12. Motility & Control Flashcards
Describe muscular contraction in muscularis of GI tract
Phasic: peristalsis/segmentation; oesophagus, small intestine, lower stomach
Tonic: minutes/hours; sphincters and fundus
How does electrical conductivity spread in the GI tract?
Gap junctions - low electrical resistance
What is the polarity of SMC of the GI tract?
Polarised - intracellularly negative
Describe the level of polarisation and how it is set
Basic electrical rhythm set by pacemaker cells (non-contractile cells of Cajal)
Pacemaker cells may depolarise to reach the threshold for an action potential
Why would an empty stomach contract?
Hunger pangs - vagus nerve activated due to a drop in glucose level
Explain the filling of the stomach
50ml expands up to 1L
Rugae flatten, SMC plasticity and receptive/adaptive relaxation
Where do peristaltic waves move towards?
Pylorus
Where are the peristaltic waves most intense?
Near pylorus
What is the purpose of the pyloric end in peristalsis?
Pours small amount of chyme into the duodenum whilst simultaneously emptying majority of contents back into stomach for further mixing
Explain the stimulation of gastric emptying
Wall distension and food presence releases gastrin, activation of CNS and local nerves, motility increased and stomach emptied
Explain the inhibition involved during the intestinal phase
Stomach emptied into duodenum causes release of inhibitory hormones such as secretin, CKK and GIP.
This causes inhibition of gastric motility and nerve reflexes.
How long is the material retained?
18-24 hours but up to a week
What is the main type of motility?
Segmentation
How often does peristalsis occur and what is the fate of the material in that time?
1-3 times a day, propels food into empty descending and sigmoid colon and rectum
What is a likely reflex as a result of peristalsis after a few times in a day?
Defaecation - gastrocoloic reflex
Describe the defaecation reflex
Distension of rectal walls by faecal movement
Depolarises sensort fibres
Parasympathetic motor fibres stimulate rectal wall contraction and relaxation of internal anal sphincter
What is diarrhoea?
Passage of watery faeces with increased volume/frequency
Give 4 reasons why food accumulates in the intestinal lumen
Osmosis
Defective ion transport
Hyper-motility of intestine
Active secretion
What is the difficulty in defaecation associated with?
Excessive dehydration of the faeces in large intestine
What may constipation result in?
Haemorrhoids
Over exposure of colonic mucosa to carcinogens
Give 4 factors that could contribute to constipation
Drugs
Lifestyle/exercise habits
IBS
Female hormones
Main function of large intestine
Storage of faecal material
Further absorption of liquids and electrolytes
No villi, therefore no further absorption
What drugs enhance motility of intestines?
Stimulant laxatives e.g senna, biscodyl
What drugs reduce motility?
Opiates
Anticholinergics
