Movement of Food - Gut Motility and Control Flashcards
What are examples of controlled motility?
swallowing, mixing, emptying of stomach and defaecation
Where are most nutrients absorbed?
small intestine
What are the 4 layers of the GI tract?
mucosa, submucosa , muscularis externa, serosa
What are GI sphincters?
Smooth muscle rings that act as valves
What are main functions of the digestive tract?
motility, secretion of juices, digestion and absorption
Describe motility?
propel ingested food from mouth to rectum
Describe secretion of juices?
Aid in digestion and absorption
Describe Digestion?
food broken down into absorbable molecules
Describe Absorption?
nutrients, electrolytes and water are absorbed from lumen of GIT to blood
What is Phasically?
smooth muscle cells in muscularis layer can cause rapid contractions and relaxation for e.g peristalsis and segmentation in oesophagus
What is Tonically?
sustained contractions lasting minutes to hours e.g sphincters in fundus
What can contractions be modulated by?
nerves, hormones, local factors
What are effector units?
SMC’s arranged in sheets of bundles to contract synchronously
What allows contractions to happen in the GI?
Smooth muscle cells connected by gap junctions allows AP to travel in all directions
Where is there low electrical resistance? and why?
in SMC gap junctions so electrical activity can spread readily for synchronous contractions
What is special about SMC’s in the GI tract?
polarised - negative inside respectively
What is the level of polarisation in the GI set by?
cells of cajal - specialised non contractile pacemaker cells
What do cells of cajal do?
generate slow wave potentials and are electrically coupled to SMC’s , lie between nerve fibres and smc’s
What can electrical activity by stimulated by?
Stretch, gastrin, ACh
What can inhibit electrical stimulation?
noradrenaline, CCK, secretin
What does parasympathetic innervation do to GI?
increase gut muscle activity, relax sphincter
What does sympathetic innervation do to GI?
inhibit gut movements and constrict sphincters
What do Hormones do in GI?
motilin increase activity
CCK or secretin decrease activity
What happens in peristalsis of phasic contractions?
adjacent segments of intestine alterate contract and relax to move food along distally
What happens in segmentation of phasic contractions?
nonadjacent segments of intestine alternate and contract/relax moving food forwards and backward to mix food
Where is peristalsis seen?
oesophagus, stomach, small and large intestine
Where is segmentation seen?
small and large intestine
What happens on an empty stomach?
contracts when blood glucose is low due to activation of vagus nerve
What happens on filling stomach?
expands from 50ml to 1L without pressure rising, ruggae flatten, relaxation and plasticity of SMC
What happens to food storage?
not much action in first 30 min then peristalsis
What happens when mixing food with secretions?
Peristaltic contractions build towards antrum region for churning
What happens with emptying of chyme intro the duodenum?
small 3ml of chyme goes into duodenum with each peristaltic wave most goes to antrum the pyloric sphincter closes to allow backflow of empying, stops reflux
What occurs during stimulation of gastric phase?
Stretch of walls release gastrin and activate CNS, increase motility and emptying of stomach
What occurs during inhibition of intestinal phase?
empty stomach contents to duodenum, releases hormones to inhibit gastric motility such as secretin and cck, inhibit nerve reflex
What is housekeeping contractions?
sweep any contents secretions debris through colon and keep intestine clean
What is the migrating myoelectric complex?
slow wave activity in duodenum as previous wave reaches terminal ileum
When does segmentation contractions occur in s.intestine?
as chyme enters as it provide through mixing
How is motility controlled in small intestine?
extrinsic and intrinsic nerves and hormones
What is the ileocaecal sphincter?
controls rate of entry into large intestine , stops bacteria and other pathogens, normally closed
What is the main function in the large intestine?
storage and release of faecal material, absorption of fluid and electrolytes has no villi
What is the main motility of large intestine?
segmentation , strong peristalsis then defaecation
What is diarrhoea?
passage of watery faeces in excess of 500ml a day from increased colonic fluid volume
In diarrhoea why would fluid accumulate in the intestinal lumen?
defective ion transport, osmosis, hypermotility of intestine and active secretion
What is constipation?
difficult in defaecation due to excessive dehydration, delayed transit inadequate dietary fibre and drugs
What are disorders of motility?
damage to extrinsic nerves, damage to intrinsic myenteric nerve plexis and migraine - stomach inactive and IBS
