2. A look at the digestive system
Animal Nutrition
A look at the digestive system

3. What do animals need to live?
Animals make energy using:
Food
Oxygen
Animals build bodies using:
Food for raw materials
Amino acids, sugars, fats, nucleotides
ATP energy for synthesis
food
ATP O2

4. Nutritional requirements
Animals are heterotrophs
Need to take in food
Why? Fulfills 3 needs …
Fuel = chemical energy for production of ATP
Raw materials = carbon source for synthesis
Essential nutrients = things animals cannot make
Elements (N, P, K, Fe, Na, Ca …), NAD, FAD, etc

5. Different ways to obtain food
filter (suspension) feeding
substrate feeding
fluid feeding
bulk feeding

7. Different diets; different lives
All animals eat other organisms
Herbivores
Eat mainly plants
Giraffes, cows, rabbits, snails
Carnivores
Eat other animals
Sharks, hawks, spiders, snakes
Omnivores
Eat plants & animals
Cockroaches, bears, raccoons, humans
Humans evolved as hunters, scavengers, & gatherers

8. intracellular digestion extracellular digestion
Getting & using food
Ingest
Taking in food
Digest
Mechanical digestion
Breaking up food into smaller pieces
Chemical digestion
Breaking down food into molecules small enough to be absorbed into cells
Enzymes (hydrolysis)
Absorb
Absorb across cell membrane
Diffusion
Active transport
Eliminate
Undigested extracellular material passes out of digestive system
intracellular digestion
extracellular digestion

11. Getting & using food Don’t forget about enzymes
Specialized proteins that catalyze reactions
Lower activation energy, and, therefore, increase the rate of digestion
Most enzymes prefer an environment of 37OC
Generally fall into 3 main categories:
Amylase
Produced in salivary glands & pancreas
Digests starch into maltose & glucose, prefers pH 7
Example: salivary amylase
Proteases
Produced by stomach glands
Digests proteins into amino acids; prefers pH 3
Example: pepsin
Lipase
Produced by pancreas
Digests lipids into glycerol & fatty acids; prefers pH (or slightly above)
Example: pancreatic lipase

12. Human digestive system Alimentary Canal

13. Common processes & structures
Movement & control
Peristalsis
Push food along by rhythmic waves of smooth muscle contraction
Sphincters
Muscular, ring-like valves that regulate the passage of material between sections of digestive system
Accessory glands
Salivary glands, pancreas, liver & gall bladder
Secrete digestive juices (enzymes + fluid)

14. Swallowing (& not choking)
Epiglottis
Problem: breathing & swallowing through the same orifice
Flap of cartilage
Closes trachea (windpipe) when swallowing
Food travels down esophagus
Esophagus
Moves food to stomach by peristalsis

15. Ingestion Mouth Mechanical digestion Chemical digestion Teeth Saliva
Breaking up food
Chemical digestion
Saliva
Amylase
Enzyme digests starch
Mucin
Mucus protein (slippery)
Protects soft lining of digestive system
Lubricates food for easier swallowing
Buffers
Neutralizes acid to prevent tooth decay
Anti-bacterial chemicals
Kill bacteria that enter mouth with food

16. mouth
break up food
moisten food
digest starch
kill germs

17. The stomach epithelium
Functions
Food storage
Can stretch to fit ~2L of food
Disinfect food
HCl = pH 2
Kills bacteria
Breaks apart cells
Mechanical digestion
Chemical digestion
Gastric juice
Mucus, HCl, & pepsinogen
Gastric gland
The stomach epithelium
cells must regenerate
every 3 days

18. Pepsin Enzyme that breaks down protein Secreted as pepsinogen
Activated by HCl
But the stomach is made out of protein!
What stops the stomach from digesting itself?
mucus secreted by stomach cells protects stomach lining

19. mouth
break up food
moisten food
digest starch
kill germs
stomach
kills germs
store food
break up food
digest proteins
cardiac sphincter
pyloric sphincter

20. Ulcers Used to think ulcers were caused by stress
Tried to control with antacids
Now know bacterial infection is cause in majority of cases
Helicobacter pylori
15% of infected individual develop ulcers
Bacteria live in neutral zone between epithelial cells and mucus
Now cure with antibiotics
Additional causes:
Excess HCl secretion
Loss of mucus barrier
Excess use of aspirin/ibuprofen
Coevolution of parasite & host
Free of H. pylori
Colonized by H. pylori
inflammation of stomach
inflammation of esophagus
H. pylori
cell damaging proteins
(VacA)
inflammatory proteins
(CagA)
helper T cells
cytokines
neutrophil cells
white blood cells

21. Small intestine Functions Chemical digestion Absorption through lining
Major organ of digestion & absorption
Chemical digestion
Enzymes
Absorption through lining
Over 6 meters long
Huge surface area = 300m2 (~size of tennis court)
Structure
3 sections
Duodenum = most digestion
Jejunum = absorption of nutrients & water
Ileum = absorption of nutrients & water

22. Duodenum 1st section of small intestines
Acidic food from stomach mixes with digestive juices from accessory glands
Pancreas
Liver
Gall bladder

23. Pepsinogen & trypsinogen What stops pancreas from digesting itself?
Digestive enzymes
Trypsinogen
Activated by peptidase
Becomes trypsin
Digests proteins
Pancreatic amylase
Buffers
Reduces acidity from stomach
Alkaline solution rich in bicarbonate (HCO3-)
small intestines
Pepsinogen & trypsinogen
Call called zymogens
What stops pancreas from digesting itself?

24. Pancreas Exocrine & endocrine gland
without ducts
Exocrine = with ducts
Pancreas
Exocrine & endocrine gland
Acinar (or secretory) cells secrete digestive enzymes into the ductile
The ductile takes the enzymes to larger and larger ducts until the pancreatic duct is reached

25. Structure of an exocrine gland

26. mouth
break up food
moisten food
digest starch
kill germs
stomach
kills germs
break up food
digest proteins
store food
pancreas
produces enzymes to
digest proteins & starch

27. Circulatory System Connection
Liver
Digestive system functions
Produces bile
Stored in the gall bladder until needed
Breaks up fats
Acts like detergents to breakup fats
Circulatory System Connection
bile contains colors from old red blood cells collected in liver =
iron in RBC rusts & makes feces brown

28. Digesting lipids
Bile is produced in the liver & stored in the gall bladder
Bile salts have a hydrophobic side & a hydrophilic side
Hydrophobic attaches to lipid
Hydrophilic interacts with water
Breaks fat globules into smaller, digestible lipids

29. mouth
break up food
moisten food
digest starch
kill germs
stomach
kills germs
break up food
digest proteins
store food
liver
produces bile
- stored in gall bladder
break up fats
pancreas
produces enzymes to
digest proteins & starch

30. Digestive enzymes

31. Transverse section of the ileum
Perpendicular to
longitudinal muscle layer
Used for peristalsis
Control diameter
of ileum
Used for peristalsis

32. Absorption by small intestine
Absorption through villi & microvilli
Finger-like projections
Increases surface area for absorption
Ooooh…
Structure & Function

33. Absorption by small intestine

34. Absorption by small intestine
A villus
Capillary network: allows transport of absorbed nutrients
Single epithelial layer: ensures minimum distance for diffusion
Lacteals: absorb lipids into lymphatic system
Membrane proteins: enzymes that do not pass through the digestive system
Can be reused
Can help with membrane transport

36. Mitochondria: provide energy for active transport
Pinocytotic vesicles: transport material in bulk
Tight junction: impermeable membrane between cells, maintains concentration gradient

37. Absorption of nutrients
Lipids are absorbed via diffusion
Water-soluble molecules are absorbed via facilitated diffusion
Glucose, amino acids, & minerals are absorbed by active transport
Glucose uses a sodium-glucose transporter and secondary active transport (see previous slide)
Endocytosis/pinocytosis is used for bulk transport

38. What is NOT absorbed? B: bile pigments
E: epithelial cells of the intestinal lining
L: lignin (carb found in plants)
C: cellulose (roughage or fiber)
H: human microflora (bacteria)

39. mouth
break up food
moisten food
digest starch
kill germs
stomach
kills germs
break up food
digest proteins
store food
liver
produces bile
- stored in gall bladder
break up fats
small intestines
breakdown all foods
- proteins
- starch
- fats
- nucleic acids
absorb nutrients
pancreas
produces enzymes to
digest proteins & starch

40. Absorption vs Assimilation
The process of taking in substances
Assimilation
The process of using subunits (amino acids, fatty acids, glycerol) to build macromolecules, which then become part of the body

41. Large intestine (colon)
Function
Reabsorption of water
Use ~9 L of water every day in digestive juices
>90% of water is reabsorbed
No enough water reabsorbed back into body
diarrhea
Too much water reabsorbed back into body
constipation

42. Microflora of large intestine
Living in the large intestine is a rich flora of harmless, helpful bacteria
Over 700 species of bacteria, plus fungi & protozoa
Escherichia coli (E. coli)
Bacteria produce vitamins
Vitamin K, biotin, folic acid, & other B vitamins
Generate gases
By-product of bacterial metabolism
Methane, hydrogen sulfide
You’ve got company!

43. Rectum Last section of colon (large intestine) Eliminates feces
Undigested materials
B-E-L-C-H
Does not use peristalsis
Uses general contractions
Inner muscle layer only
Generally occurs 1-3 times a day
Involves (voluntary) relaxation of anal sphincter & increase in intra-abdominal pressure

44. mouth
break up food
moisten food
digest starch
kill germs
stomach
kills germs
break up food
digest proteins
store food
liver
produces bile
- stored in gall bladder
break up fats
small intestines
breakdown food
- proteins
- starch
- fats
absorb nutrients
pancreas
produces enzymes to
digest proteins & carbs
large intestines
absorb water

45. Appendix
Found at the junction of the small intestine & large intestine
About 4 inches long
Function still unknown
Storehouse for good bacteria
“reboot” digestive system after illness
Vestigial structure
Useless remnant from our evolutionary past
Additional surface area for a cellulose-rich diet

46. Cecum stores food material and bacteria capable to digesting cellulose
Compare these digestive tracts- how do they demonstrate structure fits function?
Cecum stores food material and bacteria capable to digesting cellulose

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