Chapter 6: GI Phys Flashcards
List the layers of the GI Tract From Lumen to superficial
Epithelial cells (specialized)
Muscularis mucosa (contraction –> surface area differential)
Circular muscle (decreases diameter)
Longitudinal Muscle (Shortens the segment)
Meisners and Myenteric Plexus ( Enteric Nervous System, integrate motiliy )
What are the two Subdivisions of the ANS that innervate the GI tract ?
Extrinsic (Parasympathetics, Sympathetics)
Intrinsic (Enteric NS)
In the GI tract, ACh (Parasympathetics) are typically..
Excitatory.
In the GI tract, ACh (Parasympathetics) are carried by what nerves ?
Vagus (Esophagus to Hepatic Flexure) and Pelvic Splanchnic (Transverse colon to Internal Anal Sphincter)
Where do the Pre-ganglionic parasympathetic fibers synapse ?
Myenteric and Submucosal Plexus (Meissners)
Sympathetic stimulation is typically _______ to the GI tract
Inhibitory
Sympathethic cell bodies sending innervation to the GI tract originate between which levels ?
T8-L2
Sympathethic pre-ganglionics sending innervation to the GI tract synapse where ?
Prevertebral Ganglia
Sympathethic post-ganglionics sending innervation to the GI tract synapse where ?
Myenteric and Submucosal Plexus
What is the role of intrinsic (enteric) innervation ?
Coordinate and relay signals from the extrinsic PS and Sym neurons.
What is the main role of the Myenteric Plexus (Auerbachs) ?
Control the motility of the GI Smooth Muscle
What is the main role of the Submucosal (Meissners) Plexus ?
Secretion and Blood flow regulation
Receives input from mechano and chemorecepors in the GI Tract
What are the 4 Endocrine ‘Hormones’ of the GI Tract
Gastrin
CCK
Secretin
Glucose Dependent Insulinotropic Peptide (GIP)
Gastrin is secreted by which cells ? In response to what stimulus ?
G-cells of the Stomach (17 peptide)
Meals ( Peptides, AA’s, Vagus innervation, Distension of the stomach )
The biologic action of Gastrin is determined by ..
The four terminal AA residues
What inhibits the release of gastrin ?
Increased [H+] in stomach
Somatostatin
What is the physiologic action of gastrin ?
Increase [H+] by stimulating secretion from PARIETAL CELLS
Increases growth of Gastric Mucosa.
Gastrin Secreting tumor is implicit in which disease ?
Zoelinger Ellison Syndrome (although, in this disease the Gastrin tumor is in the pancreas, not in the Stomach as in normal gastrin production)
CCK is secreted by which cells ? In response to ?
I-Cells of the duodenum and jejunum
Small peptides, AA’s and FATTY ACIDS.
What is unique about CCK and its relationship with Gastrin ?
Contains the same 5 terminal AA sequence so that CCK activity also contains Gastrin like effects
What are the Main effects of CCK ?
Contraction of the Gall Bladder and relaxation of the sphincter of Oddi
Increases Pancreatic Enzyme and HCO3 release
Growth of exocrine pancreas and gallbladder (increased HCO3 by potentiating the effects of Secretin)
Inhibits gastric emptying ( Once fatty meal reaches the small intestine, CCK is released leading to delayed gastric emptying so that there is more time for intestinal digestion)
What Cells produce secretin ? Due to which stimuli ?
S-cells of the DUODENUM
H+ and fatty acids in the duodenum and
Main effects of Secretin release ?
Increase in Pancreatic HCO3 secretion
Increase in biliary HCO3 secretion
Decrease Gastric H+ Secretion
Overall: Secretin acts to neutralize H+ via HCO3 secretion (aided by CCK) and to aid in Intestinal digestion
What cells produce GIP ? Due to what stimuli ?
Epithelial cells of the Duodenum and jejunum
In response to FA’s , AA’s and Oral Glucose