4/25: Gastric Function Flashcards
What are the 3 main functions of the stomach?
- Temporary storage of ingested material
- Production of chyme (mechanical digestion and mixing)
- Meter delivery of chyme to duodenum
What special secretions does the stomach produce?
- HCl acid
- Pepsinogen
- Intrinsic factor
- Mucus
- Hormones/Paracrines
What is the function of the fundus and body?
Secretion reservoir
What is the function of the antrum?
Mixing
Grinding
What are the 4 types of gastric motility?
- Receptive relaxation
- Peristalsis (trituration/homogenization)
- Emptying
- Migrating motility complex (MMC)
What does receptive relaxation accomodate for?
The volume of the meal
What does receptive relaxation reduce?
Pressure increases preventing gastric reflux and premature gastric emptying
What does peristalsis produce?
Chyme
What is the function of peristalsis?
Trituration/homogenization
What is trituration?
Mix ingested nutrients with gastric secretions, breakdown large particles and increase SA for digestion
What sphincter controls emptying?
Pyloric sphincter
What does the migrating motility complex do?
Sweep ingested solids that cannot be digested out of stomach and through intestinal tract
What does migrating motility complex occur?
During fasting
What is gastric receptive relaxation initated by?
- stretch of gastric or duodenal wall
- protein or fat in duodenum (CCK)
What reflexes are associated with gastric receptive relaxation?
ENS (short) and Vago-vagal (long) reflexes
What is gastric receptive relaxation caused by?
Inhibitory signals (NO, VIP) from ENS
What is the function of the gastric receptive relaxation?
Accommodates increased volume of food and slows emptying
What is gastric peristalsis/trituration generated by?
Pacemaker cells (interstitial cells of cajal) located in GI smooth muscle
What do smooth muscle cells undergo?
spontaneous phases of
depolarizations and repolarizations = slow waves
or Basic Electrical Rhythm (BER) of stomach
What are the functions of gastric peristalsis/trituration?
Acts to mix and break down (triturate) gastric contents (retropulsion)
What does gastric peristalsis/trituration regulate?
Gastric emptying
What does peristaltic wave force?
Chyme through pyloric sphincter
What does gastric peristalsis/trituration cause?
Pyloric sphincter to contract reducing volume released to small intestine
What is rate of gastric emptying influenced by?
Solid vs. Liquid
Nutrient content
Force of gastric contractions
What do factors that increase force of antral contraction do to gastric emptying?
Increases it
- gastrin (gastric hormone)
- distension of stomach
What do factors that decrease force of antral contractions do to gastric emptying?
Decrease it
- contents of duodenum
What are enterogastrones?
Hormones secreted by duodenum in response to nutrients and acid in chyme
What are the three enterogastrones?
- CCK (fat, protein)
- Secretin (acid)
- GIP (carbohydrate)
Where does migrating motility complex occur?
In between meals (fasting state) approx. every 90 minutes
What is MMC intervals of?
Strong populsive contractions
What does MMC sweep?
Stomach and small intestine of indigestible material until meal is ingested
MMC is ______ to ENS and involves hormone _________
Intrinsic; motilin
What is the cell type, source, and function of HCl?
Exocrine
Parietal cell
Activation of pepsinogen, sterilization of meal
What is the cell type, source, and function of intrinsic factor?
Exocrine
Parietal cell
Vit B12 absorption
What is the cell type, source, and function of pepsinogen?
Exocrine
Chief cell
Protein digestion
What is the cell type, source, and function of mucous, HCO3?
Exocrine
Surface mucous cells
Gastroprotection
What is the cell type, source, and function of trefoil factors?
Exocrine
Surface mucous cells
Gastroprotection
What is the cell type, source, and function of histamine?
Paracrine
ECL cells
Regulation of gastric secretion
What is the cell type, source, and function of gastrin?
Endocrine
G cells
Regulation of gastric secretion
What is the cell type, source, and function of gastrin-releasing peptide?
NS
nerces
Regulation of gastric secretion
What is the cell type, source, and function of Ach?
NS
Nerces
Regulation of gastric secretion
What is the cell type, source, and function of somatostatin?
Paracrine
D cells
Regulation of gastric secretion
What is the cell type, source, and function of ghrelin?
Endocrine
Gr cells
Stimulate hunger
What gland is found in the fundus/body?
Oxyntic gland (corpus)
What does the oxyntic gland have abundant amounts of?
Parietal and chief cells
What does the pyloric gland have?
Abundant mucus secreting cells
Hormones that regulate gastric functions
What is alkaline tide?
pH of blood rises due to acid into lumen and abosrbtion of base into blood
What is alkaline tide neutralized by?
Acid thats secreted by pancreas
What are oxyntic cells activated by?
Gastrin, histamine, acetylcholine
What are oxyntic cells inhibited by?
Somatostatin
What do cells secrete?
Up to 2L/day of HCl
Intrinsic factor (IF)
Where are protein pumps inserted?
Apical membrane
What is synergism?
Combination of factors creates a greater level of acid secretion than just additive
Pharmacologically, inhibiting the activity of any one factors greatly _______ acid secretion
Reduces
What does Ach do with the oxyntic gland?
Stimulates it to release acid
What does GRP (gastrin releasing peptide) do with the oxyntic gland?
Stimulates gastrin secretion from G cells into blood
What are neurotransmitters involved in oxyntic cells?
- ACh
- GRP (gastrin releasing peptide)
What is the stimulus for the oxyntic gland?
Stretch of the gastric wall
What does the stretch of the gastric wall cause?
Short and long reflexes to be initiated
What does the short and long reflexes stimulate?
Oxyntic glands to secrete acid and intrinsic factor
What does somatostatin inhibit?
Parietal cells
What are the three phases of GI activation?
Cephalic phase
Gastric phase
Intestinal phase
What are stimulants of the cephalic phase?
Outside GI tract-
Sight of food
Smell of food
Taste of food
thoughts of food
What is the cephalic phase mediated by?
PNS - vagus nerve
What is the gastric phase mediated by?
Signals from lumen
Food in stomach
What happens during the gastric phase when food is in the stomach?
Buffers acid which increases pH to prevent stimulation of somatostatin secretion
When does the intestinal phase occur?
When there is content in the small intestine -
Increased H+, distension, osmolarity, fats in duodenum
What do the intestinal stimuli in the intestinal phase cause the release of?
Enterogastrones
What are examples of enterogastrones?
CCK
Secretin
GLP-1
GIP
What happens with a rise of the enterogastrones?
Inhibit gastrin secretion
inhibit PNS function
inhibit parietal, ECL, and G cells
decrease acid secretion
What levels is acid secreted?
Low levels
What does a lack of buffer (no food) cause?
Low pH in stomach (3)
What are basal secretions stimulated by?
Histamine and Ach
Why is gastrin low?
Due to low pH in gastric lumen
What are the functions of acid in the stomach?
- Facilitates digestion of proteins
- Protects against some pathogens
- Increases absorption of B12, iron, calcium
What are PPIs?
Proton pump inhibitor
What do PPIs bind to and inhibit?
H-K pump
**may be side effects due to functions of acids
What is intrinsic factor?
Glycoprotein secreted by oxyntic cells
Exocytosis
- secretion activated by same secretagogues that activate HCl secretion
What is the mechanism for secretion of intrinsic factor?
Unknown but different than acid secretion (inhibitors or proton pump do not inhibit intrinsic factor secretion, but does reduce its function)
What is intrinsic factor required for?
Vitamin B12 absorption
Red cell production
What does a deficiency in intrinsic factor cause?
Pernicious anemia
What do chief cells secrete?
Pepsinogen to initiate digestion of protein
Exocytosis
When is pepsinogfen activated?
To pepsin by low pH (inactivated by pH >5)
What are chief cells mainly activated by?
Local and vagal reflexes that release ACh
What is ghrelin produced by?
Endocrine cells located in oxyntic glands
What is ghrelin known as?
Appetite stimulant
What does ghrelin stimulate?
Hypothalamic NT neuropeptide Y
What does grehlin account for in patients following gastric resection?
Anorexia and weight loss
What is the flow chart of grehlin?
Why doesn’t the stomach digest itself?
Two hydrophilic layers separated by hydrophobic barrier
What is mucus secreted by in gastric mucosal barrier?
Mucous cells onto surface of epithelium
What does the gastric mucosal barrier contain long chains of?
Oligosaccharides that expand and retain water
What coats the surface of gastric epithelial cells?
Viscoelastic substances
What is viscous fingering?
Limit diffusion of acid through the plane of the gel
What is mucus secretion stimulated by?
Prostaglandins (NSAIDs)
What do trefoil proteins help with?
Stabilizing barrier
Where can ulcers be located?
Gastric
Duodenal
Esophagus
No acid =
No ulcer
What are causes of ulcers?
Helicobacter pylori-bacterial infection that destroys the gastric diffusion barrier
Zollinger-ellison syndrome-G cell tumor
What is mucosal destruction?
“gastritis”, mostly oxyntic gland mucosa damage
What are examples of emptying?
Obstruction
Gastroparesis
Dumping
