Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson on the small intestine. In this lesson today, we are going to be taking a look at the structure as well as the function of the small intestine. So the main function of the small intestine is to absorb nutrients from our food. So our food, as it exits the stomach, enters the small intestine. And as it moves through the small intestine, its main job is to absorb any nutrients from that food.
And we actually have three sections of our small intestine. And those are the duodenum, jejunum, and ileum, in this order. So the duodenum is the section of the small intestine connected to the stomach. The middle portion is the jejunum. And then the end portion that connects to the large intestine is the ileum. So those are our three sections of our small intestine.
And our small intestine is actually rather long. And this actually helps to make sure that we have enough space for all of the nutrients to be absorbed. And then the structure of the villi and microvilli within the small intestine, which we'll discuss in a moment, also increases the surface area for absorption.
So digestive enzymes secreted by various sources aid in the breakdown of proteins, fats, nucleic acids, and carbohydrates. So digestive enzymes which come from other accessory organs associated with the digestive system provide these enzymes which help break down these proteins, fats, nucleic acids, and carbohydrates. And then those substances can be absorbed by the body.
So for example, pancreatic amylase is an enzyme secreted that helps to absorb and break down starches. And lipase is an enzyme that helps to absorb and break down fats. So these enzymes aid with the absorption and the break down of these different nutrients or of these different materials as they pass through our small intestine. So enzymes are a very important part of our digestive system.
So we're going to take a closer look here at the structure of the small intestine, and specifically discuss villi and microvilli. So let's start with this diagram right here. So first of all, this diagram is just showing you an overview of the entire digestive system.
But the part that we want to focus on is the part here in pink. This is our small intestine. So it's connected to the stomach on one end. And then it's connected to the large intestine on the other end.
So if we were to take a look at our small intestine, this is going to be a cross-section of the small intestine. So the lumen, labeled here on the diagram, is the actual tube part of the intestine that food will pass through. So food will actually go through the lumen. It's the opening or the hollow part of the intestine.
And the lumen is lined with a layer called the mucosa. So the mucosa is the first layer of the small intestine. And then lining the mucosa are villi. So basically, we have these intestinal folds that form villi within the lumen of our small intestine.
So if we were to take a look a little bit closer here, we can see this here would be one of those intestinal folds. So let's say, for example, it's this intestinal fold right here. So we have the intestinal fold. And those, as I mentioned, line the whole inside layer of the small intestine to create more surface area for absorption.
So this is one of those intestinal folds. And then on each of those intestinal folds, we have these other little folds you'll notice. And each of these are villi. So this is increasing the surface area even more. So just having the fold in itself helps to increase the surface area for absorption. But if each of those folds have these little folds on it, it increases it even more.
So then if we were to take a look at just one of those little folds, that would be one villus. So villi is plural. Villus is singular.
And then if we take a look at just one villus, you can see that the border of it, you have these little tiny border cells all around the outside. So we call this a brush border cell. So we have these brush border cells bordering each villus. And then on the ends of that brush border cell, we have microvilli.
So having all of these different folds, the villi and the microvilli and the intestinal folds, all increases the surface area for absorption, so as many vitamins and minerals and nutrients can be absorbed from our food as possible. So this is kind of the breakdown of the structure of the small intestine.
So this lesson has been an overview on the structure and function of the small intestine.