The Human Body: Week 03 The Digestive System

Introduction: The role of the digestive system is to bring nutrients into the body. Almost everything we ingest, nutritious or not, is broken down and absorbed into the body. The balance between food ingestion and expenditure of energy determines a person’s weight and general health. Diseases associated with the digestive system range from anorexia and malnutrition to diseases associated with being overweight, like diabetes, atherosclerosis, and other cardiovascular ailments. These conditions negatively influence patients’ quality of life; they increase mortality rates, and impose a great economical burden on our health care system. Currently, obesity has reached epidemic heights, especially in developed countries where overeating and consumption of “junk” food has increased in recent times. In order to manage what and how much we eat, we need to know how the digestive system works. Understanding energy balance, how food breaks down, and where it ultimately ends up in our bodies may help people make smart decisions about food consumption.

 

The physiology of the digestive system: The digestive system is composed of the digestive tract and its associated glands, the salivary glands, the liver, the gall bladder, and the pancreas. For instructional purposes, the digestive system can be divided into functional segments. These segments have specific roles in breaking down food and absorbing the products into the body. The first segment consists of the mouth, the pharynx, and the esophagus. The associated glands working in this segment are the salivary glands. Chewing breaks down the food mechanically into smaller pieces, and the salivary glands secrete enzymes that start digesting the carbohydrates present in the food. After passing through this first segment, the moist semi-digested food is called the bolus. The pharynx and the esophagus direct the bolus to the stomach.

The stomach stores food and regulates how much of it passes into the small intestine. The stomach has an acidic environment and also produces some digestive enzymes; these elements help break down proteins and kill potentially harmful bacteria. However, digestion of the bolus in the stomach is limited. As the bolus passes to the first part of the small intestine (the duodenum), glands such as the gall bladder, liver, and pancreas release substances that help with the digestion and absorption of nutrients. For example, the gall bladder releases bile containing substances that act as emulsifiers, which are important for the absorption of fat. The pancreas releases insulin and glucagon, both essential for glucose metabolism. The liver produces bile, and is also crucial in detoxifying and modifying food before sending it to the general circulation.

It is in the small intestine where proteins, carbohydrates, and fats are digested further, and where most of the nutrient and water absorption takes place. The small intestine is very long (about six meters), and the epithelium surface area is vastly increased by finger-like projections, the villi, that amplify the total absorption surface area. This vast absorption bed is crucial to maximizing movement of nutrients and water from the intestine’s lumen to the blood vessels. The last section of the digestive tract is the large intestine, colon, rectum, and anus. There is no digestion in this area; here, the last of the water and nutrients are absorbed, and undigested material is stored and expelled. The intestinal flora lining the intestinal tract, with their resident bacteria, play a crucial role in digesting sugars, providing essential vitamins, and protecting us from harmful bacteria. Our bacteria keep us healthy by collaborating and constantly communicating with the immune system, and by creating an insulation wall between the intestinal lumen and the intestinal epithelium.

The role of the digestive system is to feed the body; thus, nutrients need to reach every cell in the body. The building blocks (amino acids, sugars, and fatty acids) need to be transported from the digestive tract to the blood. The digestive epithelium is specialized to allow these elements through. While some nutrients use active transport, others use facilitated diffusion to go through the digestive epithelium, the interstitial tissue, and the endothelial cells of the capillaries. Extensive capillary beds surround the digestive tract, and are in close proximity to collect all the nutrients and water from digestion. These capillaries converge into venules and eventually congregate into the hepatic portal vein, taking all the nutrients to the liver. Once in the liver, the portal vein breaks into venules, and the venules separate further into capillary beds, where the nutrients are exposed to the liver components. This is where foods are detoxified and modified; thus, maximizing the surface area of the capillary beds is important to facilitate this function. The capillaries, containing the modified nutrients and other ingested material, grow into venules and then converge into the inferior vena cava. This is the main vein taking the deoxygenated blood full of nutrients to the right ventricle of the heart. Once in the blood, nutrients are taken to every cell in the body.

           

Misconceptions about the digestive system: There are a number of misconceptions people tend to have about the digestive system, and some of them are formed early in childhood. Children are aware of digestion because they get hungry, or have stomachaches due to bad food or too much food. Most of the information students have comes from their own perceptions, or from their parents, family, friends, television, and other sources. Some of the ideas they bring to school are preconceived notions that conflict with the information their teachers give them. It is important to address these erroneous or preformed ideas before adding more information. For example, when students are asked to represent the digestive tract (“draw what is inside you”), the accessory glands like the liver, pancreas, and gall bladder are often not illustrated in the right places, or they are drawn inside a tube that represents the digestive tract ( Ramadas & Nair, 1996; Dempster & Stears, 2014). The way the digestive system is presented to students, the structural sequence of the digestive tract, should be clearly depicted, especially the spatial relationship of the accessory glands to the stomach and the small and large intestine. This will help the students to make the link between structure and function correctly.

The idea of a system is one where all the parts come together to form a structural and functional whole. Thus, the role of each part in the working of the whole system needs to be discussed individually and then holistically (how the parts interact). Students usually know the role of individual parts, but cannot show the relationship among the components. The idea that the function of all the components in the digestive “system” is necessary to complete the same task of digesting food is often lacking or incomplete. Answers to questions such as “Where does digestion take place?” or “What organ digests what food?” are usually not correct. Moreover, the organs of the body are connected; the relationship between the circulatory, digestive, nervous, and urinary systems should be constantly emphasized (Carvalho & Clement, 2007). This shows connectivity at two different levels; among the components of the digestive system, and among all systems, as is required for the proper working of the whole body.

An important issue that has a bearing on the connectivity of body systems is that of the regulation of digestion. Students usually think that the digestive system is not regulated; rather, they believe that it is automatic, and that the food moves down the digestive tract on its own ( Ramadas & Nair, 1996). The role of the brain as regulator of the digestive system, including hormone secretion, feelings of hunger, and satiety, is usually not acknowledged. Another misunderstanding refers to the permeability of the intestinal wall (Carvalho & Clement, 2007). The idea of a “tube” is that it is impermeable, and its function is to take the contents from place A to place B. Students tend not to understand that the wall is permeable, and blood absorption of nutrients and water happens through the intestinal wall. How material moves from the digestive tract to other parts of the body is perhaps not sufficiently explored. In fact, some students think that food just diffuses from the gut to other parts of the body; the role of the portal vein is never mentioned. This misunderstanding or content gap is made clear when students where asked, “how can medicine swallowed into the stomach cure a headache?” (Ramadas & Nair, 1996). Moreover, the transformation of food in the digestive tract and subsequent absorption of broken-down food is not always clear in students’ minds. Some recent scientific developments involve the role of bacteria in assisting digestion by helping with the breakdown of foods, chemically modifying foods to improve absorption, and producing essential vitamins. Students think that bacteria are always harmful, rather than helpful and essential for life. The connection between intestinal flora and health is usually under students’ radar.

This lesson plan has three parts. Section one deals with the structure and function of the digestive system, while section two covers digestion and absorption of specific foodstuff. Each section will cover one class period in order to have enough time to explore, to understand, and to generate ideas about environmental pressures that lead to disease. Section three provides the question to be addressed by students in their problem-based research in the second part of the semester. The third part will be developed by one group of students (“the experts”), and their findings will be conveyed to their peers during class presentation and group meetings as well as to the school, family, and community at the end-of-semester health fair.

 

LESSON PLAN: HIGH SCHOOL
Lesson 2: The Digestive System
[ezcol_1quarter]Main Idea:[/ezcol_1quarter] [ezcol_3quarter_end] The digestive system is a crucial physiological component of any organism, as it allows for the transport of materials that feed every cell throughout the body. It is important to identify and understand how behaviors can cause dysfunction that leads to health problems, and to explore ways to prevent them.[/ezcol_3quarter_end]

[ezcol_1quarter]Objectives:[/ezcol_1quarter] [ezcol_3quarter_end] 1. To present a health problem related to the digestive system, its environmental roots, and ways to prevent it.
2. To verbalize the importance of social action to preempt and ameliorate health problems.
3. To show the structural and functional properties of the components of the digestive system.
4. To be able to describe how ingested food is digested, and how these materials end up in each cell of the organism.
[/ezcol_3quarter_end]

[ezcol_1quarter]Students’ Skills:[/ezcol_1quarter] [ezcol_3quarter_end] Observation, application, analysis, evaluation, problem solving, comprehension, making use of knowledge, and synthesis; these skills were drawn from Bloom’s Taxonomy and the constructivist list.
NGSS connections: HS-LS1-2, 3 and 7 From Molecules to Organisms: Structures and Processes. HS-LS2-6 Ecosystems: Interactions, Energy and Dynamics.
Core ideas: LSI.A structure and function, SL1.C organization for matter and energy flow in organisms, LS2.C Ecosystem Dynamics, Functioning and Resilience. ETS1.B developing possible solutions.
Crosscutting concepts: systems; structure and function; stability and change.
S&E practices: developing and using models. Constructing explanations and designing solutions. Engaging in argument from evidence.[/ezcol_3quarter_end]

[ezcol_1quarter]Materials:[/ezcol_1quarter] [ezcol_3quarter_end] 1. For the lecture and discussion: textbooks, material reference, and slides.
2. For the activities: handout, large poster-size pieces of paper, crayons, and computers. [/ezcol_3quarter_end]

[ezcol_1quarter]Lesson (day 1):[/ezcol_1quarter] [ezcol_3quarter_end]1. Ask the students to fill out entry cards: Write three things (at least one of them has to be negative) that come to mind when you look at food advertising on TV. Allow time to ponder, and discuss the importance of learning about how food choices may affect health in positive and negative ways.

2. Write the students’ ideas on the board. This will be part of the “Bank of ideas and problems” from which the problem-based project may be crafted.

3. Communicate to the students the objectives of the lesson (write them on the board) and explain that they will be exploring the science of the cardiovascular system as a foundation to their future research projects.

4. Show a few PowerPoint slides displaying national and world statistics on obesity and malnutrition. Ask students to form pairs and to write three sentences suggesting social, economic, and political elements that may have contributed to the shown statistics.

5. Part I: In this part, students will work on an activity addressing the structure-function relationship between the components of the digestive system. Use an organizer with three parts. Students should match items from list (a), components of the digestive tract; to list (b), functions during digestion; and list (c), digestive tract or accessory gland (see handout). If time allows, the whole class can participate in making the list.

6. Ask the students to make groups of three, and to think of the digestive system as a “disassembly line.” Based on the information in part one, each student will produce a poster showing the parts of the digestive tract and locations of the accessory glands. The diagram in the handout should help students position the parts of the digestive system correctly.

7. Allow time for students to complete their work. Circulate, making sure they are on task. Ask students to hang their posters on the wall, and to play “cakewalk” or carousel. Each group should comment and give feedback to their peers by writing on a Post-it.

8. Call the class together, and show a PowerPoint slide showing the structure of the digestive system. Discuss the physiology of the system, and the role of each component. Ask students to participate as much as possible.

9. Exit card: Write down two ideas about the digestive system that are new to you, that surprise you, or that you had all wrong. Also write down one concept that is still not clear to you.

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[ezcol_1quarter]Class Closing:[/ezcol_1quarter] [ezcol_3quarter_end]
1. Collect entry/exit cards.
2. Homework: With your new understanding, and using today’s handout, draw the digestive system structure, and write at least one function for each component. Bring to class a list of things you ate during the last day or two. [/ezcol_3quarter_end]

[ezcol_1quarter]Lesson (day 2):[/ezcol_1quarter] [ezcol_3quarter_end]1. Part II: In this part of the lesson, the focus is on how different food is broken down and absorbed during digestion. Consult the expert: Simulation of a nutritional/health profile in which each group needs to consult an expert or experts. The students’ experts will give advice on how improve the health of the person being profiled.

2. Start the class by asking students to revise their posters once more, considering the work they did for homework. They will be referring to their posters constantly.

3. Ask students to put together a nice menu from the list of foods they brought as homework. Each group will receive a menu from another group, and pretend it comes from one person.

4. The task is to break down the food into carbohydrates, protein, fats, etc. Then, each component should be analyzed by asking the following questions: What component or components of the digestive system are involved in the digestion? Follow the digestive system as a “disassembly line,” and explain how and where the food is broken down and by what elements. Students should have access to books and computers to look up information (make sure they have reliable online resources).

5. Construct a food pyramid based on what the hypothetical menu looks like. Compare to a well-balanced food pyramid. Based on this, give the person advice on changes to make for a better, balanced diet.

6. Each group should present its examination and recommendation to the class.

7Exit card: “Two things that you have learned today” and “one concept you still do not understand.”

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[ezcol_1quarter]Class Closing:[/ezcol_1quarter] [ezcol_3quarter_end]
1. Collect entry/exit cards.
2. Homework: Write a small paragraph: How does food go from the digestive tract to the blood and on to the tissues?. [/ezcol_3quarter_end]

[ezcol_1quarter]Lesson (part 3: problem-based inquiry):[/ezcol_1quarter] [ezcol_3quarter_end]1. During week seven, ask students to hand in index cards listing three possible areas (in order of preference) that they would like to explore in their problem-based inquiry projects.

2. This part will be dedicated to developing the inquiry project and producing a contribution for the Health Fair. Refer to the organization part of the curriculum for details on activities for weeks eight to 15 (they will be the same for all groups). The “question” may change depending on what is in the “Bank of Ideas.” An example of a question to be presented is:

“Mary has an older brother that she loves very much. She loves to hang out with him because he is funny and happy. Mary especially looks forward to Saturdays, because her brother takes her to the park, where they spend time playing basketball. Mary is very worried, though, because last Saturday he had a terrible headache, and slept all day. Her parents were upset about something, but she did not understand why. This Saturday, her brother had another headache; this time, she overheard her parents talking about alcohol, liver, toxins, and cirrhosis. Mary is very concerned, because she does not want her brother to get sick, and misses him very much, especially on Saturdays. She wants to construct a solid case with plenty of evidence that she can present to her brother to make him stop drinking so much. The case should show how alcohol is broken down and absorbed into the body. What and how does excessive alcohol consumption damage people’s health? You need to back up your arguments with detailed, scientific knowledge, explore the possible root of the problem, and offer a solution.”

3. During the rest of the weeks (eight to 15), students will work on developing their problem-based projects:

Week 8: Place the students into groups and start problem-based inquiry work: Organizing ideas. Allocation of tasks. Research in class work.

Week 9: Group work: Reevaluation and progress. Organizing ideas. Allocation of tasks. Knowledge application.

Week 10: Progress reports. Informal go-around-the-table discussion. Each group will submit an initial proposal about their contribution to the Health Awareness Fair. Group work.

Week 11: Group presentations/peer review. The groups will then reconsider, adjust, change, and plan further actions.

Week 12: Progress report. Each group will explain their contribution to the health fair. Newsletter contribution is due.

Week 13: Formal presentations and final preparations for the fair.

Week 14: Health Fair Day.

Week 15: Reflection; post-course questionnaire or concept map.[/ezcol_3quarter_end]

 

[ezcol_1quarter]Teacher’s Reflections[/ezcol_1quarter] [ezcol_3quarter_end]1. Things that I did not cover.
2. Did I meet the lesson objectives?
3. Comments, conclusions, and modifications.
4. Pedagogical value of the lesson. Did my students learn the concepts and ideas explored in this class? Did the assessments provide enough evidence of understanding?[/ezcol_3quarter_end]

[ezcol_1quarter]Notes to the Teacher[/ezcol_1quarter] [ezcol_3quarter_end]
1. After you provide the students with a handout, go over it and clarify question or doubts.

2. It is important to provided a lot of scaffolding. Remind students about the main ideas of the digestive system and how food is processed. What is the ultimate goal?

3. Keep a book illustration or diagram of the digestive system for parts two and three. These diagrams or posters would be an interesting addition to any science classroom.

4. Introduce the common misconceptions, and make sure the students have corrected them by engaging them in conversation during small-group activities.

5. During part three, students will be engaged in self-directed research and exploration of resources in order to answer their questions. Your job is to facilitate their work. Make sure there are enough resources, and make sure they are on target. Provide challenges or scaffolding as needed.

6. During weeks eight to 15, while the groups are working on their projects, make time to meet with each group and guide them in their contribution to the fair and newsletter.

7. Make sure ALL students participate, and differences in ability and interest are meet by supporting and suggesting allocation tasks and activities.

[/ezcol_3quarter_end]

 

ACTIVITY: HIGH SCHOOL

cropped-owlet_logo.gifThe role of the digestive system is to bring nutrients and other materials into the body. Today we are exploring the connection between the structural components of the digestive system and their functions. 

 

 

YOUR ACTIVITY:

Part I:  Match an item from the first column (structure/component) to the second column (functions), and then identify them as belonging to either the gastrointestinal tract or accessory glands. Use a different colored crayon to link the terms.

 

Slide1

 

Answer the following questions:

1. The intestinal tract is about 2 meters long. Why do you think the intestinal tract is shaped like a long tube, with turns and bends?

 

2. Does the shape of the stomach tell you anything about its function?

 

3. The intestinal tract is very long, but its epithelium contains the microvilli, which are finger-like projections that increase the surface area incredibly. Their size is equivalent to a soccer field. What do you think is the function of the microvilli? Why are there so many?

 

4. Why do you think the glands’ (liver, gallbladder, and pancreas) connections to the intestinal tract are grouped together at the start of the small intestine (duodenum)?

 

 

 Using the table and the information above, finish the diagram below by placing the components of the digestive system in the right place.

Slide2

 

PART II

1. As a group, use the homework list of food, and come up with menu for a person under a fictitious name.

 

 

2. Consult the expert: Each group will act as a nutritional/health expert and give advice about how to improve the health of the person being profiled by changing food habits.

3. Use the menu provided by your client and fill in the table below.

Slide3

 

4. Think about the final products of digestion:

    1. Amino acids are mainly used to build new proteins and nucleic acids in our bodies.
    2. Monosaccharaides are used as the main fuel for the brain, and to produce energy (ATP).
    3. Triglycerides are used to make important lipids for cell membrane fluidity and energy.
    4. The surplus of these products is converted, and stored in the adipose tissue as fat.

5. Look at the relative amounts of food recommended in the food pyramid: for example, very little oil; equal amounts of grains, vegetables, and milk; and lower levels of meat, beans, and fruits.

6. Use the pyramid below, and in the space under each food group, write recommendations for your nutrition client.

Slide4

 

 

PART III

1. Below is your group question, on which your research project, your Health Fair presentation, and newsletter contribution should be based.

Mary has an older brother that she loves very much. She loves to hang out with him because he is funny and happy. Mary especially looks forward to Saturdays, because her brother takes her to the park, where they spend time playing basketball. Mary is very worried, though, because last Saturday he had a terrible headache, and slept all day. Her parents were upset about something, but she did not understand why. This Saturday, her brother had another headache; this time, she overheard her parents talking about alcohol, liver, toxins, and cirrhosis. Mary is very concerned, because she does not want her brother to get sick, and misses him very much, especially on Saturdays. She wants to construct a solid case with plenty of evidence that she can present to her brother to make him stop drinking so much. The case should show how alcohol is broken down and absorbed into the body. What and how does excessive alcohol consumption damage people’s health? You need to back up your arguments with detailed, scientific knowledge, explore the possible root of the problem, and offer a solution.”

 

2. Keep in mind the schedule and things you should be focusing on each week.

WEEK 8: You will be placed into groups, and will start problem-based inquiry work.

  • Organizing ideas: What do we know? What information have we obtained from the core knowledge explorations and from our own background knowledge?
  • Allocation of tasks: What do we need to know? What information in the social, political, economic, and scientific realms do we need to find out? Who will do it?
  • Research (books, computers, peers, teacher). In-class work.

 

WEEK 9: Group work: Reevaluation and progress.

  • Organizing ideas: What do we know? Each student will share the outcome of her/his independent research with the rest of the group.
  • Allocation of tasks: What else do we need to know? Are there any follow-up questions?
  • Knowledge application: Put the ideas together, and focus on organizing how the work will be presented.

 

WEEK 10: Progress reports.

  • Informal go-around-the-table discussion, where each group will talk about their ideas, questions, and comments. This will allow for friendly, no-pressure peer-peer and teacher-student feedback, as well as teacher guidance.
  • Each group will submit an initial proposal about their contribution to the Health Awareness Fair. Group work.

 

WEEK 11: Group presentations/peer review.

  • Each group will present their work in progress, and the rest of the class will listen and serve as peer reviewers.
  • The presentation is followed by peer review and whole-class discussion to provide feedback.
  • The groups will then reconsider, adjust, change, and plan further action.

 

WEEK 12: Progress reports.

  • Each group will talk about the changes or adjustments made in response to the teacher’s input and peer-review comments to polish presentations.
  • Each group will explain their contribution to the health fair. Newsletter contribution is due.

 

WEEK 13: Formal presentations and final preparations for the fair.

 

WEEK 14: Health Fair Day.

 

WEEK 15: Reflection, and post-course questionnaire or concept map.

 

Annotated List of Resources and Materials:

Web site addresses to explore ideas for the Health Fair:

http://fcs.tamu.edu/health/hfpg/

http://www.health-and-wellness-fairs.com/

http://www.wikihow.com/Plan-a-Health-Fair-in-a-High-School

http://www.newtownbee.com/news/education/2013/05/30/high-school-s-health-fair-best-one-yet/140095

 

Peer review guide for the problem-based projects:

Use the following questions to review your classmate’s project. Please answer the questions AND the critique with as much detailed as you can.

 

REVIEWER NAME:

 

1. What is the main topic of this project, and what its importance?

 

2. What is the biological and sociological impact? Did the writer convey this idea clearly?

 

3. What are the main ideas or aspects of the project? Did the group clearly identify the supporting ideas? Are they pertinent?

 

4. Which aspects of the project have been developed with detail and clarity? Which ones require more work?

 

5. Is the biological aspect clear and detailed enough? Does the group provide enough relevant information for the reader to understand the idea? What is confusing?

 

 

6. Does the work present the social aspect in an interesting, relevant, and clear manner? If so, how?

 

 

7. What areas of the project need more or fewer examples that illustrate or support the ideas?

 

 

8. Identify any part of the project that does not belong or is irrelevant.

 

 

9. What are the main conclusions? Does the group propose new ideas or ways to help, solve, or contribute to the problem under discussion?

 

 

10. Did you find the paper interesting, engaging, and clearly presented? What general advice can you offer to make your peer’s work better?