Chapter 21 Nutrition & Digestion

1. Chapter 21Nutrition & Digestion Overview: Obtaining and processing food Human Digestive System Diets Nutrition

2. Getting Their Fill of Krill • Animals obtain and process nutrients in a variety of ways • Humpback whales eat small fishes and crustaceans called krill • This painting shows how the whales corral their food using “bubble nets”

3. When they feed, they take in large amounts of seawater in which the fish and krill live • They must filter out the water in order to get a meal • Humpback whales strain their food from seawater using large, brushlike plates called baleen

4. They store the excess energy they harvest in the form of blubber • In about 4 months, a humpback whale eats, digests, and stores as fat enough food for an entire year • In a typical day, a humpback whale’s digestive system will process as much as 2 tons of fish and krill

5. OBTAINING AND PROCESSING FOOD Animals ingest their food in a variety of ways • Animal diets are highly varied • Herbivores are plant-eaters • Carnivores are meat-eaters • Omnivores eat both plants and other animals

6. Omnivores • Ingest both plants and animals

7. Some animals are suspension feeders, consuming particles from water • Herbivores • Feed mainly on plants

8. Mainly eat animals that eat plants • Carnivores

9. Some are fluid feeders, sucking liquids

10. The Four Stages of Food Processing • Is another word for eating • Digestion • Is the breakdown of food to small molecules • Ingestion • Absorption • Is the uptake of the small nutrient molecules by the body’s cells • Elimination • Is the disposal of undigested materials from the food we eat

11. Digestion: A Closer Look • Begins the process • Involves physical processes like chewing • Mechanical digestion • Chemical digestion • Is the breakdown of food by digestive enzymes

12. Proceeds through hydrolysis reactions • Chemical digestion • Hydrolases • Are enzymes that catalyze digestive hydrolysis reactions

13. Digestive Compartments • In animals, chemical digestion is contained safely within some kind of compartment • Food is digested in compartments housing hydrolytic enzymes • Most animals have a specialized digestive tract

14. This is called a gastrovascular cavity • Example: hydra • Relatively simple animals have a sac with a single opening

15. This is a tube running from mouth to anus • This tube is divided into specialized regions that process food sequentially • In most animals, the digestive compartment is an alimentary canal

16. HUMAN DIGESTIVE SYSTEM The human digestive system consists of an alimentary canal and accessory glands • When food is swallowed, it is moved through the alimentary canal by peristalsis • Peristalsis is rhythmic muscle contraction in the walls of the digestive tract • Ringlike sphincter muscles regulate the passage of food

17. Digestion begins in the oral cavity • The teeth break up food • Saliva moistens it • Salivary enzymes begin the hydrolysis of starch • The tongue pushes the chewed food into the pharynx

18. The Pharynx • Connects the mouth to the esophagus • Also opens to the trachea • The pharynx The food and breathing passages both open into the pharynx • The swallowing reflex moves food from the pharynx into the esophagus • At the same time, food is kept out of the trachea

19. During swallowing a reflex tips the epiglottis to close the windpipe entrance

20. The Esophagus • Is a muscular tube • Connects the pharynx to the stomach • Moves food down by peristalsis • The esophagus • Peristalsis in the esophagus moves food boluses into the stomach

21. The Stomach • Can store food for several hours • Churns food • Mixes food with gastric juices, which are acidic • The stomach • The stomach mixes food with gastric juice • The gastric juice contains pepsin, which begins the hydrolysis of protein

22. Connection: Bacterial infections can cause ulcers • New evidence suggests that a spiral-shaped prokaryote causes gastric ulcers • Helicobacter pylori growth erodes protective mucus and damages the stomach lining • Are erosions of the stomach lining

23. The Small Intestine • Is the longest part of the alimentary canal • Is the major organ for chemical digestion and absorption • The small intestine Chemical Digestion in the Small Intestine • In the small intestine, hydrolases break down food to monomers

24. Alkaline pancreatic juice neutralizes stomach acids • Its enzymes digest polysaccharides, proteins, nucleic acids, and fats • Bile emulsifies fat droplets for attack by pancreatic enzymes • It is made in the liver and stored in the gall bladder

25. Enzymes from the walls of the small intestine complete the digestion of many nutrients

26. The intestinal wall • The lining of the small intestine is folded and covered with tiny, fingerlike villi • Contains villi and microvilli • Has a large surface area for absorption • Nutrients pass through the epithelium of the villi and into the blood • The blood flows to the liver • The liver can store nutrients and convert them to other substances the body can use

27. Absorption of Nutrients • It is not technically “in” the body yet • It must be absorbed • Although food has been ingested

28. Is the first part of the small intestine • Receives digestive agents from several organs • The duodenum • The pancreas • Secretes juice that neutralizes stomach acids • The liver • Secretes bile, which helps digest fats

29. Are parts of the small intestine • Are specialized for absorption • The jejunum and ileum

30. The Large Intestine (and Beyond) • Is shorter, but wider, than the small intestine • The large intestine • The colon • Makes up most of the length of the large intestine • Absorbs water from the alimentary canal • Produces feces, the waste product of food • The rectum • Is the last 15 cm (6 inches) of the large intestine • The anus • Regulates the opening of the rectum

31. The large intestine reclaims water • Undigested material passes to the large intestine, or colon • Water is absorbed • Feces are produced

32. DIETS AND DIGESTIVE ADAPTATIONS Adaptations of vertebrate digestive systems reflect diet • Herbivores and omnivores generally have longer alimentary canals than carnivores • Plant matter is more difficult to digest than meat • Nutrients in vegetation are less concentrated than in meat

33. The cecum is a pouch where the large and small intestines connect • Examples: horses and elephants • Other mammals re-ingest their feces to recover nutrients • Examples: rabbits and some rodents • Some mammals house cellulose-digesting microbes in the colon or cecum

34. NUTRITION Overview: A healthful diet satisfies three needs • An animal’s diet provides • fuel for its activities • raw materials for making the body’s own molecules • essential nutrients that the body cannot make

35. Chemical energy powers the body • Once nutrients are inside cells, they can be oxidized by cellular metabolism to generate energy • This energy is in the form of ATP

36. Calories • A measure of the energy stored in your food • A measure of the energy you expend in daily activities • Calories are • A calorie is • The amount of energy required to raise the temperature of a gram of water by 1ºC • A kilocalorie is • One thousand calories • The unit listed on food labels

37. The energy a resting animal requires each day to stay alive is its basal metabolic rate (BMR)

38. Metabolic Rate • The metabolic rate of an organism is the rate of energy consumption per day

39. More energy is required for an active life • Excess energy is stored as glycogen or fat

40. Connection: Body fat and fad diets • The human body tends to store excess fat molecules instead of using them for fuel • A balanced diet includes adequate amounts of all nutrients

41. Fad diets are often ineffective and can be harmful

42. Connection: Vegetarians must be sure to obtain all eight essential amino acids • The eight essential amino acids that adults require must be obtained from food • They are easily obtained from animal protein • They can also be obtained from the proper combination of plant foods

43. Connection: A healthful diet includes 13 vitamins • Most of these vitamins function as coenzymes • Vitamins • Are organic molecules required in the diet for good health • Mostly function as assistants to enzymes

44. Connection: Essential minerals are required for many body functions • Minerals are elements other than carbon, hydrogen, oxygen, and nitrogen • They play a variety of roles in the body • Are inorganic substances required in the diet

45. Connection: What do food labels tell us? • Food labels provide important nutritional information about packaged foods

46. NUTRITIONAL DISORDERS • Nutritional dysfunction can cause severe problems

47. Malnutrition • Malnutrition is a dietary deficiency of one or more of the essential nutrients • Protein deficiency is an example • Undernutrition • Is caused by inadequate intake of nutrients

48. Obesity • Is an inappropriately high ratio of weight to height • Obesity

49. To some extent, a tendency toward obesity is inherited

50. Connection: Diet can influence cardiovascular disease and cancer • Choice of diet may reduce the risk of cardiovascular disease and cancer