Motility of the GI Flashcards
What is motility?
Contraction and relaxation of the walls and sphincters of the GI tract
What are the functional layers of the GI tract?
Mucosa
Submucosa
Muscularis externa
Serosa/Adventitia
What does the muscularis mucosae control?
Shape and surface area changes of the epithelium
What makes up the Enteric nervous system (intrinsic innervation of GI tract)?
Submucosal plexus of Meissner
Myenteric plexus of Auerbach
Which plexus mainly controls the GI movements?
Myenteric plexus of Auerbach
What are slow waves?
Depolarization and repolarization of membrane potential … NOT action potentials
Action potentials in the GI tract are under _____ and _____ control
Neural and Hormonal
What are phasic contractions?
Periodic contractions followed by a period of relaxation
- Seen in tissues that do most of the mixing and digesting = esophagus, stomach, SI
What are tonic contractions?
Constant level of contraction maintained
- ex. = sphincters such as the internal anal sphincter
How do you achieve a larger contraction in the GI system?
Increased number of action potentials on top of a slow wave
What stimuli can increase the slow wave amplitude and number of action potentials in the GI tract?
Stretch
Acetylcholine
Parasympathetics
What stimuli can decrease the slow wave amplitude in the GI tract?
Norepinephrine
Sympathetics
What generates and propagates slow waves?
Interstitial Cells of Cajal (ICC)
Describe the activity of the ICCs
ICCs spontaneously create slow waves which spread to other ICCs via gap junctions
- This increases the probability of ca channels opening in smooth muscle cells
- ICCs drive the frequency of contractions!
Swallowing is voluntary in the oral cavity and then it moves to involuntary reflex control. What controls the involuntary swallowing reflex in the pharynx and esophagus?
Medulla
The pharyngeal phase of swallowing propels food through what?
UES - upper esophageal sphincter
Describe the 2 types of peristaltic waves in the esophageal phase of swallowing
- Primary peristaltic wave is the continuation of the pharyngeal peristalsis and is under medulla control
- Secondary peristaltic wave occurs if the primary wave fails to empty esophageal contents and is under medulla AND ENS control
Which esophageal peristaltic wave can occur after a vagotomy? (vagus nerve removal)
Secondary peristaltic wave because it is under medulla and ENS control - so even without communication to medulla via vagus nerve, it can still occur
What is the pressure at and slightly below the UES?
High pressure
What is the pressure at and below the LES?
Low pressure
UES and LES are _____ except for when food is passing
Closed
Achalasia
INCREASED LES resting pressure
- Causes difficulty swallowing and backflow of food in throat
- can be caused by loss of NO/VIP or loss of innervation
GERD
DECREASED LES resting pressure
- Causes acid backwash into esophagus and heartburn
- can lead to Barrett’s esophagus
What are the regions of the stomach based on motility?
Orad - towards top
Caudad - towards pylorus
Describe the activity of the orad region of the stomach
Receptive relaxation = low pressure high volume
- Minimal contractile activity!!
Describe the activity of the caudad region of the stomach
Mixing and digestion occur here
- Peristaltic contractions increase as the wave approaches the antrum = phase lag decreases
Are most contents propelled backward in the stomach once they reach the bottom for further mixing and digestion?
Yes
How is the rate of gastric emptying INCREASED?
- Decrease distensible property of orad region
- Increase for of peristaltic contractions in caudad region = parasymp, gastrin, motilin
- Decrease tone of pylorus
- Increase diameter of proximal duodenum
How is the rate of gastric emptying DECREASED?
- Increase distensibility of orad region - CCK
- Decrease peristaltic contraction forces in caudad region - symp, secretin, GIP
- Increase tone of pylorus
- Decrease diameter of proximal duodenum
ENTEROGASTRIC REFLEX
What is the Enterogastric reflex?
Negative feedback from the duodenum to SLOW gastric emptying
– CCK, Secretin and GIP released!
What does the duodenum release with the enterogastric reflex?
Secretin
CCK
GIP
Gastroparesis
Slow emptying of gastric contents even without obstruction
- feeling full, loss of appetite and weight, nausea, vomiting
With what disease is gastroparesis common?
Diabetes mellitus OR injury to the vagus nerve
What does the MMC (migrating myoelectric complex) do?
Periodic bursting contractions in order to empty large particle of undigested residue
- regulated by motilin
- prevents small intestine bacterial overgrowth (SIBO)
When does MMC occur?
In 90 minute intervals during FASTING
What types of contractions does the small intestines have?
Segmentation = back and forth movements Peristaltic = wave like to propel forward
Is slow wave activity always present even if there are no contractions occurring?
Yes
In the small intestine, what hormone can stimulate contractions?
Serotonin
What coordinates the vomiting reflex?
Medulla
Describe the order of events of the vomiting reflex
- reverse peristalsis in the small intestine
- relaxation of stomach and pylorus
- forced inspiration causes increase in abdominal pressure
- LES relaxes
= expulsion of contents
The flow of contents from the SI to the LI is regulated at what juntion?
Ileocecal
Describe how contents pass from the ileum to the cecum (colon)
- Distention of ileum
- Causes relaxation of sphincter
= contents pass
Describe how contents do NOT pass from the ileum to the cecum
- Distention of colon
- Causes contraction of sphincter
= NO contents pass
The internal and external anal sphincters are under different neural control. What controls the external anal sphincter?
Somatic Pudendal nerves
What type of muscles are in the internal anal sphincter and external anal sphincter?
Internal anal sphincter = smooth muscle
External anal sphincter = skeletal muscle
Describe the motility in the colon
Mass movements that occur 1-3 times a day
What is the rectosphincteric reflex?
As the rectum fills with feces, the smooth muscle walls contract and the internal anal sphincter relaxes
The frequency of slow waves DECREASES as you move towards what?
Ileum
What stimuli inhibit the peristaltic contractions in the small intestine?
Sympathetics Epinephrine Secretin Glucagon NO/VIP
What stimuli activate the peristaltic contractions in the small intestine?
Parasympathetics - Ach
Serotonin
Gastrin, motilin, insulin
Parasympathetic innervation of the cecum, ascending colon and transverse colon?
Vagus nerve
Parasympathetic innervation of the descending colon, sigmoid colon and rectum?
Pelvic splanchnic nerve (S2-S4)
Levels of sympathetic innervation to the large intestine?
T10 - L2
What ganglion contribute to the sympathetic innervation of the large intestine?
Superior mesenteric
Inferior mesenteric
Hypogastric plexus
What is the innervation of the external anal sphincter?
Somatic pudendal nerve
