Breakin’ It Down with Bile!

Instructional Guide

Students will learn about the function of bile salts in fat digestion. They will learn that bile salts are created by the liver and stored in the gallbladder. They will understand the concept of bile salts emulsifying fats to allow digestion. Students will follow the journey of fats in foods moving through the gastrointestinal tract and will have small knowledge checkpoints throughout this lesson. 

Intended Grade Level

6th-8th grade students. They should have a basic knowledge of the organs of the GI tract and their functions. They should be familiar with the concept of digestion. 

Learning objectives

• Students will be able to name what organ creates bile salts and what organ stores bile salts
• Student will be able to identify where bile salts interact with fats in the GI tract
• Students will be able to recall what breaks down fats and where fats come from 
• Students will be able to summarize what happens to ingested fats

Lesson Format

Students will need access to a computer for the interactive book and matching portion. The crossword puzzle can be printed out. This lesson can be done independently or in small groups. No additional supplies will be needed.

1. Students will work through an interactive book. The interactive book is self-guided and will have knowledge checks to practice their knowledge (20 min). 
2. At the end of the interactive book there will be a short matching portion where student will identify fatty foods and non-fatty foods from pictures (5-10 min). 
3. After completing the matching portion, student will then work through a crossword puzzle using keywords that they learned from the interactive book (15 min).

Lesson Background

Bile is produced by the liver and stored by the gallbladder. Bile salts are synthesized from cholesterol to make a bile acid in the liver. The bile acids are then conjugated with taurine or glycine to create a bile salt. This process also helps reduce cholesterol in the body. The bile salts are then transferred from the liver to the gallbladder via bile ducts.

The gallbladder stores bile which is composed of mainly water, bile salts, bilirubin, cholesterol, phospholipids, and electrolytes. Bile release is stimulated by food entering the duodenum (small intestine) which releases hormones (cholecystokinin) which then causes the gallbladder to contract and move bile through the bile duct into the duodenum.

Bile is necessary for fat digestion and absorption in the small intestine. Most fat that enters the small intestine are not broken down and are mainly large droplets. These droplets or globules are not attracted to water meaning they are hydrophobic. Bile salts are made up of a hydrophobic side and a hydrophilic side. The hydrophobic side of bile salts attach to the hydrophobic fat globule covering the fat globule in bile salts. The covering of bile salts helps the large fat droplet break apart into a smaller fat droplet called micelles. This process is known as emulsification and is similar to how soap breaks down oil when you wash your hands or wash dishes.

The formation of micelles increases the surface area and allows more efficient breakdown by enzymes (pancreatic lipase). After chemical breakdown of micelles, the fat is then absorbed into the lining of the small intestine. Bile salts are recycled by first being reabsorbed at the end of the small intestine (ileum) and transported back to the liver via the portal vein so that they can be used again.

What happens if the biliary system is not functioning normally? The bile duct can become obstructed. This means that bile cannot flow into the small intestine. As a result, fats cannot be broken down and won’t be absorbed into the body via the small intestine. This is not good because some vitamins are fat-soluble, meaning they dissolve in fat like how table salt dissolves in water, and then these vitamins are not absorbed into the body. The fat will continue to travel through the digestive tract until it is excreted as fatty stools (steatorrhea). Another result is that the liver cannot excrete products in the bile which can lead to liver damage.

Activities

The first activity will be an interactive book where student will learn about the learning objectives listed above. The second activity is a drag and drop interactive section where students will be able to identify fatty foods vs. non-fatty foods. The third activity will be an assessment where students will fill out a crossword puzzle. This can all be found on the student page.

Common misconceptions and challenge points

Bile acids vs. bile salts. Bile acids are used to make bile salts. Bile salt = primary bile acid + taurine or glycine

Micelles are small particles that are both hydrophilic (water-liking) and lipophilic (fat-liking). Micelles have a hydrophobic inner core and a hydrophilic outer layer. They are created by bile salts attached their hydrophobic tails to fat particles and have their hydrophilic heads towards the outside environment.

Assessment

The assessment is an crossword puzzle activity that includes key terms that the students learned. They should be able to complete the activity using the given clues and the knowledge they acquired from the interactive book. 

Further exploration

Biliary System in a Medical Setting

Quick Overview of the Biliary System