Week 4 - Introduction to the Stomach Flashcards
What is the mechanism of action of NSAIDS/aspirin? Why are they not recommended for use in individuals with stomach ulceration?
Aspirin and NSAIDs block production of prostaglandins, as they inhibit cyclo-oxygenase, the enzyme that produces prostaglandins from arachidonic acid - used for treatment of fever.
Prostaglandins have an important role in the stomach in maintaining mucosal blood flow and supplying the epithelium with nutrients. Inhibiting prostaglandin production may exacerbate problems in the stomach.
What pharmacological interventions can be used to stop acid production in the stomach? Briefly outline the mechanism of action for each.
- Proton pump inhibitors: block the proton pump present in parietal cells
- H2 blockers: Block histamine receptors - histamine is a critical modulator of acid production
State examples of drugs for proton pump inhibitors and H2 blockers.
H2 blockers: cimetidine, ranitidine
Proton pump inhibitors: Omeprazole
State the direction in which the fibres of external oblique run.
Anteriorly and inferiorly
State 2 retroperitoneal blood vessels.
- Abdominal aorta
2. Inferior vena cava
Define pneumoperitoneum.
Air/gas in the peritoneal cavity
What are the causes of a pneumoperitoneum?
- Pathological
2. Laparoscopy: cavity inflated with CO2 so they can see what they are doing
Define visceral peritoneum
Part of peritoneum that envelops the intra-peritoneal organs - envelops the small bowel/liver
What is the greater omentum?
A fold of visceral peritoneum hanging down off the greater curve of the stomach
What is the lesser sac?
Part of the peritoneal cavity that lies behind the stomach
What is the foramen of Winslow (epiploic foramen)?
Communication between the greater and lesser sac
What is the recto-uterine pouch?
Pouch of Douglas
Extension of peritoneal cavity that lies between the rectum and uterus
What is the uterovesical pouch?
The extension of peritoneal cavity that lies between the uterus and bladder
What is the hepatorenal pouch?
The part of the peritoneal cavity that lies between the liver and right kidney - pouch of Morrison
What are the paracolic gutters? Why are they clinically important?
Part of the peritoneal cavity that lie lateral to the ascending and descending colon
In pathological states, they can transmit fluid
What are the attachments of the lesser omentum (fold of peritoneum)?
Liver to the lesser curve of the stomach and proximal duodenum
What is the gastrocolic ligament?
Peritoneal fold that extends between the transverse colon and the greater curve of the stomach
-Part of the greater omentum
What is the falciform ligament?
- Peritoneal fold that attaches to the anterior abdominal wall and liver
- In embryological terms: remnant of the ventral mesentery
What constitutes the mesentery of the small intestine?
The double fold of peritoneum that attached the small bowel (jejenum and ileum) to the posterior abdominal wall
What is the sigmoid mesocolon?
Fold of peritoneum that attaches the sigmoid colon to the posterior abdominal wall (sigmoid mesentery)
For what surgical procedure is a grid-iron (muscle-splitting) incision used?
Appendicectomy
For what surgical procedure is a Kocher incision used?
- Removal of the gallbladder (cholecystectomy)
- Right subcostal region
What surgical procedure uses a Pfannenstiel incision?
- Caesarian section
- Lies horizontally above the pubis symphysis
What is a laparatomy?
When the abdomen is opened through a large vertical (through the linea alba) midline incision which gives access to the abdominal contents
- Laparascopic surgery uses a small series of incisions (a few cm each) through which instruments are passed
- Nowadays, most cholecystectomies and some appendicectomies are performed using laparoscopic surgery
What does the urachus connect?
The urachus connects the allantois to the dome of the bladder during fetal development - should obliterate after the first trimester
What is the consequence of a patent urachus?
Urine can be transferred from the bladder to the umbilicus and leak out
What is the consequence of a patent vitellointestinal duct?
Would allow the transfer of meconium
What substances can chief cells produce?
Gastric lipase and pepsinogen
What substances do parietal cells produce?
HCl and intrinsic factor
Where are G cells located?
Antrum
Outline the factors which stimulate gastrin secretion.
- Peptides/amino acids in stomach lumen
2. Vagal stimulation: acetylcholine, gastrin-releasing peptide
Outline how HCl production is inhibited in the stomach.
- When food leaves, pH drops: food acts as a buffer
- Low pH stimulates D cells which release somatostatin
- Somatostatin inhibits G cells and ECL cells
- Reduced vagal activity: reduced stomach distension
Outline the steps involved in HCl production.
- Water split to produce H+ and OH-
- H+ moved into stomach lumen
- Cl- moved into stomach lumen: HCl formed in stomach lumen
- CO2 combines with OH - - forms HCO3-
- HCO3- moves into bloodstream: alkaline tide
Outline the processes involved in the cephalic phase of digestion.
- 30% of total HCl
- Parasympathetic stimuli: smelling, tasting, chewing, swallowing
- Direct stimulation of parietal cells by vagus nerve
- Stimulation of G cells by vagus nerve: GRP released
- Anticipating food: gastric motility is increased slightly
List what organs can be damaged in a wound at the umbilicus.
Small bowel
List what organs can be damaged in a wound in the left hypochondrium.
- Small bowel
- Large bowel
- Spleen
- Lung tissue potentially injured
List what organ can be damaged in the right flank.
Large bowel: ascending colon
Outline the steps involved in the gastric phase of digestion.
- 60% of HCl produced
- Stomach distension stimulates vagus nerve which stimulates parietal cells and G cells
- Small peptides and amino acids stimulate G cells
- Food acts as a buffer in the stomach - removes inhibition on gastrin production
- Enteric NS and gastrin: strong smooth muscle contractions
Outline the processes involved in the intestinal phase of digestion.
- 10% of HCl production
- Initially chyme stimulates gastrin production - partially digested proteins detected in duodenum (short phase)
- Soon overtaken by inhibition of G cells
- Detection of lipids activates enterogastric reflex: reduces vagal stimulation
- Chyme stimulates CCK and secretin (suppress secretion)
What cells in the stomach secrete mucus and bicarbonate ions?
- Surface mucus cells
2. Neck cells in gastric glands
Outline how mucus and bicarbonate ions protect the stomach lining.
- Form thick viscous alkaline viscous layer that adheres to the epithelium
- Epithelial surface kept at higher pH
State some stomach defence mechanisms.
- Mucus and bicarbonate production
- High turnover of epithelial cells: helps keep epithelia intact
- Prostaglandins: maintain mucosal blood flow, supply epithelium with nutrients
State some factors which breach stomach defences and briefly state the mechanism for each.
- Alcohol: dissolves mucus layer
- Helicobacter pylori: chronic active gastritis
- NSAIDs: inhibit prostaglandins
What are a few consequences of breaching stomach defences?
- Gastritis
- Ulceration
- Reflux disease
State some pharmacological interventions that can be used to decrease stomach acid production.
- H2 blockers: cimetidine, ranitidine
2. Proton pump inhibitors: omeprazole
Which direction does the foregut rotate in?
Clockwise
What is the lesser omentum derived from?
The ventral mesentery
What organ develops within the ventral mesentery?
The liver
What organ develops within the dorsal mesentery?
Spleen
What causes the peritoneal cavity to be divided into the lesser and greater sacs?
- Development of the spleen and liver
2. Foregut rotation
What does the dorsal mesentery develop into?
- The gastrosplenic ligament
2. Ligament from the spleen to the posterior abdominal wall
Outline the derivatives of the mesenteries from anterior to posterior.
- Falciform ligament
- Lesser omentum
- Gastrosplenic ligament
- Connection between spleen and posterior abdominal wall
What is the free edge of the lesser omentum?
Bottom edge of the ventral mesentery
Outline the contents of the free edge of the lesser omentum from top to bottom.
- Hepatic artery
- Common bile duct
- Portal vein