Download Stomach = Preliminary digestion

Different diets; different lives
 All animals eat other organisms

Herbivores
 eat mainly plants
 gorillas, cows,
rabbits, snails

Carnivores
 eat other animals
 sharks, hawks, spiders, snakes

Omnivores
 eat animals & plants
 cockroaches, bears, raccoons, humans
 humans evolved as hunters, scavengers & gatherers
Types of Digestive Systems
Single-celled organisms
digest their food
intracellularly
-Other multicellular
animals digest their
food extracellularly,
within a gastrovascular
cavity
-no specialized
regions
intracellular
digestion
extracellular
digestion
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-Specialization occurs when
the digestive tract has a
separate mouth and anus
(A tubular gut lined by an
epithelial membrane)
-More complex animals
have a digestive tract
specialized in different
regions
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
Vertebrate Digestive Systems
The digestive system consists
of a tubular gastrointestinal
tract and accessory organs
-Mouth and pharynx = Entry
-Esophagus = Delivers food
to stomach
-Stomach = Preliminary
digestion
-Small intestine =
Absorption
-Large intestine =
Concentration of wastes
-Cloaca or rectum = Waste
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 Mouth


Ingestion
mechanical digestion
 teeth
 breaking up food
chemical digestion
 saliva
 amylase

enzyme digests starch
 mucin



slippery protein (mucus)
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
Swallowing (& not choking)
 Epiglottis
problem: breathe & swallow through same orifice
 flap of cartilage
 closes trachea (windpipe) when swallowing
 food travels down esophagus
 Esophagus
 Moves lump of food called a bolus along to stomach by
peristalsis- push food along by rhythmic waves of
smooth muscle contraction

 Functions
Stomach
food storage
 can stretch to fit ~2L food
 disinfect food
 Parietal Cells release HCL
 HCl = pH 2
kills bacteria
breaks apart cells
Denatures food proteins
 chemical digestion
 Pepsin released as
Pepsinogen
enzyme breaks down
But the stomach
is made out of protein!
proteins
What stops the stomach from digesting itself?
secreted as pepsinogen
mucus secreted by stomach cells protects
 activated by HCl
stomach lining

Ulcers
Coevolution of parasite & host
 Used to think
Colonized by
H. pylori
Free of
H. pylori
ulcers were
caused by stress

tried to control
with antacids
inflammation of
stomach
 Now know ulcers
caused by
bacterial
infection of
stomach
Helicobacter pylori
 now cure with
antibiotics

inflammation of
esophagus
H. pylori
inflammatory
proteins
(CagA)
cell damaging
proteins
(VacA)
 Function
major organ of digestion & absorption
 chemical digestion
 digestive enzymes
 absorption through lining
 over 6 meters!
 small intestine has huge surface area =
300m2 (~size of tennis court)
Epithelial wall is
covered with villi,
which in turn are
covered by
microvilli


Small intestine
Small Intestine: 3 sections
duodenum = most

digestion
jejunum = absorption of
nutrients & water
ileum = absorption of
nutrients & water
Duodenum
1st section of small
intestines

acid food from stomach
mixes with digestive
juices from accessory
glands:
 pancreas
 liver
 gall bladder
Pancreas
 Digestive enzymes
peptidases
 Trypsin- proteins
 trypsinogen
 Chymotrypsin- proteins
 chimotrypsinogen
 Carboxypeptidase- proteins
 procarboxypeptidase
 pancreatic amylase- starch
Buffers
 reduces acidity
 alkaline solution rich in
bicarbonate (HCO3-)
 buffers acidity of material from
stomach


small intestines
 Digestive System Functions

Liver
produces bile
 stored in gallbladder until needed
 Salts- breaks up fats
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
 Passive transport
Absorption of Nutrients
fructose
 Active (protein pumps) transport
 pump amino acids, vitamins & glucose
 worth the cost of ATP!

 Function
Large intestines (colon)
re-absorb water
waste materials
concentrated
 eliminate feces
 use ~9 liters of water
 undigested materials
every day
 extracellular waste
in digestive
 mainly cellulose from plants
juices
 roughage
or fiber
> 90% of water
reabsorbed
not enough
water absorbed
back to body
 diarrhea
too much water absorbed

Flora of large intestines
 Living in the large intestine is a rich
flora of harmless, helpful bacteria

Escherichia coli (E. coli)
 a favorite research organism

bacteria produce vitamins
 vitamin K; biotin, folic acid & other B vitamins

generate gases
 by-product of bacterial
metabolism
 methane, hydrogen sulfide
Regulation of the Digestive Tract
Gastrointestinal activities are coordinated by the nervous
and endocrine systems
hormones
Stomach, proteins stimulate release of:
gastrin-Triggers secretion of HCl and pepsinogen
Duodenal- CCK, secretin,GIP
Inhibits stomach contractions prevent additional chyme from
entering duodenum
Stimulates
- gallbladder contraction
- pancreatic enzyme secretion
- secretion of pancreatic bicarbonate
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