GIT Flashcards
(68 cards)
What is a criteria for substances to be absorbed by small intestine
Water soluble
Describe the 3 types of gi motility
Segmentation:
- not moving, churning effect
- non propulsive contraction
- at small and large intestine
Peristalsis: propulsive force to move luminal contents
Tonic contraction: relatively prolonged contraction to isolate and divide segments, occurs at sphincters
How does esophagus prevent retrograde movement of esophageal or gastric contents
Tonic contraction (prolonged contraction) of upper and lower esophageal sphincter
How is tone of les controlled
Modulated by swallowing centre controlling involuntary movement of smooth muscle. Increase tone by cholinergic agonist, a adrenergic agonist, gastrin, substance p (increase pain). Decrease tone by b adrenergic agonist, dopamine, cck, coffee, nicotine
Function of gastric motility between meals
Clear undigested debris and slough epithelial cells
What are the 3 relaxations involved in gastric motility after a meal
Reflex, adaptive, feedback
Timing for gastric emptying of solids
Half life is 2 hours. Initial lag phase of about 1 hour (extensive mixing and retropulsion at stomach). Linear emptying phase for 1 or more hours until stomach empty.
Tell me about liquid emptying
Isotonic saline/water empty rapidly. First order kinetics between volume and rate. When nutritional value increases, higher the caloric density, slower the emptying due to feedback from small intestine. Maximum inhibition at 1M/18% glucose. Fructose less inhibition on gastric emptying compared to glucose and xylitol. 200kcal/h into duodenum
How do the 2 types of abnormal gastric emptying work
Projectile vomiting not accompanied by nausea: vomit centre in medulla activated by afferent fibres. Caused by irritation due to injury or increase in intracranial pressure.
Nausea: chemoreceptor trigger zone in brainstem activated by afferent fibres from GIT or circulating vomit inducing agents eg apomorphone
What is the function of migrating motor complex (90-120 minutes per cycle) in intestine
Housekeeping during interdigestive period: clear undigested debris and slough epithelial cells, and inhibit migration of colonic bacteria into distal epithelium
Mmc is depressed when food enters
What is the main function of the small intestine
Process and absorb nutrients. Does so by mixing chyme with digestive juices and bile, propelling chyme in caudal direction and bringing chyme in contact with microvilli
What is the function of gastrin in small intestine
Stimulate motility, increase mucin and intestinal juice production, promote relaxation of ileocecal sphincter
What is intestinointestinal reflex
Severe distension or injury to any part of the small intestine inhibit motility in rest of small intestine
What is the gastroileal reflex
Chyme in stomach triggers increased motility in ileum
Ileogastric reflex
Distension of ileum inhibit gastric motility
How does distension of proximal colon affect ileocecal sphincter
Contraction to prevent food from moving backwards from colon to small intestine
Why is transit in large intestine slow
No villi hence small absorptive area. Hence slow transit to aid microbial digestion of complex carbohydrates to volatile scfa for absorption and aid absorption of water and electrolytes
What is the effect of distension of rectal wall on anal sphincters
Relaxation of internal anal sphincter (involuntary). Contract external anal sphincter (voluntary) with the tensing of abdominal muscles.
Involuntary defecation if pressure > 55mmhg
What are 3 factors that can result in diarrhoea
Inflammation, leading to malabsorption, increasing intestinal lumen pressure. Increased bowel motility, increasing risk of diarrhea
Failure to absorb nutrient molecules effectively, osmotic action of carbs and proteins draw water into colon resulting in distension of rectal wall triggering defecation reflex
Excess secretion by small intestinal mucosa. Usually secrete large amounts of water but 99% reabsorbed. Diarrhoea if secretion exceeds absorption
How much saliva is produced per day
1-1.5L
Is it true that glands have a low rate of blood flow and metabolism
No! High rates, blood flow to glands 10 times that of blood flow to actively contracting skeletal muscle
At what ph is alpha amylase active
Ph 4-11
What is the ph of saliva
pH6.2 to 7.5
What is the function of parietal cells in stomach
Secrete HCl that kills bacteria (except helicobacter pylori which neutralises acid, and that activates pepsinogen secreted by chief cells to pepsin to digest bacteria
Secrete intrinsic factor for absorption of vitamin b12