Download Digestive System Notes

Digestive System Notes
Digestionprocess of breaking down food
into molecules the body can use
Two types of Digestion
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Mechanical Digestion -physically changing
the size of the food
-ex: grinding action of teeth
churning action of stomach
Chemical Digestion –a change in the
chemical nature of the nutrients
-ex: amylase (saliva) working on starch
Gastrointestinal Tract
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Also known as the
alimentary canal
Hollow organs that
food passes
through
Mouth (Oral Cavity)
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Teeth-mechanical
digestion
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Molars=grinding
Incisor=biting
Canine=piercing
Bicuspid= grinding
Tongue
– Keeps food in place
– Push bolus back in
mouth
More to the Mouth
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Hard Palate
– Bony, membranecovered roof of the
mouth
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Soft Palate
– Area just behind the
hard palate
– Separates the
mouth cavity from
pharynx

Uvula
– Dangling thing in
back of throat
– Part of soft palate
– Catches bacteria
and dirt particles in
mouth breathers
– Can be destroyed in
bulimics
Pharynx

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Open area at back
of mouth
Passageway for
both food and air
Epiglottis-thin flap
that prevents food
from entering the
esophagus
Esophagus
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Tube about 25 cm long
that connects pharynx
to stomach
2 layers of muscle
– Circular layer
– Longitudinal layer

Peristalsis-series of
rhythmic muscle
contractions that
pushes food through
digestive system
Stomach
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Both mechanical and
chemical digestion
3 layers of smooth
muscle that twist and
turn the stomach
– Results in the churning
action
– Makes your stomach
“growl”
Stomach

Rugae-thick
wrinkled membrane
inside stomach
– For more surface
area

Covered by a thick
layer of mucous
– To protect lining
from HCl acid
Stomach


Stomach lining dotted
with gastric pits
Gastric pits -release
secretions into
stomach
– HCl acid
– Pepsin

Both aid in the
chemical digestion of
proteins
Stomach Problems

Stomach Ulcers
– HCl acid “eats” a hole
through the lining of
stomach
– Caused by diet, stress and
some bacterial infections

Heartburn
– Cardiac sphincter at top of
stomach doesn’t close all
the way
– Gastric fluid (very acidic)
splashes up from stomach
onto esophagus
Out of the Stomach
(finally)
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After 3 to 4 hours
Chyme –paste like substance that
contains everything that was not
broken down by pepsin
Peristalsis forces chyme out of
stomach and into small intestine
Pyloric sphincter between stomach
and small intestine
Small Intestine
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Most important
organ in digestive
system
Most chemical
digestion
Most absorption of
nutrients
7 m long (21 feet)
Small Intestine

3 parts
– Duodenum
– Jejunum
– Ileum

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Secretions from liver and
pancreas enter the
duodenum
Trigger intestinal mucous
glands to release large
quantities of mucous
Enzymes and chemicals to
finish chemical digestion
– Break down fats, carbs and
proteins
Small Intestine
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Absorption –end
products of digestion
are transferred into
circulatory system
Passed through villi by
diffusion and active
transport
Villi and microvilli filled
with capillaries and
lymph vessels
Large Intestine


Key role – absorption
of water
4 parts
–
–
–
–

Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Minimal absorption of
nutrients (from
bacteria) –not even
considered chemical
digestion
Large Intestine Problems


Appendicitis
Diarrhea
– Not enough water
absorbed
– Irritation from
drugs, stress,
bacteria or parasites

Constipation
– Too much water
absorbed
Rectum and Anus

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Rectum –stores feces until peristalsis
moves it out
Anus –last sphincter muscle
Accessory Organs
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Just as important as
the other organs (think
purse)
Food does not pass
through them
Salivary Glands
Pancreas
Gall Bladder
Liver
Common Bile Duct
Salivary Glands


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3 sets
Add Amylase to
mouth
Amylase –breaks
down starch
Liver

Important in blood
sugar homeostasis
– Stores glucose as
glycogen

Produces Bile
– Brown chemical
– Emulsifies fat
– Neutralizes acids
Gall Bladder and Common
Bile Duct

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Stores bile
Connects to liver by
the common bile
duct
Problems
–
–
–
–
Gallstones
Cholesterol deposits
Form in ducts
Too much fat
Pancreas


2nd most important
organ in digestive
system
Makes a cocktail of
enzymes that are
deposited into small
intestine via the
common bile duct
– Pancreatic amylase
– Trypsin –proteins
– Lipase