 Hey everybody, Dr. O here and this is where we're going to talk about chemical digestion. So I think we've done a good job of talking about like the ingestion of food, the propulsion or movement of food. We've covered all that. We've talked about just the physical digestion that occurs, the physical breakdown of food. But chemical digestion is the most important step prior to absorption and then the last thing we would talk about would be the elimination of food that isn't absorbed and that would be defecation. So here you see just this path as food travels from your mouth to your anus. It's going to be physically broken down. It's going to be chemically broken down. And then once it's broken down into its smallest parts, that will be absorbed in your bloodstream and the rest will pass through you as fecal material. Let's go ahead and look at this. We're just going to focus on the chemical digestion part and I'll cover all the enzymes here. We'll start at the mouth. At the mouth, we do have some chemical digestion of carbohydrates and fats. I'll talk about the enzymes in a second. No real digestion in the esophagus except for the split second that it's there. The stomach is going to be involved in the chemical digestion of proteins and fats. Primarily, so carb digestion is not a big deal during the stomach. Then we get to the small intestine. All things are going to be, that's where 80% and 90% of this chemical digestion is going to take place. And then you see no chemical digestion at the end of your intestinal tract unless you're talking about what your microbiome, your gut bacteria are doing. So the point of chemical digestion is you take these large complex things. Let's say you have a steak and a mashed potato or whatever. You take the large complex proteins that are in that steak and break them down into individual amino acids. You take the large starches in that potato and break them down into individual glucose subunits. And you take the fats in that meal and you digest them. They're not broken down quite as far, but they're broken down. Remember, fats are usually triglycerides. They're going to be broken down into a monoglyceride, so that glycerol backbone with one tail and then two free fatty acids. That's the level of chemical digestion that needs to take place prior to the absorption of your food. So let's start with the enzymes and we'll go by area and then we'll go by macronutrient. Here you see salivary enzymes that you have lingual lipase that's going to come from the tongue. It's going to help start to break down the digestion of fats. That's what lipase tells you. And you have salivary amylase, which is going to help the breakdown of carbohydrates. But the lingual lipase that's in your mouth, some of that is actually still going to continue to work in your stomach. So it's kind of produced in your saliva, but it's also is active in the stomach. The stomach, you're going to have gastric lipase to help break down fats. And you're going to have pepsin. That little asterisk there is just because, remember, pepsin is released as pepsinogen or it's an inactive hormone or enzyme that needs to be activated by stomach acid. If not, it would eat your stomach. So that's what the asterisk is for there. So those are going to be the enzymes from your saliva in your mouth and your stomach. Then we go to the pancreatic enzymes. I do not ask you to know all these, but the key ones would be chymotrypsin and trypsin. Those are going to be your two protein digesting enzymes. Then we have pancreatic amylase to break down carbs and pancreatic lipase to break down lipids. Just so you see, obviously there are other enzymes involved like nucleases. We do eat DNA and RNA. It needs to be broken down, but I don't think you need to know it to that level. And then we have what's called the brush border. Hopefully you remember from earlier, the brush border is going to be the fact that you have this massive surface area in your small intestine. The cells of your small intestine are all lined with hundreds of millions of micro billi. So it creates this brush border and these would be the enzymes that finish digestion. So as you can see here, we have this dextranase is going to break down these small chains of glucose into individual glucoses. Lactase is going to break lactose down into glucose and galactose. This is more of a nutritional thing, but maltase is going to break maltose down into a glucose and another glucose. Sucrose would be the enzyme that breaks down sucrose or table sugar turning it turning sucrose into a glucose and a fructose. Those would be the key ones there, but this little bit, if digestion needs to be finished off right prior to absorption, that's going to be the job of the enzymes in your brush border. Just to go, so we went by location, now let's talk about bi macronutrient. So here you see starch or glycogen being broken down by salivary amylase and that's going to break them down into smaller and smaller carbohydrates. Your polysaccharide chains are going to be broken down into individual monosaccharides by that dextranase enzyme. The disaccharides, they just went through maltose, sucrose and lactose. They each have their own enzyme and you can see they're on the bottom what they're broken down into. We cover that in carbohydrates and nutrition class. As far as locations, salivary amylase would be in the saliva, your dextranases and the other maltases, et cetera, they're all going to be there in that brush border right before this will be absorbed into your bloodstream. Protein digestion, protein is complex to break down because you have to unravel and denature the proteins before you can even really begin to chemically digest them down into their individual amino acids. That's why protein has such a high satiety value. It takes a while to digest protein. So you can see here that no protein digestion in the mouth, in the stomach that's where hydrochloric acid will denature your proteins while the enzyme pepsin starts to chew them up and then when the food travels to the small intestine, you would have your tripsin and chymotripsin are going to be involved as well as those peptidase enzymes. But in the end, you need to break your proteins down into individual amino acids and then absorb them. Now, you could say that some really small protein chains can be absorbed, but the healthier your gut is, the more likely your proteins have to be fully digested before they can be absorbed. Lipids, so lipids are going to be a little more complicated here. I know this isn't going to get along, I didn't want to break it into four videos though, but lipids are going to be a little more complicated because they're not absorbed into your bloodstream. They're absorbed into these lactales. That's because they're real large. So as you can see here, when your big, large fats are emulsified, that's going to give them a huge surface area, but you can't just absorb the fats because oil and water don't mix. Fatty acids have to be packaged into what's called a micelle before they're absorbed by the cells in the intestine. And then they're going to be rebuilt. So you basically break down a triglyceride to rebuild it. Then they're going to be packaged in what's called a kylo-micron, and that's going to be what's absorbed into your lactales and carried through your lymphatic system. Now the next step, and we'll cover this in more other topics, but the next step, once this stuff starts to circulate, that's when you're going to start to see things like, see these lipids carried, triglycerides carried in LDL, HDL. You're good and bad cholesterol if you want to call it that. That's a topic for a whole another day. So that's the basics of the digestion and absorption of lipids. Okay, so that is chemical digestion in a nut cell. Obviously it's a 10,000 foot view, but in the end just think whatever you eat has to be properly digested so it can be mechanically, physically and chemically, so it can be properly absorbed and get into your body where we can use it to build you, this whole you are what you eat thing, right? All right, I hope this helps. Have a wonderful day, be blessed.