Digestive System

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Digestive System
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Emphases

• Overview of gross anatomy tissue organization
• Review of basic digestive processes
• Regulation of digestive processes (CNS ENS)
• Integration of gastrointestinal (GI) functions
• How and where food is broken down and absorbed

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Processes of the Digestive System Overview
Pg. 660

• Ingestion
• Motility mixing propelling
• Digestion enzymatic hydrolysis
• Secretion enzymes, water, mucus, buffers, etc.
• Absorption water soluble vs. fat soluble
• Excretion

Figure 21-1 Processes of the digestive system
How is hydrolysis different from energy
metabolism?
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Digestive Anatomy Overview
Pg. 662
Describe the 4-layer basic plan in the wall of
the Alimentary Canal.
Figure 21-2a ANATOMY SUMMARY The Digestive
System
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Digestive Anatomy Histological Overview

• Mucus neck cells
• Parietal cells
• Chief cells
• G-cells

Compare histology in the stomach to that of the
small intestine. How are the anatomical
differences related to functional differences in
these organs?.
Pg. 663
Parietal cells secrete H
Pg. 677 and 678
What keeps the body from becoming too basic as a
result?
Figure 21-2c ANATOMY SUMMARY The Digestive
System
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Digestive Anatomy Histological Overview
Pg. 663
Where is the basolateral border on this cell?
Figure 21-2e ANATOMY SUMMARY The Digestive
System
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Motility Smooth Muscle Contractions
Pg. 666

• Tonic contractions
• (esp. sphincters)
• Phasic contractions
• Slow wave potentials
• Peristalsis
• (move products)
• Segmentation
• (mixing)

How does this differ from SA node function?
Figure 21-4 Contractions in the GI tract
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Digestive Secretions (?7 L / Day From Tissues
into Lumen)
Pg. 667

• Salivary glands, pancreas, liver, stomach,
  intestine
• Water
• Enzymes
• Mucus
• Ions H, Na, HCO3-, etc.
• Hormones

Why are some secreted as proenzymes? What are
zymogen granules and where are they found?
What signals mucus secretion, and how is this
related to its function?
How would these ions be transported?
Figure 21-5 Daily mass balance in the digestive
system
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Chemistry of Digestion Carbohydrates
Pg. 668
Where does starch digestion begin?
Where are these last step enzymes located?
See also pp. 139-140 in packet for summary info.
on digestion.
Figure 21-6 Carbohydrate digestion
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Chemistry of Digestion Proteins
Pg. 669
Proteins small polypeptides amino acids

• Endopeptidases (aka proteases)
• E.g. pepsin (stomach)
• Exopeptidases
• E.g. carboxypeptidase (small intestine)

Figure 21-7 Endopeptidases and exopeptidases
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Chemistry of Digestion Fats
Pg. 669
Where does this digestion take place?
Identify the components of this molecule.
What must occur in order for the normal function
of these digestive enzymes?
Figure 21-8 Fat digestion
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Regulating Digestion CNS and Enteric Nervous
System (ENS)
Pg. 670
These are reflexes involving Autonomic motor
neurons. Where are the cell bodies of these motor
neurons located?
Where do feedforward reflexes originate?
How are these different?
Figure 21-9 The enteric nervous system
Remember this?!
See also p. 141 in packet
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Phases of Digestion Overview
Pg. 674
Figure 21-11 Overview of functions in different
regions of the digestive system
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Gastric Regulation Cephalic and Oral Phases
What stimulates the cephalic phase (long
reflexes)?
What is a secretagogue? Are there paracrine or
other chemical messages that function in gastric
phase?
What stimulates the short reflexes?
See also p. 141 in packet
Pg. 675
Figure 21-12 Long and short reflexes in the
stomach
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Regulation of the Stomach Digestive Activities
Figure 21-17 Integration of secretion in the
stomach
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Intestinal Phase Reflexes Direct Digestive Action
Pg. 679

• Control chyme entrance rate motility Why?
• Neutralize HCl, add bile enzymes Why?
• Name the secretions released from the
  pancreasgall bladder?

• Enzymes
• HCO3-
• Insulin
• Glucagon
• Bile

Figure 21-18 The intestinal phase of gastric
function