Food and Digestion

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Food and Digestion

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1. Food and Digestion

2. Food and Energy

3. Why You Need Food Food provides your body with: materials for growing, for repairing tissues, it provides energy for everything you do, and it enables your body to maintain homeostasis.

4. Nutrients The raw materials that food provides are called nutrients There are six kinds of nutrients necessary for human health: Carbohydrates – provide energy Fats – provide energy Proteins – provide energy Vitamins Minerals Water The energy in foods can be measured in units called Calories. The more calories a food has, the more energy it contains.

5. Carbohydrates Carbohydrates are composed of carbon, oxygen, and hydrogen – they are a major source of energy. Carbohydrates are divided into two groups based on their chemical structure – simple and complex carbohydrates.

6. Simple Carbohydrates Simple carbohydrates are also known as sugars. One sugar, glucose, is the major source of energy for your body’s cells. Most foods do not contain large amounts of glucose, so the body must convert other types of sugars into glucose.

7. Complex Carbohydrates Complex carbohydrates are made up of many sugar molecules linked together in a chain. Starch and fiber are complex carbohydrates. Nutritionists recommend that 50% to 60 % of the calories in a diet come from carbohydrates.

8. Fats Fats are high energy nutrients. They contain twice as much energy as an equal amount of carbohydrates. Fats: form part of the structure of cells, protect and support your internal organs, and act as insulation to keep heat inside your body.

9. Types of Fat Fats are classified as either unsaturated or saturated fats, based on their chemical structure. Unsaturated fats are usually liquid at room temperature. (i.e. olive oil, salmon) Saturated fats are usually solid at room temperature. (i.e. meat, dairy products) Nutritionists recommend that no more than 30% of the Calories eaten each day come from fats.

10. Cholesterol Foods that contain saturated fat often contain cholesterol – a waxy fatlike substance found only in animal products. Cholesterol is not a required part of your diet because your liver can make all of the cholesterol your body needs. Extra fats and cholesterol in the diet can lead to a buildup of fatty material in the blood vessels, which can cause heart disease.

11. Proteins Proteins are nutrients that contain nitrogen, carbon, hydrogen, and oxygen. They are needed for tissue growth and repair. They also play a part in chemical reactions within cells. Proteins can serve as a source of energy, but less so than fats or carbohydrates. About 12% of your daily Calorie intake should come from proteins.

12. Amino Acids Proteins are made up of small units called amino acids, which are linked together chemically to form large protein molecules. Thousands of different proteins are built from only about 20 different amino acids. Your body can make about half of the amino acids it needs - the others must come from the foods you eat.

13. Complete and Incomplete Proteins Proteins from animal sources, are called complete proteins because they contain all the essential amino acids. Proteins from plant sources are called incomplete proteins because they are missing one or more essential amino acids.

14. Vitamins In the 1700s sailors often developed scurvy, which is caused by a lack of vitamin C. In 1754 – Scottish doctor, James Lind recommended that all sailors eat citrus fruits. In 1795 - scurvy disappeared from the British Navy. Vitamins act as helper molecules in a variety of chemical reactions within the body. The body needs only small amounts of vitamins. It can make some of them on its own while others must be obtained from foods. Vitamins are classified as either fat-soluble or water-soluble. Fat-soluble vitamins dissolve in fat and are stored in fatty tissues in the body. Water-soluble vitamins dissolve in water and are not stored in the body.

15. Minerals Minerals are needed by your body in small amounts. Minerals are nutrients that are not made by living things. We obtain minerals by eating plant foods or animals that have eaten plants.

16. Water People can survive for weeks without food, but they will die within days without fresh water. Water accounts for 65% of the average person’s body weight. Water is the most important nutrient because the body’s vital processes take place in water. Water makes up most of the body’s fluids, including blood. Under normal conditions, you need to take in about 2 liters of water every day.

17. The Food Guide Pyramid The food guide pyramid was developed by nutritionists to help people plan a healthy diet. The Food Guide Pyramid classifies foods into 6 groups. It also indicates how many servings from each group should be eaten every day to maintain a healthy diet.

19. Food Labels The United States Food and Drug Administration requires that all food items except meat, poultry, fresh vegetables, and fresh fruit must be labeled with specific nutritional information. Food labels allow you to evaluate a single food as well as to compare the nutritional values of two foods.

20. Serving Size The serving size and the number of servings in the container are listed at the top of the label. The FDA has established standard serving sizes for all types of foods. The information on the rest of the label, including Calorie counts and nutrient content, is based on the serving size.

21. Calories from Fat The next item on the food label is the number of Calories in a serving and the number of Calories that come from fat. Remember that no more than 30% of the Calories you consume should come from fats. To find out if a specific food falls within this guideline, divide the number of Calories from fat by the total number of Calories then multiply by 100.

22. Daily Values Daily values are recommendations for the amounts of specific nutrients that average people should obtain from their diets each day. The percent daily value indicates how the nutritional content of one serving fits into the diet of a person who consumes a total of 2,000 calories a day.

23. Ingredients Food labels list ingredients in order by weight, starting with the main ingredient. By reading ingredient lists, people can find foods that contain nutrients they need and avoid foods that contain substances to which they are allergic.

24. Key Ideas Nutrients in food provide the body with energy and materials needed for growth, repair, and other life processes. The energy in foods is measured in Calories. The six nutrients necessary for human health are carbohydrates, fats, proteins, vitamins, minerals, and water. Water is the most important nutrient because it is necessary for all body processes. The Food Guide Pyramid classifies foods into six major groups and tells how many servings to eat from each group. Food labels list the nutrients in foods and show how the foods fit into your daily diet.

25. Section 1 Review

26. Question 1 List the 6 nutrients that are needed by the body. Answer: Carbohydrates, fat, proteins, vitamins, minerals, water.

27. Question 2 What information does the Food Guide Pyramid provide? How many food groups are there? Answer: The Food Guide Pyramid classifies food into 6 groups. It indicates how many servings from each group should be eaten on a daily basis.

28. Question 3 Explain how food labels can help a person make healthy food choices. Answer: Nutrition fact labels help a person to evaluate the nutritional contents of a single food and to compare foods.

29. Question 4 Why should you eat more complex carbohydrates than simple carbohydrates? Answer: Complex carbohydrates provide more even, long-term energy than do simple carbohydrates. Foods high in complex carbohydrates usually provide more nutrients than simple carbohydrates.

30. Question 5 Evaluate the impact of James Lind’s research into scurvy. How did this research affect people’s lives? Answer: Lind’s research was very important because it led to a simple way to avoid scurvy – eat citrus fruits.

31. The Digestive Process Begins

32. Dr. William Beaumont In 1822, Alexis St. Martin was wounded in the stomach. William Beaumont, a doctor with the US Army, saved St. Martin’s life. However, the wound never closed completely. This allowed Beaumont to study what was happening inside St. Martin’s stomach. He hypothesized that chemical reactions inside the stomach broke down foods into smaller particles.

33. Functions of the Digestive System Beaumont’s observations helped scientists understand the role of the stomach in the digestive system. The digestive system has three main functions. First, it breaks down food into molecules the body can use. Then, the molecules are absorbed into the blood and carried throughout the body. Finally, wastes are eliminated from the body.

34. Digestion Digestion allows your body to get the nutrients and energy it needs from the food you eat. There are two kinds of digestion: Mechanical – foods are physically broken down into smaller pieces. Chemical – chemicals produced by the body break foods into their smaller chemical building blocks. Absorption is the process by which nutrient molecules pass through the wall of your digestive system into your blood. Materials that are not absorbed are eliminated from the body as wastes.

35. Mechanical Digestion The process of mechanical digestion begins as you take your first bite of food. Your teeth carry out the first stage of mechanical digestion. The structures of different kinds of teeth enable them to perform specific functions. As the teeth do their work, saliva mixes with the pieces of food, moistening them into one slippery mass.

36. Chemical Digestion Chemical digestion also begins in the mouth. Chemical digestion is accomplished by enzymes. An enzyme is a protein that speeds up chemical reactions in the body. Your body produces many different enzymes. Each enzyme has a specific chemical shape – its shape enables it to take part in only one kind of chemical reaction.

37. The Start of the Process - The Mouth Even before you eat, when you smell a tasty food, see it, or think about it, digestion begins. Saliva begins to form in your mouth. When you eat, the saliva breaks down the chemicals in the food, which helps make the food mushy and easy to swallow. Your tongue pushes the food around while you chew with your teeth. When you're ready to swallow, the tongue pushes a tiny bit of mushed-up food toward the back of your throat and into the opening of your esophagus, the second part of the digestive tract.

38. The Esophagus The esophagus is like a stretchy pipe that's about 10 inches long. It moves food from the back of your throat to your stomach. When you swallow food or liquids, a special flap called the epiglottis flops down over the opening of your windpipe to make sure the food enters the esophagus and not the windpipe. After food enters the esophagus, contractions of smooth muscles push the food toward the stomach. These involuntary waves of muscle contraction are called peristalsis. They occur in the stomach and throughout the digestive system.

39. The Stomach Your stomach is attached to the end of the esophagus. It's a stretchy sack shaped like the letter J. It has three important jobs: to store the food you've eaten to break down the food into a liquidy mixture to slowly empty that liquidy mixture into the small intestine The stomach is like a mixer, churning and mashing together all of the food that comes down from the esophagus. It does this with help from the strong muscles in the walls of the stomach and gastric juices. In addition to breaking down food, gastric juices also help kill bacteria that might be in the eaten food. Digestive juice contains the enzyme pepsin and hydrochloric acid.

40. Key Ideas The functions of the digestive system are to break down food, absorb nutrient molecules into the blood, and eliminate wastes. During mechanical digestion, food is ground into small pieces. During chemical digestion, large food molecules are broken into small molecules by enzymes. Food first passes from the mouth into the esophagus, and then into the stomach. Waves of muscle contractions, known as peristalsis, keep the food moving in one direction.

41. Section 2 Review

42. Question 1 List the functions of the digestive system. Answer: To break down food into molecules that can be used by the body; to absorb the food molecules into the blood; to eliminate wastes for the body.

43. Question 2 Explain how the structure of incisors relates to their function. Answer: Incisors have sharp edges that cut food.

44. Question 3 Describe peristalsis and explain its function in the digestive system. Answer: Peristalsis consists of involuntary waves of muscle contractions that help push food through the digestive system.

45. Question 4 What is the function of pepsin? Answer: Pepsin is an enzyme in the digestive juice produced in the stomach; it breaks down proteins into shorter chains of amino acids.

46. Question 5 If your stomach could no longer produce acid, how do you think that would affect digestion? Answer: Without acid, pepsin cannot function properly, and therefore protein digestion couldn’t take place in the stomach.

47. Final Digestion and Absorption

48. The Small Intestine After the thick liquid leaves the stomach, it enters the small intestine. The small intestine is a long tube that's about 1 1/2 inches to 2 inches around, and it's packed inside you beneath your stomach. Almost all chemical digestion and absorption of nutrients take place in the small intestine.

49. Help from the Pancreas The pancreas is a triangular organ that lies between the stomach and the first part of the small intestine. The pancreas produces enzymes that flow into the small intestine. These enzymes help break down starches, proteins, and fats.

50. The Role of the Liver The liver is located in the upper portion of the abdomen. It is the largest and heaviest organ inside the body. As part of the digestive system, the liver produces bile, which helps to absorb fats into the bloodstream.

51. The Gallbladder Bile flows from the liver into the gallbladder, the organ that stores bile. The gallbladder serves as a warehouse for bile, storing it until the body needs it.

52. Absorption in the Small Intestine After chemical digestion takes place, the small nutrient molecules are ready to be absorbed by the body. Millions of tiny finger-shaped structures called villi cover the surface. The villi absorb nutrient molecules. Nutrient molecules pass from cells on the surface of a villus into blood vessels. The blood carries the nutrients throughout the body for use by body cells. The presence of villi increases the surface area of the small intestine – this greatly increased surface enables digested food to be absorbed faster than if the walls of the small intestine were smooth.

53. Villi in the Small Intestine

54. The Large Intestine The large intestine is the last section of the digestive system. It is about 1 ˝ meters long. It runs up the right-hand side of the abdomen, across the upper abdomen, and then down the left-hand side. The large intestine contains bacteria that feed on the material passing through. The material entering the large intestine contains water and undigested food such as fiber. As the material moves through the large intestine, water is absorbed into the bloodstream. The remaining material is readied for elimination from the body. The large intestine ends in the rectum. Here waste material is compressed into a solid form. This waste is eliminated from the body through the anus.

56. Key Ideas Almost all chemical digestion and absorption of nutrients takes place in the small intestine. Nutrients are absorbed into the bloodstream through the villi of the small intestine. As material moves through the large intestine, water is absorbed. The remaining material is readied for elimination.

57. Section 3 Review

58. Question 1 What two digestive processes occur in the small intestine? Answer: Chemical digestion – liquefied food mixes with digestive juices and is broken down into the building blocks of starches, proteins, and fats. Absorption – villi absorb nutrients and pass them into blood vessels.

59. Question 2 Which nutrient is absorbed in the large intestine? Answer: Water

60. Question 3 How do the liver and pancreas function in the digestive process? Answer: The liver produces bile, a substance that breaks up fat particles. The pancreas produces enzymes that help break down starches, proteins, and fats.

61. Question 4 Some people are allergic to a protein in wheat. When these people eat foods made with wheat, a reaction destroys the villi in the small intestine. What problems would you expect these people to experience? Answer: Without villi, the body cannot absorb nutrients. A person with this condition may eat large amounts of food and yet not obtain sufficient nutrients.

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