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100 Cards in this Set

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  • Back
Name the functions of GI Tract.
1) Motility
2) Secretion
3) Digestion
4) Absorption
Name the segments of the muscular GI tube and their functions.
1) Mouth - chewng, add saliva, form bolus, initiate digestion
2) Esophagus - conduit
3) Stomach - storage is main function (also grinding, acidification, digestion, flow regulation, and formation of chyme)
4) small intestine - digestion and absorption
5) large intestine - drying chyme into feces and storage of feces
Function of sphincters
regulate flow (all are tonically closed)
Name sphincters
UES
LES
Pyloric
Oddi
Illeo-cecal
Anal (internal and external)
Where in the GI tract does SECRETION take place?
1) mouth
2) stomach
3) small intestine
4) large intestine
Where in the GI tract does ABSORPTION take place?
1) small intestine
2) large intestine
What blood source are the absorbed nutrients transferred immediately into?
The hepatic portal vein
Does secretion or absorption take place in the espophagus?
NO
Where do the nutrients delivered to the hepatic portal vein go to immediately?
the liver
When inhibitory motor neurons are INACTIVE in the stomach, in what state are the LES and Pyloric Sphincter?
LES - closed
Pyloric sphincter - closed
When inhibitory motor neurons are INACTIVE in the large intestine, in what state is the Internal Anal Sphincter?
IAS - closed
When inhibitory motor neurons are ACTIVE in the stomach, in what state are the LES and Pyloric Sphincter?
LES - open
Pyloric sphincter - open
When inhibitory motor neurons are ACTIVE in the large intestine, in what state is the Internal Anal Sphincter?
IAS - open
Name the order of multiple concentric layers of gut wall from outside to lumen.
Serosa, longitudinal muscle, myenteric plexus, circular muscle, submucosal plexus, submucosa, muscularis mucosa,
lamina propria and epithelium (mucosa)
What layers make up the muscularis mucosa?
longitudinal muscle and circular muscle
What layers of the gut wall make up the enteric NS?
Myenteric plexus and submucosal plexus
In what layer of the gut wall might lymph nodes be located?
Lamina propria (mucosa)
In what layer of the gut wall might glands exist?
Submucosa
Which layer of the gut wall is thickened in sphincters?
Circular muscle
Which layer of the gut wall regulates the LENGTH of the gut?
Muscularis exerna
Name the 4 mechanisms of control of the gut.
1) Neural - fine control of discrete regions
2) Hormonal/Endocrine - generalized
3) Paracrine agent
4) Autocrine agent (ex. GFs)
What control mechanisms(s) involve secreting an agent into the extracellular space?
paracrine and autocrine
What is the largest endocrine organ in the body?
the gut
Where are hormonal agents released?
into the blood (hepatic portal vein in the GI tract)
What is the Autonomic NS made up of?
Parasympathetic and Sympathetic NS, and Enteric NS
Are the entrance and exit from the GI system controlled by intrinsic or extrinsic NS?
neither
Where do preganglionic parasympathetic fibers to the esophagus thru transverse colon originate from and what nerve do they travel thru?
the brain stem, travel thru the vagus nerve
Where do preganglionic parasympathetic fibers to the colon, rectum, and anus originate from and what nerve do they travel thru?
sacral division of spinal cord, travel thru the pelvic nerve
Parasympathetic NTs
(pre and post-ganglionic)
Preganglionic - ACh
Postganglionic - ACh and other enteric NTs
Postganglionic parasympathetic cell bodies are located where?
ganglia of the enteric NS
Is the parasympathetic part of the ANS excitatory or inhibitory to the GI tract, and how does it affect motility and secretion when stimulated?
Excitatory,
Increase motlility
Increase secretion
Is the sympathetic part of the ANS excitatory or inhibitory to the GI tract, and how does it affect motility and secretion when stimulated?
Inhibitory,
Decrease motility (inhibit ACh secretion from enteric neurons)
* also directly vasoconstrict BV, stimulates secretion, stimulates SM contraction at sphincter
Pathway of parasympathetic fibers
Brain stem/sacral spinal cord - vagus nerve or pelvic nerve - preganglionic synapse on myenteric plexus or submucosal plexus ganglion - postganglionic cell bodies here
Pathway of sympathetic fibers
thoracic/lumbar spinal cord - thru paravertebral ganglion to prevertebral ganglion where preganglionic synapse is - postganglionic fibers terminate on enteric NS fibers (may be in myenteric plexus or submucosal plexus)
Sympathtic NTs
preganglionic - ACh
postganglionic - NE
Does sympathetic NS participate in Long Arc or Short Arc reflexes?
Long Arc
Does parasympathetic NS participate in Long Arc or Short Arc reflexes?
Long Arc
Describe a long arc reflex
afferent and efferent neurons are extrinsic but effect is mediated thru the enteric NS
Examples of Sympathetic Reflexes
Generally Inhibitory, synapses in prevertebral ganglion
1) Enterogastric reflex
(intestine inhibits stomach)
2) Intestinointestinal reflex (one intestinal region inhibits another)
Examples of Parasympathetic Reflexes
Generally Excitatory
1) Vago-vagal reflex
(afferent and efferent are vagal fibers)
Does enteric NS participate in Long Arc or Short Arc reflexes?
Short Arc
Describe a short arc reflex
controls local activity - does not extend more than a few cms from stimulus
afferent and efferent both within the enteric NS
Examples of Enteric Reflex
Peristaltic Reflex
(can be modified by extrinsic NS)
Intrinsic Primary Afferent Neurons
sensory or afferent neurons in the enteric NS
Intestinofugal neurons
enteric neurons that project axons to the prevertebral ganglia and are involved in long-arc reflexes and in regulating sympathetic input to enteric NS
T/F - Most enteric neurons contain and release only one neurotransmitter
No - most release many
List NTs found in the enteric NS
1) ACh
2) Enkephalins
3) Tachykinins (TKs)
4) Vasoactive Intestinal Peptide (VIP)
5) Gastrin Releasing Peptide (GRP)
6) Somatostatin (SS)
7) NO
Function of ACh in Enteric NS (and what neurons secrete it)
1) main transmitter, increases SM contraction and secretion
2) excitatory motor neurons, interneurons
Function of Enkephalins in Enteric NS (and what neurons secrete it)
1) inhibitory to release of ACh
2) interneurons
Function of TKs in Enteric NS (and what neurons secrete it)
ex. Substance P and Neurokinin A
1) contractile for non-cholinergic responses
2) excitatory motor neurons, interneurons
Function of VIP in Enteric NS (and what neurons secrete it)
1) relaxes SM, excitatory for secretion
2) inhibitory motor neurons, excitatory secretomotor neurons
Function of GRP in Enteric NS (and what neurons secrete it)
1) stimulate acid secretion and gastrin secretion
2) long interneurons of intestine, gastric neurons
Function of SS in Enteric NS (and what neurons secrete it)
1) inhibitory - regulates release of other neurotransmitters
2) interneurons
Function of NO in Enteric NS (and what neurons secrete it)
1) relaxant (and gaseous)
* made on demand from L-Arg by Nitric Oxide Synthase (NOS)
Which NTs are often found accompanying one another in enteric neurons?
1) TK and ACh (40-50% of ENS neurons)
2) VIP and NOS (20-30% of ENS neurons)
Do some neurons contain both TK/ACh and VIP/NOS?
NO -- there is NO OVERLAP between TK/ACh neurons and VIP/NOS neurons!
Function and location of myenteric plexus
1) controls muscle activity
2) located between long and circ muscle layers of muscularis externa - fibers project into surrounding muscle as well as into submucosal plexus and mucosa
Function and location of submucosal plexus
1) control of secretion
2) located in submucosa below circular muscle - fibers project into underlying submucosa, mucosa, and to myenteric plexus (also to circular muscle sometimes)
Characteristics of gut hormones
1) are peptides
2) are amidated at C-term end
3) importance varies (most imp in stomach and small intestine)
4) criteria: present in gut, synthesized by and endocrine cell in gut, structure identified, released by appropriate phys. stimulus, produces appropriate phys. effect when infused exogenouly, and blocked by appropriate antagonists
Examples of candidate hormones vs. hormones
Hormones: Gastrin, CCK, Secretin, GIP

Candidate hormones: Enteroglucagon, PP, PYY, SS, Motilin
What cells secrete Gastrin and where are they?
G cells located in gastric antrum
What causes the release of Gastrin?
1) mechanical distension of antrum
2) vagal stimulation
3) amino acids/peptides in antrum
When is gastrin release inhibited?
When antral pH drops below 2 (negative feedback loop involving SS)
Physiological actions of gastrin:
1) stimulate acid secretion from parietal calls
2) stimulate growth of gastric mucosa
(also stimulate gastric motility, negative feedback regulates release)
What is the main form of Gastrin?
G-17
Does gastrin exist in sulfated or nonsulfated form?
Both.
What is the active poriton of Gastrin?
the C-term end

(but only 1/6th the potency of the entire G-17)
What other hormone is in the same family as Gastrin?
CCK
What is the main form of CCK?
CCK-33
Does CCK exist in sulfated or nonsulfated form?
Only sulfated.
What cells make CCK and where are they located?
I cells located in the upper small intestine (duodenum)
What is the active portion of CCK?
the C-term end is active but much less potent than the full CCK-33
What causes the release of CCk?
1) AAs/peptides in duodenum
2) FAs/monoglycerides in duodenum
Physiological actions of CCK:
1) stimulates pancreastic enzymes to be secreted
2) stimulates pancreatic growth
3) stimulates gall bladder contraction
4) inhibits gastric emptying
Explain competetive antagonism of CCK/Gastrin.
they have the same 5 aas on their C-term (which is responsible for receptor binding) so they bind to the same receptors and produce the same effects, however the agent binding (at high concentrations) to the receptor of the opposite agent prevents it from binding to its receptor and thus operates at a much lower level of activity
Which hormones have multiple forms?
Gastrin and CCK

(Secretin and GIP have only one form each)
What cells release secretin and where are they located?
S cells located in upper small intestine (duodenum)
What stimulates secretin to be released?
1) presence of acid in the small intestine

** also monoglycerides and FAs in duodenum may stimulate it
Physiological actions of secretin:
1) stimulates secretion of bicarbonate from duodenal glands, pancreas, and bilary system
2) stimulates pancreatic growth
3) inhibits gastric emptying
How many aas does Secretin have?
27 aa
What does GIP stand for?
Glucose-dependent Insulinotropic Peptide
How many aas does GIP have?
42 AA
What is the active part of GIP?
Need the whole thing to be active
Which cells release GIP and where are they located?
K cells of upper intestine (duodenum)
What causes the release of GIP?
1) Carbohydrates in duodenum
2) Monoglycerides/FAs
3) AAs/peptides
What are they physiological actions of GIP?
1) stimulates insulin secretion by the pancreas
2) inhibits acid secretion by parietal cells of the stomach
Which hormones and candidate hormones are part of the Secretin family?
GIP and Secretin (hormones)
Glucagon, VIP, PHI (candidate hormones)
* all have sequence homology, but no active segment - whole sequence needed for activity - competative antagonism exists for this family too (like within CCK/Gastrin family)
What candidate hormones are part of the pancreatic polypeptide family and what do they do?
1) Pancreatic polypeptide (PP) - released from pancreas in response to a meal
2) Peptide YY (PYY) - released from ileum in response to lipids or by neural or other hormonal stim (inhibits pancreatic enzyme secretion and indirectly relaxes gall bladder)
3) Neuropeptide Y (NPY)

** can mimic each other's actions at high concentrations
What does enteroglucagon do?
release in response to decreased blood glucose and causes liver to increase glycogenolysis, gluconeogenesis, and lipolysis
What does SS do?
released in response to acid in intestine or neural/hormonal stim.
inhibits secretion, motility, and hormone release throughout gut
What does motilin do?
released in intestine by neural stimulation and bile presence
increases motility and induces MMC in stomach
What may ghrelin do?
play role in feeding/satiety (relative of candidate hormone Motilin)
Name an example of paracrine control of gut.
Release of SS by antral D cells diffuses to G cells and inhibits the release of gastrin by G cell
Which hormones are inhibitory to gastric emptying?
Gastrin, CCK, Secretin, and GIP
Which hormones are stimulated by the presence of protein?
Gastrin, CCK, and GIP
Which hormones are stimulated by presence of fat?
CCK and GIP
Which hormones are stimulated by the vagus?
Gastrin only.
Which hormones inhibit acid secretion?
Secretin and GIP
Which hormones are responsible for pancreatic growth?
CCK and Secretin
Which hormone suppresses gastric emptying?
Secretin