D.
Digestive Processes Occurring in the Stomach
1.
Mechanical digestion consists of peristaltic movements called
___________________________.
2.
Chemical Digestion
a.
Chemical digestion
consists mostly of the conversion of
proteins into peptides by ___________________________,
an enzyme that is most effective in the
very acidic
environment (pH 2) of the stomach. The acid (HCl) is
secreted by the stomach’s parietal cells.
b.
_____________________________________________
splits certain molecules in butterfat of
milk into fatty acids
and monoglycerides
and has a limited role in the adult
stomach.
3. Absorption
a. the stomach wall is impermeable to most substances;
b. those substances which can pass through the stomach
wall include…
1)
2)
3)
4)
1.
Gastric secretion (release of gastric juice) is regulated by
nervous and hormonal mechanisms. Stimulatory
& inhibitory events
occurs in three overlapping phases: cephalic
(reflex), gastric,
and intestinal.
2. ___________________________ Phase – reflexes initiated by
sensory receptors in the head that stimulate
gastric secretion and
motility.
a. Excitatory events
– sight or thought of food & stimulation
of taste or smell receptors
b. Inhibitory events
– Loss of appetite or depression &
decrease in stimulation of the parasympathetic division of
the ANS
a.
Excitatory
events result in waves of peristalsis and
continual flow of gastric juice.
1) Stretch of the stomach as food enters
2)
pH increases when proteins enter the stomach
b. Hormonal negative feedback also regulates gastric
secretions during the gastric phase.
1)
Chemoreceptors and stretch receptors cause the
following cascade of events…
a)
the ANS releases acetylcholine
(___________________________)
b)
ACh stimulates the release of
___________________________ by G cells.
c)
Gastrin has the following effects…
i) Gastric glands
secrete gastric juice
ii) Strengthens contraction of the lower
esophageal sphincter
iii) increases motility
of the stomach
iv) relaxes the pyloric
and ileocecal
sphincters
c. Inhibitory events
– A pH lower than 2 or emotional upset
that overrides the parasympathetic division.
4. Gastric Contractile Activity
a. _____________________________________
move
toward the pylorus at the rate of ____________________
b. This basic
electrical rhythm (BER) is initiated by
pacemaker cells (cells of Cajal)
5.
Intestinal Phase - due to
activation of receptors in the small
Intestine (food has
passed to the small intestine, the stomach
needs
to stop its work).
a. ___________________________
reflex - partially
digested food enters the small intestine, it
triggers the
intestinal mucosa to secrete …
1) gastric
inhibitory peptide (GIP)
2) secretin
3) cholecystokinin (CCK)
b. The effect is inhibition of gastric secretion.
1.
Gastric emptying is the periodic release of chyme
from the
stomach into the duodenum.
2.
Gastric emptying is stimulated by two factors: distention of the
stomach and gastrin.
3. Most food leaves the stomach ___________________________
after ingestion. Carbohydrates leave
earliest, followed by proteins
and then fats.
4.
Gastric emptying is inhibited by the enterogastric
reflex and by
the hormones CCK and GIP.
5.
Vomiting is the forcible expulsion of the contents of the upper GI
tract (stomach and sometimes duodenum)
through the mouth.
V. Small Intestine and Associated Structures
A.
LIVER AND GALLBLADDER
1.
The ___________________________
is the heaviest gland in
the body
and the second largest organ in the body after the skin.
2.
Anatomy of the Liver and Gallbladder
a. The liver is divisible into ___________ and _________
lobes, separated by the ___________________________.
1)
Associated with the right lobe are the caudate and
quadrate lobes.
2)
The falciform ligament suspends the liver from
the
diaphragm & anterior abdominal wall.
b. The ___________________________ is a sac
located in
a depression on the posterior surface of the liver.
3. Histology of the Liver and Gallbladder
a.
The liver
is composed of hexagonal-shaped _________
that contain __________________ cells (liver cells or
hepatocytes), sinusoids (enlarged, leaky capillaries),
_____________________
cells (hepatic
macrophages), and
a central vein.
b. Hepatic cells produce ___________________________
that is transported by a duct system to
the gallbladder for
concentration and temporary storage.
1) Bile is partially an excretory product (containing
components of worn-out red blood cells) and
partially
a digestive secretion.
2) Bile is a yellow-green, alkaline solution.
3) Bile’s contribution to digestion is the
___________________________ of
triglycerides.
c. The liver receives
a double supply of blood from the
hepatic artery and the hepatic portal vein. All blood
eventually leaves the liver via the hepatic vein.
d. The liver also
functions in …
1)
carbohydrate, lipid, and protein metabolism;
2)
removal (detoxification) of drugs and hormones
from the blood;
3)
excretion of bilirubin;
4)
synthesis of bile salts;
5)
storage of vitamins and minerals;
6)
phagocytosis; and
7)
activation of vitamin D.
e. Anatomy of the
Gallbladder – a thin-walled, green
muscular sac
1)
The smooth muscle of the muscularis ejects
bile
form the bile duct, leading to the
duodenum of the
small intestine.
f. Bile usually does
not enter the small intestine until the
gallbladder contracts when stimulated by cholecystokinin
(CCK).
g. The fusion of
individual crystals of cholesterol is the
beginning of 95% of all ___________________________.
1) Gallstones can cause obstruction to
the outflow of
bile in any portion of the duct system.
B.
PANCREAS
1. A retroperitoneal organ divided into a head,
body, and tail.
a. The pancreas is
connected to the duodenum.
b. The pancreas lies
…
1)
deep to the greater curvature of the stomach.
2)
Its head is encircled by the duodenum.
3)
the tail abuts the spleen.
d. _____________________________________________
secrete insulin and glucagons
1) ___________________________
– causes
glucose to diffuse into tissue cells
2) ___________________________
– raises the
blood glucose level by freeing sugar (stored as
glycogen in the liver & skeletal muscles)
e. ___________________________
(clusters of secretory
cells) secrete a mixture of fluid and
digestive enzymes called
pancreatic juice.
a. Pancreatic juice contains inactive enzymes (that
are
activated in the duodenum) that digest…
1) ___________________________ – pancreatic
amylase
2) ___________________________ – trypsin,
chymotrypsin, and carboxypeptidase
3) ________________________ – pancreatic lipase
4) ______________________________________ –
ribonuclease and deoxyribonuclease
b. It also contains sodium bicarbonate which converts the
acid stomach contents to a slightly
alkaline pH (7.1-8.2)
1) this halts stomach
pepsin activity and promotes
activity of pancreatic enzymes.
3.
Inflammation of the pancreas is called pancreatitis and can
result in trypsin
beginning to digest pancreatic cells.
4.
Pancreatic secretion is regulated by nervous and hormonal
mechanisms.
a.
Secretin & CCK are released when fatty or acidic chime
enters the duodenum which stimulates
pancreatic juice
secretion
b.
Vagal stimulation also causes release of pancreatic juice.
C.
SMALL INTESTINE – where the
major events of digestion and
absorption
occur.
1. Gross Anatomy
a. The small
intestine extends from the pyloric sphincter to
the ileocecal sphincter.
b. The small
intestine is (going from the stomach to the
large intestine) is divided into the…
1)
___________________________
~ 25 cm (10
inches)
a) The bile and pancreatic ducts connect here
b) The submucosa
contains duodenal glands
which secrete an alkaline mucus that helps
neutralize gastric acid in chyme.
2)
___________________________
~ 2.5 m (8 feet)
3)
___________________________
~ 3.6 m (12
feet)
a) The submucosa
contains lymphatic nodules
(Peyer’s patches).
c. _____________________________________________
(circular folds) – are permanent ridges in the mucosa that
enhance absorption by increasing surface area and causing
chyme to spiral as it passes
through the small intestine.
2. Histology of the Small Intestine
a. The mucosa forms fingerlike ______________________
which increase the surface area of the
epithelium available
for absorption and digestion.
b. Embedded in each villus is a ______________________
(lymphatic
capillary) for fat absorption.
c. The cells of the mucosal epithelium include…
1)
___________________________ cells – absorb
digested food stuffs
a) The free surface features ______________
that increase surface area.
b) This forms the _______________________
c) The brush border contains enzymes that
break down foods
2)
___________________________
– produce
mucus
3)
enteroendocrine
cells – produce hormones that
help regulate the digestive process.
d. ___________________________________________ –
cavities of the mucosa that are lined by
glandular epithelium.
1)
These cavities secrete intestinal
juice.
2) Intestinal juice is mostly water, slightly
alkaline,
enzyme-poor, but contains mucus
3) Intestinal juice provides a vehicle for
absorption of
substances from chyme as they come
in contact with
the villi.
VI. DIGESTIVE PROCESSES (MOSTLY OCCURRING IN THE
SMALL
INTESTINE)
A.
Mechanical Digestion in the Small Intestine
1.
___________________________,
the major movement of the
small intestine, is a localized contraction
in areas containing food.
2.
___________________________
propels the chyme onward
through the intestinal tract.
B.
Chemical Digestion
1.
Carbohydrates (long chains of
simple sugars) are broken down
into ___________________________ (simple sugars) for
absorption.
a. The digestible
polysaccharide is starch; other
polysaccharides, such as cellulose, aren’t broken down by
humans.
b. Disaccharides are
composed of 2 monosaccharides
bonded together
1) Maltose, lactose, & sucrose
c. Monosaccharides are simple sugars that are absorbed
immediately
1) Glucose, galactose,
& fructose
d. Digestion of
carbohydrates begins in the mouth with
____________________________________________
e. _____________________________________________
continues the digestion of starch. Intestinal enzymes that
break down starches include…
1)
Maltase breaks maltose into
glucose
2)
Sucrase
breaks sucrose into glucose & fructose
3)
Lactase breaks lactose into
glucose & galactose
2. Proteins
are converted into ___________________________
and
___________________________ by
the following enzymes…
a. ___________________________,
secreted by the chief
cells, begins the digestion of proteins in the stomach
b. ___________________________
is produced in infants
& breaks
down milk proteins
c. Pancreatic enzymes
– ___________________________
& ___________________________ – convert proteins into
peptides in the small intestine
d. Brush border enzymes
free single amino acids in the
small intestine.
3.
Most lipid digestion, in an
adult, occurs in the small intestine.
a. Bile salts break the globules of triglycerides (fats) into
droplets, a process called ___________________________.
b. ______________________________________, due to
the increase exposed surface area of the
droplets, can
hydrolyze more triglycerides into fatty acids
and
monoglycerides.
4. Nucleic acids are broken into nucleotides
monomers by
pancreatic ribonucleases and deoxyribonuclease in the small
intestine
for absorption.
1.
The most important mechanism for regulating
small intestinal
secretion is the action of local reflexes in
response to the presence
of chyme.
2.
Hormones (vasoactive intestinal polypeptide or
VIP) also
assume a role.
3.
Parasympathetic impulses increase motility; sympathetic
impulses decrease motility.
D.
Absorption in the Small Intestine
– occurs along the entire length of
the small
intestine, & most of it is completed before the chyme
reaches the
ileum.
1.
___________________________
is the passage of the end
products of digestion from the GI tract into
blood or lymph.
2. Essentially all carbohydrates are absorbed as
_____________.
3.
Most proteins are absorbed as _________________________.
4. Absorption of Lipids
a. Long-chain fatty acids and monoglycerides
become
associated with bile salts & lecithin to
form _____________,
which are necessary for lipid absorption.
1)
Micelles are resynthesized to triglycerides,
and
formed into protein-coated spherical masses
called
___________________________.
2)
Chylomicrons are taken up by the lacteal of a
villus.
c. The plasma lipids - fatty acids, triglycerides, cholesterol
–
are insoluble in water and body fluids.
1) In order to be transported in blood
and utilized by
body cells, the lipids must be combined
with protein
transporters called ___________________________
to make them soluble.
5. Absorption of Electrolytes – occurs along the
entire length of the
small
intestine, except for ___________________________
&
___________________________ which are
absorbed in the
___________________________.
6. Absorption of Vitamins – the small intestine
absorbs dietary
vitamins,
while the ___________________________
absorbs
vitamins
___________________________.
a. Fat-soluble vitamins (___________________________)
are included along with ingested dietary
lipids in micelles.
b. Water-soluble vitamins (_________________________)
are absorbed by simple diffusion.
7. Absorption of Water
a. Water is the most abundant substance in chyme
& ___%
of it is absorbed in the ___________________________ by
osmosis.
VII. LARGE INTESTINE –
absorbs water from indigestible food residues &
eliminates them as feces.
A. Anatomy of the Large Intestine
1.
The large intestine (colon) extends from the ileocecal
sphincter
to the anus.
2.
Its subdivisions include the cecum, colon,
rectum, and anal
canal.
3.
Hanging inferior to the cecum is the _____________________.
a. Inflammation of the appendix is called appendicitis.
b. A
ruptured appendix can result in gangrene or peritonitis,
which can be life-threatening conditions.
4.
The colon is divided into the ascending, transverse, descending,
and sigmoid portions.
B.
Histology of the Large Intestine
1. The mucosa of the large intestine has no villi or permanent
circular folds. It does have a simple columnar
epithelium with
numerous globlet
cells.
2.
The muscularis contains specialized portions
of the longitudinal
muscles called ________________________________ (3 bands of
longitudinal smooth muscle), which contract and
gather the colon
into a series of pouches called ___________________________.
3. The last stages of chemical digestion occur
in the large intestine
through ___________________________, rather than enzymatic,
action.
4. Substances are further broken down and some
vitamins are
synthesized by bacterial action and absorbed by
the large intestine.
C.
Absorption and Feces Formation in the Large Intestine
1.
The large intestine absorbs ___________________________,
___________________________, and some _________________.
2.
Feces consist of water, inorganic salts, sloughed-off epithelial
cells, bacteria, products of bacterial
decomposition, and undigested
parts of food.
3. Although most water absorption occurs in the
small intestine, the
large intestine absorbs enough to make it
an important organ in
maintaining the body’s water balance.
D.
Defecation Reflex
1.
The elimination of feces from the rectum is called defecation.
2.
Defecation is a reflex action aided by voluntary contractions of
the diaphragm and abdominal muscles. The
external anal sphincter
can be voluntarily controlled (except in
infants) to allow or postpone
defecation.
3.
___________________________
refers to frequent defecation
of liquid feces. It is caused by
increased motility of the intestine and
can lead to dehydration and electrolyte
imbalances.
4. ___________________________
refers to infrequent or difficult
defecation and is caused by decreased motility
of the intestines, in
which feces remain in the colon for
prolonged periods of time. It
may be alleviated by increasing one’s
intake of dietary fiber and
fluids.
A. The effects of the four major digestive
hormones - gastrin, secretin,
CCK,
and GIP - are to regulate gastric secretion and motility, as well as
secretion of the pancreas, liver, and
gallbladder.
B.
___________________________ promotes secretion of gastric juice
and increases gastric motility.
C.
___________________________ promotes secretion of bicarbonate
ions into pancreatic juice and bile. It
inhibits secretion of gastric juice and
promotes normal growth and maintenance of the
pancreas. It enhances
the effects of CCK. Overall, it causes
buffering of acid in chyme.
D.
___________________________
(Cholecystokinin) stimulates
secretion of pancreatic juice rich in digestive
enzymes and ejection of bile
into the duodenum. It also slows gastric
emptying.
E.
___________________________
(Gastric inhibitory peptide) inhibits
gastric gland secretion and gastric motility
during the gastric phase.
A.
___________________________ – cavities are started by acid-
producing bacteria that reside in dental
plaque.
B.
___________________________ – crater-like lesions in the mucous
membrane of the GI tract in areas exposed to
gastric juice. The three
well-defined causes of peptic ulcer disease (PUD)
are…
1)
the bacterium Helicobacter pylori
2)
nonsteroidal
anti-inflammatory drugs, such as aspirin
3)
hypersecretion of HCl.
C.
___________________________ – saclike outpouchings
of the wall of
the colon in places where the muscularis has become weak.
1)
Inflammation within the diverticula, known as diverticulitis, may
cause pain, nausea, vomiting, and either
constipation or
an increased frequency of defecation.
D. One of the most common and deadly
malignancies of the GI tract is
colorectal
cancer, second only
to lung cancer in males and third after
lung and breast cancer in females
E.
___________________________ is an inflammation of the liver and
can be caused by viruses, drugs, and
chemicals, including alcohol.
1.
Hepatitis A
(infectious hepatitis) is spread by
___________________________.
a. It does not cause lasting liver damage.
2.
Hepatitis B is spread
primarily by _______________________,
_______________________, and _________________________.
a. It can produce ___________________________
and
possibly ___________________________ of the liver.
b. Vaccines are available to prevent hepatitis B infection.
3.
Hepatitis C is often
spread by _________________________.
a. It can cause cirrhosis and possibly liver cancer.
4.
Hepatitis D is
transmitted like hepatitis B. A person must be
infected with hepatitis B before contracting
hepatitis D.
a. It results in severe liver damage and has a
___________________________.
5.
Hepatitis E is spread
like hepatitis A.
a. It is responsible for a very high mortality rate in
___________________________.
F. ______________________________________________________ is a chronic
disorder characterized by
self-induced weight loss, body-image and other
perceptual disturbances, and
physiologic changes that result from
nutritional depletion.
G.
In some individuals, there is a failure of the intestinal mucosal cells
to
produce the
enzyme lactase. This results in ___________________________
___________________________, the inability to
digest the sugar lactose found
in milk and other dairy
products.
1. It is characterized by diarrhea, gas,
bloating, and abdominal
cramps after ingestion of
diary products.
disease occurs when the lower esophageal
sphincter fails to close
adequately after food has entered the stomach,
resulting in stomach
contents refluxing into the inferior portion
of the esophagus.
1.
HCl from the stomach contents irritates the
esophageal wall
resulting in heartburn.