Chapter 45

1. Chapter 45 Processing Food and Nutrition

2. Heterotrophs • Organisms that obtain nourishment from the organic molecules manufactured by other organisms • Nutrients used to • Run the systems of the body • Make compounds for metabolic processes • Grow and repair tissue

3. Nutrition • Process of taking in and using food • Malnutrition results from dietary intake that is either below or above required need • Undernutrition (particularly protein deficiency) • Obesity (common in the US)

4. Food processing • Ingestion • Taking of food into the digestive cavity • Digestion • Process of breaking down food mechanically and chemically • Absorption • Nutrients pass through the lining of the digestive tract and into the blood

5. Food processing, cont. • Egestion or elimination • Food that is not digested and absorbed is discharged from the body

6. In cnidarians and flatworms • Food is digested in the gastrovascular cavity • The gastrovascular cavity serves as both mouth and anus

7. Simple invertebrate digestive systems

8. In more complex invertebrates and in all vertebrates • The digestive tract is a complete tube with an opening at each end • Digestion takes place as food passes through the tube

9. Digestive tract with two openings

10. Various parts of the digestive tract are specialized to perform specific functions • Food passes in sequence through • The mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus

11. Human digestive system

12. Mechanical and enzymatic digestion of carbohydrates begin in the mouth • Mammalian teeth include incisors for biting, canines for tearing, and premolars and molars for crushing and grinding • Three pairs of salivary glands secrete saliva

13. Teeth and diet

14. Tooth structure

15. As food is swallowed, it is propelled through the pharynx and esophagus • A bolus of food is moved by peristalsis • The mixing and propulsive movements of the digestive tract are known as motility

16. Peristalsis

17. In the stomach • Food is mechanically digested by vigorous churning • Proteins are enzymatically digested by pepsin • Rugae are stomach folds that expand with food • Gastric glands secrete hydrochloric acid and pepsinogen

18. Structure of the stomach

19. After several hours in the stomach • Chyme leaves the stomach through the pylorus and enters the small intestine • Most enzymatic digestion takes place in the duodenum • The liver produces bile, which emulsifies fats

20. After several hours in the stomach, cont. • The pancreas releases enzymes that digest protein, lipid, and carbohydrates, as well as RNA and DNA • The large intestine eliminates undigested waste and incubates bacteria that produce Vitamin K and certain B vitamins

21. The liver and pancreas

22. Digestion of carbohydrate, protein, and lipid • Nutrients in chyme are enzymatically digested as they move through the digestive tract • Polysaccarides are digested to the disaccharide maltose by salivary and pancreatic amylases

23. Digestion of carbohydrate, protein, and lipid, cont. • Maltase splits maltose into glucose • Proteins are split by pepsin and by proteolytic enzymes into the final product of amino acids • Lipids are emulsified by bile salts and then hydrolyzed by pancreatic lipase

24. Summary of digestion

25. Some hormones that regulate digestion

26. Structural adaptations that increase the surface of the digestive tract • The surface area of the small intestine is greatly expanded by • Folds in its wall • Intestinal villi • Intestinal microvilli

27. Villi and microvilli

28. Lipid absorption • Nutrients are absorbed through the thin walls of the intestinal villi • The hepatic portal vein transports amino acids and glucose to the liver

29. How the body uses fat

30. Absorption of other nutrients • Fatty acids and monacylglycerols enter epithelial cells in the intestinal lining where they are reassembled into triacyglycerols • They are packed into chylomicrons • The lymphatic system transports chylomicrons to the blood circulation

31. Nutritional requirements for dietary carbohydrates • Most carbohydrates are ingested in the form of complex carbohydrates • Fiber is a mixture of cellulose and other indigestible carbohydrates • Carbohydrates are used mainly as an energy source

32. Lipids are used as • An energy source • Components of cell membranes • To synthesize steroid hormones and other lipid substances • Most lipids are ingested in the form of triacyglycerols

33. Proteins • Serve as enzymes • Are essential structural components of cells • The best distribution of essential amino acids is found in the complex proteins of animal foods

34. How the body uses protein

35. Vitamins • Organic compounds required in small amounts for many biochemical processes • Many serve as components of coenzymes

36. Vitamins, cont. • Fat-soluble vitamins include A, D, E, and K • Water-soluble vitamins are the B and C vitamins

37. The vitamins

38. Minerals are inorganic nutrients ingested as salts dissolved in food and water • Trace elements are minerals required in amounts less than 100 mg per day

39. Some important minerals and their functions

40. Basal metabolic rate (BMR) • The body’s cost of metabolic living • Total metabolic rate • BMR plus the energy used to carry on daily activities

41. Energy input and output • When energy (kilocalories) input equals energy output, body weight remains constant • When energy input exceeds energy output, body weight increases • When energy output exceeds energy input, body weight decreases

42. Current hypotheses regarding the regulation of food intake and energy homeostasis • Researchers are identifying signaling molecules • The hormone leptin • The neuropeptite Y (NPY), a neurotransmitter produced in the hypothalamus