GI motility lecture Flashcards
In GI tract
what are slow waves?
what are spikes? what are they stimulated by?
what stimulates hyperpolarization
slow waves are oscillating rest potential.
spikes: slow waves excite spike action potentials, calcium influx and muscle contraction. stimulated by stretch, ACh, parasympathetics
norepinephrine
sympathetics
intrinsic enteric nervous system (ENS) is made up of which two interconnected plexuses in GI tract wall
myenteric plexus: between longitudinal and circular muscles > controls GI motility
submucosal plexus > controls secretion and local blood flow
Hirschsprung’s disease
congenital abscence of myenteric plexus usually involving part of distal colon. The pathologica section of colon lacks peristalsis and undergoes cont spasm leading to obstruction/ severe constipation
describe oral phase swallowing
1) oral: voluntary initiation of swallowing in oral cavity. Tongue pushes against hard palate and contracts to force lubricated bolus into oropharynx.
Achalasia
GORD
Achalasia: LES fails to relax causing food to remain in oesophagus, caused by vagal of myenteric defect
GORD: LES tone lost leading to flow of gastric acid into oesophagus. may be linked to hiatus hernia
results in inflammation, ulceration
3 stages as food enters stomach
storage: vagovagal reflex reduces muscle tone
mixing: spontaneous slow waves initiate weak peristaltic mixing producing retropulsion
emptying: pyloric pump contracts forcing chyme into duodenum
Which hormones trigger decreased gastric emptying. Which cells are the hormones secreted from.
What factors trigger the hormone release
mucosal cells in duodenum:
secretin released by S cells
GIP (K cells) and CCK (I cells)
other endocrine cells release unidentified enterogastrone
triggered by pH less than 3.5, hyper/hypotonic solutions and fat digestion products
Dumping syndrome
Dumping syndrome: rapid emptying of gastric contents into s.intestine occurs following a large meal after gastrectomy.
symptoms: nausea, pallor, sweating, vertigo and sometimes fainting
cause: hypertonic duodenal contents
Gastroparesis
stomach fails to empty, preventing proper digestion
symptoms: bloating/ nausea
what is migrating motor complex (MMC)
cyclic motor pattern occurs during fasting state. peristaltic sweep of intestinal contents every 90 mins
intrinsic control but modified by vagal and hormonal (Eg motilin) stimulation
absence can lead to bacterial overgrowth
Order of layers of gi tract from outside in
Serosa > muscularis externa > submucosa > mucosa
With regards to slow waves/ spike potential.. what does excitatory transmitters do and what does inhibitory transmitters do ? Give examples of each
Excitatory: ca2+/na + channels open, resting membrane potential depolarised, slow waves cross threshold to generate a spike potential
Eg stretch, acetylcholine, parasympathetics
Inhibitory: k+ channels open, efflux occurs, hyperpolarising membrane potential so slow waves can’t reach threshold
Eg noradrenaline, sympathetics
2 types smooth muscle contraction in gi tract
1) segmentation for mixing: bursts of circular muscle contraction and relaxation. Back and forth pendular movements also occur. Both results in small food particles developing
2) peristalsis for propulsion: requires innervation from myenteric plexus. Distension from compression of bolus stimulates intrinsic primary afferent neurons (IPAN) which synapse with cholinergic interneurons. Excitatory efferent motor neurons release ACh and SP = contraction behind bolus. Inhibitory efferent motor neurons release NO, VIP and ATP= relaxation in front of bolus .
Extrinsic ANS control, sympathetic and parasympathetic vertebral origin and effects on gi tract
Symp(T8-12): inhibits secretomotor activity and causes vasoconstriction. Noradrenaline directly inhibits smooth muscle or inhibits enteric neurons
Para(Vagal and Sacral nerves): excitatory effect on gi tract
Gastrin
A) site of secretion
B) stimulus for secretion
C) actions
A) g cells of antrum, duodenum and jejunum
B) protein, distension, nerve( inhibits release)
C) stimulates gastric acid secretion and mucosal growth. Stimulates gastric emptying
CCK
A) site of secretion
B) stimulus for secretion
C) actions
A) I Cells of small intestine
B) protein, fat,acid
C) stimulates pancreatic secretions, gallbladder contraction. Inhibits gastric emptying.
Secretin
A) site of secretion
B) stimulus for secretion
C) actions
A) s cells small intestine
B) acid,fat
C) stimulates pepsin secretion and bicarbonate secretion. Inhibits gastric acid secretion. Inhibits gastric emptying
Gastric inhibitory peptide (GIP)
A) site of secretion
B) stimulus for secretion
C) actions
A) k cells duodenum and jejunum
B) protein, fat, carbohydrate
C) stimulates insulin release, inhibits gastric acid secretion, inhibits gastric emptying.
Motilin
A) site of secretion
B) stimulus for secretion
C) actions
A) m cells of duodenum and jejunum
B) fat, acid, nerve
C) stimulates gastric and intestinal motility
Describe pharyngeal phase swallowing
Involuntary. Bolus causes glossopharyngeal stimulation of swallowing centre in medulla oblongata. Motor efferents cause muscle contraction in trigeminal, glossopharyngeal and vagal nerves
Soft palette elevates over posterior nares
Epiglottis closes off larynx
Respiration inhibited
Upper oesophageal sphincter relaxes
Pharyngeal muscle contraction propels bolus into oesophagus
Describe oesophageal phase swallowing
1) primary peristaltic wave. Striated and smooth muscle contraction
2) secondary wave (stretch)
Intrinsic myenteric nerves, vagal excitation, vagal inhibition for relaxation if lower oesophageal sphincter
Regulation of emptying of stomach
Excitatory: neuronal stimulation of myenteric reflexes
Gastrin (some motility)
Inhibitory: duodenal enterogastric reflexes
Hormones
What controls segmentation and peristalsis in small intestine (neuronal and hormonal)
Stretch/ gastroenteric reflex
Endocrine hormones :
Excite: Gastrin, CCK, insulin, motilin, serotinin
Inhibit: glucagon and secretin
Stimulation of what opens ileocaecal valve, and two things that can go wrong
Gastroileal reflex
1) peristaltic rush: mucosal irritation, ANS
2) paralytic Ileus: loss of peristalsis following mechanical trauma
A) Describe the large intestine anatomically briefly
B) function (3 things)
C) motility
A) 3 bands longitudinal muscle form taeniae coli with haustral bulges
B) absorption of water and electrolytes by enterocytes. Formation of faeces (distal), commensal microbiome
C) motility: mixing contractions from haustrations
Propulsion: slow peristaltic and mass movement
Process of elimination of faeces
Filling following mass movement stimulates stretch receptors and defecation reflex
Involuntary internal anal sphincter relaxation occurs via ENS and P/S ANS
external sphincter relaxation via somatic pudendal nerve
