1. 33
Animal Nutrition

2. ??? feeders ??? feeders ??? feeders ??? feeders Baleen Caterpillar
Figure 33.5
??? feeders
??? feeders
??? feeders
Baleen
Caterpillar
Feces
??? feeders
Figure 33.5 Exploring four main feeding mechanisms of animals 2

3. Nutrient molecules enter body cells Mechanical digestion Chemical
Figure 33.4
Nutrient molecules
enter body cells
Mechanical
digestion
Chemical
digestion
(enzymatic
hydrolysis)
Undigested
material
Figure 33.4 The four stages of food processing 1
Ingestion 2
Digestion 3
Absorption 4
Elimination 3

4. Main Ideas to know:
Different types of digestive systems in different organisms
The role of circulatory system in human digestive system
Feedback loops- role of nervous system in the human digestive system
Insulin and glucagon

5. Specialized compartments:
Most animals process food in specialized compartments
These compartments reduce the risk of an animal digesting its own cells and tissues
Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients
Video: Hydra Eating 5

6. Mouth Tentacles Food 1 Digestive enzymes released 2 Food particles
Figure 33.6
Mouth
Tentacles
Food 1
Digestive enzymes
released 2
Food particles
broken down
Figure 33.6 Digestion in a hydra 3
Food particles
engulfed and digested
Epidermis
Gastrodermis 6

7. Crop Esophagus Gizzard Intestine Pharynx Anus Mouth (a) Earthworm
Figure 33.7
Crop
Esophagus
Gizzard
Intestine
Pharynx
Anus
Mouth
(a) Earthworm
Foregut
Midgut
Hindgut
Esophagus
Crop
Esophagus
Rectum
Stomach
Figure 33.7 Variation in alimentary canals
Gizzard
Anus
Intestine
Mouth
Anus
Crop
Mouth
Gastric
cecae
(b) Grasshopper
(c) Bird 7

8. More complex animals have a complete digestive tract or an alimentary canal with a mouth and an anus
The alimentary canal can have specialized regions that carry out digestion and absorption in a stepwise fashion 8

9. Duodenum of small intestine
Figure 33.8
Tongue
Oral cavity A
Mouth B
Salivary
glands
Esophagus C
Stomach J
Gallbladder
Sphincter
Small
intestine I
Liver
Sphincter
Pancreas
Large
intestine K
Figure 33.8 The human digestive system D E
Rectum
Anus F
Duodenum of
small intestine G H 9

10. The Oral Cavity, Pharynx, and Esophagus
The first stage of digestion is mechanical and takes place in the oral cavity
Salivary glands deliver saliva to the oral cavity through ducts
Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers
Saliva also contains mucus, a viscous mixture of water, salts, cells, and glycoproteins 10

11. The tongue shapes food into a bolus and provides help with swallowing
The throat, or pharynx, is the junction that opens to both the esophagus and the trachea
The esophagus connects to the stomach
The trachea (windpipe) leads to the lungs 11

12. Digestion in the Stomach
The stomach stores food and secretes gastric juice, which converts a meal to a mixture of food and digestive juice called chyme 12

13. Chemical Digestion in the Stomach
Gastric juice has a low pH of about 2, which kills bacteria and denatures proteins
How does the stomach withstand this extreme environment?
Gastric juice is made up of hydrochloric acid (HCl) and pepsin
Pepsin is a protease, or protein-digesting enzyme, that cleaves proteins into smaller peptides
Why is it better to release gastric juice only when necessary? 13

14. 1 Liver Food Gallbladder Stomach Gastric juices Stimulation Inhibition
Figure 33.17a 1
Liver
Food
Gallbladder
Stomach
Gastric
juices
Gastrin
Stimulation
Inhibition
Pancreas
Figure 33.17a Hormonal control of digestion (part 1: gastrin stimulation)
Duodenum of
small intestine 14

15. Esophagus Sphincter Stomach Sphincter Small intestine 10 m Folds of
Figure 33.9
Esophagus
Sphincter
Stomach
Sphincter
Small
intestine
10 m
Folds of
epithelial
tissue
Gastric pit
on the interior
surface of
stomach
Epithelium 3
Production of gastric
juice
Pepsinogen
Pepsin
(active
enzyme) 2 1
Pepsinogen and
HCI secreted into
lumen
Gastric gland
HCI
Chief
cell 1
Figure 33.9 The stomach and its secretions 2
HCI converts
pepsinogen to
pepsin.
Mucous cell H
Cl−
Parietal
cell 3
Pepsin activates
more pepsinogen,
starting a chain
reaction.
Chief cell
Parietal cell 15

16. 2 Bile Chyme CCK Stimulation CCK Inhibition HCO3−, enzymes Secretin
Figure 33.17b 2
Bile
Chyme
CCK
HCO3−, enzymes
Figure 33.17b Hormonal control of digestion (part 2: CCK and secretin stimulation)
Secretin
Stimulation
CCK
Inhibition 16

17. Absorption in the Small Intestine
The small intestine has a huge surface area, due to villi and microvilli that project into the intestinal lumen
The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorption
Transport across the epithelial cells can be passive or active depending on the nutrient
Animation: Membrane Transport 17

18. Villi Microvilli (brush border) at apical (lumenal) surface Lumen
Figure 33.11b
Villi
Microvilli (brush
border) at apical
(lumenal) surface
Lumen
Epithelial
cells
Blood
capillaries
(toward
capillary)
Epithelial
cells
Figure 33.11b Nutrient absorption in the small intestine (part 2: villi and microvilli)
Capillary
Basal
surface
Lacteal
Nutrient
absorption
Lymph
vessel 18

19. 3 Gastric juices Stimulation Inhibition Secretin and CCK Figure 33.17c
Figure 33.17c Hormonal control of digestion (part 3: CCK and secretin inhibition)
Stimulation
Inhibition 19

20. Absorption in the Large Intestine
The colon of the large intestine is connected to the small intestine
The cecum aids in the fermentation of plant material and connects where the small and large intestines meet
How might the size of the cecum vary from an herbivore and a carnivore?
The human cecum has an extension called the appendix, which plays a very minor role in immunity 20

21. Junction of the small and large intestines
Figure 33.13
Ascending
portion
of colon
Small
intestine
Appendix
Figure Junction of the small and large intestines
Cecum
Junction of the small and
large intestines 21

22. Small intestine Small intestine Stomach Cecum Colon (large Intestine)
Figure 33.16
Small intestine
Small
intestine
Stomach
Cecum
Figure The alimentary canals of a carnivore (coyote) and herbivore (koala)
Colon
(large
Intestine)
Carnivore
Herbivore 22

23. A major function of the colon is to recover water that has entered the alimentary canal
Where else in the body do we recover water?
The colon houses bacteria (e.g., Escherichia coli) that live on unabsorbed organic material; some produce vitamins
Feces, including undigested material and bacteria, become more solid as they move through the colon
Some organisms might need to eat their feces to maximize nutrient absorption! 23

24. Two sphincters between the rectum and anus control bowel movements
Feces are stored in the rectum until they can be eliminated through the anus
Two sphincters between the rectum and anus control bowel movements
One is involuntary and the other is voluntary 24

25. Rumen Reticulum Esophagus Intestine Omasum Abomasum
Figure 33.15
Rumen
Reticulum
Esophagus
Intestine
Omasum
Abomasum
Figure Ruminant digestion 25

26. Concept 33.4: Evolutionary adaptations of vertebrate digestive systems correlate with diet
Digestive systems of vertebrates are variations on a common plan
However, there are intriguing adaptations, often related to diet 26

27. Mutualistic Adaptations
Many herbivores have fermentation chambers in their alimentary canals, where mutualistic microorganisms digest cellulose
Rabbits and some rodents harbor mutualistic bacteria in their large intestines and ceca
The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants, including deer, sheep, and cattle 27

28. 1 Liver Food Gallbladder Stomach Gastric juices Stimulation Inhibition
Figure 33.17 1
Liver
Food
Gallbladder
Stomach
Gastric
juices
Gastrin
Stimulation
Inhibition
Pancreas
Duodenum of
small intestine 2 3
Bile
Secretin
and CCK
Chyme
Figure Hormonal control of digestion
Gastric
juices
CCK
HCO3−, enzymes
Secretin
CCK 28

29. Regulation of Energy Storage
When an animal takes in more energy than is needed for metabolism and activity, excess energy is stored
In humans, the liver and muscle cells are used first; energy is stored as glycogen
When glycogen depots are full, additional excess energy is stored as fat in adipose cells
When fewer calories are taken in than expended, the body expends liver glycogen, muscle glycogen, and then fat, in that order

30. Glucose Homeostasis
Insulin and glucagon together maintain glucose levels
Insulin levels rise after a carbohydrate-rich meal, and glucose entering the liver through the hepatic portal vein is used to synthesize glycogen
When glucose concentration is low in the hepatic portal vein, glucagon stimulates the liver to break down glycogen and release glucose into the blood
Insulin and glucagon are produced in the pancreas in beta cells and alpha cells, respectively
Animation: Homeostasis

31. Secretion of insulin by pancreas Transport of glucose into body cells
Figure 33.19
Secretion
of insulin by
pancreas
Transport of
glucose into
body cells
and storage
of glucose
as glycogen
Stimulus:
Blood glucose
level rises
after eating.
Homeostasis:
70–110 mg glucose/
100 mL blood
Stimulus:
Blood glucose
level drops
below set point.
Figure Homeostatic regulation of cellular fuel
Breakdown of
glycogen and
release of
glucose into
blood
Secretion
of glucagon
by pancreas 31

32. Diabetes Mellitus
Diabetes mellitus is a disease caused by a deficiency of insulin or a decreased response to insulin in target tissues
Cells are unable to take up glucose to meet their metabolic needs
Fat becomes the main substrate for cellular respiration

33. Type 1 diabetes is an autoimmune disorder in which the immune system destroys the pancreatic beta cells
Type 2 diabetes is characterized by a failure of target cells to respond normally to insulin
Heredity is a factor in type 2 diabetes
Excess body weight and lack of exercise increase the risk

34. Regulation of Appetite and Consumption
Overnourishment causes obesity, which results from excessive intake of food energy with the excess stored as fat
Obesity contributes to diabetes (type 2), cancer of the colon and breasts, heart attacks, and strokes
Researchers have discovered several of the mechanisms that help regulate body weight 34

35. Ghrelin, a hormone secreted by the stomach wall, triggers a feeling of hunger before meals
Insulin and PYY, a hormone secreted by the small intestine after eating, both suppress appetite
Leptin, a hormone produced by adipose (fat) tissue, also suppresses appetite and may regulate body fat levels 35

36. Secretions from pancreas
Figure 33.UN02
Veins to heart
Hepatic portal vein
Lymphatic system
Liver
Absorbed food
(except lipids)
Absorbed
water
Mouth
Stomach
Lipids
Esophagus
Figure 33.UN02 Summary of key concepts: mammalian digestive system
Small intestine
Anus
Secretions
from salivary
glands
Secretions
from gastric
glands
Secretions from liver
Large
intestine
Rectum
Secretions from pancreas 36