NME 2.18 Flashcards
describe the membrane potentials for the interstitial cells of cajalin myenteric plexi?
- unstable membrane potentials
- keep fluctuating below threshold
which extrinsic factor is excitatory?
- ACh
which extrinsic factor is inhibitory?
- noradrenaline
what happens to the small intestine during interdigestive phase?
- tonus activity
- spontaneous contraction of smooth muscle
- inherent mechanisms of tone and rhythmicity may be augmented by a background of transmitters such as ACh
- around 12 contraction/minute
- every fifth contraction is augmented by contraction of teh antrum due to transmission of slow waves crossing the sphincter
- prevent content from flowing back to duodenum
what does the migrating myoelectric complex do during interdigestive phase?
- each cycle involves contraction of adjacent segments of small intestine
- last 10 minutes
- begin in stomach and migrate to proximal small intestine
- periodic sweep of contents towards colon
- helps to clean small intestine from residual food and secretion
- prevent migration of colonic bacteria into ileum
what happens to the migrating myoelectric complex during interdigestive phase for fasting individuals?
- cycles of smooth muscle contractions with average frequency of around 1.5 hrs
during digestive period is there peristaltic propulsion or non propulsive mixing or both?
both
what is segmentation?
- contraction of rings of circular muscles along small intestine
- rings of muscle relax then adjacent segments contract
- result in mixing
what happens to segmentation when chyme enters duodenum?
- increase in frequency and strength
what does mixing do?
- alkaline pancreatic juice
- bile mix with acid
what is minute rhythm?
- when segmentation occurs that last 1 minute followed by interval when contraction are weak or absent
where does minute rhythm occur?
jejenum
are there difference in large intestine during inter-digestive periods?
- no difference
describe the bowel motility in large intestine?
- constant non propulsive churning through haustration and propulsive mass peristalsis 1 to 3 times a day
what are the 4 components of defecation reflex?
- increase activity of sigmoid colon
- distention of rectum
- reflex contraction of rectum
- relaxation of internal and external anal sphincter
what does defecation reflex cause?
- mass movement in the colon moving the faecal material into the rectum
is defecation reflex under sympathetic or parasympathetic control?
parasympathetic
what reflex is defecation reflex considered as?
spinal reflex and conscious control
what influence the defecation reflex?
- mediated by impulses of internal nerve plexi
- refinforced by autonomic reflex transmitted by spinal cord
- influenced by signals from higher centres
what happens during mass peristalsis at rectum?
- there will be rectal distention which cause relaxation of internal anal sphincter
- external anal sphincter is maintained and resist increase pressure by further contraction of pudendal nerve
what pressure will there be urge to defecate?
18 mmHg
what presssure does compulsive defecation occurs?
55 mmHg
how is voluntary defecation initiated?
- voluntary relaxation of external anal sphincter
- abdominal muscular contraction
what is hirschsprung disease?
- absence of submucosal and myenteric ENS ganglia
- internal anal sphincter does not relax after rectal distention
