Stomach Physiology and Pathology Flashcards
What is the stomach?
a J-shaped enlargement of GI tract directly inferior to diaphragm in abdomen
what is the most distensible part of the GI tract?
stomach
what are the functions of the stomach
- serves as reservoir for food before release into SI
- mixes saliva, food, and gastric juice to form chyme
what are the 4 main regions of the stomach?
- cardia
- fundus
- body
- pyloric
what are the 2 sphincters of the stomach?
- lower esophageal
- pyloric
what are the 2 main curvatures of the stomach?
- lesser
- greater
the main arterial supply comes from where?
celiac trunk of aorta
what are the 4 main arterial supply to the stomach?
- Hepatic artery
– right gastric
– right gastro-omental - celiac trunk
–left gastric - splenic artery
– left gastro-omental
which veins does the stomach drain into?
drain into hepatic portal vein or superior mesenteric vein
specifically, tell me the vein and where it drains into
○ Left gastric vein
§ Hepatic Portal Vein
○ Right gastric
§ Hepatic Portal Vein
○ Left gastro-omental vein
§ Superior Mesenteric Vein
○ Right gastro-omental
§ Superior Mesenteric Vein
in terms of innervation of the stomach, the parasympathetic supply comes from?
anterior and posterior vagal trunks from vagus nerve
in terms of innervation of the stomach, the sympathetic supply comes from?
from T5-T9 segments of sympathetic trunk, passes to celiac plexus via greater splanchnic nerve
what is part of the mucosa of the stomach
- epithelium
- lamina propria
- muscularis mucosae
epithelium and lamina propria are arranged into ?
glands
glands have 3 regions:
- pit
- neck (isthmus)
- base
what are the different cell types of the stomach glands?
- surface mucus cells
- parietal cells (oxyntic)
- chief cells (zymogenic)
- enteroendocrine cells
what lines the surface of the stomach and gastric pits
simple columnar epithelium
surface mucus cells have lots of what ? which are large glycoprotein
mucin granules
what are found within the neck of gastric glands/mucus neck cells
simple columnar epithelium
parietal cells are what shape?
rounded/pyramidal shape
what are the functions of these parietal cells?
produce HCL and IF
where are parietal cells mainly found
in upper half of gastric gland
where are chief cells found?
in lower regions of gastric glands
what is the function of the chief cells?
pepsinogen secretion
where are enteroendocrine cells found?
found deep within gastric pits
what are the different types of enteroendocrine cells?
- enterochromaffin-like cells
- G-cells
- D- cells
what does enterochromaffin-like cells secrete?
histamine
what does G-cells secrete
gastrin
what does D-cells secrete
somatostatin
the submucosa is made up of ?
dense, irregular collagenous CT
what are the 3 layers of muscularis externa
- inner oblique
- middle circular
- outermost longitudinal
what are the 4 different stages of the stomach motility
- food entry into stomach
- storage in fundus
- mixing (aka churning)
- emptying into small intestine
what are the functions of the lower esophageal sphincter?
- controls movement of food into the stomach
- also prevent reflux of gastric contents into the esophagus
what is required of the sphincter to facilitate entry of food into the stomach?
relaxation
what is initiated for the relaxation of the lower esophageal sphincter?
initiated by a vasovagal reflex called receptive relaxation which is triggered by swallowing and esophageal distension
where is the food stored in the stomach?
fundus
what is gastric accommodation
the presence of food stretches the stomach walls and reduces the tone in muscular wall of body of the stomach
what initiates mixing waves of food in the stomach?
gastric pacemakers
what is it called when waves start in mid- to upper portion and move toward pyloric antrum
propulsion
the contractions in pyloric antrum “grinds” the food bolus called?
grinding
the pylorus opening is very small so antral contents are pushed back upstream toward body of stomach, this is called?
retropulsion
what can only leave the stomach through the pyloric sphincter
only liquid
gastric acids are released from ?
parietal cells
what is the pH of gastric acid?
pH of 1-2
gastric acid is composed of?
- hydrochloric acid
- large amounts of KCI and small amounts of NaCl
what are the functions of gastric acid?
- digestions of denaturation of protein
- bacteriostatic
- needed for conversion of pepsinogen to pepsin
what is the secretion mechanism of gastric acid?
- Water dissociates into H+ and OH- in cell cytoplasm
- CO2 combines with OH- to form bicarbonate ions by enzyme: carbonic anhydrase
- H+ is pumped into lumen of canaliculus via H+/K+ ATPase
- H+/K+ ATPase is blocked by the class of drugs called “proton pump inhibitors”
- Cl- transported passively from cytoplasm of parietal cell into lumen of canaliculus
- Parietal cells can be stimulated by several sources:
○ Acetylcholine acting on Muscarinic receptors
§ Parasympathetic stimulation
○ Gastrin acting on CCK2 receptors
○ Histamine acting on H2 receptors
Histamine is stored and released form ? of the stomach
enterochromaffin-like cells
what are the functions of histamine
- acts on H2 receptors on parietal cells
- stimulates release of gastric acid
- stimulates vasodilation
gastrin is secreted by ?
G cells
gastrin is secreted in response to?
- stomach distension
- vagal stimulation
- presence of partially digestion proteins (peptides and amino acids)
what are the functions of gastrin?
○ Acts on ECL cells to stimulate release of histamine
○ Directly stimulates parietal cells by binding to CCK receptor
Parietal cells can be inhibited by?
- somatostatin
- prostaglandins
somatostatin is also known as ?
growth hormone inhibiting hormone
somatostatin is released from what?
D cells
what are the functions of somatostatin?
- acts on parietal cells to reduce secretion of gastric acid
- also reduce release of gastrin, secretin, and histamine
- suppresses released of pancreatic hormones
somatostatin is secreted in response to?
luminal H+ which is negative feedback
the phases of gastric acid secretion after meals can be divided into 3 phases which are?
- cephalic
- gastric
- intestinal
the cephalic phase is triggered by ?
smell, sight, taste, thought and swallowing food
the cephalic phase is primarily mediated by the ?
vagus nerve
the vagus nerve releases ?
Ach
what does the Ach do?
§ Ach acts directly on parietal cells to release H+
§ Ach acts on ECL cells to release histamine
§ Ach acts on D cells, inhibiting release of somatostatin
Vagus nerve also releases ? to induce gastrin release from G cells
GRP
food enters the stomach, distending the gastric mucosa and activating what?
vagovagal reflex and local ENS reflex
partially digested proteins stimulate G cells to produce ?
gastrin
what stimulates D cells to secrete somatostatin, which inhibits gastrin production (think negative feedback)
low luminal pH
explain the intestinal phase of gastric acid secretion
- Presence of amino acids and partially digested peptides in proximal intestine
○ Stimulates G cells in duodenum to secrete gastrin
what are some intrinsic factors for secretion of gastric acid
glycoprotein and pepsinogen
glycoprotein is secreted by ?
parietal cells
what is the function of glycoprotein
required for the absorption of vitamin B12 in the ileum
pepsinogen is secreted by ?
chief cells
pepsinogen is spontaneously cleaved to ? in the presence of HCI
active pepsin
how is pepsinogen secretion stimulated?
§ Ach release from vagus nerve or ENS
□ Ach bind to M receptors on chief cells
□ *Most important stimulus
§ Presence of acid in the duodenum triggers secretin from S cells
□ Secretin also stimulates chief cells to release more pepsinogen
the gastric diffusion barrier is maintained by:
- mucus gel layer on surface epithelium
- bicarbonate microclimate adjacent to surfacce epithelial
- tight junctions in gastric glands
mucus combines with phospholipids, electrolytes, and water to form a ?
gel layer
the gel layer protects against:
acid, pepsin, bile acid, and ethanol
what is mucin secretion induced by?
- vagal stimulation
- chemical irritation
