 Let's summarize the important components of our human digestion. So food mostly contains carbs, which is sugars, proteins, which is useful in building muscle, and fats, which is storage of food. Digestion is breaking them down into their tiny components. What are those components? Well, the component of carbs is basically glucose. The component of proteins, proteins are made up of amino acids. And the components of fats is basically fatty acids and glycerol. Now, where do these things happen? Well, just from the colors, you can kind of see inside mouth, mostly the carbs digestion happens. Stomach is responsible for digesting proteins. And small intestine is the one that digests almost all of it, eventually breaking them down into their components. But you can see fats are mostly broken down in the small intestine. And once you have these broken down tiny components, they're all absorbed by the small intestine. Then they go into the blood, circulate through your body. Then what happens in the large intestine? Well, once all of these things are absorbed, the remaining stuff is sent into your large intestine, no breaking down, no absorption of any nutrients, but to absorb any remaining water. You know, we are body wants water, so it's good to save that water. So we'll absorb any remaining water, send it back into your body. And now the remaining stuff, which is even more solid now, that is thrown out of your body through anus. So this is the overview of how digestion happens in your body. Now let's dig one step further. So now let's look at the different enzymes that break these things down. There are a lot of them, we'll only focus on the main ones. So in the mouth, the enzyme that breaks down carb carbohydrates is present in your saliva. And that's called salivary amylase, or I'm just going to write it as amylase, but it's there in your saliva. It helps in breaking down carbs. Then the food goes into your isofagus and then it pushes down into the stomach. And in the stomach is where your protein start getting broken down. The enzyme that is produced in the stomach for breaking out proteins is called pepsin. And then the whole thing enters into your small intestine. In the small intestine, as I mentioned, again, all of these things get further broken down. To further break down proteins, the enzyme in the small intestine is trypsin. And the enzyme that breaks down fat in the small intestine is lipase. So these are the major enzymes that are responsible for breaking these things down. Finally, let's get down to one more level of detail. So in the stomach, we know there is pepsin that breaks down proteins now, right? But pepsin requires an acidic medium. It only works in acidic medium. So that's why your stomach produces acid, which you might be aware of. And this acid inside the stomach is called HCL, hydrochloric acid. But how do we ensure that the hydrochloric acid does not destroy your stomach itself? Well, to protect the lining of the stomach, the stomach also produces mucus. Now, this means the food that enters from the stomach into the small intestine is very acidic. And that causes a big problem. Because all the enzymes inside the small intestine, they do not work in the acidic medium. They require a basic medium. So that's problem number one. But this is the second problem. Remember, till now fats have not been broken down. And over here, fats are large molecules. It's very hard for the lipase enzyme to break down these fats. It's not very easy. So how do we solve for this problem? Well, this is where we are going to secrete another juice into our small intestine to make sure the whole thing becomes basic. And this juice is called bile juice. Where does the bile juice come from? It's not coming from the stomach. I don't have any more space to write over here, but it comes from our liver. So it's the liver that secretes bile juice. And what it does is it converts this whole medium into more alkaline, more basic medium. So it has become more basic. But it also solves the second problem. Remember how fats were not broken down till now and lipase has a very hard time breaking it down? Well, guess what? Bile also breaks down fat into small droplets. So bile also has that effect. It breaks down the fat into small droplets. This breaking down of fat into small droplets, we give a name to it. It's called emulsification. Some fancy names. Emulsification. It basically means breaking down of fat into small droplets. And now that you have broken it down into small droplets, lipase can nicely act on it and break it further down into fatty acids and glycerol. And here's one last final, final detail now to remember. Where does trypsin and lipase, where do they come from? Well, they are not produced by small intestine. They are produced in pancreas. So it's the pancreas that produce trypsin that produce lipase. They secrete it into the small intestine and then they start working their magic on breaking down these things. So there's a lot of action that's happening over here. So it all starts with pepsin needing acidic medium because of which HCL is produced in the stomach. And then the liver produces bile juice, which makes it basic in the small intestine. This ensures the enzymes from the pancreas, the trypsin and lipase work. But additional benefit of bile is that it also emulsifies the fat. And finally, small intestine itself produces more enzymes to break down everything else into their component parts. And now all of this is absorbed by the small intestine. And to ensure maximum amount of absorption happens, the small intestine has these finger like projections that increase the surface area, which are called villi. So this increases the surface area and it maximizes the chances of absorption so that maximum amount of nutrients is absorbed in our body. And then finally whatever is left goes into the large intestine where water is reabsorbed. And then the solid mass is excreted through the anus.