Subject:

Biology

Type of Lesson:

Use of videos/group work/teacher demo/concept mapping

Grade:

10

CSEC OBJ: B2.6, 2.9

Describe and relate to specific regions of the human alimentary canal, the intake of food, its breakdown into small molecules, its absorption and digestion. Describe what happens to the products of digestion after their absorption

Term:

Easter

UNIT: 5

Nutrition - digestion

Duration:

2 x 40 mins*

Lesson: 17

Absorption of products of digestion

Week: 6 *The lesson is designed to carry homework that can flow into another class. Objectives As a result of this lesson, you will be able to: 1 ) relate the structure of the small intestine to its function in the absorption of food. 2 ) describe the main events associated with carbohydrate and protein metabolism in the liver. 3 ) describe how the body makes use of the various end-products of digestion. Prerequisite Student Knowledge You should be familiar with: 1 ) Identifying the main regions of the digestive system on an appropriate diagram. 2 ) understanding the meaning of the terms diffusion, osmosis and active transport. 3 ) know that the circulatory system is responsible for the transport of various materials around the body and that blood flows in it in one direction inside the vessels. 4 ) the circulatory system consists of a network of blood vessels, the smallest of which (capillaries) have thin walls through which materials can easily pass by various mechanisms. Important Points Important points in this lesson: 1 ) The end-products of digestion must pass from the lumen of the gut into the blood vessels (capillaries) and lacteals so as to be transported to various parts of the body for use. Lymphatic vessels or lacteals are a part of the lymphatic system, another transport system within the body that allows for effective transport of fatty acids and glycerol. 2 ) The ileum (small intestine) is well adapted for the process of absorption. It is relatively long and highly folded. The inner surface is also covered with fingerlike projections called villi,

the cells of which have highly folded membranes forming microvilli. All of these features serve to dramatically increase the surface area available for absorption. Each villus is also equipped with a good blood supply through a network of capillaries as well as lacteals (all just beneath the surface). 3 ) The liver is a major processing center for digested food (carbohydrate, protein and lipid metabolism), as well as the storage of certain minerals and vitamins. It, along with hormones produced by the pancreas, is involved in the regulation of blood sugar levels. The liver also facilitates detoxification, breakdown of red blood cells and heat generation. 4 ) The end-products of digestion serve a variety of functions in the human body. Key Terms lacteal

villus / villi

microvilli

absorption

assimilation

deamination

Challenge Areas 1 ) You can interview a person suffering from diabetes to find out how the condition has affected their lifestyle and how they cope. 2 ) You can also find out about the cause, signs and symptoms of cirrhosis of the liver and suggest reasons why proper liver care is important.

Equipment/Material Needed Notebook, textbook, laptop computer and multimedia projector, fresh tripe (from the butcher or grocery store), 3 sheets of legal sized paper, paper towel, water. Note to Student Your teacher may show you a part of the ‘tripe’ of a cow or a pig. This is a helpful way by which you can better understand the structures shown in the textbook. There is no smell and there is no need to be ‘scornful’ of these parts of animal intestines. Human intestines are very similar to these.

Introduction 1 ) Introductory Activity – A Story A ) Listen carefully to the beginning of the following story that your teacher will read. You will be required to find I ) a suitable ending, I I ) a moral for the story.

Try This!

Would he die of starvation? Would he be rich or poor? Can he maintain A man himself worked for five thousand of dollars each day. At the end of each day, he would take every cent of the money without using his money? earned and place it into a vault at his workplace. While doing this, he received help from no one to take care of his

needs…..

B ) Complete the story to indicate what would happen to the man over a period of time. C ) What is true in this story is also true of the work of the digestive system. Can you define the term ‘digestion’? The end-products of digestion represent the money earned in the story. If it were to remain in the digestive system, it would eventually be passed out and provide rich manure for soil animals and microbes! Digestion alone is not enough. In fact it is just the beginning. In this lesson we will look at what would represent part of a good ending to the story as we answer the question: What happens to the end-products of digestion? Body of Lesson 1 ) Review of digestion A ) Before we look at what happens to the end-products, we will re-cap the story of how we ended up with those end-products in the first place by filling out the missing words in the flow chart provided as Worksheet 17.1. You may work in pairs for this activity. B ) Now, recall the dinner menu that you had created in the previous lesson. Note that the end-products would be similar to those identified on our concept maps. Remember that most foods contain a combination of various nutrients e.g. milk contains sugars, fats and proteins. We will now look at what happens to the end-products. The first part of that answer is absorption.

2 ) Relationship between structure and function A ) Use your everyday experiences to define the term ‘absorption’ and to give examples of it. B ) Watch as your teacher folds and rolls a sheet of absorbent paper towel to look like the one shown in Figure 17.1.

Notes

The cow’s digestive tract is different from ours in that there are other chambers thorough which the food passes before it reaches the true stomach and the small intestine.

Figure 17.1 She then pours water through it. Describe what happens to the water that touches the sides, as the water is being poured through the cylinder. How well does this model represent what happens in the small intestine? As our food passes through this long soft, cylindrical tube that is the small intestine, exactly how is our food absorbed? C ) Can you identify the location of the small intestine on the unlabelled chart that is on the board? Can you suggest two ways in which the small intestine differs in structure from the stomach? Suggest what would be the main benefit of having such a long tube. D ) Length is not the only feature shown by the small intestine that makes it well suited to absorption. Remember that inner surfaces of different parts of the gut vary according to function. Look at the pieces of tripe in Figure 17.2. Can you identify muscle layers of the gut wall that would be responsible for helping to move food along? Carefully observe the folds that are present and emphasize that these folds increase surface area available for production of digestive juices and for absorption.

Source: http://www.vivo.colostate.edu/hbooks/pathphys/digestion/herbivores/rumen_anat.html Figure 17.2 E ) Look at these photos in Figure 17.2 which show ways in which the different parts of the gut have folds to increase surface area. Look again at the sample of tripe. Slit one part open to show the folds. Click here to check your answers. 3 ) Absorption in the small intestine A ) Think again of the paper towel model of the small intestine made earlier and the question that was asked - How well does this model represent what happens in the small intestine? As our food passes through this long soft, cylindrical tube that is the small intestine, exactly how is our food absorbed? Now consider: What is absorption? How are nutrients absorbed? Is our model a good model?

B ) View the following video and use the video to formulate a definition of absorption. http://www.youtube.com/watch?v=Uzl6M1YlU3w Now, based on the video shown, can you say whether or not our model was a good one and why. C ) The remaining question looks at the structure of the wall of the small intestine or ileum and how it is adapted for absorption. Let us look at the next video. When ever you hear or see an adaptation for absorption please raise your hand so that we can pause the video to make note of it on the chalk board. http://videos.howstuffworks.com/hsw/23824-the-human-digestive-system-the-smallintestine-video.htm D ) Watch as your teacher demonstrates how folding increases surface area by folding sheets of paper to show how more sheets could be accommodated over the same distance if folded, e.g. 1 sheet vs. 2or 3 as shown in Figure 17.3:

Figure 17.3 E ) Continue watching the video. Note that although the large folds can be seen with the naked eye, villi are only visible with the use of a light microscope. If your school has a microscope slide of a villus you may look at this. However, later on you will examine the structure of a villus in more detail. F ) Continue viewing the video. Remember that lymphatic vessels are part of another transport /drainage system present in the body called the lymphatic system. The fluid transported is called lymph. Use your unlabelled diagram of a villus as in Worksheet 17.2, and label it and attach to your notebook. Check that your labels are correct. G ) Look again at the concept maps and on it indicate which substances pass into the bloodstream and which pass into the lacteals. Can you name the various process by which materials can pass into and out of cells? Click here to check your answers. 4 ) Assimilation – What happens to absorbed food. A ) We will now discuss what happens to food once it reaches the blood stream and the lacteals. You will learn a new word - Assimilation – watch as the teacher writes up the definition. B ) The small blood capillaries join to form larger blood vessels called venules, which then join to form a large blood vessel called the hepatic portal vein which takes the blood over to the liver. We think it might be like Kingston’s sewer system that eventually takes sewerage to the NWC’s treatment plant. Also remember that the contents of the lymph vessels will eventually be poured into the blood stream at another location.

C ) A number of things happen to nutrients as they pass through the liver, and after they leave it D ) Complete viewing the video that you watched before. http://videos.howstuffworks.com/hsw/23824-the-human-digestive-system-the-smallintestine-video.htm E ) Working in groups of three, try to answer the questions that the teacher gives you. You may use the text to help research possible answers to what is written on the slips of paper. F ) You can continue your research at home, on the internet etc. and your group needs to meet and prepare to make presentations of the findings at the next class. Check to ensure that you have the important points mentioned in the Worksheet 17.2 at the end of the lesson. Click here to check your answers.

Closure In-Class Assignments 1 ) Work in small groups to create a test paper consisting of 3 multiple choice questions and one essay type question based on what was learnt in today’s class. Provide an answer key for the questions. Out-of-Class Assignment 1 ) Completion of the research activity on liver function and assimilation.

Notes Notes osmosis Diffusion,

and active transport

The vessels of the are three processes lymphatic system are used when called lymphatic vesselsmaterials pass through cell or lacteals (‘lact-’ – membranes. These having to do with milk) processes because they appear or milky whitemechanisms when fatty are used acids and glycerol move to pass for materials into them. through cells of the

intestinal walls into the cells of the blood vessels and then into the blood or lymph itself.

Supplemental Glossary of Terms Absorption

Passage of the end-products of digestion through

the gut wall and into the blood stream Assimilation

The use that the body makes of food

Deamination

Removal of the nitrogen containing amino group from an amino acid in the liver.

Lacteal

Small lymphatic vessel

Microvilli

Folding of the cell membrane of individual cells to form a ‘brush-border’ that increases surface area

Villus (plural villi)

Microscopic projections on the inner surface of the small intestine (ileum) that increase surface area available for absorption

CSEC Questions 1 ) Using an annotated diagram ONLY, illustrate the sites where digestion occurs in humans. (4 marks) 2 ) Describe TWO features of the system which make it suitable for digestion. (4 marks) (2005) 3 ) With reference to the products of digestion in humans, illustrate why the liver is sometimes referred to as the ‘chemical laboratory’ of the body. (6 marks) )(2005) 4 ) Using ONLY a fully annotated diagram, show how the human digestive system is able to effectively perform its function. Suggest ONE way in which the digestive system protects itself from disease-causing organisms in food. (10 marks) (2007) Recommended Materials 1) Worksheet 17.1: Summary of Digestion 2) Worksheet 17.2:Structure of a villus Bibliography Atwaroo-Ali, L. (2003). CXC Biology. Oxford, UK: Macmillan Caribbean Publishers. Campbell, N. (1996). Biology (4th Edition.) San Francisco, California: The Benjamin /Cummings Publishing Company, Inc. Carrington, Agard and Sealy. (1995). Biology – Skills for Excellence. Harlow, UK: Longman Caribbean. Chinnery, L., Glasgow, J., Jones, M., Jones, G. (2001). CXC Biology. Harlow, Cambridge: Cambridge. Roberts, M. & Mitchelmore, J. (1985). Biology for CXC. Cheltenham, UK: Thomas Nelson and Sons, Ltd.

Worksheets Worksheet 17. 1: Summary of Digestion 1) Instructions: Complete the flow chart in Figure 17.4 which shows the nutrients which require digestion as well as the intermediate and end-products of digestion.

NUTRIENTS

Carbohydrates

END PRODUCTS

polypeptides

starch

sucrose

Fat droplets

glucose

galactose

Figure 17.4 2) List the other nutrients that are present in our diet, but do not require digestion. __________________________________________________________________________ __________________________________ Click here for answers Worksheet 17.2: Structure of a Villus 1) Label the diagram in Figure 17.5 to indicate the main parts of a villus.

A Villus

Figure 17.5 2 ) Important work done by the Liver A ) The body’s glucose levels are regulated by the liver. Insulin produced by the pancreas is used to convert excess glucose to glycogen for storage in the liver and muscles. This glycogen can be re-converted to glucose in the liver if the body needs it. Sometimes excess sugars are also converted into fat. B ) Excess amino acids are transformed into a carbohydrate for storage in the liver, by removal of the nitrogen containing amino group. The process is called deamination. C ) The liver is also a storage site for certain vitamins and minerals e.g. vitamin D and iron. D ) The liver also helps to remove excess cholesterol from the body by excreting it into the bile. E ) The liver is also important in detoxification e.g. in the breakdown of alcohol, and all of the activity going on results in the organ releasing a lot of heat. This heat is a by product of a process called respiration in which certain end-products are further broken down to release energy.

Click here for answers

Answers Worksheet 17. 1: Summary of Digestion 1) Instructions: Complete the flow chart in Figure 17.4 which shows the nutrients which require digestion as well as the intermediate and end-products of digestion.

Figure 17.1 2) List the other nutrients that are present in our diet, but do not require digestion. Expected answer: Minerals, vitamins, water.

Worksheet 17.2: Structure of a Villus

1) Label the diagram in Figure 17.5 to indicate the main parts of a villus.

outer layer of cells lacteal A Villus

blood capillaries

Figure 17.5