Gastric Disorders of Nutrient Processing Flashcards
What is the goal of the stomach? (8)
- Maximize efficient intake of energy/nutrients
- Store rapidly ingested energy/nutrients with highly variable volume, consistency, particle size, energy density
- Begin process of breaking down energy/nutrient sources for further digestion/absorption - Increase surface/volume
- Delivery of energy/nutrients to small intestine and match its capacity
- Expel indigestible components - Air up through esophagus (belch) or colon less; Solids: down to colon
- Rapidly expel toxic material: vomiting
- Help defend against invaders (which could eat our food/damage us)
- Perform functions without damaging/digesting itself
What is proximal gastric motor function?
What is the purpose of this function?
What nerve mediates it?
Initially a receptive relaxation of fundus tone
Allows accommodation/storage of ingested meal
Reflex mediated via vagus nerve
Subsequent increase in tonic and phasic contractions
Push meal into antrum
What is the distal gastric motor function?
What mediates it?
What is the role of the pacemaker?
How do contractions propagate?
Baseline slow wave activity in muscle cell membrane potential
Mediated by interstitial cells of Cajal
Spread distally from pacemaker site: Frequency is 3/minute
Contractions (vagally mediated) sweep in a ring towards pylorus
What is the pyloric motor function?
How are its contractions timed?
What function does it serve?
Sphincter to block egress of large food particles (sieve)
Closure timed with oncoming antral ring contractions
1-2 mm in size and liquids pass through
What is the role of duodenal motor activity?
Pattern of coordination of duodenal contractions can facilitate or inhibit emptying of gastric contents into small bowel lumen
Preparation for vomiting
What neural receptors are responsible motor feedback control?
What afferents do they use?
What is the rate of energy delivery?
Receptors in small intestine identify nutrient delivery
Act via vagal afferents to alter gastric motility, retard emptying
Results in relatively constant (1-4 kcal/min) delivery of energy to small intestine
What is the feedback control roles (in response to and effect of) of secretin, somatostatin, cholecystokinin?
Secretin
Released in response to entry of lipids, amino acids or HCl into duodenum
Relaxes gastric tone, inhibits contractions, increases non-propulsive duodenal contractions
Somatostatin
Release in response to acid/peptides
Inhibits gastric emptying
Cholecystokinin
In response to delivery of fat
Inhibits gastric motility
What is the role of PYY, GLP-1/Glucose-dependent insulinotropic peptide, Ghrelin in terms of motor feedback control?
PYY – Illeal brake
Shuts down stomach movement
Nutrients to distal small intestine
GLP-1 and Glucose-dependent insulinotropic peptide
Secreted in small intestine in response to glucose delivery
GLP-1 also in response to colonic fermentation
Inhibition on gastric motility before insulin
Ghrelin
Increases emptying speed
What is the rate of glucose emptying?
What did the insulin-glucose clamp studies reveal?
Constant linear (1-4 kcal/min) emptying of glucose from stomach regardless of concentration
Increased blood sugar levels result in delayed solid and liquid meal emptying
What is role of chornic caloric intake on gastric motility?
What is anorexia nervosa?
How is motility in the obsese?
GI tract adapts to ongoing nutritional intake
Reduced calorie intake/weight loss causes delayed gastric emptying
Anorexia nervosa: Reverses on refeeding
Brief overfeeding accelerates gastric emptying in normal eeight subjects
Gastric emptying faster in the obese
What is a scintigraphy?
What is its limitation and what needs to be controlled for?
Nuclear medicine test to assess emptying non-invasively
Radiolabeling of solid or liquid
Detects amount at specific timepoints
Does not measure total emptying
Normal values depend on the type of food
When does fasting occur?
What is the characteristic of the contractions in fasting activity?
What solids can pass?
Occurs at end of meal
Onset delayed 1 hour for each 200 kcal ingested
Every 90 min (1 to 6 hours) with fast
Maximum strength, frequency (3/min) and coordination of contractions
Allows clearance of large (> 7 mm) indigestible solids from gut and enteric coated meds
What is the consequence of contraction failure?
Impaired triturtion of solids
Delayed delivery of nutrients
Retention of gastric contents
Pain, early saiety, nausea, vomiting, poor delivery
What are the consequences of accomodation failure?
Limits amount that can be ingested without discomfort
Pain/bloating
Early satiety
Nausea/vomiting
Weight loss
Food moves too rapidly into small bowel
What are the consequences of small bowel?
Extensive distension
Bloating, pain, symptomatic hypotension
Particles too large
Poorly timed for biliary secretions
Inadequate time for nutrient absorption (weight loss, nutrient deficiencies)
Colonic bacterial fermentation (flatus, bloating, osmotic diarrhea, cramps)
Humoral lag in response resulting in initial rising blood glucose followed by compensatory hypoglycemia (Reduced glucose delivery)
Unbuffered HCl to duodenum
