Digestive System

1. Digestive System • Obtaining nutrients

2. Nutrition

3. Energy • Body cells need energy to run cell processes. • Animals obtain chemical energy from food. Energy is derived from breaking chemical bonds. • Food energy is measured in units called calories.

4. Food labeling • A typical label for packaged food lists calories and major nutrients. • While the information is incomplete, it does help people make some important choices.

5. Lipids Many lipids are made up of fatty acids and glycerine. • Lipids are fats, oils, and waxes. • Lipids are energy dense, containing 9 calories per gram. • Lipids are used for storing energy, making cell membranes, and synthesizing steroid hormones.

6. Carbohydrates • Sugars and starch are the carbohydrates that humans can digest. “Fiber” is indigestible carbohydrates, such as cellulose and inulin. • Glucose is needed by all body cells as energy. Nerve cells must have glucose to operate. Starch is made up of glucose.

7. W O R K T O G E T H E R • Sometimes my students describe sugars or starch as “fatty,” or tell me that sugar has lots of fat in it. Look at the diagrams of starch, sugar, and fat in your notes. Are they right or not?

8. Proteins Proteins are made up of amino acids. • Amino acids from digested proteins are used by cells to build all the proteins that our body needs. • Humans need a balance of the 20 amino acids, which can be obtained from animal proteins, or by blending plant protein sources.

9. W O R K T O G E T H E R • Since there are 20 different amino acids, and hundreds or thousands of amino acids in a single protein, there are billions of possible combinations and therefore many, many different, distinctive proteins. We’ve learned about some already. Name some proteins we’ve learned about. (Hint: “Meat” is a source, not a protein.)

10. Macromolecule summary

11. Minerals • Sodium, potassium, zinc, iron, calcium, copper, and selenium are among the minerals that humans need. • Most minerals can be found in whole grains, fruits, vegetables, nuts, and meats. Highly processed foods may be deficient.

12. Major Minerals

13. Vitamins • Vitamins play many different roles in metabolism. • We do not obtain energy from vitamins; however, some vitamins are necessary to run energy-related processes in cells.

14. Major Vitamins

15. Antioxidants Moral of the story: eat colorful food • Free-radicals are released by cell damage and many cell processes. • Anti-oxidants, such as Vitamins C and E, and many plant pigments, combine with free radicals and reduce their effects, which slows cell aging. No, Skittles don’t count as “colorful food!”

16. The monomers of proteins: • Simple sugars • Lipids • Amino acids • Depends on the protein

17. Humans obtain energy from: • Carbohydrates • Vitamins • Minerals • Antioxidants • All of these

18. Mom says carrots make you see better. Any reason why this might be true? • No, but they do contain antioxidants. • Yes. Beta carotenes in carrots are converted to Vitamin A. • No, it’s just an old folk belief.

19. Which nutrients are “anti-aging” because they prevent free-radical damage? • Lipids • Minerals • Antioxidants • B-vitamins

20. Which vitamin can you overdose on? • B vitamins • Vitamin C • Vitamin A • None – you can’t overdose on vitamins.

21. W O R K T O G E T H E R • Trick question: what ingredient in “energy drinks” actually gives you energy? • What would be incorrect about a label that said, “calorie-free energy drink”?

22. Digestion

23. Two-way digestion • Simple animals have a single digestive pouch with a single opening. • Food enters through the opening, waste leaves through the same opening. • These organisms must finish digesting before eating again.

24. One-way digestion • More complex animals have one-way digestion. • Food enters one opening and waste leaves from another. • Animals with one-way systems can eat any time, which is an advantage.

25. Mechanical digestion • In humans, mechanical digestion takes place in the mouth. • Human incisors and canines are adapted for tearing food, while molars are adapted for grinding food. • Saliva, which contains enzymes, mixes with food.

26. Stomach • Acid digestion occurs in the stomach. • Gastrin, a hormone, stimulates acid release. • Pepsin, an enzyme that breaks up proteins, requires an acidic environment to become active.

27. Stomach problems • Stomach ulcers cause pain when the stomach is empty. These are bacterial infections that create ulcerations. • Acid reflux is often due to weakness in the sphincter muscle at the top of the stomach.

28. Duodenum • Alkaline digestion takes place in the upper small intestine, the duodenum. • Enzymes from the pancreas require an alkaline environment to be active.

29. Pancreas and Liver • Pancreas releases pancreatic juice, containing bicarbonate, lipases, proteases, and amylase. • The liver makes bile, which emulsifies fats. Bile is made from cholesterol, which is made in the liver.

30. Small intestine • The walls of the small intestine are lined with millions of microvilli. This is the site of nutrient absorption. • Small intestines also produce many digestive enzymes to break large polymers completely down into monomers.

31. Villi and microvilli

32. Digestion and pH

33. Large intestine • Water from digested food is absorbed in the large intestine. • Bacteria present in the large intestine feed on unabsorbed nutrients, and produce several vitamins. • Fecal material is formed from fiber and other undigested material.

34. Most digestion occurs in: • The mouth • The stomach • The small intestines • The large intestines

35. Digestion of starches begins in the: • Mouth • Stomach • Small intestine • Large intestine

36. Why do we have microvilli? • To protect the intestinal lining. • To vastly increase the intestine’s surface area. • To block acids coming from the stomach.

37. Does a colon need cleaned? • Products like these raise worry in people who believe their colon is “dirty.” These are laxatives that are unnecessary, or even harmful. • “Cleansing” products can disrupt bowel function and do not cure any real illnesses. A diet high in fiber is a healthier option.

38. Hormones and digestion • Many hormones produced by the digestive system itself are responsible for appetite and digestion. • Gastrin in the stomach, produced when food is present, signals release of acid. • Secretin signals the release of sodium bicarbonate by the pancreas. • Ghrelin and Leptin, recently discovered, control appetite. Changes in these hormones cause overeating, because people with too little of these hormones don’t realize they’re full.

39. Hormones • NOVA Science Now video: Hormones and Obesity