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Lecture 16 Digestive (GI) System
What enzyme breaks down starch?
Amylase; comes from the salivary glands
Where is the enzyme located?
What enzyme breaks down proteins?
Pepsin
What cells secrete it?
Chief cells in gastric pits of stomach
What is its precursor molecule and what is
needed to activate the enzyme?
Pepsinogen; needs HCL to cut it into pepsin.
WHAT ARE THE FOUR LAYERS OF THE GI
TUBE?
From internal to external, the layers of this
tube are the mucosa, submucosa, muscularis,
serosa.
WHAT TWO TYPES OF ACTIONS DOES THE
MUSCULARIS EXTERNA ALLOW FOR?
Peristalsis-- rhythmic contraction to push
something along.
Segmentation-- A back-and-forth squeezing of
the muscle to grind up food. Food moves
forward then backward a little, then forward
again. Function is to churn up the food inside.
WHAT ARE 5 FUNCTIONS OF THE STOMACH?
Store Food
Mechanically churns food into a paste
called CHYME
Kill bacteria
Some digestion: of proteins
Some absorption: of water, alcohol
WHAT DO PARIETAL CELLS SECRETE?
PARIETAL CELLS in the stomach secrete
hydrochloric acid and digestive
enzymes which kill bacteria in the
stomach.
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WHAT DO CHIEF CELLS SECRETE?
CHIEF CELLS secrete PEPSIN to digest
protein.
WHAT IS THE FUNCTION OF GOBLET CELLS IN
THE STOMACH?
make mucus to prevent the stomach
from digesting itself. Bacterial
infection can erode this area =
GASTRIC ULCER.
WHAT VITAMIN NEEDS INTRINSIC FACTOR
Vitamin B12 needs intrinsic factor to be
TO BE ABSORBED? WHAT IS THE NAME OF
absorbed.Lack of Vitamin B12 = Pernicious
THE DISEASE WITH A LACK OF THIS VITAMIN? Anemia
WHAT ORGAN PRODUCES BICARBONATE?
WHAT HORMONE IS NEEDED TO STIMULATE
THE ORGAN TO MAKE BICARBONATE?
Pancreas
WHAT IS THE FUNCTION OF THE GALL
BLADDER?
Stores bile. It does not make the bile, the
liver does. Bile emulsifies (breaks down) fat.
WHAT IS THE FUNCTION OF THE JEJUNUM?
The jejunum is where most of the digestion
and absorption of food occurs.
WHAT IS THE TERMINAL PORTION OF THE
SMALL INTESTINE?
The ileum
WHAT IS THE INTESTINAL CRYPT (CRYPT OF
LIEBERKUHN)
The INTESTINAL CRYPT (CRYPT OF
LIEBERKUHN):
Secretin
 Is where the new epithelial cells come
from
 These epithelium are pushed upwards into
the villi to replace the digested cells
 In this crypt are cells that produce
enzymes and hormones
 In the villis is a fenestrated capillary bed,
which needs to absorb a lot of material
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WHAT ARE THE THREE REGIONS OF THE
SMALL INTESTINE?
WHAT ARE THE FUNCTIONS OF THE
DUODENUM?
Deuodenum, Jejunum, Ileum
This is where digestion begins.
It is the site of action of liver and
pancreas secretions.
WHAT IS THE FUNCTION OF THE SMALL
INTESTINE?
 Absorbs carbohydrates, fats, and proteins
(although protein enzymes have already
begun working earlier in the digestive tract
in the stomach)
 The walls of the small intestine secrete
most of the digestive enzymes that are
active in its lumen.
WHAT ARE LACTEALS?
LACTEALS are large lymphatic
capillaries in each villa whose function is to
absorb breakdown products of fat. The vessel
is large so it won’t get clogged up.
WHAT IS CROHN’S DISEASE?
CROHN’S DISEASE…
 An autoimmune disease of the GI Tract
 Most commonly affects the small intestine
 Inflammation causes pain and diarrhea
(may be bloody)
 Genetic cause (high risk if siblings have it)
 No cure; just treatment of symptoms
WHAT ARE THE FUNCTIONS OF THE LARGE
INTESTINE?
 Absorbs a LOT of water and salts
 Absorbs electrolytes (Na, K, etc)
 Stores feces for defecation
Contains bacteria (E. coli)
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WHAT ARE THE FUNCTIONS OF THE
BACTERIAL IN THE LARGE INTESTINE?
WHAT IS THE CECUM?
o Makes vitamins (B12, K)
 B12 requires intrinsic factor
for absorption
o Allows material to move through large
intestine easier
o Keeps out harmful bacteria
o Eat things you can’t digest
 Fiber and some sugars that we don’t
have enzymes for
The ileum enters into the first region of the
large intestine called the CECUM. The ileocecal valve separates these and controls the
amount of chime that enters into the large
intestine.
WHAT IS THE FUNCTION OF THE SIGMOID
COLON?
THE SIGMOID COLON allows for the passage
of gas without passage of feces.
HOW DOES THE LEVATOR ANI MUSCLE
CONTROL DEFECATION?
 When relaxed, it allows only gas to pass
 When contracted, the feces can pass
 Controls defecation by lifting the anal
canal superiorly around the feces.
 DIVERTICULUM (Diverticula is plural) can
form, a small pouch in the large intestine.
Inflamed pouches = DIVERTICULITITS.
Painful and often need to be surgically
removed. Unknown cause.
COLITIS - Inflammation of the colon.
WHAT IS A DIVERTICULUM?
WHAT IS COLITIS?
WHAT TESTS ARE AVAILABLE TO CHECK FOR
COLON CANCER?
 SIGMOIDOSCOPY OR COLONOSCOPY
o they look for growths on the walls of
the intestine = POLYPS, which are
pre-cancerous growths.
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WHAT ARE 7 FUNCTIONS OF THE LIVER?




THE LIVER HAS 2 LOBES SEPARATED BY
WHAT LIGAMENT?
The liver has a right and left lobe, separated
by the FALCIFORM LIGAMENT.
WHAT IS THE PORTAL CIRCULATION?
Almost all of the blood coming from the
digestive system drains into a special
venous circulation called the portal
circulation. This is because it contains all
the nutrients and toxins that have been
absorbed along the digestive tract from
ingested food. Before these absorbed
substances can go into the systemic
circulation (the main blood circulation in
the body), it must be filtered first to
remove or detoxify toxic substances first.
This filtering and detoxification is one of
the functions of the liver.
 The 1ST capillary bed picks up nutrients
 The second delivers these nutrients to liver
cells.
THE HEPATIC PORTAL SYSTEM HAS 2
DISCTINCT CAPILLARY BEDS SEPARATED BY A
PORTAL VEIN. WHAT IS THE FUNCTION OF
THESE CAPILLARIES?
What is the HEPATIC TRIAD
Makes blood
Makes blood proteins (clotting factors)
Regulates glucose levels
Processes fats (if liver is damaged, it will
interfere with digestion of lipids)
 Makes cholesterol
 Processes amino acids
Detoxifies chemicals
The HEPATIC TRIAD
1. ARTERIOLE from the hepatic artery
2. VENUOLE from the hepatic portal vein
3. BILE DUCT, which goes to the gall
bladder
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There are LIVER SINUSOIDS that have gaps.
Cells that line the sinusoids are called WHAT?
Cells that line the sinusoids are called
HEPATOCYTES, and each one faces the
sinusoid and is in contact with blood.
WHAT ARE KUPFFER CELLS?
 Macrophages within the sinusoids
 As blood flows through the sinusoids,
they phagocytize old erythrocytes
 The released Hgb is given to the
hepatocytes, which convert it to
bilirubin, one of the main components
of bile.
HEPATITIS - Infection of the liver (can be
deadly)
WHAT IS HEPATITIS?
WHAT IS CIRRHOSIS?
WHAT IS JAUNDICE? IS IT A DISEASE?
CIRRHOSIS - When the hepatocytes die and
are replaced by connective tissue. Often
caused by alcoholism which kills the
hepatocytes.
A connection of the bile canaliculi and the
sinusoid so some BILIRUBIN can enter the
blood. BILIRUBIN is yellow-green (a lot of it is
brown and is what gives the feces its color)
JAUNDICE – Yellowing of the skin. Jaundice is
not a disease; it is a symptom of liver
disorder. It first shows up in the sclera
because it is white there.
HOW DO GALL STONES form?
 Gall Bladder functions to Store and
Concentrate Bile.
It does not secrete bile; that is done by the
liver
bile salts crystallize
THE PANCREAS IS MADE UP OF WHAT 2
TYPES OF CELLS? What do they secrete?
 ACINAR CELLS: secretes digestive enzymes
 ISLETS OF LANGERHANS: secretes insulin
WHAT IS THE FUNCTION OF THE GALL
BLADDER?
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What are the two kinds of digestion?
Mechanical
Chemical
Which layer of the digestive tube contains lots Submucosa
of elastic fibers, blood vessels, and lymphatic
vessels?
The hepatic portal system has two distinct
capillary beds separated by a portal vein. The
functions of these two capillary beds are
what?
The first picks up nutrients and the second
delivers these nutrients to liver cells.
What structure flaps over the glottis when we
swallow food?
Epiglottis
Which vitamin requires intrinsic factor in
order to be absorbed?
Vitamin B12
What are the three main characteristic of the
large intestine?
1) It absorbs much of the water and salts
2) It contains the ascending, transverse,
and descending colon.
3) It contains an abundant bacteria.
What are the four main characteristics of the
small intestine?
It is the site of nutrient absorption
It breaks down fats, proteins, and
carbohydrates
Breakdown products of fats enter its lacteals.
Its walls secrete most of the digestive
enzymes that are active in its lumen.
Where does food first encounter proteinsplitting enzymes?
Stomach
When the acidic contents of the stomach
enter the normally alkaline duodenum, what
hormone is released that causes the pancreas
to secrete bicarbonate?
Secretin
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What is the semi-fluid paste called that is a
result of the food in the stomach being
repeatedly squeezed and mixed with
gastric juice?
What are four characteristics of the
duodenum?
Chyme
1) It receives chyme from the stomach.
2) It is within the body cavity with the ileum
or jejunum (not retroperitoneal).
3) It is shorter than either the ileum or
jejunum.
4) It is the site of action of liver and pancreas
secretions.
What are the five the primary functions of the 1. Store Food, so it can be slowly released
stomach?
into a small intestine.
2. Churns food into a paste (chime) by
mechanical means
3. Kill bacteria.
4. Starts digestion of proteins.
5. Some absorption of water, alcohol
Does it dehydrate food materials before
passing them to the small intestine?
No
Does it store food for later use in the form of
fat?
No
What is the terminal portion of the small
intestine called?
Ileum
Which layer of the digestive tract is
responsible for the peristaltic waves that
propel materials from one portion to
another?
muscularis externa
Of the basic digestive processes, the one in
which nutrients enter capillaries is called
what?
Absorption
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What is the only role of the levator ani muscle It lifts the anal canal superiorly around the
in defecation?
feces.
What is the correct sequence of layers in the
mucosa, submucosa, muscularis, serosa
wall of the alimentary canal, from internal to
external?
What is the digestive organ primarily
responsible for the absorption of water?
Large intestine
Why are bacteria are abundant in the large
intestines, but not in the small intestines or
the stomach?
Secretions of parietal cells kill bacteria in the
stomach, and the Ileocecal valve prevents
the bacteria in the large intestines from
migrating up into the small intestines.
What is the only function of the greater
omentum?
Stores fat
The epithelium that lines the stomach and
intestines is simple columnar. What are the
basic functions of this epithelium?
secretion and absorption
Digestion of what food type would be affected Lipids
the most if the bile—secreting liver were
severely damaged?
What are three functions of the liver?
1) detoxification of poisons
2) picking up and processing of nutrients from
the portal blood
3) storage of some vitamins
Does it produce digestive enzymes?
No
Which cells secrete digestive enzymes in the
pancreas?
Acinar cells
Which region of the pancreas secretes
insulin?
Islets of Langerhans
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