1. Processing Food and Nutrition
Chapter 46

2. Learning Objective 1
Describe food processing, including ingestion, digestion, absorption, and egestion or elimination
Compare the digestive system of a cnidarian (such as Hydra) with that of an earthworm or vertebrate

3. Nutrition
The process of taking in and using food

4. Food Processing Feeding Digestion Absorption Egestion (elimination)
selection, acquisition, and ingestion of food
Digestion
breaking down food mechanically, chemically
Absorption
nutrients pass from digestive tract into blood
Egestion (elimination)
undigested, unabsorbed food discharged

5. Cnidarians and Flatworms
Food digested in gastrovascular cavity
only one opening
serves as both mouth and anus

6. Gastrovascular Cavities

7. Enzymes secreted by inner layer
Wastes
Food
Tentacle
Mouth
Food
Enzymes secreted by inner layer
Figure 46.2: Simple invertebrate digestive systems.
(a) Hydras and (b) flatworms (planarians) have a gastrovascular cavity, a digestive tract with a single opening that serves as both mouth and anus.
Gastro- vascular cavity
Food absorbed
(b) Exhalation.
Gastrodermis
(a) Hydra
Fig. 46-2a, p. 992

8. Gastrovascular cavity Epidermis
(b) Flatworm
Gastrovascular cavity
Epidermis
Food particles
Pharynx
Mouth
Food absorbed
Figure 46.2: Simple invertebrate digestive systems.
(a) Hydras and (b) flatworms (planarians) have a gastrovascular cavity, a digestive tract with a single opening that serves as both mouth and anus.
Enzymes
Wastes
Lining of the intestine
Food
Fig. 46-2b, p. 992

9. Complex Invertebrates and Vertebrates
Digestive tract is complete tube
with opening at each end
As food passes through tube
digestion takes place
Parts of digestive tract are specialized
to perform specific functions

10. Complete Digestive Tract

11. Gizzard Crop Esophagus Intestine Pharynx Anus Mouth Wastes Food
Figure 46.3: Digestive tract with two openings.
The earthworm, like most animals, has a complete digestive tract extending from mouth to anus. Various regions of the digestive tract are specialized to perform different food-processing functions.
Fig. 46-3, p. 992

12. Explore various digestive systems by clicking on the figure in ThomsonNOW.

13. KEY CONCEPTS
Food processing includes ingestion, digestion, absorption, and elimination

14. Adaptations for Obtaining Food

15. KEY CONCEPTS
Many animal adaptations are associated with mode of nutrition

16. Learning Objective 2
Trace the pathway traveled by an ingested meal in the human digestive system
Describe the structure and function of each organ involved

17. Human Digestive System 1
Mouth
Mechanical, enzymatic digestion of carbohydrates
Mammalian teeth
incisors for biting
canines for tearing food
premolars, molars for crushing and grinding

18. Teeth and Diet

19. Incisors Canines Premolars Molars (a) Carnivore. Fig. 46-6a, p. 994
Figure 46.6: Teeth and diet.
Premolars
Molars
(a) Carnivore.
Fig. 46-6a, p. 994

20. Canine Incisors Premolars Molars (b) Herbivore. Fig. 46-6b, p. 994
Figure 46.6: Teeth and diet.
Premolars
Molars
(b) Herbivore.
Fig. 46-6b, p. 994

21. Canines Incisors Premolars Molars (c) Omnivore. Fig. 46-6c, p. 994
Figure 46.6: Teeth and diet.
Incisors
Premolars
Molars
(c) Omnivore.
Fig. 46-6c, p. 994

22. Tooth Structure

23. (b) X-ray of a healthy tooth.
Enamel Gum
Crown
Pulp cavity
Pulp
Neck
Dentin
Cementum
Root canal
Root
Spongy bone
Nerve
Figure 46.7: Tooth structure.
Vein
(a) Human lower molar. Sagittal section showing the crown, neck, and root.
Artery
(b) X-ray of a healthy tooth.
Fig. 46-7, p. 995

24. Human Digestive System 2
Three pairs of salivary glands
secrete saliva (enzyme salivary amylase digests starch)
Pharynx and esophagus
carry food to stomach

25. Human Digestive System 3
Peristalsis
waves of muscular contraction
pushes bolus of food along digestive tract
Stomach
mechanical digestion by vigorous churning
enzyme pepsin in gastric juice digests proteins

26. Peristalsis

27. Relaxed muscle layer Esophagus
Circular muscles contract, constricting passageway and pushing bolus ahead
Longitudinal muscles contract, shortening passageway ahead of the bolus
Relaxed muscle layer
Food bolus
Sphincter open
Sphincter closed
Figure 46.8: Peristalsis.
When the sphincter (ring of muscle) at the entrance of the stomach opens, food enters the stomach.
A bolus is moved through the esophagus by peristaltic contractions.
Stomach
Stomach
Fig. 46-8, p. 995

28. Human Digestive System 4
Rugae
folds in stomach wall
expand as stomach fills with food
Gastric glands secrete
hydrochloric acid
pepsinogen (precursor of pepsin)

29. Stomach Structure

30. Longitudinal muscle layer
Visceral peritoneum
Esophagus
Sphincter
Circular muscle layer
Longitudinal muscle layer
Oblique muscle layer
Pyloric sphincter
Figure 46.9: Structure of the stomach.
From the esophagus, food enters the stomach, where it is mechanically and enzymatically digested.
(a) The wall of the stomach has been progressively removed to show muscle layers and rugae.
Rugae
Duodenum
Fig. 46-9a, p. 996

31. Openings into gastric glands
Epithelium
Lymph nodule
Figure 46.9: Structure of the stomach.
From the esophagus, food enters the stomach, where it is mechanically and enzymatically digested.
(b) Stomach lining and gastric glands.
Gastric mucosa
Fig. 46-9b (1), p. 996

32. Chief cell Parietal cell Nuclei Surface epithelium Chief cells
Figure 46.9: Structure of the stomach.
From the esophagus, food enters the stomach, where it is mechanically and enzymatically digested.
(b) Stomach lining and gastric glands.
Parietal cells
Gastric glands
Gastric glands
Fig. 46-9b (2), p. 996

33. Human Digestive System 5
Chyme
soup of partly digested food
leaves stomach through pylorus
enters small intestine in spurts
Duodenum
location of most enzymatic digestion
produces several digestive enzymes
receives secretions from liver and pancreas

34. Structure of Digestive Tract

35. Inner circular fibers Outer longitudinal fibers MUSCLE LAYER
VISCERAL PERITONEUM
Lymph nodule
Villi
Blood vessels
SUBMUCOSA
Figure 46.5: Wall of the digestive tract.
From inside out, the layers of the wall are the mucosa, submucosa, muscle layer, and visceral peritoneum.
Nerve fibers
MUCOSA
Inner circular fibers Outer longitudinal fibers
MUSCLE LAYER
Fig. 46-5, p. 993

36. Human Digestive System 6
Liver produces bile
which emulsifies fats
Pancreas releases enzymes
digest protein, lipid, carbohydrate, RNA, DNA
Trypsin and chymotrypsin
digest polypeptides to dipeptides

37. Human Digestive System 7
Pancreatic lipase
degrades fats
Pancreatic amylase
digests complex carbohydrates

38. Liver and Pancreas

39. Stomach Inferior vena cava Right lobe of liver Right hepatic duct
Common bile duct
Figure 46.11: The liver and pancreas.
The gallbladder stores bile from the liver. Note the ducts that conduct bile to the gallbladder and the duodenum. The stomach has been displaced to expose the pancreas.
Pancreas
Hepatic portal vein
Pancreatic duct
Gallbladder
Duodenum
Fig , p. 998

40. Human Digestive System 8
Large intestine
cecum, colon, rectum, anus
eliminates undigested wastes
incubates bacteria (produce vitamin K, certain B vitamins)

41. Human Digestive System

42. Parotid salivary gland
Sublingual salivary gland
Pharynx
Submandibular salivary gland
Esophagus
Liver
Stomach
Duodenum
Gallbladder
Pancreas
Transverse colon
Ascending colon
Figure 46.4: Human digestive system.
The human digestive tract is a long, coiled tube extending from mouth to anus. The small intestine consists of the duodenum, jejunum, and ileum. The large intestine includes the cecum, colon, rectum, and anus. Locate the three types of accessory glands: the liver, pancreas, and salivary glands.
Jejunum
lleum
Descending colon
Cecum
Sigmoid colon
Vermiform appendix
Rectum
Anus
Fig. 46-4, p. 993

43. Insert “Human digestive system”
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44. Learn more about human digestion by clicking on the figures in ThomsonNOW.

45. KEY CONCEPTS
Various parts of the vertebrate digestive system are specialized to perform specific functions; accessory glands (liver, pancreas, and salivary glands) secrete fluids and enzymes important in digestion

46. Learning Objective 3
Describe the step-by-step digestion of carbohydrate, protein, and lipid

47. Carbohydrate Digestion
Polysaccharides
digested to disaccharide maltose by salivary and pancreatic amylases
Maltase in small intestine
splits maltose into glucose (main product of carbohydrate digestion)

48. Protein Digestion Proteins are split Dipeptidases by pepsin in stomach
by proteolytic enzymes in pancreatic juice
Dipeptidases
split small peptides into amino acids

49. Lipid Digestion Lipids are emulsified by bile salts
then hydrolyzed by pancreatic lipase

50. Learning Objective 4
What structural adaptations increase the surface area of the digestive tract?

51. Surface Area of the Small Intestine
Greatly expanded by
folds in wall (rugae)
intestinal villi (projections of mucosa)
microvilli (plasma membrane projections of epithelial cells of villi)

52. Villi and Microvilli

53. Figure 46.10: Villi and microvilli.
Fig a, p. 997

54. Epithelial cells lining villus Villi
Capillary network
Nerve fiber
Openings of intestinal glands
Mucosa
Goblet cells
Intestinal glands
Figure 46.10: Villi and microvilli.
Submucosa
Lacteal
Lymph vessel
Muscle layer
Visceral peritoneum
(b)
Fig b, p. 997

55. Figure 46.10: Villi and microvilli.
Fig c, p. 997

56. Learning Objective 5
Compare lipid absorption with absorption of other nutrients

57. Nutrient Absorption
Nutrients are absorbed through thin walls of intestinal villi
Hepatic portal vein transports amino acids and glucose to liver

58. Lipid Absorption 1 Fatty acids and monoacylglycerols
enter epithelial cells in intestinal lining
are reassembled into triacylglycerols
then packaged into chylomicron droplets

59. Lipid Absorption 2 Chylomicrons Lymphatic system
also contain cholesterol and phospholipids
are covered by a protein coat
Lymphatic system
transports chylomicrons to blood circulation

60. Learning Objective 6
Summarize the nutritional requirements for dietary carbohydrates, lipids, and proteins
Trace the fate of glucose, lipids, and amino acids after their absorption

61. A Balanced Diet Humans and other animals require carbohydrates lipids
proteins
vitamins
minerals

62. Carbohydrates 1 Most are ingested as polysaccharides
starch and cellulose
Polysaccharides are complex carbohydrates
Fiber
mixture of cellulose, other indigestible carbohydrates

63. Carbohydrates 2 Carbohydrates Glucose concentration in blood
used mainly as energy source
Glucose concentration in blood
is carefully regulated
Excess glucose
is stored as glycogen
or converted to fat

64. Lipids 1 Used to Most lipids are ingested as triacylglycerols
provide energy
form components of cell membranes
synthesize steroid hormones, other lipid substances
Most lipids are ingested as triacylglycerols

65. Lipids 2 Fatty acids are converted to molecules of acetyl coenzyme A
which enter citric acid cycle
Excess fatty acids
are converted to triacylglycerol
stored as fat

66. Lipids 3
Lipids are transported as large molecular complexes (lipoproteins)
Low-density lipoproteins (LDLs)
deliver cholesterol to cells
High-density lipoproteins (HDLs)
collect excess cholesterol
transport it to liver

67. Fat Metabolism

68. make triacylglycerols
Fat cell
Fat
Fatty acids +
Glycerol
Transported in blood
Liver
Fatty acid +
Glycerol
Enters cellular respiration
G3P
Used to
make triacylglycerols
Acetyl CoA
Glucose
Converted to other lipids
Ketone bodies
Enters cellular respiration
Figure 46.13: How the body uses fat.
The liver converts glycerol and fatty acids to compounds that are used as fuel in cellular respiration. Recall from Chapter 8 that G3P is glyceraldehyde-3-phosphate.
Other cells
Pyruvate or acetyl CoA
Converted to other lipids
Enters cellular respiration
Fig , p. 1002

69. make triacylglycerols Acetyl CoA
Fat cell
Fat
Fatty acids +
Glycerol
Transported in blood
Liver
Fatty acid
Used to
make triacylglycerols
Acetyl CoA
Converted to other lipids
Ketone bodies
Enters cellular respiration +
Glycerol
Enters cellular respiration
G3P
Glucose
Figure 46.13: How the body uses fat.
The liver converts glycerol and fatty acids to compounds that are used as fuel in cellular respiration. Recall from Chapter 8 that G3P is glyceraldehyde-3-phosphate.
Other cells
Pyruvate or acetyl CoA
Converted to other lipids
Enters cellular respiration
Stepped Art
Fig , p. 1002

70. Proteins 1 Proteins serve as enzymes
and essential structural components of cells
Best distribution of essential amino acids
in complete proteins of animal foods
Excess amino acids
are deaminated by liver cells

71. Proteins 2 Amino groups are converted to urea Remaining keto acids are
excreted in urine
Remaining keto acids are
converted to carbohydrate and used as fuel
converted to lipid and stored in fat cells

72. Protein Metabolism

73. Enters cellular respiration
AMINO ACIDS
Catabolism
Anabolism
Excess amino acids
Structural proteins, hemoglobin, myosin, actin, enzymes, plasma proteins
Deamination
NH3 (ammonia) + -keto acids
Liver
Fat
Urea
Pyruvate, -ketoglutarate
Enters cellular respiration
Acetyl CoA
Ketone bodies
Figure 46.14: How the body uses protein.
The liver plays a central role in protein metabolism. Deamination of amino acids and conversion of the amino groups to urea take place there. In addition, many proteins are synthesized in the liver. Note that you can gain weight on a high-protein diet, because excess amino acids can be converted to fat.
To kidneys
Acetyl CoA
Fatty acids + glycerol
Triacylglycerol
Storage in fat cells
Fig , p. 1003

74. Learning Objective 7
Describe the nutritional functions of vitamins, minerals, and phytochemicals

75. Vitamins
Organic compounds required in small amounts for biochemical processes
components of coenzymes
Fat-soluble vitamins
vitamins A, D, E, K
Water-soluble vitamins
B and C vitamins

76. Minerals Inorganic nutrients ingested as salts Trace elements
dissolved in food and water
Trace elements
minerals required in small amounts
(< 100 mg/day)

77. Phytochemicals Plant compounds that promote health Oxidants
many are antioxidants that destroy oxidants
Oxidants
free radicals, other reactive molecules
damage DNA, proteins, unsaturated fatty acids by snatching electrons

78. KEY CONCEPTS
Most animals require the same basic nutrients: carbohydrates, lipids, proteins, vitamins, and minerals

79. Learning Objective 8
Contrast basal metabolic rate with total metabolic rate
Write the basic energy equation for maintaining body weight, and describe the consequences of altering it in either direction

80. Measuring Metabolism Basal metabolic rate (BMR) Total metabolic rate
body’s cost of metabolic living
Total metabolic rate
BMR plus energy used to carry on daily activities

81. Energy If energy (kcal) input equals energy output
body weight remains constant
If energy output exceeds energy input
body weight decreases
If energy input exceeds energy output
body weight increases

82. Learning Objective 9
In general terms, describe the effects of malnutrition, including both undernutrition and overnutrition

83. Undernutrition Form of malnutrition Essential amino acids
causes fatigue
depresses immune function
Essential amino acids
nutrients most often deficient in diet

84. Protein Deficiency

85. Overnutrition Obesity
serious form of malnutrition
excess fat accumulates in adipose tissues
factor in heart disease, diabetes mellitus, other disorders
Person gains weight taking in more energy (kilocalories) than expended in activity

86. KEY CONCEPTS
Basal metabolic rate is the body’s cost of metabolic living
When energy (kilocalories) input equals energy output, body weight remains constant

87. Learning Objective 10
Summarize current hypotheses about the regulation of food intake and energy homeostasis, including the roles of leptin and neuropeptide Y

88. Leptin Hormone produced by fat cells
in proportion to body fat
Signals brain about status of energy stores

89. Effect of Leptin

90. Neuropeptide Y (NPY) Neurotransmitter produced in hypothalamus
increases appetite
Slows metabolism when leptin levels and food intake are low

91. Insert “Chronology of leptin research”
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92. Learn more about leptins and body weight by clicking on the figure in ThomsonNOW.