Gastric acid physiology Flashcards
What is anterior to the stomach?
Liver
What is posterior to the stomach?
pancreas, colon, diaphragm, spleen
What marks the caudal aspect of the gastric body?
Incisura angularis
What is the fundus in contact with?
hemidiaphragm and the spleen
What are the two types of gastric mucosa that you find in the stomach?
Oxyntic gland mucosa and pyloric gland mucosa. The oxyntic gland mucosa is prox 80% and secretes acid into the body and fundus.
The pyloric mucosa is in the antrum (20% of stomach). Here, GASTRIN is synthesized and released.
Describe, very basically, the embryological formation of the stomach
- Dilation of distal foregut
- Dorsal aspect grows more rapidly=greater curvature
- Stomach rotates 90 degrees clockwise
What does the right vagus innervate?
posterior stomach wall (primordial right side)
What does the left vagus innervate?
Anterior stomach wall (primordial left side)
What are the five layers of the stomach?
- Mucosa
- Lamina Propria
- Submucosa
- Muscularis propria
- Serosa
What’s in the submucosa?
Connective tissue containing lymph, A/V, enteric plexus, plasma cells
What is in the muscularis propria?
3 muscle layers: inner oblique, middle circular, and outer longitudinal
What kinds of cells are in the neck?
parietal and mucous neck cells and PRECURSOR cells
What kinds of cells are in the base?
Chief cells, Enterochromaffin Like Cells, G and D cells
What do precursor cells do?
They migrate upwards < 1week to become surface mucous cells or downwards (>1 week) to become parietal or chief cells
What are the motor fxns of the stomach?
Reservoir for food (Fundus/Body)
mixes, grinds food (antrum)
Empties slowly into duodenum (Pylorus)
Pepsinogen secretion
What is significant about the cardia?
Trasition zone from squamous to columnar
Shallow gastric pits with more surface mucous cells
What is significant about the antrum?
Regulates gastric secretion through Gastrin/Somatostatin
What kind of gastric pits do you see in the fundus/body?
DEEP pits
Parietal, Chief cells mostly
Also ECL and D cells
What kind of gastric pits cells do you see in the antrum?
INTERMEDIATE pits
Endocrine cells: G and D cells
What are the secretions of the fundus and body?
H+
Intrinsic factor
Pepsinogens
Lipase
What do chief cells secrete?
Pepsinogen and gastric lipase
What happens in an individual parietal cell when it is stimulated?
Tubulovesicles with H/K ATPases attach to the canaliculus, which expands. The exchanger pumps H+ into the canaliculus which releases HCl into the lumen
What stimulates the parietal cell?
Acetylcholine
Gastrin (works on ECL)
Histamine (increases cAMP intracellularly, required fro gastrin secretion)
How does the parietal cell generate acid
H/K ATPase pumps H out, and K in.
- An open K channel allows K to “recycle” back in and out
- A Cl- pump maintains electroneutrality
- Carbonic anhydrase converts CO2+OH- into HCO3- which diffuses into the plasma
What happens to the alkaline tide?
Bicarb is released interstitially to the surface epithelium to buffer the gastric mucosa
At low secretion rates, what do you see in the gastric juices?
NaCl. Low Potassium and H+. Looks like interstitial fluid, with some bicarb present.
At high secretion rates, what is the composition of gastric juices?
HCl. Levels of Potassium and sodium are low.
Concentrations of what ions are higher in gastric juices than plasma?
H+, Cl, and K are higher. Na+ concentration is lower
What are components of soluble mucus?
Mucin with disulfide bridges
What is insoluble mucous?
Mucous secreted by surface mucous cells in response to physical or chemical stimuli
What enhances soluble mucus secretion?
Acetylcholine from vagal nerve stimulation
What are the endocrine hormones in gastric acid secretion?
Gastrin
CCK
Secretin
Glucose dependent insulinotropic peptide
What disrupts the gastric mucosa?
aspirin, ethanol, NSAIDs, bile salts
What are the hormones with paracrine secretion?
somatostatin and histamine
What are the neurocrine hormones?
Ach and gastrin releasing peptide
What stimulates gastrin release?
Amino acids
Stomach distention
Vagal stimulation by GRP
What does gastrin do?
Stimulates acid secretion thru ECL or by releasing histamine which binds to parietal cells
- Directly stimulates parietal cells
- Stimulates mucosal growth
- Stimulates pepsinogen
What inhibits gastrin?
LOW pH of stomach and somatostatin
What are the phases of acid secretion?
- Interdigestive (basal diurnal rhythm)
- Cephalic (thru vagus)
- Gastric (food in stomach, distention, peptides)
- Intestinal (digestion products)
What are the most important phases of acid secretion?
Gastric (50%)
Cephalic (30%)
How does gastrin stimulate acid release by the parietal cell?
Directly
Indirectly by stimulating the ECL cell to release histamine
What is an important stimulator in the intestinal phase?
Amino acids stimulate gastrin release
However, Chyme and other eneterogastrones inhibit acid secretion and gastric emptying (GIP, CCK, Secretin)
