Transcript Chapter 9: Digestive System

UNIT B: Human Body Systems
Chapter 8: Human Organization
Chapter 9: Digestive System: Section 9.3
Chapter 10: Circulatory System and
Lymphatic System
Chapter 11: Respiratory System
Chapter 12: Nervous System
Chapter 13: Urinary System
Chapter 14: Reproductive System
UNIT B Chapter 9: Digestive System
Chapter 9: Digestive System
In this chapter, you will learn
about the structure and function
of the digestive system.
What is our current understanding
of the structure and function of the
digestive system, including the
stomach?
Alexis St. Martin was an unexpected live test subject
for Dr. William Beaumont’s research on how the
digestive system works.
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Which substances produced by the
stomach and other organs help with
the chemical breakdown of foods?
UNIT B Chapter 9: Digestive System
Section 9.3
9.3 Digestive Enzymes
Digestive enzymes help break down the major components of
food: carbohydrates, proteins, nucleic acids, and fats.
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UNIT B Chapter 9: Digestive System
Section 9.3
Carbohydrate Digestion by Enzymes
The digestion of starch (a carbohydrate) begins in the mouth.
• Salivary amylase (produced by the salivary glands) digests
starch into maltose (a disaccharide)
• Pancreatic amylase (produced by the pancreas) and maltase
(produced by the small intestine) then convert maltose in the
small intestine to glucose (a monosaccharide). Glucose can be
absorbed by the small intestine.
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UNIT B Chapter 9: Digestive System
Figure 9.11 Digestion and
absorption of nutrients.
a. The breakdown of
carbohydrates, such as starch,
involves amylase enzymes.
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Section 9.3
UNIT B Chapter 9: Digestive System
Section 9.3
Carbohydrate Digestion by Enzymes
Other disaccharides, such as lactose, have their own enzyme
that digests them in the small intestine.
• Lactase is an enzyme that digests lactose, a sugar found in
milk.
o Individuals who have a lactase deficiency often have
symptoms of lactose intolerance (diarrhea, gas,
cramps) caused by the fermentation of non-digested
lactose by intestinal bacteria
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UNIT B Chapter 9: Digestive System
Section 9.3
Protein Digestion by Enzymes
The digestion of proteins begins in the stomach.
• Pepsin is an enzyme produced by gastric glands that acts on
proteins to produce peptides.
• Trypsin (produced by the pancreas) and peptidases (produced
in the small intestine) break down peptides into amino acids
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UNIT B Chapter 9: Digestive System
Figure 9.11 Digestion and
absorption of nutrients.
b. Protein digestion involves
the action of protease
enzymes.
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Section 9.3
UNIT B Chapter 9: Digestive System
Section 9.3
Fat Digestion by Enzymes
• Lipase (produced by the pancreas) acts in the small intestine
and digests fat molecules in the fat droplets after they have
been emulsified by bile salts
• Glycerol and fatty acids enter the cells of the villi, where they
are rejoined and repackaged as lipoprotein droplets
(chylomicrons) before entering the lacteals
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UNIT B Chapter 9: Digestive System
Figure 9.11 Digestion and
absorption of nutrients.
c. For fat digestion, bile salts
emulsify the fats so that lipase
enzymes can digest the
particles.
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Section 9.3
UNIT B Chapter 9: Digestive System
Section 9.3
Regulation of Digestive Enzymes
Enzymes function best at an optimum temperature and pH
that helps maintain the proper shape to fit their substrate.
• Since the digestive system is maintained at a constant
37ºC, enzymatic activity is largely controlled by pH
o The pH of the stomach is between 1 and 2 but can
increase to around 7.4 to 7.8 when sodium bicarbonate
in pancreatic juice is released from the pancreas
o This increase in pH occurs after chyme enters the
duodenum, and allows different digestive enzymes to
be active depending on the pH
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UNIT B Chapter 9: Digestive System
Section 9.3
Check Your Progress
1. Describe where in the digestive tract the chemical
digestion of each of the following types of nutrients
occurs: carbohydrates, proteins, and fats.
2. Identify the final molecule (monomer) resulting from
the digestion of carbohydrates, proteins, and fats.
3. Explain how the structure of the digestive system
assists in regulating the digestive enzymes.
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UNIT B Chapter 9: Digestive System
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Section 9.3