PHYS GIT Motility - Week 4 Flashcards
What structures make up the small intestine?
Duodenum, jejunum, ileum.
Motility processes in the small intestine.
- Mixing contractions/segmental contractions – local contractions which mix chyme from stomach w alkaline secretions & digestive enzymes.
(Post nutrient absorption in the small intestine) - Peristaltic contractions/migrating myoelectric complex – initiated by increasing chyme pH or motilin concentration -> remaining luminal contents are pushed into the large intestine.
What nerves modulate mixing contractions in the small intestine?
Stretch receptors of stomach wall -> sensory information to CNS -> parasympathetic control.
What nerves modulate peristaltic contraction of the small intestine?
ENS & ANS.
What structures make up the large intestine?
Cecum, ascending, transverse, descending & sigmoid colons, rectum.
Motility processes in the large intestine.
- Mixing contractions/haustrations - local contractions which allow time for absorption of water & electrolytes
(Post water & electrolyte absorption in the large intestine) - Peristaltic contraction/mass movement – haustra disappear -> faeces move into the rectum -> trigger defecation reflex.
What nerves modulate haustrations in the large intestine?
Localised activation of myenteric nerves & circular smooth muscle cells.
How many mass movements do most people have per day?
3-4, but can be up to 10.
What nerves modulate peristaltic contractions in the large intestine?
Gastrocolic/duodeno-colic reflexes mediated by parasympathetic nerves.
Explain consistency of faeces through large intestine.
Chyme (fluid) from SI -> fluid @ ileocecal valve -> semi-fluid @ ascending colon -> mush @ transverse colon -> semi-mush @ descending colon -> semi-solid @ sigmoid colon -> solid @ rectum.
Excess motility results in ….. and what type of faeces?
Less absorption & diarrhoea/loose faeces.
Poor motility results in ….. and what type of faeces?
Greater absorption & hard faeces/constipation.
2 types of constipation
Slow transit or obstruction.
2 types of diarrhoea
Organic or functional.
What does a mass movement cause?
Movement of faeces from sigmoid colon -> rectum. Triggers defecation reflex.
Explain the roles of autonomic, enteric & somatic motor nerves in the defecation reflex.
Autonomic Nerve Activation: stretch receptors activated -> stretch receptors synapse @ spinal cord neurons -> activation of parasympathetic nerves @ rectal wall & internal anal sphincters -> rectal contractions -> internal anal sphincter relaxation.
& Enteric Nerve Activation: rectal contractions -> activation of inhibitory myenteric neurons -> internal anal sphincter relaxation.
& Somatic Motor Nerve: inhibition of somatic motor nerves -> external anal sphincter relaxation -> defecation.
NB: Increased gut secretions also involved in the defecation reflex.
What happens if you cannot or do not wish to defecate when you feel the urge to?
If we cannot or do not wish to defecate, then somatic motor nerve inhibition -> external anal sphincter contraction -> reverse peristalsis -> movement of faeces back into sigmoid colon (faeces will wait here until the next mass movement).
What chemical substance triggers the migrating myoelectric complex?
Motilin (hormone).
