Villi Help the Small Intestine? (Lisa Pieleszek)

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Title: Villi Help the Small Intestine?

Principle(s) Investigated: How do villi help the small intestine absorb nutrients?

NGSS Standards : Planning and carrying out investigations, Developing and using models, Analyzing and interpreting data, constructing explanations, using math and computational thinking

Materials: Per group: water, scissors, 30-mL graduated cylinder, metric ruler, 2 plastic cups, 3 cardboard tubes, 2 paper towel sheets, pencil

Procedure:

1) Cut cardboard tube 1 lengthwise, and flatten it.

2) Lay paper towel sheet 1 over the flattened cardboard. Cut paper towel sheet 1 to the same size as the cardboard tube.

3) Use the ruler to determine the area (area = width x length) of the flattened sheet.

4) Record the measurement onto spreadsheet.

5) Roll paper towel sheet 1 lengthwise until the sides meet, but do best not to overlap.

6) Insert this towel sheet 1 inside cardboard tube 2.

7) Use the ruler to determine the area (area= width x length) of paper towel sheet 2.

8) Record the measurement onto spread sheet.

9) Fold paper towel sheet 2 back and forth in a zigzag pattern (each fold should be about 1-11/2 cm), as for a fan or accordian fold.

10) Roll paper towel sheet 2 lengthwise until the sides meet.

11) Insert paper towel sheet into cardboard tube 3.

12) Predict which model will absorb more water. Record your prediction into spreadsheet.

13) Stand each tube with the paper towel sheets in them into a plastic cup.

14) Slowly pour 30 mL of water down the inside of each tube.

15) Remove the tubes from the water.

16) Use the graduated cylinder to measure the quantity of water left in each cup, and record it in the spreadsheet.

Student prior knowledge: Be able to multiply, Be able to use a metric ruler, Know basic organs of the digestive tract (mouth, esophagus, stomach, small intestine, large intestine), Some exposure to surface-to-volume ratio concept

Explanation:

Most of the chemical digestion and absorption of the food we eat occurs in the small intestine. The small intestine is about 6 meters long and about 3 cm in diameter. Compare that to the large intestine which is about 1.5 meters long, but 6 cm in diameter. The surface of the small intestine is covered with finger-like projections called villi (singular = villus). Villi is a latin word meaning shaggy hair. These villi are covered with thousands of microvilli. The folds and projections of villi provide a large surface area to absorb nutrients. Each villi has capillaries/vessel to take specific nutrients to specific places. The nutrients only have to go through a one-cell membrane to get to these capillaries/vessels which allows for quick absorption.

The capillaries absorb the products of carbohydrate and protein digestion. The lymph vessels absorb the undigested fats and some fatty acids. The cardboard tube represents the small intestines. The paper towel sheet 1 represents the intestinal lining without villi. The paper towel sheet 2 represents the intestinal lining with villi. The water represents the volume of nutrients in the chyme being absorbed. Chyme is the mixture of stomach fluids and broken down food. We pour the water slowly because it simulates what happens in the small intestine. When proteins enters the small intestine, it triggers the release of an enzyme, cholecystokinin (CCK). CCK has many functions, including slowing intestinal contractions to make sure more nutrients are absorbed. Sheet 1 couldn't absorb as much water because the surface area-to-volume ratio was smaller than that of sheet 2.

Our body needs to be able to absorb nutrients to maintain homeostasis ( a topic of discussion from earlier in the year). When homeostasis is disrupted in the small intestine as in celiac disease, Crohn's disease, or other types of inflamation of the small intestine, absorption of nutrients is decreased. If left untreated, this can lead to malnutrition.

Questions & Answers:

1) What happens to absorption when part of the small intestine becomes damaged/destroyed from Celiac disease?

Eating foods with gluten (wheat, rye, barley, some oats) triggers the autoimmune system which responds by damaging or destroying villi. Since villi are responsible for absorption, absorption cannot take place when they are damaged/destroyed. This results in malnutrition. The picture below shows normal intestinal villi vs. destroyed villi.

2) Once damaged/destroyed, can the small intestine be repaired?

Yes, once the cause of damage is eliminated. The villi die off, and can be replaced in a few days. For example, if the cause was gluten, then you'd eliminate gluten in your diet. If the cause was bacterial, then antibiotics may be needed.

3) Why do I feel tired after eating a large meal?

It sounds counter-intuitive doesn't it? Food provides us energy. However after eating a large meal consisting of carbohydrates, proteins, and some fats we feel tired. Well, it takes energy to produce enzymes to break down carbohydrates, fats, proteins to usable forms. Then the mode for absorbing most of these nutrients into the villi and into the bloodstream is through active transport. Remember from earlier discussions of cell structure and functions, active transport requires energy. All of these processes requires enough energy that it makes us feel tired. Once the nutrients have been transported from the bloodstream to new cells, we begin to feel energized.

Applications to Everyday Life:

One application is that air filters work in a similar way. There are several types of air filters available. A flat filter doesn't have the folds like a pleated filter, so it has less surface area for the volume of air going through it. Filtrete has air filters that are able to filter microscopic particles such as bacteria, mold, pollen, dust, pet dander. The polluted air is passed from the home air through the air filter. The air being filtered is like the nutrients being absorbed. If Filtrete made this filter flat, the microscopic particles would clog up the filter really fast. One would have to replace the filter more often. This is not environmentally or economically sound. So by increasing its surface area with the folds it can filter more particles and be used longer. Filtrete recommends that you change the filter every 1-3 months.

Another application would be buying and using cloth towels for drying. Cheaper towels have less loops (known in the industry as pile) and will absorb less water than more expensive towels with more pile. This happens because each loop acts like the villi in that they absorb. In this case, the absorption is water. There is less surface area in the cheaper towels (Can you see the "bald spots" in the first towel?).

A third application is ice melting. Ice cubes have a higher surface area to volume ratio than crushed ice. Let's say you have the same volume of water in a large block of ice as in several smaller pieces of crushed ice. The only difference is the size of the cubes/pieces. Melting occurs on the outside of the ice. The smaller pieces have more contact with the warmer environment which allows the heat to transfer to more of the ice. Watch the video below to see a time-lapse comparison between 2 types of ice shapes and melting. Also, watch the video in the explanation section for a great visual of surface area-to-volume ratio.