in this video we're going to take an overview of the digestive system we'll take a look at what it does how it works and the different organs they need to know about then in the next video we'll take a closer look at the enzymes that we use in the process in order to function properly humans have to eat loads of food which is mostly used for energy so that we can move about and keep our metabolism running the three main groups of nutrients that we need are carbohydrates like starch and glucose proteins and fats unfortunately though these are locked up inside large molecules which themselves are inside big pieces of food the role of digestion therefore is to break all this food down into tiny pieces so that we can absorb it into our body cells this process relies on both physical breakdown and chemical breakdown by enzymes as we'll see let's start at the top once you place some food in your mouth you break it down physically by chewing you also release saliva from your salivary glands which helps make the mixture more liquid and also contains salivary amylase which is an enzyme that helps break down carbohydrates next you swallow the food so that they can pass down your gullet which is also known as your esophagus and almost straight away it passes through to your stomach now the stomach is basically a muscular sac and it has three important things that you need to know about one it contracts its muscular walls to push the food around and mix it two it produces pepsin which is a protease enzyme that breaks down proteins and three it produces hydrochloric acid which kills bacteria and also provides the right environment for the pepsin enzyme to work after an hour or so in the stomach the food is squeezed out into the small intestine the small intestine is where the digested food will be absorbed into the bloodstream but it's also the place where most of the digestion will take place and produces digestive enzymes itself to help digestion that said it's actually an organ called the pancreas that makes most of the digestive enzymes and it pushes them into the small intestine in the form of pancreatic juices another organ that secretes things into the small intestine is the gallbladder but at this time it's releasing bile rather than digestive enzymes this bile has two main rules one is that it neutralizes the acid from the stomach making the ph more ideal for the digestive enzymes to function and it can do this because the bile itself is alkaline its other role is emulsifying fats which basically means that it helps break big blobs of fat into tiny droplets and this helps because it gives the fat a much bigger surface area for the digestive enzymes to work on now one thing we need to point out is that the bile isn't made in the gallbladder it's actually made in the liver it's just stored in the gallbladder until it's released into the small intestine getting back to our intestine once the food has been digested into lots of tiny pieces it can be absorbed across the lining of the intestine straight into the bloodstream and it's worth taking a closer look at how this works because the lining of the intestine is an example of an exchange surface and you need to be able to describe how it's adapted to its function if we take a closer look at the inside lining of the small intestine we see that there are loads of these little finger-like projections which are called villi these massively increase the surface area of the small intestine which means that digested food can be absorbed into the bloodstream much more quickly two other adaptations to notice are that the villi only have a single layer of surface cells which means that the nutrients only have to diffuse a very short distance and that they have a very good blood supply which maintains the concentration gradient okay so let's imagine that all the useful nutrients have been absorbed into the bloodstream at this point there's still a lot of material left in the small intestine this is because lots of the food that we eat isn't actually digestible and because of all the secretions for example from the pancreas stomach and gallbladder the leftover material is going to be really watery so next it passes into the large intestine which absorbs all of this excess water leaving behind feces that are stored in the rectum until they're removed we've now covered every part of the process in detail but before we finish let's just quickly recap the order everything happens in so that you can clearly see the whole process from start to finish first we take some food and put it in our mouth where we chew it and the slider glands add saliva it then goes down the gullet or esophagus and passes into our stomach once the stomach has done its thing it's pushed out into the small intestine where it mixes with pancreatic juices from the pancreas and also bile that was stored in the gallbladder but remember made in the liver while the food is in the small intestine it's continually broken down and digested and once small enough to be absorbed from the small intestine into the bloodstream once everything that can be absorbed has been absorbed the leftover material will move into the large intestine where all of the water is absorbed back into the body leaving behind feces in the rectum and that's everything for today if you found this video useful then please do give us a like and subscribe and hopefully we'll see you next time