1. Chapter 41
Animal Nutrition

2. Overview: The Need to Feed
Every meal reminds us that we are heterotrophs, dependent on a regular supply of food
In general, animals fall into three categories:
Herbivores eat mainly autotrophs (plants and algae)
Carnivores eat other animals
Omnivores regularly consume animals as well as plants or algal matter

4. An adequate diet must satisfy three needs:
Fuel for all cellular work
Organic raw materials for biosynthesis
Essential nutrients, substances that the animal cannot make for itself
Main feeding mechanisms: suspension feeding, substrate feeding, fluid feeding, bulk feeding

5. LE 41-2a
Baleen

6. LE 41-2b
Caterpillar
Feces

7. Video: Lobster Mouth Parts Video: Shark Eating a Seal

8. Concept 41.1: Homeostatic mechanisms manage an animal’s energy budget
Nearly all of an animal’s ATP generation is based on oxidation of energy-rich molecules: carbohydrates, proteins, and fats

9. Glucose Regulation as an Example of Homeostasis
Animals store excess calories as glycogen in the liver and muscles and as fat
Glucose is a major fuel for cells
Hormones regulate glucose metabolism
When fewer calories are taken in than are expended, fuel is taken from storage and oxidized

10. LE 41-3 STIMULUS: Blood glucose level rises after eating. Homeostasis:
90 mg glucose/
100 mL blood
STIMULUS:
Blood glucose
level drops
below set point.

11. Caloric Imbalance
Undernourishment occurs in animals when their diets are chronically deficient in calories
Overnourishment, or obesity, results from excessive intake, with excess stored as fat

12. LE 41-4
100 µm

13. Obesity as a Human Health Problem
The World Health Organization now recognizes obesity as a major global health problem
Obesity contributes to a number of health problems, including diabetes, cardiovascular disease, and colon and breast cancer

14. Researchers have discovered several of the mechanisms that help regulate body weight
Over the long term, homeostatic mechanisms are feedback circuits that control the body’s storage and metabolism of fat
Hormones regulate long-term and short-term appetite by affecting a “satiety center” in the brain

15. LE 41-5
Ghrelin
Insulin
Leptin
PYY

16. The complexity of weight control in humans is evident from studies of the hormone leptin
Mice that inherit a defect in the gene for leptin become very obese

18. Obesity and Evolution
The problem of maintaining weight partly stems from our evolutionary past, when fat hoarding was a means of survival
A species of birds called petrels become obese as chicks due to the need to consume more calories than they burn

20. Concept 41.2: An animal’s diet must supply carbon skeletons and essential nutrients
An animal must obtain carbon skeletons from its food to build complex molecules
Besides fuel and carbon skeletons, a diet must supply essential nutrients in preassembled form
A malnourished animal is missing one or more essential nutrients in its diet

21. Herbivores may suffer mineral deficiencies if they graze on plants in soil lacking key minerals

23. Malnutrition is much more common than undernutrition in human populations

24. Essential Amino Acids
Animals require 20 amino acids and can synthesize about half from molecules in their diet
The remaining amino acids, the essential amino acids, must be obtained from food in preassembled form
A diet that provides insufficient essential amino acids causes malnutrition called protein deficiency

26. Most plant proteins are incomplete in amino acid makeup
Individuals who eat only plant proteins need to eat a variety to get all essential amino acids

27. Essential amino acids for adults
LE 41-10
Essential amino acids for adults
Methionine
Beans
and other
legumes
Valine
Threonine
Phenylalanine
Leucine
Corn (maize)
and other grains
Isoleucine
Tryptophan
Lysine

28. Some animals have adaptations that help them through periods when their bodies demand extraordinary amounts of protein

30. Essential Fatty Acids
Animals can synthesize most of the fatty acids they need
The essential fatty acids are certain unsaturated fatty acids
Deficiencies in fatty acids are rare

31. Vitamins
Vitamins are organic molecules required in the diet in small amounts
13 vitamins essential to humans have been identified
Vitamins are grouped into two categories: fat-soluble and water-soluble

34. Minerals
Minerals are simple inorganic nutrients, usually required in small amounts

36. Concept 41.3: The main stages of food processing are ingestion, digestion, absorption, and elimination
Ingestion is the act of eating
Digestion is the process of breaking food down into molecules small enough to absorb
Absorption is uptake of nutrients by body cells
Elimination is the passage of undigested material out of the digestive compartment

37. LE 41-12 Small molecules Pieces of food Chemical digestion
(enzymatic hydrolysis)
Nutrient
molecules
enter body
cells
Mechanical
digestion
Food
Undigested
material
INGESTION
DIGESTION
ABSORPTION
ELIMINATION

38. Digestive Compartments
Most animals process food in specialized compartments
These compartments reduce risk of self-digestion

39. Intracellular Digestion
In intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles

40. Extracellular Digestion
Extracellular digestion is the breakdown of food particles outside of cells
It occurs in compartments that are continuous with the outside of the animal’s body

41. Video: Hydra Eating Daphnia
Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients
Video: Hydra Eating Daphnia

42. LE 41-13 Mouth Tentacles Gastrovascular cavity Food Epidermis Mesoglea
Gastrodermis
Nutritive
muscular
cells
Flagella
Gland cells
Food vacuoles
Mesoglea

43. More complex animals have a digestive tube with two openings, a mouth and an anus
This digestive tube is called a complete digestive tract or an alimentary canal
It can have specialized regions that carry out digestion and absorption in a stepwise fashion

44. Crop Gizzard Esophagus Intestine Pharynx Anus Mouth Typhlosole
LE 41-14a
Crop
Gizzard
Esophagus
Intestine
Pharynx
Anus
Mouth
Typhlosole
Lumen of intestine
Earthworm

45. Foregut Midgut Hindgut Esophagus Rectum Anus Crop Mouth Gastric ceca
LE 41-14b
Foregut
Midgut
Hindgut
Esophagus
Rectum
Anus
Crop
Mouth
Gastric ceca
Grasshopper

46. Esophagus Stomach Mouth Crop Anus
LE 41-14c
Esophagus
Stomach
Gizzard
Intestine
Mouth
Crop
Anus
Bird

47. Concept 41.4: Each organ of the mammalian digestive system has specialized food-processing functions
The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts
Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder
Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal

48. LE 41-15a Cardiac orifice Tongue Oral cavity Parotid gland Salivary
Sublingual gland
Pharynx
Esophagus
Submandibular gland
Pyloric
sphincter
Liver
Stomach
Ascending
portion of
large intestine
Gall-
bladder
Pancreas
Ileum
of small
intestine
Duodenum of
small intestine
Small
intestine
Large
intestine
Rectum
Anus
Appendix
Cecum

49. A schematic diagram of the human digestive system
LE 41-15b
Salivary
glands
Mouth
Esophagus
Gall-
bladder
Stomach
Small
intestines
Liver
Pancreas
Large
intestines
Rectum
Anus
A schematic diagram of the
human digestive system

50. The Oral Cavity, Pharynx, and Esophagus
In the oral cavity, food is lubricated and digestion begins
Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers

51. The region we call our throat is the pharynx, a junction that opens to both the esophagus and the windpipe (trachea)
The esophagus conducts food from the pharynx down to the stomach by peristalsis

52. LE 41-16_3 Bolus of food Tongue Epiglottis up Epiglottis up Pharynx
down
and open
Glottis
Esophageal
sphincter
contracted
Epiglottis
down
Esophageal
sphincter
relaxed
Esophageal
sphincter
contracted
Larynx
Trachea
Glottis up
and closed
Esophagus
Relaxed
muscles
To lungs
To stomach
Contracted
muscles
Relaxed
muscles
Stomach

53. The Stomach
The stomach stores food and secretes gastric juice, which converts a meal to acid chyme
Gastric juice is made up of hydrochloric acid and the enzyme pepsin
Pepsin is secreted as inactive pepsinogen; pepsin is activated when mixed with hydrochloric acid in the stomach
Mucus protects the stomach lining from gastric juice

54. LE 41-17 5 µm Interior surface of stomach Gastric gland Mucus cells
Esophagus
Cardiac orifice
Stomach
Pyloric sphincter
5 µm
Small
intestine
Folds of
epithelial
tissue
Interior surface of stomach
Epithelium
Pepsinogen and HCl
are secreted into the
lumen of the stomach.
Pepsinogen
Pepsin
(active enzyme)
Gastric gland
HCl
HCl converts
pepsinogen to pepsin.
Pepsin then activates
more pepsinogen,
starting a chain
reaction. Pepsin
begins the chemical
digestion of proteins.
Mucus cells
Chief cells
Parietal cells
Chief cell
Parietal cell

55. Gastric ulcers, lesions in the lining, are caused mainly by the bacterium Helicobacter pylori

56. LE 41-18
Bacteria
Mucus
layer of
stomach
1 µm

57. The Small Intestine
The small intestine is the longest section of the alimentary canal
It is the major organ of digestion and absorption

58. Enzymatic Action in the Small Intestine
The first portion of the small intestine is the duodenum, where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself

59. Bile Liver Gall- bladder Stomach Acid chyme Intestinal juice
Pancreatic
juice
Pancreas
Duodenum of
small intestine

60. The pancreas produces proteases, protein-digesting enzymes that are activated after entering the duodenum

61. Membrane-bound enteropeptidase
LE 41-20
Pancreas
Membrane-bound
enteropeptidase
Inactive
trypsinogen
Trypsin
Other inactive
proteases
Active
proteases
Lumen of duodenum

62. The liver produces bile, which aids in digestion and absorption of fats
The epithelial lining of the duodenum, called the brush border, produces several digestive enzymes
Enzymatic digestion is completed as peristalsis moves the chyme and digestive juices along the small intestine

63. Pancreatic carboxypeptidase
LE 41-21
Carbohydrate digestion
Protein digestion
Nucleic acid digestion
Fat digestion
Oral cavity,
pharynx,
esophagus
Polysaccharides
Disaccharides
Salivary amylase
Smaller polysac-
charides, maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intes-
tine
Polysaccharides
Polypeptides
DNA, RNA
Fat globules
Pancreatic amylases
Pancreatic trypsin
and chymotrypsin
Pancreatic
nucleases
Bile salts
Maltose and other
disaccharides
Fat droplets
Nucleotides
Smaller polypeptides
Pancreatic carboxypeptidase
Pancreatic lipase
Amino acids
Glycerol, fatty
acids, glycerides
Epithelium
of small
intestine
(brush
border)
Small peptides
Nucleotidases
Nucleosides
Disaccharidases
Dipeptidases, carboxy-
peptidase, and
aminopeptidase
Nucleosidases
and phosphatases
Monosaccharides
Amino acids
Nitrogenous bases,
sugars, phosphates

64. Hormones help coordinate the secretion of digestive juices into the alimentary canal

65. LE 41-22
Key
Liver
Stimulation
Inhibition
Entero-
gastrone
Gall-
bladder
Gastrin
CCK
Stomach
Pancreas
Secretin
Duodenum
CCK

66. Absorption of Nutrients
The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen
The enormous microvillar surface greatly increases the rate of nutrient absorption

67. LE 41-23 Key Nutrient absorption Vein carrying blood Microvilli
to hepatic portal
vessel
Microvilli
(brush border)
Blood
capillaries
Epithelial
cells
Muscle layers
Epithelial cells
Large
circular
folds
Lacteal
Villi
Lymph
vessel
Villi
Intestinal wall

68. Each villus contains a network of blood vessels and a small lymphatic vessel called a lacteal

69. Amino acids and sugars pass through the epithelium of the small intestine and enter the bloodstream
After glycerol and fatty acids are absorbed by epithelial cells, they are recombined into fats within these cells
These fats are mixed with cholesterol and coated with protein, forming molecules called chylomicrons, which are transported into lacteals

70. LE 41-24 Fat globule Bile salts Fat droplets coated with bile salts
Micelles made
up of fatty acids,
monoglycerides,
and bile salts
Epithelium
of small
intestine
Lacteal
Epithelium
of lacteal

71. The Large Intestine
The large intestine, or colon, is connected to the small intestine
Its major function is to recover water that has entered the alimentary canal
Wastes of the digestive tract, the feces, become more solid as they move through the colon
Feces pass through the rectum and exit via the anus

73. The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins

74. Concept 41.5: Evolutionary adaptations of vertebrate digestive systems are often associated with diet
Digestive systems of vertebrates are variations on a common plan
However, there are intriguing adaptations, often related to diet

75. Some Dental Adaptations
Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet
Mammals have specialized dentition that best enables them to ingest their usual diet

76. LE 41-26 Incisors Canines Molars Premolars Carnivore Herbivore
Omnivore

77. Stomach and Intestinal Adaptations
Herbivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation

78. LE 41-27 Small intestine Stomach Small intestine Cecum Colon (large
Carnivore
Herbivore

79. Symbiotic Adaptations
Many herbivores have fermentation chambers, where symbiotic microorganisms digest cellulose
The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants

80. LE 41-28
Intestine
Rumen
Reticulum
Esophagus
Abomasum
Omasum