GI Tract Physiology and Intro to Gut Microbiome (Week 10) Flashcards
Approximately how much food passes through the GI tract in an average lifespan?
60 tonnes
True or False: The GI tract is the largest interface between host, environmental factors, and antigens
True
What are the three types of movement that take place along the GI tract?
1) Peristalsis
2) Segmentation
3) Migrating motor complex (MMC)
What is peristalsis?
- waves of smooth muscle contractions that propel the food bolus throughout the GI tract; involves contraction behind/proximal the food bolus and relaxation in front/distal the food bolus
- involves the entire GI tract, starting @ esophagus
- may be stimulated by distension (stretch) of smooth muscle cells
- function is to propel food forward along GI tract
What is segmentation?
- multiple contraction points produced by the coordination of smooth muscle cells and interstitial cells of Cajal (ICC)
- occurs within small intestine and large intestine
- function is to promote mixing of food particles to increase interactions between the villi of the enterocytes and various food particles to promote absorption
What is the migrating motor complex (MMC)?
- small movements, almost a vibration, that occurs predominantly during fasting (in between meals);1.5-2hr intervals
- occurs within stomach and small intestine (a few other locations too)
- movement is promoted by motilin (secreted by Mo-cells), located in the duodenum
- function is suspected to be a self-cleaning mechanism, as this movement causes small food particles and bacteria to be dislodged from the intestinal wall and prevents bacteria from travelling from LI to SI
What condition is a lack of migrating motor complex (MMC) associated with?
small intestinal bacterial overgrowth (SIBO)
What are considered the “pacemakers of the GI tract”?
interstitial cells of Cajal (ICC)
Interstitial cells of Cajal (ICC) form a network with each other and with smooth muscle via ______________, as well as enteric motor neurons
gap junctions
True or False: Interstitial cells of Cajal (ICC) are found in specific areas of the GI tract
False
ICC are found throughout the entire GI tract
ICC generate ________ (slow/fast) waves that do not typically lead to muscle contractions, and _____________ that do trigger smooth muscle contractions when there is an additional stimulus
slow,
spike potentials
What additional factors/stimuli can increase excitability of smooth muscle cells?
- muscle stretch (distension)
- acetylcholine
- other GI hormones
What can decrease excitability?
norepinephrine
(causes hyperpolarization)
True or False: The enteric nervous system (ENS) is composed of sensory, motor, and interneurons
True
The enteric nervous system is organized into what two plexuses?
1) submucosal plexus (Meissner’s)
2) myenteric plexus (Auerbach’s)
Where is the submucosal plexus (Meissner’s plexus) located?
between the layers of the submucosa and circular muscle layer
Note: only present in small intestine and large intestine
Where is the myenteric plexus (Auerbach’s plexus) located?
between circular and longitudinal muscle layers
Note: this is through the entire GI tract
What is the function of the submucosal plexus/Meissner’s plexus?
to regulate motility, local blood flow, secretions, and epithelial cell function
What is the function of the myenteric plexus/Auerbach’s plexus?
to regulate motility
True or False: Although the enteric nervous system (ENS) can function independently, the CNS does innervate the GI tract in several places, providing additional regulation and modification of the ENS
True
Does the sympathetic nervous system stimulate or oppose GI motility?
oppose
Does the parasympathetic nervous system stimulate or oppose GI motility?
both (can stimulate and oppose; more complex)
What are some nerves that connect the CNS to the ENS?
- vagus nerve
- pelvic splanchnic nerves
- thoracic sympathetic trunk
What cells and their secretions promote motility?
I cells –> cholecystokinin
Enterochromaffin cells –> serotonin
G cells –> gastrin
Mo cells –> motilin
beta-pancreatic cells –> insulin