Regulation of GI tract Function Flashcards
What are 3 Major control mecahnisms of GI function?
1) neural
2) paracrine
3) endocrine
What are EEC’s?
Enteroendocrine cells
Where are EEC’s located?
gastric, intestinal, pancreatic, closely associated with secretory cells
What do EEC’s contain? What stimulates release of their contents? (generally)
secretory granules
Chemical/mecahnical stimuli
EEC’s are a part of what system?
Diffuse neuroendocrine system (DNES)
What eefects do EEC’s have on GI? (5 effects)
1) motility
2) absorption
3) appetite and satiety
4) fluid and enzyme secretion
5 major hormones of EEC’s?
Gastrin
somatostatin
gastric inhibitory peptide
cholecystokinin
secretin
What are the 3 targets of paracrine regulation from EEC’s?
1) smooth muscle
2) absorptive enterocytes
3) glandular secretory cells including other EEC’s
What are ECL cells?
gastric enterochromaffin-like cells
What do ECL cells secrete?
What effect do these secretions have?
Histamine
Binds to H2 receptors on neiighbouring patietal cells causing ACID PRODUCTION
Other than Histamine what are 3 other Paracrine regulatory agents?
1) adenosine
2) nitric oxide
3) prostaglandins
Give 3 examples of regulatory molecules in GI tract that have endocrine AND paracrine functions?
1) Cholecystokinin (CCK)
2) Secretin
3) Peptide YY
4) GLP-1/2 (bonus)
What causes release of CCK?
partially digested fat/protein in duodenum
What effect does Serotonin (5-HT) have?
regulates smooth muscle and water absoprtion
also associated with inflammatory responses of gut (BLESSING AND A CURSE)
What is the “little brain of the gut”?
ENS - enteric nervous system
4 types of neurons in the ENS?
1) Intrinsic primary afferent neurons
2) Excitatory motor neurons
3) inhibitory motor neurons
4) Interneurons
What do intrinsic primary afferent neurons respond to? (4 things)
stretch, muscle tone, pH, food stuf conecntraitons (glucose, lipids, a.a’s)
What do the excitatory motor neurons of the ENS promote?
smooth muscle contraction and secretory activity
What do inhibitory motor neurons do in the ENS?
Inhibit smooth muscle contraction
What are the 2 plexuses that the ENS is organized into?
Inner submocosal plexus (Meissner’s)
Outer myenteric plexus (Auerbach’s) - between longitudinal and circular muscle
What do the 2 plexuses of the ENS regulate?
outer myenteric (auerbach’s plexus) - regulates GI tract secretions
Inner muscosal (Meissner’s plexus) - Regulates gut motility
Parasympathetic inervation of GI stimulates (3 things)
- glandular secretions
- smooth muscle contraction
- vasvular smooth muscle relaxation, vasodilation, and increased blood flow
Nerves that confer sympathetic regulation to GI tract? (3)
1) celiac
2) superior mesenteric
3) inferior mesenteric
What does sympathic innervation inhibit in GI tract? (3 things)
1) glandular secretions
2) gut smooth muscle contraction
3) vascular smooth muscle relaxation, vasodilation, and increased blood flow
What initiates the BER (basic electrical rhythm) of the GI tract?
INTERSTITIAL CELLS OF CAJAL
What effect does acetylcholine and Norepinephrine have on BER of GI tract? (specifically spike potentials)
ach - spike potential frequency increased
NE - spike potential frequency decreased
What are the 2 basic forms of motility in the gut?
1) propulsive waves - propel and mix food
2) mixing waves - “chop” chyme
What is segmentation (GI motility)?
pattern of rhythmic contractions driven by the superimposition of programmed ENS on BER (basic electrical rhythm)
What initiates peristalsis?
peristalsis is initiated in response to stretching of the gut wall by a bolus of food
what is the speed range (in cm/s) of peristalsis in the gut?
2-25 cm/s
Does peristalsis require extrinsic innervation?
NO
What is the main thing responsible for peristalsis?
internal myenteric (Auerbach’s plexus)
How does sympathetic and parasympathetic innervation affect peristalsis?
sympathetic innervation - inhibits peristalsis force and contraction
Parasympathetic - increases rate and force of peristalsis contraction
What are MMCs?
peristalsis-like motor patterns that are present during fasting
What are the 4 phsaes of MMC?
D1, D2, J1,J2,J3
What is the role of MMC?
“house cleaning” of undigested food remnants through GI tract
What well known sign does MMC produce?
audible borborygmous - stomach growling
What is the function of Haustrations? (segmented appeareance of Large intestine?)
functions to turn over feces to maximize water absorption
What are the 5 LONG RANGE reflexes of the gut?
1) gastro-enteric reflex
2) Gastro-ileal reflex
3) gastro- and duodeno- colic reflexes
4) ileo-gastric reflex
5) Intestino-intestinal reflex
What are the 4 activatory reflexes (long range reflexes)?
1 - gastro enteric
2- gastro-illeal
3) gastro-colic
4) duodeno-colic
What are the 2 inhibitory reflexes?
1- illeo-gastric
2 - intestino - intestinal
4 Main mucosal and pancreatic secretions
1 - mucus
2- water
3- enzymes and factors
4- electrolytes
What activates gastric acid production (3 things)?
1) gastrin (from G-cells)
2) histamine (secreted by ECL cells)
3) Acetylcholine (from stretch-sensitive neurons and parasympathetic nerves)
What is gastric acid production inhibited by? (2 things)
- somatostatin (from D cells)
- prostaglandins
What cell releases Gastrin? WHere it is located?
G cells; located in pyloric region of stomach
What are 4 things that activate gastrin secretion?
- vagal stimulation
- stretch or distention of stomach
- amino acids from partial protein digestion
- stimulants
What inhibits gastrin secretion?
excess acid which stimualtes D cells to produce somatostain
What are the 2 non-hormonal functions of the pancreas?
- alkaline mucus production
- enzymes for digestion of carbs, protein, and lipids
What are the 2 hormones that control the pancreas?
- secretin (from S cells)
- CCK (from I cells)
Where is Secretin secreted from?
S-cells of intestinal mucosa
What stimulates production of secretin?
Presence of fats and acid in intestine
What does secretin do to pancreas?
STimulates the release and production of bicarbonate ion
What effect does secretin ahve on the stomach? (2 things)
inhibits acid secretion in stomach; causes contraction of pyloric sphincter
What is CCK secreted in response to?
H+ ions, amino acids, small peptides
What does CCK promote the secretion of ? (2 things)
- alkaline pancreatic juice
- enzymes from exocrine cells
