Introduction Flashcards
Regions of GIT
▪️buccal cavity- chewing and secretion of saliva
▪️oesophagus- swallow food by peristalsis action
▪️stomach- storage, peptic digestion-pepsin, sterilises contents of food through H+, intrinsic factor produce VB12
▪️duodenum-fat absorption, proteins and carb digestion, Ca and Fe absorption
▪️jejunum- water and electrolyte uptake
▪️ileum- bile salt reabsorption and uptake VB12 transport
▪️colon- storage, water and electrolyte uptake
▪️rectum and anus- defaecation
Secretions of the GIT
▪️salivary glands- mucus (lubrication) analyse
▪️stomach- HCL, pepsin, mucus (protection)
▪️pancreas- HCO3-(neutralise), protease, lipase, amylase
▪️liver and gallbladder- bile salts, HCO3-
▪️large intestine- mucus
Major Hormones in GIT
▪️stomach
-gastrin-acid secretion
-somatostatin-inhibitor of the gut
▪️Upper SI
-cholecystokinin(cck)- gallbladder contraction, pancreatic enzyme secretion
-secretin- HCO3- secretion
-gastric inhibitory peptide- inhibits gastric release, gastric emptying
-motilin- involved in fasting
▪️ileum and colon
-GLP1- reducing appetite,blood sugar levels
-peptide YY- appetite, gastric emptying
-neurotensin- fat uptake, smooth muscle contraction
Extrinsic innervation
▪️voluntary (conscious control)
-swallowing- hypoglossal nerve 12
-defaecation (EAS)- pudendal nerve
▪️autonomic
-lower oesophageal sphincter- vagus nerve
-colonic activity and IAS- pelvic splanchnic nerve
Sympathetic nervous system of GIT
▪️noradrenaline
- salivary glands- drys up quickly as BV constrict therefore less electrolytes
- vasoconstriction of gut BV- digestion stops
- decrease motility of gut wall
- contraction of sphincters
(aided by release of adrenaline in fight/flight response)
Parasympathetic nervous system of the GIT
▪️ACh
- salivary glands- increase secretion
- increase motility and tone of gut wall
- relaxation for sphincters
- gut secretions
- pancreas secretions
- defaecation
(facial nerve 7, glossopharyngeal nerve 6, vagus nerve 10)
Structure of gut wall
▪️lumen ▪️epithelium- renewed when damaged ▪️mucosa- blood vessels bringing in nutrients for cell renewal ▪️submucosa ▪️circular muscle- peristalsis ▪️myenteric plexus ▪️longitudinal muscle- tone of wall ▪️mesothelium
Intrinsic nerves of GIT
▪️cell bodies within the gut itself and sensory neves that sense stretching and chemical signals
▪️connect with extrinsic nerves which sends signals to parasympathetic nerves
-submucosal plexus
-myenteric plexus- between C and L muscle
Control of smooth muscle in GIT
▪️interstitial cells of Cajal (ICC)
- pacemakers of the gut
- create basal electric rhythm-slow waves of contraction that occur all the time
- only when a threshold is reached is when AP is generated and causes muscle contraction
- SI and LI
The migrating myoelectric complex (MMC)
▪️phase I
-quiescence- nothing is happening (food in gut)
▪️phase II
-random contractions- in antrum (bottom of stomach) and duodenum (digestion is complete)- waves of contraction that helps clear out the gut
▪️phase III
-rapid burst of contractions- max duration and amplitude- induced by hormones and nerves
▪️phase IV
-declining in activity, links with phase I
▪️feeding can disrupt the cycle,every 45-180 mins
▪️responsible for rumbling of stomach when in-between eating
Intestinal movement- segmentation
▪️alternate contractions of adjacent segments that help churn and mix the food
-longitudinal muscle
Intestinal movement- peristaltic reflex
▪️need a presence of food
▪️bolus of food causes distension reflex of circular muscle which triggers interneurons to activate:
-excitatory neurones behind of bolus to release ACh and cause contraction (ascending contraction)
-inhibitory neurones in-front of bolus that release VIP/NO to relax muscle to bolus can move forward (descending relaxation)
Removing indigestible material in GIT
▪️bacteria breaks down some indigestible fibre into short chain fatty acids to fuel bowel
▪️as new food hits stomach/SI, it tells LI that food needs to be cleared out (mass movements)
-food in stomach: gastric-colic reflex which shifts indigestible matter into anal-rectal area
-food in duodenum: duodena-colic reflex doing the same
▪️distension of rectum leads to defaecation reflex
-signal to brain then colon for mass movements
-IAS is relaxed but cannot defaecate as conscious control is needed through pudendal nerve to relax EAS
