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Essentials of Pathophysiology
CHAPTER 28
STRUCTURE AND FUNCTION OF THE
GASTROINTESTINAL SYSTEM
PRE LECTURE QUIZ TRUE/FALSE
The digestive tract is a single-layered tube.
T  The gastrointestinal tract is innervated by
both the sympathetic and parasympathetic
nervous systems.
T  The gastrointestinal tract is the largest
endocrine organ in the body.
T  Each day, approximately 7000 mL of fluid is
secreted into the gastrointestinal tract.
T  Absorption is the process of moving nutrients
and other materials from the external
environment of the gastrointestinal tract into
the internal environment.
F 
PRE LECTURE QUIZ

Digestion

Esophagus
Ileum

Peristaltic
stomach


The __________ is a tube that connects the
oropharynx with the stomach.
The small intestine, which forms the middle
portion of the digestive tract, consists of three
subdivisions: the duodenum, the jejunum, and
the __________.
__________ movements are rhythmic
propulsive movements that occur when the
smooth muscle layer constricts, forming a
contractile band that forces the intraluminal
contents forward.
The __________ serves as a reservoir for
ingested solids and liquids.
__________ is the process of dismantling
foods into their constituent parts.
THE JOB OF THE BOWEL



Food:
 Movement
 Breakdown
 Absorption
Keeping dangerous gut contents out of the
blood
Keeping blood contents from being lost into
the gut lumen
Sequentially number parts through which food travels

1
1
2
3
8
4
7
6
9
5
12
10
11
BOWEL AND MESENTERIES
Abdomen
QUESTION
Tell whether the following statement is true or
false.
The mesentery contains the intestine’s blood
supply.
ANSWER
True
An extension of the visceral peritoneum, the
mesentery contains blood vessels that supply
oxygen and nutrients to (arteries) and eliminate
CO2 and waste from (veins) the intestines.
PRADER-WILLI SYNDROME


It is traditionally characterized by hypotonia, short stature, hyperphagia,
obesity, behavioral issues (specifically OCD-like behaviors), small hands
and feet, hypogonadism, and mild mental retardation.
Plasma ghrelin levels are extremely high
Discussion:

What are the effects of this disorder?

ghrelin
a gastrointestinal hormone produced by epithelial cells lining the fundus
of the stomach; appears to be a stimulant for appetite and feeding, but
is also a strong stimulant of growth hormone secretion from the anterior
pituitary

Ghrelin levels increase before meals and decrease after meals. It is
considered the counterpart of the hormone leptin,
PRADER-WILLI SYNDROME

This is a picture
of a child with
Prader-Willi
Syndrome, first
with a small,
undersized
figure, then as
an obese
teenager later in
life.
SCENARIO
A woman has a pancreatic tumor that
secretes gastrin- a hormone that
stimulates the secretion of gastric juice.
Question
 What complication is likely to develop?
Why?
SCENARIO

A man cannot produce cholecystokinin.
Question
 What problems will this cause him?
CARBOHYDRATE DIGESTION



Mouth: Salivary amylase
Duodenum: pancreatic amylase
 Polysaccharides  disaccharides
Brush border enzymes
 Disaccharides  monosaccharides
 Monsaccharides absorbed into blood
PROTEIN DIGESTION

Stomach: pepsinogen
 Activated
to pepsin by acid in stomach
 Breaks proteins into polypeptides

Duodenum: pancreatic trypsinogen
 Activated
to trypsin in duodenum
 Breaks proteins into polypeptides

Brush border enzymes
 Breaks
polypeptides into 2–3 amino acid
peptides
 Peptides absorbed into blood
FAT DIGESTION



Duodenum: bile
 Emulsifies fats
Duodenum: pancreatic lipase
 Breaks triglycerides into glycerol and fatty acids
Jejunum
 Packages digested fats as chylomicrons
 Passed to the lymph
QUESTION
Digestion of which substance begins in the
mouth?
a. Carbohydrates
b. Protein
c. Fat
d. All of the above
ANSWER
Carbohydrates
Carbohydrate digestion begins in the mouth with
salivary amylase; protein digestion begins in
the stomach with pepsinogen; fat digestion
begins in the small intestine with bile and
pancreatic lipase.
a.
DISCUSSION
Which is the best choice to reduce fat digestion?

Suppress duodenal hormone secretion

Suppress the activity of chief cells in the
stomach

Decrease intrinsic factor secretion

Block gall bladder contraction

Inactivate pancreatic lipase
QUESTION
How would fat digestion be affected if bile levels
decreased?
a. It would increase.
b. It would decrease.
c. It would have no effect—fat digestion is mainly
affected by amylase.
d. It would have no effect—fat digestion is mainly
affected by lipase.
ANSWER
It would decrease.
Bile emulsifies fat so that it can be more easily
digested. Decreased amounts of bile would
lead to decreased fat emulsification and
decreased ability to break down/digest fats.
b.