CHAPTER 28

STRUCTURE AND FUNCTION OF THE GASTROINTESTINAL SYSTEM

Essentials of Pathophysiology

PRE LECTURE QUIZ TRUE/FALSE

The digestive tract is a single-layered tube. The gastrointestinal tract is innervated by

both the sympathetic and parasympathetic nervous systems.

The gastrointestinal tract is the largest endocrine organ in the body.

Each day, approximately 7000 mL of fluid is secreted into the gastrointestinal tract.

Absorption is the process of moving nutrients and other materials from the external environment of the gastrointestinal tract into the internal environment.

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T

T

T

T

PRE LECTURE QUIZ 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.

Digestion

Esophagus

Ileum

Peristaltic

stomach

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

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9

1

2

3

4

5

6

7

8

101112

Sequentially number parts through which food travels

BOWEL AND MESENTERIES

Abdomen

QUESTION

Tell whether the following statement is true or false.

The mesentery contains the intestine’s blood supply.

ANSWER

TrueAn 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. Carbohydratesb. Proteinc. Fat d. All of the above

ANSWER

a. CarbohydratesCarbohydrate 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.

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

b. 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.