GI Physiology and Motility Flashcards
What is the muscular structure of GI tract?
Outer Myenteric plexus - longitudinal
Inner submucosal plexus- Circular
Describe the parasympathetic innervation of the GI tract
Vagus nerve for as far as ‘Canon’s point’ of descending colon for non-sphinteric muscles
Pelvic nerves (S2-4) for descending colon, rectum, bladder and urethral sphincter
Describe the sympathetic innervation of GI tract
3 prevertebral ganglia - coeliac, superior mesenteric and inferior mesenteric.
These then travel in splanchnic nerves with long post-ganglionic fibres
Sympathetic control inhibits non-sphinteric muscles and excites sphinteric muscles
What is the result of sympathetic innervation and how does it occur?
Vasoconstriction bu inhibiting cholinergic post-ganglionic neurones. The neurotransmitter aerosols out from variscotes so it is a slow process
What innervates the salivary glands?
parasympathetic division of CN7 and CN9
What makes up saliva? and what are functions of each component
Hyptonic NaCl and Mucus - lubrication
Salivary amylase - digestion (and cleans teeth)
Bacteriocidal agents such as SCN, Iodide and lysosome
Bacteria which produce Hydrogen ions
How can hydrogen producign bacteria cause damage?
Attack hydroxyappetite of enamel dentine, leading to carices, infected pulp and enterococous faecalis infection - can cause endocarditis- can cause ludwig angina
What is achlasia, how does it present and how can it be treated?
Thickening of / absence of relaxation of circular muscle layers - spasm due to peristaltic failure.
Will prevent bolus travelling forward unless with large drink - shows as birds beak on LOS x-ray
Treat with rigiflex balloon dilation, or per oral endoscopic myotomy
What is the muscular make up of the oesophagus and how can each be pathologically affected?
Upper 1/3 striated muscle- polymyositis and myasthenia gravis
Lower 2/3 smooth muscle- achlasia and Scleroderma (thickening of tissue under dermis, causing weak LOS, absent peristalsis and oesophagitis)
How is enteric neurotransmission mediated?
Interstitial cells of Cajal- mediate reflex activity in absence of CNS
Name two other neuro-hormonal influences on gut motility
Motilin and opioid receptors
What is the migratin gmotor complex and when is it present?
The MMC is a cyclic contraction sequence occurring every 90 minutes when in the interprandial (fasting) period, acting to cleanse the stomach and intestine in 4 phases:
1. Prolonged period of quinescece 2. Increased frequency of contractility 3. Few minutes of peak electrical and mechanical activity 4. Decline in activity to merge into the next phase 1
How is the MMC regulated?
Motilin is a polpeptide hormone produced by M cells in small intestine. It is secreted at 90 minute intervals to facilitate MMC. It also causes contraction of gastric fundus, enhancing gastric emptying.
What drug mimics the action of motilin?
Erythromycin
How does gut motility change after a meal?
- The cehalic phase is the secretory phase, where the vagus nerve causes secretion of enzymes due to sight, smell or taste of food.
- In the Gastric Phase, gastric tone reduces and the fundus expands, in order to accomodate the meal. MMC is replaced by contractions of varyign amplitude and frequency, allowing for mixing and digestion.
- The Intestinal Phase sees solids and liquids transported at same rate but as liquids leave solids first, these reach caecum first
