The document discusses animal digestion and the diversity of digestive systems, from intracellular digestion in simple animals like sponges to the more complex extracellular digestion systems involving organs like the mouth, stomach, liver, pancreas and intestines found in animals like humans. It also covers how different digestive systems have evolved adaptations to efficiently digest different foods and maintain homeostasis. Feedback systems help regulate blood sugar levels through interactions between the pancreas, liver, and cells.

1. Animal Digestion
Gazelle and Python

2. How do animals get their food?
filter (suspension) feeding substrate feeding
fluid feeding bulk feeding

3. Eating a balanced diet
 What happens if an animal’s diet is
missing an essential nutrient?
 deficiency diseases
 scurvy — vitamin C (collagen production)
 rickets — vitamin D (calcium absorption)
 blindness — vitamin A (retinol production)
 anemia — vitamin B (energy production)
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4. Digestion System Diversity
Intracellular Digestion Extracellular Digestion
• food particles engulfed • the breakdown of food
by phagocytosis particles outside of
• food vacuoles fuse cells
with lysosomes • occurs in
containing hydrolytic compartments that
enzymes are continuous with
• Example: sponges the outside of the
animal’s body
• Examples: hydra,
worms, insects,
humans
intracellular
digestion

5. Digestive System Diversity
Animals, such as hydra,
with simple body plans
have a single opening
pouch called the
gastrovascular
cavity that functions
in both digestion and
distribution of
nutrients.
extracellular
digestion

6. Digestive System Diversity
More complex animals, such as
humans, have a digestive
tube, the alimentary canal,
with two openings, a mouth
and an anus.
Everybody’s got one!

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

8. Maintaining Homeostasis
• Interactions between certain organs
help to regulate homeostasis.
• Example:
• After stomach mechanically breaks
down food, enzymes are produced by
the stomach and small intestine to
chemically digest them into nutrients.
• These nutrients are absorbed by the
small intestine and eventually delivered
to cells.

9. Maintaining Homeostasis:
Ooooooh!
Stomach Zymogen!
• Functions
 disinfect
food
HCl = pH 2
 kills
bacteria
 breaks apart cells
 Components of HCl are
produced by parietal cells
 chemical
digestion
Example: pepsin
 enzyme breaks down proteins
 chief cells secrete 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

10. Maintaining Homeostasis:
Small intestine
 Function
 chemical digestion
digestive enzymes
 absorption through villi & microvilli:
 finger-like projections
 increase surface area for absorption
 over 6 meters!
 small intestine has huge surface area = 300m 2
(~size of tennis court)
 most nutrients are absorbed across the
epithelium of the small intestine
 Structure
 3 sections
 duodenum = most digestion
 jejunum = absorption of nutrients & water
 ileum = absorption of nutrients & water

11. Duodenum
 1st section of small intestines
 acidfood from stomach mixes with
digestive juices from accessory glands:
 pancreas
 liver
 gall bladder

12. Accessory Organ:
Pancreas
 Digestive enzymes
 peptidases
 trypsin
 trypsinogen
 chymotrypsin
 chimotrypsinogen small intestines
 carboxypeptidase
 procarboxypeptidase
• pancreatic amylase
 Buffers
 reduces acidity
 alkaline solution rich in
bicarbonate (HCO3-)
 buffers acidity of material from
stomach Explain how this is a
molecular example of
structure-function theme.

13. Accessory Organ: Liver
 Digestive System Functions
 produces bile
 bile contains bile salts
o stored in gallbladder until needed
o break up and absorb fats in the duodenum
 act 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

14. Evolutionary Adaptations of
Vertebrate Digestive Systems
 specializationin teeth
 length of digestive system
 number & size of stomachs

15. Digesting cellulose
 How well you digest cellulose
governs life strategy of herbivores
starch
cellulose
bond between the sugars governs digestibility

16. Cow
can digest cellulose well;
no need to eat
supplemental sugars
Gorilla
can NOT digest cellulose
well; must supplement with
sugar source, like fruit

17. Mutualistic Adaptations
 How can cows digest cellulose efficiently?
 symbiotic bacteria in stomachs help digest cellulose-
rich meals caprohagy ruminant
 rabbit vs. cow adaptation: eat feces vs. chew cud
Ruminants
additional
mechanical
digestion by
chewing food
multiple times
after mixing it
with enzymes

18. Maintaining Homeostasis through Feedback
Example: Regulation of Blood Sugar
insulin
body liver stores reduces
cells take glucose as appetite
pancreas up glucose glycogen
from blood
high
liver
blood glucose level
(90 mg/100 mL blood)
low
liver
triggers releases
hunger glucose pancreas
Is this a negative or
positive feedback
liver glucagon system?

19. Homeostatic Imbalance
Diabetes mellitus
• caused by a deficiency of insulin or a
decreased response to insulin
• marked by elevated blood glucose
levels