Chapter 27
Structure and Function of the
Gastrointestinal System
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
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
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
• <insert figure xxx>
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Bowel and Mesenteries
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
Tell whether the following statement is true or false.
The mesentery contains the intestine’s blood supply.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
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.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Prader-Willi Syndrome
• Plasma ghrelin levels are extremely high
Discussion:
• What are the effects of this disorder?
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Scenario
A woman has a pancreatic tumor that secretes
gastrin.
Question
• What complication is likely to develop? Why?
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Scenario
• A man cannot produce cholecystokinin.
Question
• What problems will this cause him?
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Carbohydrate Digestion
• Mouth: Salivary amylase
• Duodenum: pancreatic amylase
– Polysaccharides  disaccharides
• Brush border enzymes
– Disaccharides  monosaccharides
– Monsaccharides absorbed into blood
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
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
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
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
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
Digestion of which substance begins in the mouth?
a. Carbohydrates
b. Protein
c. Fat
d. All of the above
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
a. 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.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
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
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
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.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
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.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins