Animal Nutrition II (Ch. 41)
Guest lecturer: Letitia Reichart (Letty)
Keywords
• Roles of mouth,
stomach, sm.&lg.
Intestine in digestion
• Pepsin, pepsinogen
• Villi, microvilli
• Cecum
• Cellulose
• Cellulase
• Acid chyme
• Enzymatic hydrolysis
• Peristalsis
Mammalian Digestive System
• Alimentary canal
• Accessory glands
– Salivary glands, pancreas, liver, gallbladder
• Food moved by peristalsis
Mouth (oral cavity)
• Mechanical
– Teeth
– Saliva
• Enzymatic
– Salivary amylase –
breakdown of starch
and glycogen
Throat (pharynx) & Esophagus
• Throat – junction to
esophagus & trachea
– Epiglottis
• Esophagus – uses
peristalsis to move food
to stomach
Contracted
muscles
Relaxed
muscles
Stomach
Stomach
• Stores food
• Secretes gastric
juices
– Acid chyme
Digestive mechanisms in stomach
Cardiac
orifice
• Mechanical
• Chemical
• Enzymatic
Esophagus
Liver
Pyloric
sphincter
Stomach
Gallbladder
Pancreas
Mechanical
Cardiac
orifice
• Mixing and
churning
– Smooth muscle
– Every 20 seconds
Esophagus
Pyloric
sphincter
Stomach
Chemical
• Hydrochloric acid (HCl)
• pH around 2
– Also breaks food down
Enzymatic
• Pepsin
– Breaks down proteins
Why doesn’t pepsin digest stomach?
Gastric pit
Interior surface of stomach
Gastric gland
Mucus cells
Chief cells
Parietal cells
Activation of pepsin
Pepsinogen
Pepsin
(active enzyme)
HCl
Chief cell
Parietal cell
Stomach
Cardiac
orifice
• After mechanical and
enzymatic digestion:
-Acid chyme (nutrientrich broth)
- Pyloric sphincter to
the small intestine
Pyloric
sphincter
Stomach
Small intestine
• Most of:
– Enzymatic
digestion occurs
here
– Absorption of
nutrients into the
blood stream
occurs here
Small
intestine
Figure 41.21 p. 859 in Campbell
Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Protein digestion
Nucleic acid digestion
Fat digestion
Polysaccharides Disaccharides
Salivary amylase
Smaller polysaccharides, maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intestine
Polysaccharides
Pancreatic amylases
Polypeptides
DNA, RNA
Pancreatic trypsin
and chymotrypsin
Pancreatic
nucleases
Smaller polypeptides
Nucleotides
Maltose and other
disaccharides
Pancreatic lipase
Amino acids
Disaccharidases
Monosaccharides
Bile salts
Fat droplets
Pancreatic carboxypeptidase
Epithelium
of small
intestine
(brush
border)
Fat globules
Glycerol, fatty
acids, glycerides
Small peptides
Nucleotidases
Dipeptidases, carboxypeptidase, and
aminopeptidase
Nucleosides
Amino acids
Nucleosidases
and phosphatases
Nitrogenous bases,
sugars, phosphates
Figure 41.19 p. 858 in Campbell
Liver
Bile
Gallbladder
Stomach
Acid chyme
Intestinal
juice
Pancreas
Duodenum of
small intestine
Pancreas
• Secretes proteases into duodenum
Inactive form
Active form
Trypsinogen
Trypsin
Procarboxypeptidase Carboxypeptidase
Chymotrpsinogen
Chymotrypsin
Why doesn’t the small intestine digest
itself?
Membrane-bound
enteropeptidase
Pancreas
Fig. 37.13
Inactive
trypsinogen
Other inactive
proteases
Active
proteases
Lumen of duodenum
Trypsin
Active
proteases
Liver
• Produces bile that is stored in gallbladder
• Bile contain bile salts
• Bile salts aids digestion and absorption of fats
Vein carrying blood
to hepatic portal
vessel
Most nutrient
absorption
occurs in small
intestine
Muscle layers
Large
circular
folds
Villi
Intestinal wall
Structure of
small intestine
Blood
capillaries
Epithelial
cells
Lacteal
Lymph
vessel
Villi
Microvilli
(brush border)
Microvilli
• Aid in nutrient transport
across epithelial cells of
sm. intestine into
bloodstream
Epithelial cells
Large intestine (colon)
• Major function is to reabsorb water
Ascending
portion of
large intestine
Ileum
of small
intestine
Large
Intestine
Rectum
Anus
Appendix
Cecum
Here are a few review questions
What would happen if you had a
defect in pepsin production?
What would happen if you had a
defect in pepsin production?
• A. carbohydrate would not be digested well
• B. meat would not be digested at all
• C. perhaps decreased absorption of protein
What would happen if you had a
defect in salivary amylase
production?
What would happen if you had a
defect in salivary amylase
production?
•
•
•
•
A. You would die
B. You would be unable to digest starch
C. The pH of the stomach would be affected
D. None of the above
Which of the following would
you least like to donate to science
while you are still alive?
• A. Cecum
• B. Pancreas
• C. Reproductive organs
What would happen if you had a
defect in small intestine
enteropeptidase?
What would happen if you had a
defect in small intestine
enteropeptidase?
• A. Pancreatic enzymes would not be
activated
• B. Liver enzymes would increased
• C. Your small intestine would become
blocked
• D. None of the above
Variations of vertebrate digestive
system
• Herbivorous mammals
– Specialized fermentation chambers
Stomach
Coyote vs.
Small intestine
Koala
Small
intestine
Cecum
Colon
(large
intestine)
Carnivore
Herbivore
Why does herbivory require
specializations?
• Plant tissue
– Harder to break up
– Contains cellulose
– Nutrients less concentrated than meat
Structure of cellulose
Only bacteria and protozoa can
break down cellulose
Via the enzyme
cellulase
Small intestine
Cecum
Stomach
• Pouch at junction
between lg and sm
intestine
• Large cecum in
rabbits, some rodents,
koala, horses
• Full of symbiotic
bacteria
Cecum
Colon
(large
intestine)
Herbivore
Symbiosis
• “living together”
Small intestine
Cecum
function
Stomach
• Fermentation
chamber
• Bacteria breakdown
cellulose
• Feces must be
reingested
Cecum
Colon
(large
intestine)
Herbivore