Intro + GIT motility Flashcards
(20 cards)
Function of GIT (general & nutritive)
- mechanical & chemical digestion and processing of food
- absorption of nutrients for the normal functioning of the body
- to maintain metabolism (food provides us with energy)
- for defense (defend against abrasion, enzymes and acid)
- secretion by glandular organs (secrete acids, enzymes and salt)
- defecation
- integration with other system (hepatobillary liver, heart lungs and kidney)
- ingestion > digestion> absorption> defecation
electrical activity in GI smooth muscle
- pacemaker cells produces slow waves that helps with regulating motility with the GIT eg: segmentation and peristalsis
- BER = basal electrical rhythm, rhythmic contractions happens in the stomach and in the small intestine, gradually decreases and is absent in the colon (non plausible segmentation)
- contractile forces is being regulated by nervous system
nervous system
- parasympathetic: increase in contractile forces
- sympathetic innervation: decrease in contractile forces
- an action potential can trigger contractile forces, the stronger the action potential = stronger contractile forces
activity pattern of smooth muscle
1) sphincters - always contracted to keep the sphincters close only relaxes to open
2) blood vessels - partially contracted and helps to control blood pressure
3) stomach and intestine - rhythmic contraction
4) urinary bladder and esophagus - always relax unless required to shift bolus in particular direction or emptying of bladder
muscle fiber contraction between smooth and skeletal muscle
agents that causes contraction of the smooth muscle would result in relaxation of skeletal muscles and vice versa
esophageal motility
function: help transport the bolus from the oral cavity into the stomach
- has upper and lower esophageal sphincters to protect the esophageal epithelial cells by preventing reflux and retrograde movement of the esophageal content and the acidic gastric contents
upper esophageal sphincter (UES)
- skeletal muscles
- controlled by swallowing centre
lower esophageal sphincter (LES)
- cardiac sphincter
- modulated by swallowing centre
what increases and decrease LES tone?
increase LES tone
- gastrin, cholinergic agonist, alpha adrenergic agonist
decrease LES tone = making the sphincter weaker, higher chance of reflux
- CCK, beta adrenergic agonist, coffee, tea, alcohol
function of gastric motility
- during interdigestive period when there is no food in the stomach, there is still rhythmic contractions to clear the undigested debris and sloughed the epithelial cells
- the arrival of the bolus in the stomach results in gastric distention and relaxation to accommodate for the food
the proximal stomach does not have rhythmic contractions as its purpose is to hold the bolus when it arrives
gastric receptive relaxation
gastric adaptive relaxation
feedback relaxation
gastric receptive relaxation
- triggered by dry swallowing or mechanical stimulation by pharynx or esophagus
- the stomach needs to relax its toning so that it can accommodate for the distention when the food arrives
- mediated by mechanoreceptors of the stomach
gastric adaptive relaxation
- dont need any stimulus from the pharynx and esophagus to result in this adaptive relaxation.
- the proximal stomach will expand in order to accommodate for the food in order to ensure stable intra gastric pressure
- mediated by the vago vagal reflex arc in the brainstem and the volume (arrival of food will increase volume and pressure so need to expand in order to maintain stable pressure)
feedback relaxation
- when the food gets release into the duodenum it is regulated by the pyloric sphincter, to release the chyme batch by batch
- this is to also ensure maximal digestion by the secretion produced from the liver and pancreas (has all the digestive enzymes that helps to break down carbohydrates, lipids and proteins) & also to ensure maximum contact with the microvilli of the small intestine to maximize absorption
pyloric sphincter
-helps to regulate the chyme entry into the duodenum
- prevents the reflux of the intestinal and gastric chyme
- the intestinal juice has high bicarbonate concentration so is more alkaline in nature but the gastric juices in the stomach is extremely acidic which can end up damaging the intestinal cells
regulation of gastric emptying
3 inhibitory reflexes
1) gastro gastric: regulates stomach motility
2) duodeno gastric: distension of the small duodenum region slows down gastric emptying
3) entero gastric: when the chyme in the stomach is too acidic, this inhibitory reflex would prevent the emptying of the over acidic chyme
hormonal: gastrin (G cells produces gastrin) increases gastric emptying
CCK, GIP and secretin decreases gastric emptying
neural control: anger and aggressiveness increases gastric emptying, pain and depression decreases gastric emptying
nature of the food can also slow down gastric emptying
1) solid food vs liquid food
2) food containing high is fats and proteins
3) chyme with high acidity and high osmotic pressure
factors that modify gastric liquid emptying
1) water or isotonic saline empty rapidly
liquid food generally empties faster than solid food but the emptying of liquid food also relies on the first order kinetics in which a bolus 300 ml vs bolus 150 ml.
bolus 150ml will empty faster than 300 ml bolus
2) nutrients delayed gastric emptying
- higher the caloric density the slower the emptying
- presence of amino acid and carbohydrates
amino acid tryptophan slows down gastric emptying rates
carbohydrates, fructose is less potent than glucose and xylose so they don’t affect gastric emptying as much
factors modifying emptying of digestible solids
digestible solids can slow down gastric emptying rates but if the solids have high fats and proteins it will be slower, the size of the solids the bigger it is the slower it is
abnormal gastric emptying (vomiting)
1) presence of nausea
- caused by vomiting agents circulating in the body or afferent nerve fibers induce nausea at the brain stem where the chemoreceptors are at
2) no nausea involved
- occurs due to injury or increase in intra cranial pressure that causes the vomiting centre in the medulla to induce projectile vomiting without nausea
types of intestinal motility
1) segmentation (move front and back)
- short range movement
- localised reflex
2) peristalsis
- short range movement
- moving chyme/bolus in a particular direction, involves teamwork between the circular and longitudinal muscles relaxation and contraction
3) migration motor complex
- long range movement
- for interdigestive periods
- preventing the migration of the microflora found in the colon into the distal ileum
function of small intestine motility
- to process and absorb nutrients
- important for the mixing of chyme with the secretions from pancreas and liver and mix with intestinal juices as well for efficient digestion continuing from the stomach
- propelling chyme
- bringing chyme into contact with microvilli for absorption
regulation of intestinal motility
gastrin stimulates increase in intestinal motility and relaxation of the ileocecal sphincter
2 inhibitory reflex
1) intestino intestinal reflex - distension or injury in any regions of the intestine would inhibit motility in the rest of the small intestine
2) ileogastric reflex - distension of the intestine slows down the release of chyme from the stomach (gastric motility)
gastroileal reflex - presence of chyme in stomach triggers motility in ileum
colonic motility
in the large intestine the movement of the chyme is slow this is to ensure that the chyme is mixed and ferment with the colonic bacteria
mainly it is for the storage and the production of fecal material
in the large intestine there is not much digestion but there is still minimal reabsorption of water and electrolytes happening hence there is still non propulsive segmentation (not rhythmic anymore) important for
- mixing of the colonic contents
- slow progression of content to allow time for water and electrolytes reabsorption
- retrograde movement (back and forth action to ensure mixing and fermentation)
defecation results in mass peristalsis
slow transit time and vigorous mixing movement aids?
- microbial digestion of complex fermentable carbohydrates in plant residues and short chain fatty acids
- reabsorption of water and electrolytes
defecation
defecation results in mass movement (mass peristalsis) usually after meals, dugs like opiates can decrease mass movement
the distention of the rectal wall would trigger defecation reflex
- the internal anal sphincter and the external anal sphincter (skeletal muscle) need to both relax so that defecation can occur
- to defecate, voluntary increase in intra anal pressure by tensing abdominal muscle
- when the intra anal pressure surpass normal pressure, defecation can no longer be controlled
- delay defecation results in further compaction of fecal material resulting in constipation
abnormal colonic motility
1) diarrhea
- due to increase in bowel motility in response to inflammation
- due to failure in absorbing nutrients molecules effectively
- due to excess secretion by small intestinal mucosa
2) constipation
- due to inadequate consumption of fiber in diet
- lack of exercise
- repeated voluntary inhibition of defecation reflex
3) incontinence (involuntary control)
- sensory malfunction
- incompetence of IAS due to surgery or mechanical injury
- disorder of neuromuscular mechanism of the EAS due to surgery or mechanical injury
