we call the lacteal now because of fat structure which if you remember a triglyceride or a true fat is made out of one glycerol molecule and three fatty acids when we're actually breaking the fats down we need to move these components separately into the bloodstream now first of all glycerol is water soluble which means that it's really easy to absorb and it goes straight into the villus keeping in mind it goes into the villus but not necessarily into the bloodstream fatty acids on the other hand are insoluble and the only way to get them into the bloodstream or even into the villas for that matter we're going to combine them with bile now once both of these substances are inside of our vellus and if we have a look at our diagram you can see here that we started off with a larger lipid in other words a large fat and you see what we've done is we've taken this three uh ball-like structure and we've had to break it down into smaller lipids for the simple reason of facilitating absorption but now that we're inside the villus so we've moved through the cell membranes that line our villus we now need to move into a specialized structure called a lacteal now once we've moved into the villus itself the fatty acids in the glycerol reform together once more and they enter the specialized structure called the lacteal which is this structure running down the middle of the villus the lacteal is part of the lymph system it's separate from our capillary system and that's because fats need to be processed slightly differently before they enter the bloodstream itself now once we've mixed this substance into the lacteal this substance is known as kyle which is part of our vocabulary so let's round this lesson up looking at our terminology recap so we looked at villi which were the structures that line the small intestine they increase the surface area and they aid in absorption and those villi are covered in even further smaller microvilli yet again increasing the surface area now these micro veli are lined with columnar epithelium remember those are the cells that look like columns and they are filled with mitochondria in order to improve their efficiency now that mitochondria provides energy for the necessary absorption and we learned about diffusion and diffusion is when substances move along a concentration gradient in particular we learned about active transport which is when we need energy in order to move substances from a low concentration to a higher concentration which goes against what diffusion normally is normally diffusion is from a high to a low active transport is from a low to a high we also learned about monosaccharides and amino acids being the monomers or the smallest components of carbohydrates and proteins respectively and how they enter into the bloodstream then we looked at glycerol and fatty acids which is what makes up our fats and how those lipids need to move into the villus and the way in which they do that is slightly different you need to add bile because fats are not soluble in water so they're not going to move into the capillary system on their own and when those fats do actually end into the villi they don't go directly into the capillary instead they're going to a specialized tube called a lacteal which is part of the lymph system and once that fatty liquid is in the lacteal we call it kyle thank you once again for listening i hope that you've learned something today and use this video as much as possible to consolidate what you've learned in class and i will see you again bye