LESSON 2.5 WORKBOOK. Blood glucose in sleep, a 5 mile run and after that Big Mac

Transcription

1 LESSON 2.5 WORKBOOK Blood glucose in sleep, a 5 mile run and after that Big Mac Using the things we have explored throughout Unit 2, in this lesson we will expand upon our knowledge of how the metabolic pathways affect specific body systems. We will focus on which organs are primarily involved in each metabolic pathway, and relate this to how the body maintains blood glucose homeostasis under three conditions: fasting, feasting and exercise. We will link the steps in metabolism that we have learned to real life experiences, and apply this knowledge to understand potential lifestyle changes. Now that we have an idea of how the body maintains glucose homeostasis, lets apply that knowledge to some real-life situations. We will use two characters, Edna and Mimi, as example of how metabolism changes depending on the food that we eat and our physical activity levels. The metabolism of Mimi We will begin by following our first character, Mimi, through a normal day. Mimi is a high school student that spends her time socializing with friends or studying. The food that she eats and the exercise she does are listed below. 7:00 am After a full night s sleep Mimi wakes up and eats a bowl of frosted wheat cereal with fat free milk for breakfast. Mimi s glycogen stores were being used up while she slept, so the sugars from the cereal will replenish those stores. Any extra glucose will be converted to fat and stored. The liver and muscle store glucose as glycogen. The liver converts extra glucose to triglycerides, which are stored in the adipose. Amino acids from the milk will be used to make new proteins. 1. What is the main source of energy used while you sleep? Amino acids. Fatty stores. Glycogen stores. d. No energy is used while you sleep. 99

2 10:00 am Mimi gets hungry so she eats a serving of flavored yogurt. 1:00 pm Mimi eats a cheeseburger and drinks a soda for lunch. 3:00 pm Mimi rides her bike around her neighborhood for 30 minutes. 7:00 pm Dinnertime! A bean, rice, cheese and vegetable burrito is for dinner tonight. 9:00 pm Mimi eats a bowl of ice cream for dessert. Because of her high sugar breakfast, Mimi s blood glucose levels have already peaked and are lowering, making her hungry. The fat, protein and sugar of the yogurt will mostly go into storage. This meal is made up of carbohydrates, protein and fat, and because her glycogen stores haven t been used up, energy from this meal is largely stored as fat. Glucose that is already in the blood will get used up first to release energy for exercise. Some glycogen stores may be broken down if blood glucose is not enough. The fiber from the beans and vegetables will help slow the digestion and absorption of the carbohydrates, protein and fat in this meal. The glycogen that was broken down during Mimi s bike ride is replenished. Extra energy goes into Mimi s fat stores. Mimi hasn t done anything to burn off her dinner, so nearly all of the energy from the ice cream is stored as fat. Some glucose will be stored as glycogen, but most of it will get converted to triglycerides and stored in the adipose. Almost all of the glucose will get converted to triglycerides and stored in the adipose. Exercise acts like insulin and brings glucose into the muscle cells to be used. Glycogen from the liver and muscle will be broken down. Some glucose will be stored as glycogen, and some will get converted to triglycerides and stored in the adipose. The glucose is converted to triglycerides in the liver and stored in the adipose. The fat will get stored as triglycerides in the adipose. 2. Where do muscles get glucose during exercise? From their own glycogen stores. From the livers glycogen stores. From gluconeogenesis. d. All of the above. 100

3 The case of exercising Edna Edna is also a high school student, and is very active! Edna is on the cross-country team and loves to run. Because Edna exercises regularly she has more muscle mass than Mimi. This means that Edna will burn more energy to maintain her weight than Mimi, and will use up her glycogen stores quicker. Muscles need glucose to make ATP to be able to contract. Once the available glucose in the blood is used up, other sources of glucose are used. Muscles will also rely on fatty acids for energy once the glucose is gone, but producing ATP from fatty acids takes much longer than from glucose, so fatty acids will only be used after the quick sources of energy (glucose and glycogen) are exhausted. Using the table below we can follow Edna through her day. To learn more about the effects of exercise on metabolism read the notes below the table that are marked with either a * or **. 6:00 am Edna wakes up early and runs a mile before going to class. 7:00 am For breakfast Edna eats a protein shake and a banan 1:00 pm At lunch Edna eats the same things as Mimi: a cheeseburger and a can of sod Glycogen stores were already being used up as Edna slept, so energy for her run comes from gluconeogenesis and breaking down amino acids and triglycerides. This is a low carbohydrate meal, but Edna s glycogen stores are getting low! Fructose from the banana will be converted to glucose in the liver and stored. Amino acids and triglycerides are used in gluconeogenesis. Because Edna burns glucose faster than Mimi, her glycogen stores are already being used by lunch. The glucose replenishes glycogen stores, and the fat will be used both for energy now and stored for later. The pancreas senses low glucose and releases glucagon. Exercise causes glucose to enter muscle cells** The liver and muscle break down glycogen into glucose. The liver converts amino acids, lactic acid* and triglycerides to new glucose. Triglycerides are broken down into glycerol and fatty acids and released from the adipose. Glycogen stores in the liver and muscle will be filled up. The glucose will replenish glycogen stores and be used for energy now. The fat will be used for energy and get stored as triglycerides. 101

4 DEFINITIONS OF TERMS Lactic acid An acid containing three carbons that is formed in the muscles during strenuous exercise. For a complete list of defined terms, see the Glossary. Workbook 3:00 pm Edna skips an afternoon snack to go to her one-hour crosscountry practice. 7:00 pm For dinner Edna eats a baked potato, green beans and roasted chicken breast. Glycogen will be broken down to glucose during practice. By the end of practice Edna s glycogen stores are used up and her liver is creating new glucose for her muscles. Glucose is made from amino acids as well as from the lactic acid being produced in her muscles*. The fiber from the vegetables will help slow the digestion and absorption of the carbohydrates, protein and fat in this meal. The glucose from the starch in the baked potato replenishes the glycogen that was broken down during exercise. Extra energy goes into Edna s fat stores. *Lactic acid can be used to make glucose During exercise the rate of the citric acid cycle can t always keep up with the amount of glucose that is being supplied to the muscles. This is because the citric acid cycle requires oxygen to be delivered from the lungs via the blood. During anaerobic exercise like running or dancing you breathe heavily because not enough oxygen is being supplied to your brain and muscles. The citric acid cycle slows down and molecules from glycolysis build up, namely pyruvate. (Pyruvate is the molecule in the last step of glycolysis before acetyl CoA is made.) Pyruvate is converted into lactic acid, which causes the burning sensation you may feel in your muscles during exercise. Lactic acid can be converted back to glucose in the liver, where it is re-released into the blood. Exercise acts like insulin and brings glucose into the muscle cells to be used. Glycogen from the liver and muscle will be broken down. Proteins in the muscle will break down to release amino acids. The liver will make new glucose from amino acids, lactic acid and fat. Most glucose will be stored as glycogen. Amino acids will be used to rebuild the proteins that were broken down during exercise. Figure 1: During exercise glucose can be converted into lactic acid, or lactate in the muscle because of limited oxygen. This is transported to the liver where it is converted to glucose through gluconeogenesis. 3. Why do we breath heavier during strenuous exercise? To increase oxygen for glycolysis. To increase oxygen for the citric acid cycle. To breathe out lactic acid. d. All of the above. 102

5 **Exercise can act like insulin The act of using your muscles can trigger a response that is similar to the effects of We previously learned that insulin tells the liver to store extra energy. Insulin also has an important role in the muscles: to bring glucose into the cells so that it can be used. During exercise, glucose from the blood can be brought into the muscle cells without the aid of This is important for people who are living with diabetes and do not have normal absorption of glucose. In this way, incorporating exercise into their daily routine can help regulate the blood glucose concentrations of someone with diabetes. 4. Which of the two characters likely burns more calories in a day? Mimi. Edn They are likely the same. 103

6 STUDENT RESPONSES What would the difference in glucose homeostasis be if someone were to go for a long run in the morning before they ate anything, compared to running an hour after eating lunch? Remember to identify your sources Workbook 104

7 TERMS TERM Lactic Acid DEFINITION An acid containing three carbons that is formed in the muscles during strenuous exercise. For a complete list of defined terms, see the Glossary. Workbook 105