Lecture 4: Motility of the GI Tract Flashcards
what are the basic layers of the GI tract
- mucosa
- submucosa
- muscularis externa
- serosa
what is motility of the GI tract governed by
- involuntary contraction of smooth muscle with pacemaker interstitial cells of Cajal
- except for upper oesophagus and external anal sphincter
what is motility of the upper oesophagus and external anal sphincter governed by
voluntary striated skeletal muscle
what controls GI motility and secretion intrinsically
enteric nervous system
what makes up the enteric nervous system
- myenteric plexus for motility
- submucosal plexus for secretion and local blood flow
what are endocrine hormones secreted by
entero-endocrine cells in the epithelial layer of GI mucosa
where is cholecystokinin secreted and what does it do
- secreted by I cells of small intestine
- inhibits gastric emptying
where is motilin secreted and what does it do
- secreted by M cells of duodenum and jejunum
- stimulates GI motility
what stimulates depolarisation
- stretch
- hormones eg motilin
- acetylcholine release
what causes hyperpolarisation
- inhibitory enteric nervous system
- noradrenaline
- hormones eg secretin
what happens in Hirchsprung’s disease
- rare congenital absence of myenteric plexus, usually in distal portion of colon
- leads to lack of peristalsis, leading to obstruction and severe constipation
what are the 3 stages of deglutition
1) oral
2) pharyngeal
3) oesophageal
what are the sections of the pharynx
- nasopharynx
- oropharynx
- laryngopharynx
where is the swallowing centre in the brain
- medulla oblongata
- pons in brain stem
what happens in achalasia
- lower oesophageal sphincter fails to relax causing food to remain in oesophagus
- could be due to vagal or myenteric defect
- causes distension, inflammation, infection and ulceration
what happens in gastro-oesophageal reflux
- lower oesophageal sphincter loses its tone, leading to flow of acidic gastric contents into oesophagus
- could cause hiatus hernia
- causes inflammation and ulceration
what allows the stomach to store food
- vagovagal reflex
- mediates receptive relaxation
- reduces muscle tone and allows reservoir function
how is emptying of the stomach regulated
excitatory: - ENS/ANS stimulation - motilin inhbitory: - ANS regulation - duodenal enterogastric reflexes - secretin - cholecystokinin
what effect does gastric chyme have on the contents of the small intestine
- makes it more acidic
- makes it hyper/hypo-tonic
- increases fat digestion products
which hormones cause decreased gastric emptying
- secretin
- gastric inhibitory peptides
- cholecystokinin
what is dumping syndrome
- rapid emptying of gastric contents into small intestine
- occurs following a big meal after gastrectomy
- causes nausea, pallor, sweating, cramps, vertigo and sometimes fainting
what is gastroparesis
- stomach fails to empty
- causes bloating and nausea
- may be caused by gastric cancer or peptic ulcers
- occasionally observed in severely diabetic patients
what give the small intestine a large surface area
- plicae circulares
- villi projections of mucosa
- brush border microvilli on epithelial cell surface
which hormones are involved in peristalsis of the small intestine
excitation: - gastrin - cholecystokinin - insulin - motilin - serotonin inhibition: - secretin - glucagon
what are the muscle specialisations in the large intestine
- longitudnal muscle is thickened to form three bands
- taeniae coli
- which tonically contract
- to form haustral bulges
