GI system: L25 - Motility of the GI tract Flashcards
Describe the propulsion aspect of motility function.
Coordinated contraction (behind the bolus) and relaxation causing pressure gradients propels bolus along at a controlled rate (fast or slow depending) so that digestion can occur efficiently and thoroughly. Very slow propulsion allows food/waste to be stored in the GI tract.
Describe the reduction aspect of motility function.
Reduces the size of particles (by mechanical digestion), so that the surface area available for chemical digestion is increased.
Describe the mixing aspect of motility function.
Motility mixes food with GI secretions. This is important so that food can be lubricated for ease of movement, and mixed with enzymes for digestion.
Describe the absorption aspect of motility function.
Motility brings food into contact with absorptive surfaces, so it may be efficiently and thoroughly absorbed.
Describe the motility pattern: mastication.
Voluntary movement of jaw, reduces the size of food and mix it with saliva so it may be swallowed.
Describe the motility pattern: storage.
Relaxation of smooth muscle in the fundus and body of stomach. This allows the stomach to accomodate an increasing volume of food without increasing pressure.
Describe the motility pattern: peristalsis.
Occurs in the oesophagus, stomach and intestines. Propulsive, moves food from one tract to another. Occurs by sequential contraction of adjacent segments of smooth muscle.
Describe the motility pattern: segmentation.
Intestines only. Moves chyme back and forth through lots of contraction and relaxation throughout intestines, allowing maximum mixing with enzymes and exposure to absorptive surfaces.
What is basic electrical rhythm?
Otherwise known as slow wave, is the spontaneous variations in membrane potential. Without any external stimulus, membrane potential of smooth muscle will slowly reach threshold (slow wave). When wave reaches threshold, action potential fires causing muscle contraction.
BER determines frequency of contractions. Strength of contraction regulated by nervous or hormonal reflexes.
What system coordinates smooth muscle to produce motility patterns in the fasting and fed state?
Enteric nervous system. During fasting, motility is reduced.
What is the Migrating motor complex?
A few hours after a meal, migrating motor complex (MMC) will cause waves of motility clears the stomach to small intestine of products of digestion and excess secretions in 3 phases: Inactivity, intermittent, intense activity which lasts from an hour for inactivity, to intense which lasts 10 minutes.
Describe motility patterns occurring at the mouth.
Mastication and swallowing - voluntary.
Describe motility patterns occurring at the oesophagus.
Rapid transfer of material from mouth to stomach (to clear pathway quickly for air). Involuntary pressure gradients formed by peristalsis.
Describe motility patterns occurring at the stomach.
When fasting, stomach shrinks to a small volume and migrating motor complex acts.
Peristalsis in distal stomach: Peristaltic waves initiated on greater curvature moves chyme to the pylorus.
When fed, retropulsion occurs, which is when the majority of chyme doesn’t fit through the sphincter and instead the chyme propels backwards, helping mechanically breakdown food and mix with enzyme-rich gastric secretions. Peristalsis also pushes food down the stomach.
Storage in proximal stomach: Highly distensible rugae allows huge increases in volume.
Describe motility patterns occurring at the small intestines.
Segmentation occurs to mix chyme with enzyme-secreting substances to allow for chemical digestion. Exposes more nutrients to absorptive surfaces. Peristalsis moves chyme along so that the stomach can empty more into the duodenum for processing.
