2. Lecture 10 Outline (Ch. 41) I. Animal Nutrition Overview Food Intake
Digestive Compartments
Adaptations
Energy sources and stores
Preparation for next lecture

3. Overview: The Need to Feed
Food is taken in, taken apart, and taken up in the process of animal nutrition
In general, animals fall into three categories:
Herbivores eat mainly autotrophs (plants, algae)
Carnivores eat other animals
Omnivores regularly consume animals as well as plants or algal matter

4. Essential Parts of Diet
Chemical energy (converted to ATP)
Organic carbon and nitrogen
Essential nutrients must be obtained from dietary sources
Essential amino acids
Essential fatty acids
Vitamins
Minerals

5. Essential Parts of Diet
Meat, eggs, cheese - provide all nine essential amino acids ( “complete” proteins)
Individuals eating only plant proteins need specific plant combinations for all essential amino acids
Beans and
other legumes
Corn (maize) and other grains
Lysine
Essential amino acids for adults
Tryptophan
Isoleucine
Leucine
Phenylalanine
Threonine
Valine
Methionine

6. Essential Parts of Diet
Animals can synthesize most fatty acids they need
The essential fatty acids are certain unsaturated fatty acids that must be obtained from the diet
Vitamins: organic molecules needed in small amounts
13 essential vitamins for humans
Fat-soluble & water-soluble
Vitamin A
Vitamin D
Vitamin E
Vitamin K
B-complex
Biotin/B7
Vitamin C (ascorbic acid)

7. Minerals Minerals: inorganic nutrients, small amounts needed Calcium
Phosphorus
Potassium
Sulfur
Chlorine
Sodium
Magnesium
Iron
A diet missing a certain essential part or not enough calories overall leads to malnourishment or undernourishment

8. Food Intake Ingestion: the act of eating
Suspension feeders - many aquatic animals, which sift small food particles from the water
Substrate feeders are animals that live in or on their food source
Fluid feeders suck nutrient-rich fluid from a living host
Bulk feeders eat relatively large pieces of food

9. Rock python, a bulk feeder
Humpback whale, a suspension feeder
Baleen
Leaf miner caterpillar, substrate feeder
Caterpillar Feces
Mosquito, a fluid feeder
Figure 41.6 Four main feeding mechanisms of animals
Rock python, a bulk feeder

10. Food Intake
Digestion: process of breaking food down into molecules small enough to absorb. In chemical digestion, enzymatic hydrolysis splits bonds in molecules
Ingestion
Digestion
Absorption
Elimination
Undigested material
Chemical digestion (enzymatic hydrolysis)
Nutrient molecules enter body cells
Small molecules
Mechanical digestion
Food
Pieces of food 1 2 3 4
Absorption is uptake of nutrients by body cells
Elimination is the passage of undigested material out of the digestive compartment

11. Digestive Compartments
Most animals process food (i.e. hydrolysis) in specialized compartments
Reduces risk animal digesting its own cells/ tissues
Gastrovascular cavity
Food
Epidermis
Mouth
Tentacles
Gastrodermis
Gastrovascular Cavity:
For both digestion and distribution of nutrients
Cells secrete digestive enzymes

12. Digestive Compartments
Esophagus
Mouth
Pharynx
Crop
Gizzard
Typhlosole
Intestine
Lumen of intestine
Anus
(b) Grasshopper
Foregut
(c) Bird
(a) Earthworm
Midgut
Hindgut
Rectum
Gastric cecae
Stomach
Digestive Compartments
More complex animals: digestive tube with two openings (mouth, anus)
“Tube within a tube”
Called alimentary canal
Specialized regions, carry out digestion and absorption stepwise

13. Digestive Compartments
Cecum
Anus
Ascending portion of large intestine
Gall- bladder
Small intestine
Large intestine
Rectum
Pancreas
Liver
Salivary glands
Tongue
Oral cavity
Pharynx
Esophagus
Sphincter
Stomach
Duodenum of small intestine
Appendix
A schematic diagram of the human digestive system
Mouth
Food moves by peristalsis
Mammalian alimentary canal and accessory glands that secrete digestive juices through ducts

14. Oral Cavity, Pharynx, Esophagus
Larynx
Trachea
Pharynx
Tongue
Esophagus
Food
To stomach
To lungs
Epiglottis down
Esophageal sphincter relaxed
Epiglottis up
Sphincter relaxed
Relaxed muscles
Contracted muscles
Stomach
Food  bolus, saliva added, digestion begins with amylase and mucus
Pharynx, junction opens to both the esophagus and the trachea (windpipe)
Esophagus conducts food pharynx to stomach by peristalsis
Epiglottis blocks entry to the trachea, and larynx.

15. Digestion in the Stomach
The stomach stores food and secretes gastric juice, which converts a meal to acid chyme
Esophagus
Small intestine
Epithelium
Stomach
Sphincter
Parietal cell
Chief cell
Folds of epithelial tissue
Pepsin
Pepsinogen
HCl H+
Cl–
Mucus cells
Gastric gland 1 2 3
5 µm
Highly folded
Gastric juice - hydrochloric acid (parietal cells) and the enzyme pepsin (chief cells)
Pepsin initially secreted as pepsinogen
Mucus protects the stomach lining from gastric juice

16. Digestion in the Small Intestine
The small intestine: longest section of alimentary canal
Major organ of enzymatic digestion and absorption
1st: duodenum
acid chyme from stomach mixes with digestive juices from pancreas, liver, gallbladder, and the small intestine itself.
2nd: jejunum
3rd: ileum

17. Digestion in the Small Intestine
pancreas
proteases trypsin & chymotrypsin
amylase & lipase
bicarbonate neutralizes the acidic chyme
liver/gallbladder
bile aids digestion and absorption of fats
small intestine
lining of duodenum (brush border) produces several digestive enzymes
jejunum and ileum mainly absorb water & nutrients

18. Oral cavity, pharynx, esophagus Stomach pancreas) Small intestine
Fat digestion
Nucleic acid digestion
Protein digestion
Fat (triglycerides)
DNA, RNA
Nucleotides
Pancreatic
nucleases
Pancreatic lipase
Glycerol, fatty acids,
monoglycerides
Nucleotidases
Nucleosides
Nucleosidases
and
phosphatases
Nitrogenous bases,
sugars, phosphates
Amino acids
Dipeptidases, carboxy-
peptidase, and
aminopeptidase
Small peptides
Pancreatic carboxypeptidase
Smaller
polypeptides
Pancreatic trypsin and
chymotrypsin
Small polypeptides
Proteins
Pepsin
Carbohydrate digestion
Polysaccharides
Disaccharides
Salivary amylase
polysaccharides
Maltose
Pancreatic amylases
Disaccharidases
Monosaccharides
Small
intestine
(enzymes
from
epithelium)
pancreas)
Stomach
Oral cavity,
pharynx,
esophagus

19. Absorption in the Large Intestine
The colon of the large intestine is connected to the small intestine
The cecum aids in fermentation of plant material,
- connects where the small and large intestines meet
Human cecum extension (appendix), minor role in immunity
Feces stored in rectum until eliminated

20. Absorption in the Large Intestine
The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins
Two sphincters between the rectum and anus control bowel movements
Internal smooth muscle sphincter (involuntary)
External striated muscle sphincter (voluntary)

21. Mutualistic Adaptations
Many herbivores have symbiotic microorganisms that digest cellulose
The most elaborate adaptations in ruminants
Esophagus
Omasum
Abomasum
Intestine
Rumen
Reticulum 1 2 4 3

22. Adaptations
Herbivores generally longer alimentary canals than carnivores; longer time needed to digest vegetation
Coprophagy – method to recover more nutrients by ingesting feces
Cecum
Small intestine
Herbivore
Carnivore
Colon (large intestine)
Stomach
Small intestine
Enzymes for digesting plant matter

23. Energy Sources and Stores
Pancreas releases insulin – cells uptake sugars
Stimulus: Blood glucose level rises after eating.
Homeostasis: 90 mg glucose/
100 mL blood
Stimulus: Blood glucose level drops below set point.
Pancreas releases glucagon – liver releases sugars

24. Energy Sources and Stores
Animals store excess calories as glycogen in the liver and muscles
Energy secondarily stored as adipose, or fat, cells
Fewer calories taken in than expended  fuel is taken from storage and oxidized
Excessive intake of food energy, excess stored as fat
Obesity contributes to diabetes (type 2), colon and breast cancer, heart attacks, and strokes
100 µm
Fat cells

25. Energy Sources and Stores
Leptin
PYY
Insulin
Ghrelin
The complexity of weight control in humans is well-studied
Mice that inherit a defect in the gene for leptin become very obese
hypothalamus
Ghrelin – secreted by stomach, stimulates appetite
Insulin – secreted by pancreas, suppresses appetite
Leptin – released by fat cells, suppresses appetite
PYY – secreted by Sm. Intestine, suppresses appetite

26. Obese mouse with mutant ob gene (left) – mutant
for leptin production – next to wild-type sibling mouse.

27. Things To Do After Lecture 10…
Reading and Preparation:
Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms.
Ch. 41 Self-Quiz: #2, 3, 4, 5, 6 (correct answers in back of book)
Read chapter 41, focus on material covered in lecture (terms, concepts, and figures!)
Skim next lecture.
“HOMEWORK” (NOT COLLECTED – but things to think about for studying):
Describe the pathway that food molecules take from ingestion through elimination – where appropriate, indicate which digestive enzymes are secreted and what biomolecules are broken down.
Define, and then list: necessary vitamins and minerals.
Explain the difference between a substrate feeder and a bulk feeder.
Compare the function of leptin and ghrelin – where and when are each secreted/released?