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Digestive System
Do It Now
1. What are the two functions of an animal
digestive system? (2 points)
2. Write the following in correct order and briefly
list its function:
Anus, rectum, mouth, stomach, esophogus, small
intestine, large intestine (16 points)
3. Where are villi and microvilli found? (1 point)
4. What is the function of villi and micro villi? (1
Extra credit: What is chyme?
Collect 24 hours data
Decant liquid down the drain.
Throw away bag.
Put stuff back where you got it!!!
 Take
in food
 Process food - Digestion
 Absorb nutrients
Homeostasis of Blood Glucose
 What
are the two main
nutrients carried by blood for
cellular respiration?
 Why must blood glucose levels
be maintained at a certain
 Animals
must supply carbon
skeletons necessary to build all
needed molecules.
 Animals must supply themselves
with essential nutrients that can
not be made with their enzymes.
 Minerals and vitamins
Ingestion – Where is the animal in
the Food Web
Herbivores – eat only plants, mouthparts
adapted to their food source, coevolution
with bacteria and protists to digest
cellulose, longer small intestine
Carnivores – eat only animals,
mouthparts, shorter small intestine
Omnivores – somewhere in between!
Feeding Mechanisms
Suspension feeding – food particles
removed from water
Substrate feeding – live on the food
source e.g. leaf miners, dung beetles
Deposit feeding – earthworms take in soil
and remove organic material
Fluid feeding – mosquito, leaches
Bulk feeding – large meals, not much
Food Processing
Ingestion – Digestion – Absorption
Ingestion – teeth – dentition, tongue
Digestion physical or chemical – hydrolytic
Absorption – once food is broken down,
the materials must be absorbed and
transported throughout the body.
Intracellular Digestion
Paramecium example
Gastrovascular Cavity
Hydra and planarian
Alimentary Canal
Mouth EsophagusStomachSmall
IntestineLarge IntestineRectumAnus
Mouth digestion of starch via amylase
Stomach – pepsin begins digestion of protein
into smaller polypeptides
Small intestine – breakdown and absorb
Large intestine – reabsorption of water and
Gastrointestinal System
Function-physical and
chemical breakdown of
Includes alimentary canal
and accessory organs
Accessory organs: Salivary
glands, tongue, teeth,
liver, gallbladder, and
Alimentary canal
Mouth- physical and
chemical breakdown.
Mastication-the act of
Saliva contains
enzyme amylase to
break down
Pharynx- contains
opening to trachea as
well. Epiglottis covers
opening of trachea.
tube dorsal to trachea
Relies on a rhythmic
wave-like motion
called peristalsis
Esophagus- transverse view
Sphincter-a circular
muscle that constricts
a passage or closes a
natural orifice
Cardiac sphincter
Pyloric sphincter
Food sits in stomach
for 1-4 hours. Gastric
juices contain
hydrochloric acidactivates pepsin, kills
Small intestine: not so
small! 20ft x 1’’
Duodenum- 1st 10
inches. Bile and
pancreatic juice enter
Jejunum- next 8 ft.
Ileum- final 12 ft.
When food leaves
small intestine,
digestion is complete
Small intestine has
lots of enzymes:
maltase, sucrase,
lactase, amylase.
Digested food is
absorbed into the
Large intestine- 5 ft x
2’’. Separated from
small intestine by
ileocecal valve
Final absorption of
water, storage of
indigestible material,
absorption of vitamins
B and K by bacteria.
Colon connects to
rectum- anal canal
opens to the anus
(final opening). Fecal
material is expelled.
But Wait! What about the accessory
organs: Liver, gall bladder and
 Liver- largest gland in
your body
Secretes bileemulsifies fat, makes
them water soluble.
Stores glucose in the
form of glycogen
Makes clotting
Detoxifies blood
Gall bladder- stores
and concentrates bile
Pancreas- produces
insulin, pancreatic
juices amylase and
lipase. Insulin
regulates the uptake
of glucose by the cells
What parts of the model accurately
portrayed the action of the digestive
How could we improve this model of
What organs are play a part in digestion,
but are not present in the alimentary
Stomach example
Physical churning
Acid released by cells in response to the
hormone Gastrin that is released when a
person eats.
Pepsinogin is also released by separate cells –
the acid in the stomach changes the shape of
pepsinogin to its active form pepsin. Pepsin
stimulates more acid – positive feedback.
Acid and Pepsinogin do not mix until they
reach the lumen of the stomach or else it
would digest the stomach. Stomach lumen is
coated with mucus to protect it.
Stomach continued
The food + water + acid and enzymes =
acid chyme which passes to the the
duodenum of the small intestine.
Ulcers – most caused by a bacteria called
Helliobacter pylori treated with antibiotics
Small Intestine
Duodenum – beginning of small intestine
the chyme is acidic, digestive enzymes are
secreted by the pancreas, liver, and gall
bladder (bile), but are active in a neutral
pH. Cells add Sodium bicarbonate to
neutralize the acid chyme.
Jejunum – villi and micro villi absorb
The End of the Line
7 liters of liquid are passed through the
stomach and small intestine each day.
Much is reabsorbed by microvilli into
lacreal cells in the small intestine.
More water and minerals are reabsorbed
by the large intestine.
Food digestion takes 12-24 hours. Longer
= less water, Shorter = more water
And then
More cellulose in the diet = faster
E. coli lives in the large intestine on
undigested food. The bacteria produce
vitamins and some strains help to fight off
infections by out-competing the bad guys.
Interesting Adaptations
Herbivores have a longer cecum – usually
with symbiotic prokaryotes and protists
that digest cellulose.
Rabbits have their symbionts living in their
large intestine instead. They eat the
digested food (poo) from the first time
around and the typical pellets you see are
food that has been through twice.
Deer, cows, horses
They have a four chambered alimentary canal.
They end up “chewing the cud” cud is made
up of food after it has been metabolized by the
protists and bacteria.
It passes through the digestive system again.
Ruminents actually get most of their nutrition
from the digestion of the microorganisms living
inside of them!