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GUT PHYSIOLOGY
Introduction
Dr. Jack Grider
Rm 12-004 Sanger Hall
828-1853
[email protected]
2009
Digestive Processes
ANATOMY
Salivary Glands
Liver
Pancreas
duodenum, jejunum, ileum
Rectum
red denotes a sphincter
SPHINCTERS
Summary of Gut Physiology
Layers of the Gut Wall
Control Mechanisms
Fourth mechanism: autocrine
Neural Control Mechanisms
Hormone/Paracrine agent
CNS Control
- Extrinsic
- Autonomic N.S.
ANS
Extrinsic Control Mechanisms
P.S.N.S. is excitatory
Extrinsic/Autonomic
S.N.S. is inhibitory
Sympathetic Nervous System
Presynaptic Inhibition
Sympathetic Nervous System
Afferent/Sensory Neurons
Extrinsic Primary
Afferent
REFLEXES THAT CONTROL
GUT FUNCTION
Long Arc Reflexes: PSNS
SNS
Extrinsic/Autonomic N.S.
Long Arc Reflexes: PSNS
Vago-Vagal Reflex
CNS
Extrinsic/Autonomic N.S.
Long Arc Reflexes: SNS
3 pathways
Extrinsic/Autonomic N.S.
Long Arc Reflexes: SNS
Intestino-Intestinal reflex
Intrinsic/Enteric N.S.
The “little brain”
or
“mini-brain”
Intrinsic/Enteric N.S.
Intrinsic/Enteric N.S.
Short Arc Reflexes
Intrinsic/Enteric N.S.
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Many neuronal types
IPANs (sensory)
Intestinofugal
Interneurons & motor neurons
Transmitters: Ach/ TKs (~45%)
VIP/NO (~25%)
Enk, GRP, SSt,. …….
Hormonal Control Mechanisms
Blood
vessel
Hormonal Control Mechanisms
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All gut hormones are polypeptides
All are amidated at C-terminal end
Importance varies: proximal vs. distal
Criteria
Candidates vs. putative hormones
Hormonal Control Mechanism
Gastrin
• Multiple forms: G-17, G-14, G-34 etc.
• Tyr-12 can be sulfated (equal amounts)
• C-terminal end
• Synthesized in G-cells of terminal antrum, minor
amounts in duodenum.
• Released by: protein digestion products
•
antral distension(direct, vagal & ENS)
•
vagal stimulation (cephalic phase)
Hormonal Control Mechanism
Gastrin
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Physiological Action: Gastric HCl secretion
growth of mucosa (trophic)
stimulation of gastric motility (?)
Negative feedback regulates release
Pharmacological effects (impt. sulfation)
Zollinger-Ellison Syndrome
Hormonal Control Mechanism
Cholecystokinin
• Multiple forms: CCK-8, CCK-33, CCK-39,
CCK-58 etc.
• Sulfated in 7th AA from C-terminal end.
• C-terminal end
• Synthesized in I cells of duodenum (CCK-8,
-4 in neurons of ENS and CNS)
• Released by:protein digestion products
monoglycerides/FFA, HCl (minor)
Hormonal Control Mechanism
Cholecystokinin
• Physiological Action:
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pancreatic enzyme secretion
gallbladder contraction
mucosal growth & pancreatic growth (trophic)
inhibit gastric emptying in high conc.
Pharmacological Action
Hormonal Control Mechanism
Secretin
• Single form: 27 AA
• Structure similar to GIP, VIP, Glucagon
• Released from S cell in proximal small
intestine.
• Released by: HCl
monglyceride/FFA (minor)
Hormonal Control Mechanism
Secretin
• Physiological Action
– stimulate bicarbonate ion secretion from
duodenal glands, duct cells of biliary and
pancreatic system,
– growth of pancreatic tissue
– inhibits acid secretion and gastric emptying.
Hormonal Control Mechanism
Glucose-dependent
Insulinotrophic Peptide (GIP)
• Singular form: 42 AA
• Structure similar to Secretin, VIP, Glucagon
• Synthesized in K cells of proximal small
intestine
• Released by: nutrients in proximal small
intestine.
• Physiological action: Stimulate insulin
secretion by the pancreas
– inhibit gastric acid secretion (?)
Hormonal Control Mechanism
Candidate Hormones
• Enteroglucagon
• Pancreatic polypeptide family (PP, PYY,
NPY)
• Somatostatin
• Motilin & Ghrelin
• Many more ...
Paracrine Control Mechanisms
• Local control
• Somatostatin, Histamine, GRP