Physiology -- Intestinal Motility Flashcards
4 functions of the upper small intestine
- Neutralization
- Osmotic equilibration
- Digestion
- Absorption
2 motor activities of the small intestine
- Effective mixing
- Slow propulsion
Time for food to be propulsed through the small intestine
2 - 4 hours
5 characeristics of intestinal BER
Note the wave form
- Constantly present (not initiative of contractions)
- Propagated from cell to cell
- Constant frequency for a given region
- Detectable in both longitudinal and circular muscle
- Unknown origin, but probably ICC
7 characteristics of intestinal ERA
- Intermittent
- Phase-locked to BER
- Stimulus = ACh and stretch
- Ca++ independent
- In longitudinal and circular fibers
- Cell to cell propagation
- # spikes/burst proportional to magnitude of stimulus
Describe how the action potential propagates through the intestinal muscle
When an AP is elicited in intestinal muscle fibre, it travels (via gap-junctions) and activates adjacent fibres which contract (synchronously along circumference and sequentially along the longitudinal axis)
Describe the intrinsic frequency of intestinal BER
Depends on the cells (i.e. the portion of the small intestine) –> decreases distally
Compare the coupling of intestinal cells versus stomach in terms of BER
Not as good
Compare 3 aspects of proximal SI BER versus distal SI BER and what these mean
- f of BER is greater in proximal
- Excitability of smooth muscle is great in proximal
- Thickness of smooth muscles is greater in proximal
THEREFORE, both frequency and amplitude of contraction is greater in proximal SI
Most common type of contractile activity
Sementation
Myogenic properties of segmentation in SI
- Stimulus = distension
- Only circular muscle involved
ENS properties of segmentation in SI
- Organizes over longer distances
- Pattern-generated circuity –> alternating segments become disinhibited and therefore capable of contracting
Modulatory factors for segmentation in SI
ANS (vagus, sympathetic) and hormones
Function of segmentation in SI
Mixing
Slow propulsion
Pressure produced by segmentation in SI
5 - 10 mmHg
Length of segments in SI segmentation
1 - 5 cm
Define slow net aboral movement
Slowness of meal movement through SI (2-4 to 6 hours)
Describe peristalsis in the intestine
- Infrequent, irregular
- Weak, shallow
- Travels for short (a few cm) distances only
What controls intestinal peristalsis
- Local reflexes (integrity of ENS essential)
- Modulated by ANS and hormones
Descibre intestinal peristalsis relative to bolus position (Law of the Intestine)
Radial stretch –> receptors –> neural nediation–>
Behind bolus:
- Circular muscle contracts
- Longitudinal muscle relaxes
Ahead of bolus
- Circular muscle relaxes
- Longitudinal muscle contracts
Describe the circuitry involved in bolus movement by peristalsis according to the Law of the Intestine
Describe the pressure changes in the ileocecal sphincter based on the location of distension
Normal state of ileocecal sphincter and why
High pressure state (+40 mmHg) = closed
Effect of circular muscle contracting in colon
Production of haustra