23 11-13 Flashcards
Gross anatomy of the stomach?
15-25cm/6-10” long
Regions: cardiac (surrounds area where food enters from esophagus), fundus (dome shaped part tucked beneath diaphragm - storage), body (midportion), pylorus (inferior, funnel shaped)
Convex lateral surface is the greater curvature, medial is lesser curvature.
Lesser omentum (runs from liver to lesser curvature) and greater omentum (drapes inferiorly from greater curvature to cover small intestine.)
Pyloric canal - where food is churned.
Served by vagus nerve and thoracic splanchnic. Arterial supply from gastric/splenic/veins to hepatic portal.
Functions of the stomach?
Storage (50-4liters)
Mechanical/chemical breakdown of food, forming chyme
Production of intrinsic factor (glycoprotein required for absorption of B12 in small intestine)
Protection
Absorption (small nonpolar substances, i.e. alcohol/aspirin)
Structural modifications of the wall of the stomach that enhance the digestive process?
Oblique layer: Has an extra (though incomplete) layer of muscularis which runs obliquely allowing food to be mixed.
Rugae: longitudinal folds that increase surface area.
Sphincters: Pyloric, gastroesophageal
Describe the mucosal layer of the stomach.
Simple columnar epithelium of mucous/goblet cells which produce a protective coat of alkaline mucus (surface is insoluble mucus, bicarbonate rich fluid underneath). Indented with gastric pits from which gastric glands extend deep into mucosa.
What type of cells do the gastric pits contain?
Chief cells, parietal cells, mucous neck cells, and surface epithelium at the beginning
- Name the cell types responsible for secreting the various components of gastric juice
mucous neck cells, parietal, chief, enteroendocrine, surface mucous cells
Mucous neck cells
Scattered in the neck, produce a thin, soluble mucus. Acidic
Parietal cells
Fuzzy pitchfork shape, lots of surface area for secretion of HCl and intrinsic factor
Chief cells
Mainly in basal region of gastric glands. Produce pepsinogen (inactive form of pepsin) and gastric lipase - 15% of lipolysis.
Enteroendocrine cells
Release chemical messengers: Histamine, serotonin, somatostatin, gastrin
Surface mucous cells
Continously secrete an alkaline product containing mucin
What creates the mucosal barrier (protection) in the stomach?
- Thick coating of bicarbonate rich mucus
- Epithelial cells of the mucosa are joined by tight junctions that prevent gastic juice from entering underlying tissues
- Damaged epithelial cells are shed an quickly replaced by division of undifferentiated stem cells where the gastric pit meets gastric glands.
- What are the 3 reflexes that regulate gastric secretion and stomach motility?
Cephalic phase, gastric phase, intestinal phase
Cephalic phase
Happens before food enters the stomach - triggered by the sight/taste/aroma/thought of food.
Sight/thought of food –> cerebral cortex
OR
stimulation of taste and smell receptors
THEN –> Hypothalamus –> Vagus nerve –> stomach secretions.
Gastric phase
Most important stimuli: distension, peptides, low acidity.
Stomach distension –> local reflexes –> stomach secretions
OR
stomach distension –> vagovagal reflexes –> Medulla –> vagus nerve –> stomach secretions
OR
Food chemicals (esp. peptides/caffeine) and rising pH –> G cells –> gastrin release –> Stomach secretions.
Intestinal phase
Presence of partially digested food or distention in duodenum –> gastin release to blood –> brief stomach secretions.
Enterogastric reflex?
Actually 3 reflexes:
inhibits local reflexes,
inhibits vagal nuclei,
activates sympathetic fibers that tighten the pyloric sphincter.
Protects the small intestine from excess acidity, matches the small intestine’s capacity to process chyme.
Define and account for the alkaline tide
Alkaline tide is the phenomemon of the blood leaving the stomach being more alkaline than the blood that enters.
Happens because of HCl formation - from carbonic acid, H+ is pumped into the stomach lumen, bicarbonate into the blood.
HCl formation
Histamine/Ach/Gastrin must be bound.
Co2 from IF enters parietal cell.
Co2 +H20 –> H2CO3 –> HCO3- + H+.
H+ is pumped into the stomach lumen.
HCO3- in the cell and Cl- in the IF are transferred by antiporter.
Cl- enters the stomach lumen.
H+ and Cl combine
Helicobacter pylori
Can burrow like a drill through the mucus and destroy the protective mucosal layer. More than 1/2 population has helibacter, but pathological effects occur in 10-20% of infected individuals. Cause ulcers.
HCl functions
- Denature food/cellulose/collagen/protein
- Pepsinogen –> pepsin
- Protection (too acid for bacteria)
Sphincters (ape oil)
Anal, pyloric, esophageal, oddi, ileococal
Aside from preparing food for the small intestine, what is the only essential stomach function?
Releasing intrinsic factor
CCK cholecystokinin
Site: Duodenal mucosa
Stimulus: Fatty chyme
Target: Stomach - inhibit secretion
Liver/pancreas - potentiates secretin’s action on these organs
- Pancreas - increases enzymatic secretions
- Gallbladder - stimulates to contract and expel bile
Hepatopancreatic sphincter - relaxes sphincter to allow entry of bile and pancreatic juice into duodenum.
