GI NeuroPhysiology Flashcards
What kind of diet would you reccomend for a patient with liver cirrhosis? Why?
a low protein diet because the conversion of protein to urea occurs in the liver
What kind of diet would you reccomend for a patient with pancreatic insufficiency? Why?
a low fat diet
What kind of diet would you reccomend for a patient with diabetes mellitus? Why?
a low carb diet
smaller portions, but more times/day
What kind of diet would you reccomend for a patient with gout? Why?
A low nucleic acid diet
What are the end products of carbohydrates and how do we excrete them?
-CO2 by breathing
What are the end products of Triglycerides and how do we excrete them?
-CO2 by breathing
What are the end products of Nitrogen from proteins and amino acids and how do we excrete them?
-Urea in urine
Which of these drugs is effective when taken orally?
Insulin Nitroglycerine Growth Hormone Prednisone Epinephrine
Prednisone because it can survive digestion.
Insulin and predinsone are proteins, so they will be digested like other proteins.
Nitroglycerine and epinephrine have half lives that are too short to be absorbed.
What is the nervous control of the GI tract?
-enteric (intrinsic) nervous system
- Extrinsic (central) nervous system
- sensory afferents
- parasympathetic motor
- sympathetic motor
What are the components of the enteric nervous system?
- secretomotor (efferent) cells
- interneurons
- sensory (afferent) neurons
- mechanoreceptors
- chemoreceptors
- osmoreceptors
What do secretomotor cells of the enteric nervous system do?
- influence smooth muscle cells and epithelial cells that secret or absorb things
- also influence enteric endocrine cells
What are the components of the extrinsic nervous system?
- Sympathetic motor nerves
- parasympathetic motor nerves
- sensory afferent nerves
Why isn’t the extrinsic nervous system input to the GI tract necessary for life?
-the ENS can operate entirely within the GI wall without external input form the brain
Where is the blood supply, lymphatics, and nerve supply of the GI tract carried?
-the mesentary
What does innervation of the gut control?
- muscle contraction
- blood flow
- secretions
- absorption
What NT is released by the presynaptic and post synaptic neurons of the parasympathetic nervous system?
-Acetylcholine
Where does the majority of the parasympathetic innervation of the GI tract come from?
- Vagus nerve
- dorsal motor nucleus of X
Where does innervation of the distal colon come from?
- Sacral spinal cord
- S2-S4
What do fibers from the rostral DVN do to GI smooth muscles?
-stimulate it by releasing:
- acetylcholine
- substance P
What do fibers from the caudal DVN do to GI smooth muscles?
-inhibit them by relasing:
- vasoactive intestinal peptide (VIP)
- NO
- ATP
What are the three types of fibers in the vagus nerve to the fore & midgut?
- rostral DVN
- Caudal DVN
- Afferents from gi lumen
What effect will a drug that is an inhibitor of acetylcholine esterase enzyme have on the GI system?
-Diarrhea
Can insulin, epinephrine, and nitrates be administered orally?
-no, they will be digested
What percentage of fibers in the vagus nerve supplying the GI tract are afferent sensory fibers?
80%
Where do afferent sesnory fibers from the GI tract in the vagus synapse before reaching the RVN and CVN?
-nucleus tractus solitarius
Describe the action of sympathetic postganglionic neurons on non-sphincter muscle and sphincter muscle in the GI tract?
Non-sphincter muscle:
-NE is inhibitory activating a-2 receptors & B-2 receptors
Sphincter Muscle:
-NE stimulates contraction via a-1 receptors
What are the three types of gastrointestinal signaling peptides?
- Hormonal
- Paracrine
- Neurocrine
What are the hormonal GI signaling peptides?
- Gastrin
- CCK
- GIP
- Secretin
- Insulin
- Glucagon
What are the paracrine GI signaling peptides?
- Histamine
- Somatostatin
- Prostaglandins
What are the neurocrine GI signaling peptides?
- Acetylcholine
- NE
- DA
- NO
- VIP
- GRP
- Enkephalins
- Substance P
- Neuropeptide Y
Which side of the spinal cord does fine touch information travel on?
-Dorsal
What side of the spinal cord does pain information travel on?
-Venral
How does 5HT affect the GI tract?
-it enhances GI motility by stimulating smooth muscle contraction
How do opiates affect the GI tract?
-they inhibit GI motility by stimulating smooth muscle relaxation
Carcinoid tubors generally secrete serotonin. A patient with high levels of serotonin is likely to have:
A. Constipation
B. Diarrhea
C. Depression
-B. Diarrhea
What percentage of 5HT in the body is produced in the GI tract?
90-95%
What signals decrease GI motility by relaxing smooth muscle?
- NO
- ATP
- VIP
- DA
- Morphine
- NE
What signals increase GI motility by contracting smooth muscle?
- ACh
- Substance P
- 5-HT
Are acetycholine, NE, DA, 5HT, ATP, and NO fast acting peptides or slow acting?
-fast acting
List the sphincters of the GI tract in order of food flow. Which of these are striated muscle?
- Upper esophageal (striated)
- Lower esophageal
- Pyloric
- Ileocecal
- Internal anal
- External Anal (striated)
What are the three types of gut reflexes?
- enteric reflex
- Secretory reflex
- Long-Range Reflexes
What is the enteric reflex?
- forms basis of peristaltic movment
- sensory neurons feed information into chains of excitatory interneruons (ab-oral) and inhibitory interneruons (ab-anal)
- Result, activation of sensory fibers initiates a contraction behind the site of stimulation and a relaxation in front of the site of stimulation
What is the secretory reflex?
-Same as enteric, but motor output pathways target the secretory cells of the gut or blood vessels
Describe the mechanism of the Vagovagal reflex.
- distension of fundus in stomach stimulates vagal afferent to synapse in nucleus tractus solitarius
- this info is conveyed to dorsal vagal nucleus
- then parasympathetic efferents to the fundus of the stomach release NO, VIP, ATP to relax smooth muscles
Describe receptive relaxation.
- consists of fundus and upper body of stomach
- serves as a food resevoir
- vagovagal reflex initiates receptive relaxation
- accommodates food with very little increase of pressure upon filling
- allows digestion that started in the oral cavity to continue
What are the two inhibitory long range gut reflexes?
- Ileogastric reflex
- Intestino-intestinal reflex
What are the three excitatory long range gut reflexes?
- gastro-enteric reflex
- gastro-ileal reflex
- gastro and duodeno-colic reflexes
What is the ileo-gastric reflex?
-distension of an ileal segment inhibits gastric motility
What is the intestino-intestinal reflex?
-cessatio nof intestinal motility upon excessive distention or rough handling or peritonitis
What is the Gastro-enteric reflex?
-distention of the stomach increases the excitability of the small intestine
What is the Gastro-ileo reflex?
-distension of the stomach intensifies the activity of the terminal ilieum and opens the ileo-cecal sphincter
What are the Gastro/duodeno-colic reflexes?
-distension of the stomach or duodenum initiates mass movements of the colon
An accident victim has total spinal cord paralysis from
T12 and down. This person is likely to present with:
A. Can not control acid secretion in stomach
B. Will have problems with bladder control
C. Will have problems with defecation
D. Will have problems with bladder and defecation
D. Will have both bladder and defecation problems
What is Ileus, and what are it’s medical consequences?
- ineffective intestinal propulsion in the absence of a mechanical obstruction
- can happen after surgery
- lasts 48-72 hours
-consequences are accumulation of gas and secretions which results in overgrowth of small intestinal bacteria, ischemia/necrosis, and dehydration
What is the difference between multiunit and unitary smooth muscle?
- Multiunit smooth muscle has nervous input to each individual cell
- unitary smooth muscle has nervous input, but most communication is through gap junctions between SMCs
Is most smooth muscle in the GI tract unitary or multiunit?
-unitary
Which one of these signals will NOT relax
the smooth muscle in the GI tract?
A. Nitric oxide B. ATP C. VIP D. Beta 2 receptor agonist E. Serotonin (5-Hydroxytryptamine / 5-HT)
E. Serotonin
What type of muscle is the most energy efficient?
-smooth muscle
What cells produce the GI pace maker activity, generating the slow waves?
-interstitial cells of Cajal
How many slow waves per minute does the stomach, duodenum, jejunum, ileum, and descending colon have?
Stomach: 3/min
Duodenum: 12/min
Jejunum: 9/min
Ileum: 6/min
Descending colon: 3-12/min
What flux of ions is responsible for depolarization of smooth muscle cells in the duodenum?
-calcium influx
Basal electric rhythm (BER) in the GI system is
generated by specialized pace-maker cells of Cajal.
These interstitial cells of Cajal are: A. Specialized enteric secretory cells B. Specialized smooth muscle cells C. Specialized vagal neurons D. Specialized enteroendocrine cells E. None of the above
B. Specialized smooth muscle cells
When is it easiest to depolarize smooth muscle cells?
-when neurotransmitters are present that depolarize the cells almost to threshold
Describe the relative contraction and relaxation during segmentation.
- contraction occurs only in the spot where the bolus is
- this divides the bolus, and pushes one portion upstream, and one downstream
- this allows it to mix with the boli that surround it
What is the purpose of the Migratory Myoelectric Complex (MMC)?
- housekeeping
- propels the bolus through the ileum to clear the GI tract of material.
- It clears food greater than 2mm, deqsuaminated cells, secretions, and bacteria
How often does the MMC occur?
-every 90 min between feeding
What is the hormone responsible for MMC?
-Motilin
After dating for three years, you just got married. Your spouse
loves to go on a week-long cruise that came as a wedding gift.
However, you are easily prone to sea sickness and
looking for an anti-emetic drug.
Which of these drugs will act as an anti-emetic drug?
A. Acetylcholine agonist B. Acetylcholine blocker C. Substance P agonist D. Serotonin agonist E. Serotonin blocker
B or E
Between meals, GI tract is swept from stomach colon
to push bacteria where they belong (to distal colon).
Interdigestive GI motilty (migratory Motor Complex / MMC)
is controlled by:
A. Motilin B. Serotonin C. VIP D. Secretin E. Prostaglandins
A. Motilin
In what pathologies are the interstitial cells of cajal density decreased?
- colon of patients with slow transit constipation
- the stomach of patients affected by diabetes mellitus
What is gastroparesis and what common condition does it result from?
- delayed gastric emptying
- food sits in the stomach for many hours, undigested
- may cause nausea and vomiting
- also makes it harder to control blood sugars
-results from diabetic neuropathy
What two GI conditionscan be caused by diabetes mellitus?
-diabetic neuropathy can lead to:
Gastroparesis
Diarrhea
What causes diabetic neuropathy?
- hyperglycemia induced damage to the peripheral nervous system
- loss of schwann cells, myelinated axons, and a population of sensory neurons in DRG
