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
• (neural, hormonal, and paracrine messages)
• 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. 678

• 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. 680
Describe the 4-layer basic plan in the wall of
the Alimentary Canal.
Is this single-unit or multi-unit smooth muscle?
Figure 21-2a ANATOMY SUMMARY The Digestive
System
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Digestive Anatomy Histological Overview
Compare histology in the stomach to that of the
small intestine (next slide). How are the
anatomical differences related to functional
differences in these organs?

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

Pg. 685
Parietal cells secrete H
What keeps the body from becoming too basic as a
result?
Histology of the Stomach
Pg. 681
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Digestive Anatomy Histological Overview
Pg. 681
Where is the basolateral border on this cell?
Identify this structure its function.
Figure 21-2e ANATOMY SUMMARY The Digestive
System
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Motility Smooth Muscle Contractions
Pg. 683

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

How does this differ from SA node
function? Compare this to skeletal and cardiac
muscle.
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Digestive Secretions (?7 L / day from tissues
into lumen)
Pg. 684

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

Why are some secreted as pro-enzymes? 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. 694
Does any significant carbohydrate digestion by
amylase occur in the stomach? Explain.
(salivary and pancreatic)
Where are these last step enzymes located?
(intestinal epithelium)
Figure 21-6 Carbohydrate digestion
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Chemistry of Digestion Proteins
Pg. 695
Proteins small polypeptides amino acids
(aka proteases e.g. pepsin in stomach)
Pancreatic Endopeptidases
enterokinase

• Trypsinogen Trypsin
• Chymotrypsinogen Chymotrypsin

(intestinal lumen)
intestinal epithelium
intestinal lumen
Trypsin
Pancreatic Exopeptidases
Procarboxypeptidase Carboxypeptidase
Trypsin
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Chemistry of Digestion Fats
Pg. 698
Identify the components of this molecule.
Where does this digestion take place? Why, in
this location?
What must occur in order for the lipid-digesting
enzymes to work?
What are the roles of gastric lipase and
pancreatic lipase in fat digestion?
Micelle
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Regulating Digestion Role of the CNS and Enteric
Nervous (ENS) Systems
Pg. 690
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?!
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Phases of Digestion Overview
Pg. 700
Figure 21-11 Overview of functions in different
regions of the digestive system
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3 Phases in Gastric Regulation
What stimulates the cephalic phase (long
reflexes)?
What initiates the gastric phase? Are these
short or long reflexes? What is a
secretagogue? Are there paracrine or other
chemical messages that function during the
gastric phase?
Pg. 701
Figure 21-12 Long and short reflexes in the
stomach
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Regulation of Gastric Secretion
Pg. 704
Do these action occur in the gastric phase, the
cephalic phase, or both?
Figure 21-17 Integration of secretion in the
stomach
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Intestinal Phase Reflexes Direct Digestive Action
Pg. 706

• 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