1. Animal nutrition Animal diet needs Overview of food processing
Evolutionary adaptations of vertebrate digestive systems

2. Animal diet needs It must provide fuel for cellular work
It must supply the organic raw materials needed to construct organic molecules
Essential nutrients that the animal cannot make from raw materials must be provided in its food

3. Fuel for cellular work
Most of the energy budget from food goes into ATP production
Nearly all of an animal’s ATP generation is based on the oxidation of energy-rich molecules: carbohydrates, proteins, and fats

4. Raw materials for biosynthesis
When an animal takes in more calories than it needs to produce ATP, excess can be used for biosynthesis
Animals can fabricate a great variety of organic molecules from a source of organic carbon and organic nitrogen

5. Nutrients in preassembled form
Animals require 20 amino acids
And can synthesize about half of them
The remaining amino acids, the essential amino acids
Must be obtained from food in preassembled form

6. Protein in animal products are complete in amino acid make up
Most plant proteins are incomplete
Corn (maize) and other grains
Beans and other legumes
Essential amino acids for adults
Methionine
Valine
Threonine
Phenylalanine
Leucine
Isoleucine
Lysine
Tryptophan
Figure 41.10

7. Animals can synthesize most of the fatty acids they need
The essential fatty acids are certain unsaturated fatty acids

8. Vitamins are organic molecules
Required in the diet in small amounts
Minerals are simple inorganic nutrients
Usually required in small amounts

9. Overview of food processing
The four steps of food processing
Ingestion, digestion, absorption, elimination
Digestive systems in animals

10. Food processing The four stages of food processing Figure 41.12
Small molecules
Pieces of food
Chemical digestion (enzymatic hydrolysis)
Nutrient molecules enter body cells
Mechanical digestion
Undigested material
Food 1
INGESTION
DIGESTION 2
ABSORPTION 3
ELIMINATION 4
Figure 41.12

11. Sponges digest their food entirely by the intracellular mechanism
Azure vase sponge (Callyspongia
plicifera)
Osculum
Spicules
Water
flow
Flagellum
Collar
Food particles
in mucus
Choanocyte
Phagocytosis of
food particles
Amoebocyte
Choanocytes. The spongocoel
is lined with feeding cells called
choanocytes. By beating flagella,
the choanocytes create a current that
draws water in through the porocytes.
Spongocoel. Water
passing through porocytes
enters a cavity called the
spongocoel.
Porocytes. Water enters
the epidermis through
channels formed by
porocytes, doughnut-shapd
cells that span the body wall.
Epidermis. The outer
layer consists of tightly
packed epidermal cells.
Mesohyl. The wall of this
simple sponge consists of
two layers of cells separated
by a gelatinous matrix, the
mesohyl (“middle matter”).
The movement of the choanocyte
flagella also draws water through its
collar of fingerlike projections. Food
particles are trapped in the mucus
coating the projections, engulfed by
phagocytosis, and either digested or
transferred to amoebocytes.
Amoebocyte. Amoebocytes
transport nutrients to other cells of
the sponge body and also produce
materials for skeletal fibers (spicules). 5 6 7 4 3 2 1
Figure 33.4

12. Animals with simple body plans
Have a gastrovascular cavity that functions in both digestion and distribution of nutrients
Gastrovascular cavity
Food
Epidermis
Mesenchyme
Gastrodermis
Mouth
Tentacles
Food vacuoles
Gland cells
Flagella
Nutritive muscular cells
Figure 41.13

13. Animals with a more complex body plan
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

14. Alimentary canals

15. The human digestive system

16. From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 3)

17. Secretion of gastric juice

18. Gastric ulcers, lesions in the lining
Are caused mainly by the bacterium Helicobacter pylori
1 µm
Bacteria
Mucus layer of stomach
Figure 41.18

19. The duodenum

20. The enormous microvillar surface
Is an adaptation that greatly increases the rate of nutrient absorption
Epithelial cells
Key
Nutrient absorption
Vein carrying blood to hepatic portal vessel
Villi
Large circular folds
Intestinal wall
Lymph vessel
Blood capillaries
Lacteal
Microvilli (brush border)
Muscle layers
Figure 41.23

21. After glycerol and fatty acids are absorbed by epithelial cells
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

22. These fats are then mixed with cholesterol and coated with proteins
Forming small molecules called chylomicrons, which are transported into lacteals
Fat globule
Lacteal
Epithelial
cells of
small
intestine
Micelles made
up of fatty acids,
monoglycerides,
and bile salts
Fat droplets
coated with
bile salts
Bile salts
Large fat globules are emulsified by bile salts in the duodenum. 1
Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides, which then form micelles. 2
Fatty acids and mono- glycerides leave micelles and enter epithelial cells by diffusion. 3
Chylomicrons containing fatty substances are transported out of the epithelial cells and into lacteals, where they are carried away from the intestine by lymph. 4
Figure 41.24

23. Enzymatic digestion in the human digestive system

24. The large intestine, or colon
Is connected to the small intestine
Figure 41.25

25. A major function of the colon
Is to recover water that has entered the alimentary canal
The wastes of the digestive tract, the feces
Become more solid as they move through the colon
Pass through the rectum and exit via the anus

26. The colon houses various strains of the bacterium Escherichia coli
Some of which produce various vitamins

27. Evolutionary adaptations of vertebrate digestive systems
Ingestion adaptations
Digestion adaptations

28. Dentition and diet

29. The digestive tracts of a carnivore (coyote) and a herbivore (koala) compared

30. Symbiotic Adaptations
Many herbivorous animals have fermentation chambers
Where symbiotic microorganisms digest cellulose

31. The most elaborate adaptations for an herbivorous diet
Have evolved in the animals called ruminants
Figure 41.28
Reticulum. Some boluses also enter the reticulum. In both the rumen and the reticulum, symbiotic prokaryotes and protists (mainly ciliates) go to work on the cellulose-rich meal. As by-products of their
metabolism, the microorganisms secrete fatty acids. The cow periodically regurgitates and rechews the cud (red arrows), which further breaks down the
fibers, making them more accessible to further microbial action.
Rumen. When the cow first chews and
swallows a mouthful of grass, boluses
(green arrows) enter the rumen. 1
Intestine 2
Omasum. The cow then reswallows
the cud (blue arrows), which moves to
the omasum, where water is removed. 3
Abomasum. The cud, containing great numbers of microorganisms,
finally passes to the abomasum for digestion by the cow‘s own
enzymes (black arrows). 4
Esophagus