GI Motility Flashcards
What are the four functions of the GI tract?
- digestion
- secretion
- absorption
- motility
What role do the epithelium and mucosa play in the functions of the GI tract?
Secretion and absorption
What is the role of smooth muscle in the function of the GI tract?
motility
What portions of the GI tract are responsible for motility?
Mouth to rectum
What part of the GI tract is responsible for absorption?
Mostly the intestines (specifically the small intestine) although the stomach can absorb some water
What portion of the GI tract is responsible for digestion and secretion?
Almost the entire tract
What are the two components of the enteric nervous system? What does each component do?
myenteric plexus: smooth muscle activity
submucosal plexus: secretory activity
Describe the four layers of the GI tract
- Mucosa (which contains epithelium)
- Submucosa (which contains submucosal plexus)
- Muscularis propria (which contains circular and longitudinal layers, in between which lies the myenteric plexus)
- serosa
Describe parasympathetic innervation in the GI tract
preganglionic parasympathetics release Ach onto nicotinic receptors
Describe sympathetic innervation in the GI tract
postganglionics release NE onto alpha one receptors on blood vessels and sphincters. Also onto adrenergic receptors on enteric motor and interneurons
Describe the chemical mediators released by each of the following:
- myenteric plexus
- submucosal plexus
- sensory neurons
Mesenteric: Ach and serotonin
Submucosal: Ach and VIP
Sensory neurons: substance P or calcitonin gene-related peptide (CGRP) which excites enteric neurons
Where do you find smooth muscle with syncytium gap junctions?
Stomach and intestines. NOT found in esophagus and gall bladder
Which has a higher slow wave frequency? Stomach or duodenum?
duodenum (12/min) which stomach only 3/min
Can slow waves generate action potentials?
no, which is why external inputs are required
Describe sympathetic activity on slow wave depolarization
decreases amplitude or even abolishes wave
Describe parasympathetic activity on slow wave depolarization
increases amplitude by enhancing motility
Define peristalsis
coordinated contraction and relaxation of circular and longitudinal muscles
What produces dilation in GI motility?
contraction of longitudinal muscle and relaxation of circular muscle
What decreases lumen size?
contraction of circular muscle upstream
What is segmental mixing/moving?
alternating contraction and relaxation of circular muscle in adjacent segments
What is it called when lower esophageal sphincter is not fully opening?
achalasia (dysfunction of myenteric ganglia)
What happens with prolonged relaxation of lower esophageal sphincter?
GERD
What is the job of the proximal stomach?
serves as a reservoir with tonic contractions and slow waves without AP’s
What is the job of the distal stomach?
Grind tritutrate (crush, grind and rub food); phasic contractions and slow waves WITH action potentials
Where would you find more longitudinal muscles on the stomach
distal stomach with fibers that are continuous with duodenum
Where do you find circular muscles on the stomach?
everywhere but the distal portion; does not continue with duodenum
What is the function of the pylorus?
to control the size of particles exiting the stomach
What initiates gastric relaxation?
swallowing, mechanoreceptorstretch and relaxation supplemented by duodenal mechano- and chemo- receptors via CCK receptors on vagal afferents
What increases the amplitude of contraction of slow wave?
parasympathetic increases amplitude and sympathetic decreases amplitude
What happens when you increase the amount of the force of contraction?
increase in the amount of gastric emptying per contraction (controlled by neural and hormonal input)
What controls the rate of contraction?
intrinsic basic electrical rhythm
What controls the size of pyloric opening?
extrinisic (vagal) pathways and intrinsic (myenteric) pathways
What is the main job of the large intestine?
to concentrate and store fecal matter before defecation
What does the large intestine absorb?
The main function is active sodium absorption which water follows
How is the motility of the colon compared to other parts of the GI tract?
slow! 2-4 days
How is motility of the colon different than peristalsis?
the muscles remain contracted for some time after a mass movement, there is no MMC but an intense contraction, known as mass movement, forces fecal matter toward the rectum
What kind of muscle is on the external anal sphincter?
smooth muscle and skeletal muscle
What mediates relaxation of internal spincter?
NO and VIP
Describe the defecation reflex
a contraction of the rectum, relaxation of the internal anal sphincter, contraction of the external anal sphincter and increased peristaltic activity in the sigmoid colon; eventually pressure point is reached at which the external anal sphincter relaxes and feces are expelled
