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***Don’t forget that we covered enzymes, so you will likely have to know more detail than is given in this chart.***
***Study Tip: Draw a long tube on a piece of paper (the bigger, the better) and label the different parts of the digestive tract (mouth,
esophagus, stomach, etc.). Then label all the secretions and changes to the food (bolus to chyme to feces/waste) and where digestion and
absorption happens for carbohydrates, protein and fat.***
Organ/Body Part
Structure
Function
Secretions
MOUTH
-contains teeth, tongue,
-Mechanical Digestion occurs via the Teeth
-Saliva (contains amylase to
hard and soft palates and
mechanically breaking food down. Incisors at
break down starches and
Eg. “Park gates”
salivary glands
the front of the mouth are specialized for
provides lubrication for the
–separate groups of people
-the point of ingestion
cutting; Canines are specialized for tearing;
food).
into individuals (break apart
-beginning of physical (and
molars specialized for grinding.
food).
some chemical) digestion
-often send you straight to the
-Tongue is 1) involved in tasting of food; it
showers to rinse before
contains taste buds and when food is in solution,
getting in the water (saliva
it is able to activate taste bud receptors and 2)
moistens food).
pushes food between the teeth while chewing
and to the back of the mouth to initiate
swallowing.
-Hard Palate is involved in the crushing of food
-Soft Palate (uvula) can cause regurgitation
-Chemical Digestion begins in the mouth via
saliva produced by the Salivary Glands. Saliva
has multiple functions, which include 1) to
moisten/lubricate food so its easier to swallow,
2) putting food into solution so that we can taste
with our taste buds, and 3) contains amylase
which breaks down starches into simpler
carbohydrates.
Overall Function: Mouth The mouth is primarily involved in breaking food into smaller pieces and lubricating it so it travels easily down the
esophagus. Saliva secreted by the salivary glands into the mouth begins digestion of carbohydrates. No absorption occurs in the mouth.
ESOPHAGUS
-approximately 25 cm
-smooth, circular, muscular
tube
-mucus membrane
begins at the back of the mouth in an area called -mucus secreting cells line the
the pharynx
esophagus to moisten the food
Eg. “The bullet” (water slide)
-the pharynx also houses the opening to the
bolus and prevent food from
-a straight shoot down, very
trachea (windpipe)
getting caught.
quick ride
-once the food is mixed with saliva and starts
-slide is kept wet so no one
traveling down the esophagus, it is referred to
gets stuck.
as a bolus.
-if you were to get stuck,
-during swallowing, the esophagus undergoes
someone would likely come
peristalsis, which is a series of wave-like,
save you, push you down
rhythmic, involuntary contractions that pushes
(muscles)
the food bolus down to the stomach…like
squeezing a tube of toothpaste from the bottom
to the top to push the toothpaste out through
the opening.
-involuntary peristalsis means that food will
always move down the esophagus towards the
stomach, regardless of body position.
-a flap called the epiglottis covers the opening
to the trachea (windpipe) during swallowing to
prevent food from going “down the wrong tube”
and ending up in the lungs.
Overall Function: Esophagus The only purpose of the esophagus is to transport food (a bolus) from the mouth to the stomach. This is
accomplished via peristalsis (think: tube of toothpaste) and mucus lubrication. No digestion or absorption occurs here.
STOMACH
-J-shaped or saddle-bag
shaped.
-can store up to 1.5 litres of
food.
-VERY acidic – pH ranges
from 2 – 3.
-strong muscular layer
surrounds mucosal
epithelium (lining)
Eg. “The Wave Pool”
-this is where everyone floats
around and gets mixed up by
the huge waves (similar to the
food bolus’ that are mixed
with acid and pepsin by the
waves/ churning of the
stomach).
-The cardiac sphincter allows for the passage of
the food bolus into the stomach (you wouldn’t
want food stuck in your esophagus), but
prevents backflow of stomach juices (chyme)
back into the esophagus. This can occur,
however, and is known as acid reflux or
heartburn.
-Mechanical digestion occurs via the contraction
of the muscular stomach walls, churning and
mixing the stomach contents.
-mucus (protects stomach lining
from acid)
-HCl (acid kills bacteria/viruses)
-Pepsinogen (converted into its
active form, pepsin, by HCl,
which then breaks apart
protein)
-there are 2 sphincters
(muscles) in the stomach;
one at the opening from the
esophagus (cardiac), and
one where the stomach
meets the small intestine
(pyloric).
-Chemical digestion occurs via the secretion of
gastric juices by cells lining the stomach.
-Gastric juices include mucus, HCl, and
pepsinogen (as well as other substances).
-Mucus is involved in the protection of the
stomach lining (from HCl and pepsin).
-HCl is a very strong acid that kills bacteria and
viruses (pathogens) and also converts
pepsinogen into pepsin.
-Pepsinogen (inactive form) is secreted into the
stomach, and in the presence of HCl, is
converted to pepsin (active form of enzyme).
-Pepsin is an enzyme that breaks peptides
(proteins).
-food stays in the stomach for quite a while (4
hours), which is the reason we feel full/satisfied
for hours after we eat.
-Once food is mixed with gastric juices (the food
mixed with the juices is now called chyme), it
leaves the stomach in small squirts into the
small intestine.
-The pyloric sphincter prevents too much chyme
from entering the small intestine, instead
allowing for small amounts of chyme to be
squirted into the small intestine little by little.
Associated Disorder/Disease:
-Ulcers can happen when the stomach doesn’t
properly produce mucus; stomach lining is
exposed to acid, causing damage.
-Ulcers can also occur due to bacterial infections
Overall Function: Stomach The stomach is a very acidic environment due to HCl acid secretions. A mucus coating (secretions) protects the lining
from the acid. The stomach secretes pepsinogen, which is converted to its active form, pepsin in order to break down proteins. The muscular wall
of the stomach contracts to mix the contents. 2 sphincters control what enters and leaves the stomach. Digestion of protein begins here. No
absorption occurs in the stomach.
SMALL INTESTINE
-long tube-like structure,
-When chyme enters the small intestine, it is
-mucus to protect the lining.
approximately 7m in length, very acidic and contains protein-digesting pepsin -prosecretin (converted to
Eg. “Lazy River”
2.5cm in diameter.
-arrival of chyme in the S.I.(duodenum) triggers
secretin in the presence of
-People float slowly and gently -Inside, the small intestine
the conversion of prosecretin (inactive) into
chyme)
through the park, perhaps
has folds on top of folds to
secretin (active). Secretin then signals the
getting hit by rambunctious
increase the surface area
pancreas to secrete bicarbonate, which
kids occasionally. This is
and allow for maximal
buffers/neutralizes the acid.
similar to the chyme moving
absorption (villi and
slowly through the small
microvilli).
-Chemical Digestion occurs within the
intestine, occasionally being
-The length of the small
duodenum via secretions from the pancreas
joined by secretions from
intestine is broken into 3
(digestive enzymes – discussed below) and liver
ducts (pancreatic, bile).
areas: 1)the duodenum, 2)
(bile – discussed below).
the jejunum and 3)the
OR
ileum.
-Absorption occurs in the small intestine.
“River full of fish”
-The small intestine has
Nutrients from the food/bolus/chyme that has
-If a river full of fish is slowly
both a muscular wall and
been digested are absorbed through the
rapidly past you, it is quite
mucus secreting cells
membrane lining the small intestine and are
difficult to catch very many
(especially at the
passed along into the capillaries (circulatory
fish. 1) Slower river increases duodenum).
system – carbohydrates and amino
number of fish you are able to
acids/proteins) or the lacteal system (fats).
catch (Small amounts of
slowly moving chyme allow for
more time for absorption). 2)
The number of fish you can
catch is limited by the number
of people that can stand along
the river bank to catch them.
If the river bank curves in and
out, more (surface) area
allows for more people to
catch the fish. (Villi increase
surface area and therefore
increase absorption). 3) There
is some sort of mutation in
your family that results in
more than 2 hands for each
person. More hands catch
more fish. (Microvilli on top of
the villi further increase
surface area for maximal
absorption).
Overall Function: Small Intestine The small intestine is very long and therefore can be broken into areas based on function. The beginning of the
small intestine (duodenum) is where more digestion occurs via secretions from the pancreas and liver (pancreatic and bile ducts, respectively).
These secretions are also of particular importance in neutralizing/buffering the acidic chyme entering from the stomach. Digestion of proteins and
fats occurs early in the small intestine/duodenum (thanks to secretions from accessory organs). Absorption of nutrients (completely digested food)
occurs in the small intestine as well, but later on.
PANCREAS
-thin, “feathery”, looks like a - Exocrine compartment is involved in
-trypsinogen (inactive) is
tongue.
production and secretion of digestive enzymes
converted to trypsin (active –
Unfortunately, there is no
-very soft/squishy tissue
required for digestion and bicarbonate required breaks large
water –park reference for the that is lobuled (bumpy).
for the neutralization/buffering of chyme.
proteins/polypeptides into
accessory organs. Feel free to -“2 for the price of 1”; the
-Digestive enzymes include:
smaller ones/peptides) in the
make your own, or use other
pancreas is comprised of 2
-Trypsinogen (inactive) is secreted by the
small intestine by an enzyme
analogies as a study tool.
compartments – exocrine
pancreas and is converted to trypsin (active)
called enterokinase.
and endocrine. The
by enterokinase (another enzyme) once it
-erepsins (break down small
exocrine compartment is
enters the small intestine. Trypsin breaks
proteins/peptides into individual
made up of cells that
down large proteins into smaller ones.
amino acids) are also released
secrete digestive enzymes
-Erepsin are also released by the pancreas to
by the pancreas.
into ducts (“tubes”) that
further break down proteins
-pancreatic amylase further
merge into a common
-Amylase continues to break down
breaks down carbohydrates.
pancreatic duct. This duct
carbohydrates (digestion of which began in
-Lipases break down lipids to
empties into the small
the mouth).
continue fat digestion.
intestine.
-Lipases break down lipids.
Overall Function: Pancreas The pancreas is dual-purpose organ. There is an endocrine and an exocrine compartment; it is the exocrine
compartment that contains the digestive enzymes. The pancreas secretes many enzymes that continue digestion of protein, lipids and
carbohydrates in the small intestine. These enzymes travel through the pancreatic duct to the small intestine. Although no digestion or absorption
occurs in the pancreas, enzymes secreted from the pancreas are essential for digestion in the small intesitine.
Liver and Gall Bladder
Liver
-Produces and secretes bile, which is comprised -Bile is produced by the liver
-a very large and heavily
of bile salts, which are important in the
and stored in the gall bladder.
vascularized (has a lot of
digestion of fats
-Bile emulsifies fat in the small
blood vessels supporting it)
-bile is secreted by the liver and stored in the
intestine once released.
organ.
gall bladder.
-sits above the stomach
-when there is fat in the small intestine, the liver
Gall Bladder
secretes CCK (cholecystokinin) into the blood,
-a round sac tucked
which travels to the gall bladder, instructing it to
underneath the liver.
release bile salts.
-Bile is released from the gall bladder into the
bile duct, which carries it to the small intestine.
-Once it reaches the small intestine, bile
emulsifies fats (breaks them apart)
-the liver is also important in detoxification,
which is why liver damage is associated with
alcoholics.
Overall Function: Liver and Gall Bladder The liver’s primary function is to produce and secrete bile, which is stored in the gall bladder. When fat is
present in the small intestine, a message is sent to the liver resulting in the release of CCK. CCK travels through the blood stream to signal the gall
bladder to release bile into the bile duct, which leads to the small intestine. Bile then acts on the fat and emulsifies it. No digestion or absorption
occurs in the liver or gall bladder, but the bile produced and secreted by these organs is important for fat digestion in the small intestine.
Large Intestine
-1.5m long, 7.6 cm diameter -Digestion is already complete as (waste)
-Made up of the ascending
material enters the large intestine.
(going up), transverse
-Material moves slowly through the large
(across) and descending
intestine, allowing for the absorption of water
(going down) colon.
before the waste is excreted.
-The large intestine lines the -Components such as cellulose in the diet cannot
perimeter of the small
be digested and slow the material moving
intestine.
through the large intestine, allowing for
increased water absorption and a thorough
cleaning of the intestine.
Rectum and Anus
Eg. “The Log Ride”
-6-8 inches long.
- a muscular organ that
contracts VOLUNTARILY.
-When waste is present/building up in the large
intestine, the nervous system signals a bowel
movement.
-waste is received from the large intestine and
stored in the rectum until a voluntary muscle
contraction expels the waste through the anus.