 First, we're going to talk about how nutrients are digested. So let's look at our three main categories of nutrients that we want to absorb. We want to absorb carbohydrates. We want to absorb proteins. And we want to absorb lipids or fats. Of course, we also are going to want to absorb different vitamins. I mean, there's other stuff, water. There's all sorts of stuff that we're going to want to absorb. But when we eat anything, it doesn't come, most things don't come with our nutrients in a form that we can just automatically absorb. The process by which we absorb these different nutrients, we're going to take an entire section to talk about each one of them. In this section, I just want to get our brains around how we're going to actually break them up. First of all, there's lots of forms of digestion. We can actually have mechanical digestion where you bust it up by chomping it up. So you could take a piece of bread, which is full of carbs, and chomp it into smaller pieces. That's awesome, go for it, chomp away. But the bottom line is that even the mechanical digestion of chomping, mechanical digestion gets you only so far. So we're going to have to add some chemicals, and the chemicals are enzymes. And all three of these rely on different enzymes to begin the digestion process or complete the digestion process. Mechanical digestion, that's fantastic. That's actually going to increase surface area of the food you ate, super important, makes it so that the enzymes can be more efficient and effective at dealing with your food that you put into your digestive system. But ultimately, the enzymes are going to do the hard work. So carbohydrate digestion begins in the mouth with salivary amylase. And salivary amylase breaks up starch. So starch is like a huge chain of glucose molecules. Salivary amylase is going to break up glucose, starch molecules into smaller pieces. Dysaccharides or trisaccharides, little smaller chunks of smaller sequences, smaller groups of glucose molecules. Because starch is a big string of glucose molecules, I say that part yet, it begins in the mouth, but then in the small intestine, holy starch madness, holy carbohydrate digestion madness. We've got enzymes such as maltase, which breaks down a disaccharide called maltose, which is made of two glucose molecules. We have lactase, which breaks down lactose, which is made of galactose and glucose. And then we have another one, another example is, oh, hell, sucrose. Well, of course, sucrose, which breaks down sucrose, which is a fructose and a glucose. What? So all of these enzymes break down sugars into monosaccharides. And monosaccharides are what we are going to absorb. In the very next section, we're going to look at how we absorb monosaccharides from the lumen of the digestive tract and into the bloodstream. Proteins, we have multiple proteases that are involved in protein digestion. Again, we can bust them up all we want, but we need the chemicals to break them down. This begins in the small, I mean in the stomach. And if you remember from anatomy, we had a pepsinogen, which was a protein enzyme that was produced by cells in the stomach. And pepsinogen is activated by hydrochloric acid into pepsin. Pepsin is the active protein digester. So the low pH of the stomach will actually denature the proteins and fold them in a way that makes them kind of spread out a little bit more. So then the active protein enzyme pepsin can come in and cleave the amino acids into smaller chunks. There is more digestion that happens in the small intestine. All sorts of different enzymes are active in the small intestine that are breaking proteins down into one to two amino acid long chains, bundles, groups of two amino acids together or one amino acid together. And lipids are kind of dealt with in a different way. We do have various lipases. These are fat digesters. Lipases are going to break the lipids up into the component parts of lipids. But somebody who's really important in this process, and I'm going to make them green even though they aren't involved with proteins, it's bile. Bile helps emulsify fats. Emulsify the fats. And basically what that means is the bile makes it so that the fat can be dissolved in the water. We know that if we add fat and water together, oil and water, they don't mix. They're like, dude, that oil stuff, keep that somewhere else in the oil. It's like, don't mess with me, water. You're a punk, stay away. Bile gets in there. It's kind of like surfactant in the alveoli. It gets in there and it surrounds the lipids and helps the lipids basically get surrounded by water molecules. When that happens, it increases surface area so that the lipases can do their job. The lipases are going to break the fats down into particular size pieces that are then going to be absorbed. So let's start by looking at the carbohydrates, how we absorb the monosaccharides after they've been broken down by the enzymes.