Motility Flashcards
Which cells govern involuntary contraction of smooth muscle
Pacemaker interstitial cells of Cajal (ICC)
oesophagus and anal sphincter have striated skeletal muscle - voluntary
What system allows central modification
Extrinsic autonomic sympathetic and parasympathetic
Extrinsic Autonomic Nervous System
ANS modifies basal activity of ENS (intrinsic enteric NS)
Parasympathetic - via vagus and pelvic splanchnic nerves
Sympathetic - via thoracolumbar innervation
Intrinsic Enteric Nervous system (ENS)
Reflex contraction in response to stretch, nutrients, irritation and hormones
Myenteric plexus (Auerbach’s) in muscularis layer - motility
Submucosal plexus - secretion/blood flow
What does CCK stimulate
Pancreatic secretions, gallbladder contraction, growth of exocrine pancreas
Inhibits gastric emptying
What does Motilin stimulate
Gastric motility and intestinal motility
Which types of electrical activity cause contraction
Slow waves: cyclical oscillations initiated by pacemaker ICCs; causes contraction by further depolarisation to threshold levels
Spike potentials: result in Ca2+ influx when threshold is reached; provide basic electrical rhythm (3-12 minutes)
2 types of contraction
Segmentation - circular muscle contraction and relaxation - pendular movements - for mixing
Peristalsis - wave of contraction - movement aborally
Excitatory and inhibitory stimulation of emptying the stomach
Excitatory: ENS/ANS; hormones (motilin)
Inhibitory: ANS regulation; duodenal enterogastric reflexes; hormones (CCK, secretin/GIP)
Motility in small intestine
Digestion over 3-5 hours
Hormonal and ANS neural stimuli control
Stretch receptors trigger propulsive peristalsis
Excitation hormones: gastrin, CCK, insulin, motilin, serotonin
Inhibitory: secretin and glucagon
Propulsive peristaltic reflexes
Gastroenteric reflex - activates myenteric plexus
Gastroileal - forces chyme through ileocaecal valve into caecum
Migrating Motor Complex (MMC) - every 90 minutes sweeps food into colon; ENS /motilin control
Absence leads to bacterial overgrowth
Muscle in large intestine
Longitudinal thickened to form 3 bands - taniae coli, which contract tonically to form haustral bulges
Motility in large intestine
Absorption of electrolytes and water Microbiome aids digestion and synthesis of Vitamin K and B ENS control Haustral churning Mass movements 2-3x per day
Motility reflexes in LI
Gastri-colic and duodeno-colic reflexes - mass movements occur after meals on stretching via ANS
Defecation
Mass movements
Stretch receptors stimulated -> ENS and parasympathetic ANS
Involuntary contraction of longitudinal muscle in rectum opens IAS
Relaxation of external anal sphincter is voluntary
