PLO’s
• C1 - analyze the functional
interrelationships of the structures of the
digestive system
Food – What’s in it for you?
Fig. 12.1
Digestion
• Digestion is the process of breaking
down large molecules of food into a
form that can be absorbed and utilized
by cells of the body
• Consists of both physical and chemical
processes (What’s the difference?)
Mouth
• Food is broken
down physically
by chewing
• Tongue tastes
food and aids in
swallowing
• Salivary glands produce salivary
amylase (digests starch)
Pharynx
•
•
•
•
Passage for food and air
Separates into two separate passages
Swallowing occurs by reflex action
Epiglottis prevents food from entering
the trachea
Fig. 12.3
Esophagus
• Food is pushed along by muscular
contractions called peristalsis
• Cardiac (esophogeal) sphincter is a
muscular ring located between stomach
and esophagus
Stomach
• Stores food
• Muscular action mixes food with gastric
juice
• Gastric glands produce mucus, pepsin,
and HCl (pH 2)
• Begins digestion of proteins
• Chemical digestion of protein begins
Fig. 12.5
• Chyme (partly digested food + gastric
juice) leaves the stomach through the
pyloric sphincter
Duodenum
• First part of
the small
intestine,
where food
enters after it
leaves the
stomach
• Sodium bicarbonate
neutralizes the pH
• Bile enters from the gall
bladder (emulsifies fats)
• Pancreatic enzymes
digest starch, protein
and fats
Small Intestine
• Most digestion and
absorption occur
here
• Length and large
surface area allow for
maximum absorption
of food
• Material is moved
along by peristalsis
• Blood vessels
surround the small
intestine
• Cells in intestinal wall
produces more
digestive enzymes
Intestinal Villi
• Walls contain villi
and microvilli to
increase surface
area for
absorption (these
contain blood and
lymph vessels)
• Sugars and amino
acids enter the
blood via
capillaries leading
to the hepatic
portal vein
• Fatty acids and
glycerol enter
lacteals (lymph
vessels)
Large Intestine (Colon)
• No digestion
occurs here
• Consists of the
ascending,
transverse,
descending and
sigmoid colon
• Absorption of
water, salts and
some nutrients
• Anaerobic bacteria
break down indigestible
materials and produce
some vitamins (vitamin
K and B)
• Feces moves
along by
peristalsis, is
stored in the
rectum and exits
via anal sphincter
REVIEW
Animation and quiz
• List the structures that food passes
through in your body, from beginning to
end.
• What happens at each location?
Accessory Organs
• Several organs
and glands
contribute to the
digestive process
even though food
does not pass
through them
Pancreas
• Cells in the pancreas
produce pancreatic
juice, which contains
sodium bicarbonate
and several enzymes
to digest
carbohydrates,
proteins and fats
• Pancreatic juice is
secreted into the
duodenum via the
pancreatic duct
• The pancreas also has an endocrine
function (hormone secreting)
• insulin is produced in the pancreas and
secreted into the blood when blood
glucose is high (after eating)
• stimulates body cells to take up glucose
(lowers and regulates blood sugar
levels)
• Another hormone, glucagon, is secreted
to increase blood sugar levels
Liver
• Is considered the “gatekeeper” to the
blood as it regulates blood composition
in several ways
• Blood leaving the
digestive tract first
goes to the liver
via the hepatic
portal vein
• Blood leaves the
liver via the
hepatic vein
Liver functions:
• Contributes to digestion by producing
bile (helps break down fats)
• Stores excess glucose as glycogen
• Converts glycogen to glucose when
needed
• Stores iron and some vitamins
• Removes and breaks down toxins from
the blood
• Regulates blood cholesterol levels
• Synthesizes blood
proteins
• Produces urea from
amino acid breakdown
(which is later excreted
by the kidneys)
• Breaks down hemoglobin
from old red blood cells;
components of
hemoglobin breakdown
are excreted in bile,
giving it its green colour
Gall Bladder
• Attached to the liver
• Stores bile and secretes it into the
duodenum via the common bile duct
when fats are present
Appendix
• Not really an accessory
organ since it has no
apparent digestive
function
• Found at the end of the
cecum (where the small
and large intestine join)
• Thought to have
functions associated
with the immune system