lecture 3 - GI motility Flashcards
Where in the GI tract is striated skeletal muscle located?
Pharynx and anus
What are the 3 key muscular layers found in the digestive tract?
Muscularis mucosae, inner circular muscle, outer longitudinal muscle
What is the nature of the activity of the smooth muscle in the GI tract?
Spontaneous, slow wave
Which cells generate smooth muscle contraction in the gut?
Pacemaker cells
What are slow waves in terms of GI motility?
‘waves’ of depolarisation of the membrane potential in the smooth muscle that only sometimes reach threshold to generate contractions.
How is the frequency at which slow waves reach threshold modulated?
By SNS inputs, which either depolarise or hyperpolarise the membrane, making it easier or harder respectively for a slow wave to meet threshold.
How can smooth muscle in the GI tract be modulated by the SNS to produce stronger and more frequent contractions?
SNS can depolarise the cell membranes, meaning that the slow waves reach threshold more often and depolarise more, causing more calcium to be released, resulting in stronger, more frequent contractions
What are the inputs that can be used to alter GI motility?
Stretch, SNS innervation, hormones, reflex loops
What is the name for the motility cycle that occurs between meals?
Inter-digestive motor cycle
What is the main motility pattern that occurs during the inter-digestive motor cycle?
Migrating Motor Complex
How long after a meal does the migrating motor complex typically occur?
4-5 hours
Which 2 motility patterns happen when there is food in the tract?
Peristalsis, segmentation
Where in the GI tract does peristalsis occur?
Oesophagus, stomach, small intestine, large intestine
What is the function of peristalsis?
Propulsion - pushes chyme/faeces through the tract
What is the mechanism through which peristalsis produces propulsion?
Proximal squeeze and distal relax around the bolus
