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Small Intestine

Small Intestine

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This lesson will examine the structure of the small intestine and its role in digestion.

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Tutorial

What's Covered

Welcome to this lesson on the small intestine. In this lesson today, you are going to be taking a look at the structure as well as the function of the small intestine. Specifically, you will learn about:

  1. Main Function
  2. Structure

1. Main Function

The main function of the small intestine is to absorb nutrients from our food.

Term to Know

    • Small Intestine
    • A part of the digestive tract where the majority of nutrients are absorbed.

As food exits the stomach it enters the small intestine and moves through the small intestine. The main function of the small intestine is to absorb nutrients from food.

Digestive enzymes secreted by various sources aid in the breakdown of proteins, fats, nucleic acids, and carbohydrates. These digestive enzymes come from other accessory organs associated with the digestive system and make it easier to break down these proteins, fats, nucleic acids, and carbohydrates for absorption.

Example Pancreatic amylase is an enzyme that helps to absorb and break down starches while lipase is an enzyme that helps to break down and absorb fats. In summation, these enzymes aid with the break down and absorption of these different nutrients as they pass through the lumen of the small intestine.

Terms to Know

    • Peristalsis
    • Wave-like muscle contractions that push contents through the small intestine.
    • Amylase
    • An enzyme that breaks down carbohydrates in the digestive system.
    • Lipase
    • An enzyme that breaks down fats in the digestive system.

Big Idea

Enzymes are a very important part of our digestive system.


2. Structure

There are three sections of the small intestine called the duodenum, jejunum, and ileum, in this order. The duodenum is the section of the small intestine directly connected to the stomach, the middle portion is the jejunum and then the end portion that connects to the large intestine is the ileum.

Terms to Know

    • Duodenum
    • The first section of the small intestine.
    • Jejunum
    • The middle section of the small intestine.
    • Ileum
    • The last section of the small intestine which connects to the large intestine.

The small intestine is actually rather long which actually helps to make sure that you have enough space for all of the nutrients to be absorbed. The structure of villi and microvilli within the small intestine also increases the surface area for absorption.

Terms to Know

    • Villi
    • Small finger-like projections that line the mucosa and act to increase surface area and absorb nutrients.
    • Microvilli
    • Hair-like projections that cover villi and aid in absorption of nutrients.

Take a look at the diagram below to get a closer look at the structure of the small intestine.

The diagram above is showing you an overview of the entire digestive system or the alimentary canal. The part that you want to focus on is the part in pink; your small intestine which is connected to the stomach on one end and to the large intestine on the other end. This is a cross-section of the small intestine, so the lumen is the actual tube part of the intestine that food will pass through, which is the opening or the hollow part of the intestine.

The lumen is in contact with the layer called the mucosa, which is the first layer of the small intestine. The lining of the mucosa are called microvilli, which are intestinal folds that form villi within the lumen of our small intestine. On each of those intestinal folds, you have other little folds and each of these are villi which increase the surface area of the mucosa. By increasing the surface area with these intestinal villi we have an much larger surface area for absorption.

If you to take a look at just one of those little folds, that is an individual villus; villi is plural. If you take a look at just one villus you can see that the border of it there are tiny border cells all around the outside called a brush border. Every villus has a brush border and each brush border contains microvilli which in turn create a very large surface area for absorption.

Big Idea

Having all of these different folds, villi and microvilli, and the intestinal folds, all increases the surface area for absorption. This ensures as many vitamins and minerals and nutrients overall can be absorbed from our food as possible.


Summary

So this lesson has been an overview on the structure and function of the small intestine. The structure of the intestine was covered with brief descriptions of how each part contributes. Such as he duodenum is the section of the small intestine directly connected to the stomach and the villi and microvilli, and the intestinal folds, all increase the surface area for absorption.

Keep up the learning and have a great day!


Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
  • Lipase

    An enzyme that breaks down fats in the digestive system.

  • Amylase

    An enzyme that breaks down carbohydrates in the digestive system.

  • Peristalsis

    Wave-like muscle contractions that push contents through the small intestine.

  • Ileum

    The last section of the small intestine which connects to the large intestine.

  • Jejunum

    The middle section of the small intestine.

  • Duodenum

    The first section of the small intestine.

  • Microvilli

    Hair-like projections that cover villi and aid in absorption of nutrients.

  • Villi

    Small finger-like projections that line the mucosa and act to increase surface area and absorb nutrients.

  • Small Intestine

    A part of the digestive tract where the majority of nutrients are absorbed.