Mechanisms of GI tract motility and its control Flashcards
What anatomical features are involved in gut motility?
- Muscle in wall of GI tract (mainly smooth, some skeletal)
- Nervous system (enteric but some control by ANS)
- Endocrine influences (linking presence of food recognised by the epithelial cells in the lumen to increased motility)
- Sphincters/valves at some critical points to ensure coming and one way movement
Give the layers of the GI tract (inside outwards)
Lumen, mucosa, submucosal plexus, circular muscle, myenteric plexus, longitudinal muscle
What are these two layers of the GI tract involved with?
- Myenteric plexus
- Submucosal plexus
- Mainly involved in coordination of muscle contracted influenced by autonomic supply
- Mainly involved in sensory functions and local responses to stimulation of sensory nerve endings in mucosa
Give the details on the neurone types destinations of the enteric (intestine)
Where is overall regulation from?
Motor neurons:
- To smooth muscle
- Vasomotor to intrinsic arteriole (blood flow to get to the gut)
- Secretomotors (to cells regulating acid secretion by the stomach)
- To epithelium (enteroendocrine cells)
Interneurons:
- Various kinds (for co-ordination of reflexes)
Sensory Neurons:
- Chemosensitive
- Mechanoreceptors
Overall: the ANS
How do we keep food going in one direction?
Give the 5 of the GI tract
This requires valves or sphincters between adjacent segments of the GI tract
Where are these … Upper oesophageal sphincter Lower oesophageal sphincter Pyloric sphincter (controls movement from stomach to duodenum) Lleo-caecal sphincter (to the colon) Anal (internal and external) sphincters
Give and explain the 3 stages of mastication
- Oral: tongue pushes bolus against palate & back of mouth, triggering swallowing reflex
- Pharyngeal: upper oesophageal sphincter relaxes while epiglottis closes to protect airways
- Oesophageal: bolus moves downwards into oesophagus, propelled by peristalsis (and gravity)
Explain the nervous innovation of the oesophagus
Upper: somatic motoneurons
Lower: autonomic neurones of the ENS
In relation to the bolus, what part of the intestine contracts to get it to move forward?
Behind the bolus
Give the 3 anatomical details of the lower oesophageal sphincter
- Functional sphincter formed by tonic contraction of circular smooth muscle in wall of abdominal oesophagus - relaxes only when swallowing and vomiting
- Angle at which the oesophagus enters the stomach is on the side so that intragastic pressure closes the oesophagus by squashing one wall
- Surrounding diaphragm restricts the orifice diameter:
contracts during inspiration and when intra-abdominal pressure rises
What two things happen to the stomach when food arrives?
What region is the food moved towards?
- Internal rughae flatten
- Muscle wall relaxes by reflex action
The pyloric region (bottom of stomach).
Explain the waves of gastric motility
Pacemaker sets off contractile waves.
Waves get stronger as you reach the pyloric zone.
Raising pressure in the pyloric antrum, squirting liquid chyme through narrow sphincter.
Narrow sphincter and incomplete occlusion of pyloric antrum lumen by the contraction, causes larger lumps to be regurgitated back into the wider part of the antrum for more mixing.
Explain the motility of the small intestine
Main motility is segmentation.
Simultaneous contractions of different segments results in the mixing.
Overall transit rate is slow.
Peristalsis less frequent here (to allow time for digestion and absorption).
Small pressure gradient (higher in proximal end than distal end). Also helps forward movement of chyme.
Explain the passage from small to large intestine
- Via another valve and sphincter
Valve prevents reflux back into ileum.
Smooth muscle sphincter.
Relaxes in response to upstream pressure.
Constricts in response to downstream pressure and to sympathetic stimulation.
What are the two mechanisms for motility in the large intestine?
- Haustrations: for mixing (short segments where the muscle in wall constricts)
- Mass movements (for bulk movements) due to contraction of larger segments of muscle.
What 2 sphincters controls the exit point?
Internal and external anal sphincter.