Stomach Flashcards
Layers of the stomach (x4)
Mucosa: epithelium, 2 layers
- Lamina propria: glues mucosa down to muscularis mucosa
- Muscularis mucosa: puts the mucosa into folds
Submucosa: glues mucosa to muscularis level
- Where BVs, nerves + lymphatics come in
Muscularis: two layers = peristalsis
- Inner circular
- Outer longitudinal
Serosa/adventitia: secretes serosal fluid
- Glues epithelium to muscularis
Enteric nervous system + components
- Coordinates peristalsis
2 components
- Myenteric plexus: muscular contractions, mechanical digestion (between circular + longitudinal muscles)
- Submucosal plexus: regulates secretions (in submucosa)
- Interstitial cells of Cajal: pacemakers of the gut
- Sets a rhythm for contractions to occur, ANS has an effect on how fast/slow
ANS and ENS connection
- Para + sym can both regulate myenteric plexus (signals for contractions) and submucosal plexus (release enzymes)
- Parasympathetic = increased
- Sympathetic = decreased (constricts BVs that go to the gut)
- Parasympathetic NS can also go directly to the end muscles for fine tuning (ganglia sit in organs)
Where are sympathetic GI tact ganglia located?
In collateral ganglia (sits on the arteries)
- Celiac, superior/inferior mesenteric ganglia
Parasympathetic ganglia
- Located in organ walls
- Sigmoid colon + rectum are controlled by pelvic splanchnic nerves (sacral parasympathetic output)
The peritoneum
- Parietal peritoneum: lines the abdominal pelvic cavity
- Mesentery: fold of peritoneum, suspends SI from dorsal abdominal wall
- This is how nerves/BVs get in and out of the small intestine
- Visceral peritoneum: serosa of SI
Folds of the peritoneum
Falciform ligament: divides liver in half
- Only one that originates form ant. abdominal wall
Lesser omentum: connects lesser surface of stomach to inferior surface of liver
Greater omentum: yellow (full of fat cells), goes across SI
- Hangs off greater curvature of stomach + attaches to large intestine
- Lots of BVs & lymphatic tissue here (creates antibodies & the fat cells are a good place to store excess energy)
Mesentery: suspends the small intestine
Mesocolon: part of mesentery that attaches colon to abdominal wall
Alterations of layers in the stomach
- Rugae: specialized foldings of the mucosa, allows stomach to expand
- Innermost oblique muscle layer: additional layer of the muscularis, helps in mechanical digestion
Regions of the stomach
- Cardia region: closest to heart & LES
- Fundus: holding area for semi-solid food
- Body: where the 3 layers of muscularis are well-developed, intense rugae (flattens to expand stomach)
- Pyloric region: 3 regions
- Pylorus: where pyloric sphincter is, controls chyme –> SI
- Pyloric canal: leads to sphincter
- Pyloric antrum: opening to pyloric canal
Why is intrinsic factor important?
- Stomach produces intrinsic factor
- Intrinsic factor binds to Vit B12 (this is absorbed later on)
- Vit B12 is necessary for DNA synthesis
Stomach blood supply
Celiac trunk: supplies most of the blood to the stomach
- R/L gastric a. come off of celiac trunk to form an anastomosis, ensures BF to stomach
R/L gastro-mental a. also come off of celiac trunk to form an anastomosis
- Services greater curvature + greater omentum
Stomach venous drainage
**All veins eventually drain into the hepatic portal vein
- L/R gastric drains lesser curvature
- L/R gastro-mental dump into superior mesenteric v. (drains most of SI and some of LI)
- Splenic v. drains left gastromental + short gastric
What is a gastric pit?
- Invaginations of the stomach mucosa
- Where mucus is produced
- Deeper in the pit is where HCl is produced & enzymes (pepsin + gastric lipase)
Mucous cells
Produce mucus (mucin + water + bicarb anion), how stomach protects itself from HCl
Parietal cells
Secretes HCl & intrinsic factor (to absorb Vit B12)
Chief cells
Secrete pepsinogen & gastric lipase (enzymes of gastric juice)
G cells
Secretes gastrin (endocrine hormone, released locally & gets into BS to act on distal cells)
What happens when G cells get activated?
- Increased parietal cell activity (more HCl)
- Increased chief cell activity (more digestive enzymes)
- Tightening of LES (so HCl doesn’t enter esophagus)
- Increase of motility (more churning from 3 muscle layers)
- Relaxation of pyloric sphincter (so chyme can exit)
How is HCl made?
- Transport protein used for H+ (facilitated)
- ATPase H+ pump is used to pump H+ into the gut lumen (switches with K+)
- Bicarb anion goes through an anti porter (secondary active transport)
- Allows it to move and Cl- is brought in
- Bicarb enters BS and pH of blood goes up
- Cl- leaves into gut lumen via ion channel
What increases the production of HCl?
- Gastrin: from G cells
- ACh: from parasympathetic nerve fibers
- Histamine: from mast cells (lamina propria)
- Released onto parietal cells to get them to keep making HCl
Hyper secretion of HCl
- Increased HCl production but same amount of mucus
- Erosion of mucosa
3 phases of digestion
- Cephalic phase
- Gastric phase
- Intestinal phase
Cephalic phase
- Preparation for food (parasympathetic output)
- Talks to submucosal plexus (increased enzymes), G cells (more gastrin) & myenteric plexus (more contractions)
- Gastrin is also able to ramp up both plexi by talking directly to the epithelium
Gastric phase
- Caused by distention of stomach from food (stretch receptors)
- Chemoreceptors detect increased pH cause by the food
- Activates neural parasympathetic impulses
- Local reflex to the plexi and G cells
Intestinal phase
- Stretch receptors sense distention of the duodenum
- Chemoreceptors sense the presence of partially digested food (fatty acids + glucose)
- Signals back to stomach (via neural + hormonal responses) to tell the stomach to slow down
- Secretin released by endocrine cells (from duodenum): tells submucosal plexus to make less enzymes and less HCl acid
- CCK is released & acts on myenteric plexus to lower contractions
- Enterogastric reflex: less para and more sym (reduces stomach’s chemical digestion)
- Long acting neural reflex involving the brainstem
