4: Stomach Flashcards
What are the functions of the stomach? (3 things)
- Stores food
- Disinfects food
- Breaks food → chyme
How does the stomach break food down into chyme? (2 things)
- Chemical disruption: acid + enzymes
- Physical disruption: motility
What are the indents in the Stomach mucosa called?
Gastric pits
What do gastric pits open into?
Gastric glands
What are the cells of the Gastric Pits?
Neck cells
What are the cells of the Gastric Glands? (4 things)
- Parietal cells
- Chief cells
- Endocrine cells (G cells)
- SMC
What do Neck cells secrete? (2 things)
(Gastric Pit Cell)
- Mucus
* Sticky so stays on stomach lining - HCO3-
* Secreted into mucus, provides buffer for H+ ions
What do Parietal cells secrete?
(Gastric Gland Cell)
HCl
- Keeps stomach pH below 2
What do Chief cells secrete?
(Gastric Gland Cell)
Proteolytic enzymes (Pepsin)
- Breaks down proteins →peptides
What do Endocrine cells secrete?
(Gastric Gland Cell)
Gastrin
Bind to receptor on Parietal cell → stimulates HCl secretion
What is the mechanism of HCl secretion? (4 steps)
- H2O in Parietal cell → H+ + OH-
- H+ pumped into Stomach through Canaliculi (invaginations in wall)
* Canaliculi has proton pump: H+ pumped agains concentration gradient using ATP - OH- combines with CO2 → HCO3-
- HCO3- secreted into blood / ECF
H+ and HCO3- secreted at 1:1 ratio
Why are the Canaliculi of the stomachs Parietal cells clinically important?
They can be inhibited by Proton Pump Inhibitor Drugs to reduce stomach acid
What are Parietal cells stimulated by? (3 things)
- Ach
- Gastrin
- Histamine
How does Ach stimulate Parietal cells? (3 steps)
- Food arrives → Gastric distension (stretching)
- Stretching causes Post-ganglionic PS neurones to release Ach
- Ach acts on Muscarinic (M3) receptors on Parietal cells
How does Gastrin stimulate Parietal cells? (2 steps)
- Presence of Ach stimulates → Endocrine Cells (G Cells) to secrete Gastrin
- Gastrin binds to surface receptors on Parietal cell
What is Gastrin inhibited by?
Low stomach pH (feedback control)
Because Gastrin makes Parietal cells make HCl so if pH already low then you don’t neeeeeeed it
How does Histamine stimulate Parietal cells? (3 steps)
- Gastrin + Ach stimulate Mast Cells → release Histamine
- Histamine binds to H2 receptors on Parietal cells
- Stimulates acid secretion via cAMP
What are the 3 phases of Gastric secretion?
- Cephalic Phase (High)
- Gastric Phase (High)
- Intestinal Phase (Low)
How is Gastric secretion stimulated in the Cephalic phase? (High acid) (3 steps)
- Sight, smell, swallowing → activates PNS
- PNS stimulates Ach release
- Ach stimulates Parietal cells
- Directly
- via Histamine
Called cephalic phase because sight smell and swallowing happens in the head innit
How is Gastric secretion stimulated in the Gastric phase? (High acid) (5 steps)
- When food reaches stomach → Gastric distensions (stretching)
- Stretching stimulates Ach release (via Post-ganglionic PS neurones)
- Food also buffers acid, increasing the pH, this disinhibits Gastrin → Gastrin secreted
- Acid + enzymes breakdown proteins → peptides
- Peptides stimulate Gastrin
Called gastric phase because everything happens in stomach innit
How is Gastric secretion inhibited in the Intestinal phase? (Low acid)
- When chyme leaves stomach → stimulates 2 hormones:
- Cholecystokinin (CCK)
- Gastric Inhibitory Polypeptide
- CCK & GIP antagonise Gastrin → Low acid secretion
- No food to buffer acid so pH decreases → low pH inhibits Gastrin → Low acid secretion
Called intestinal phase because food has gone to intestines now innit
What drugs can be used to reduce Gastric acid secretion? (2 things)
- Anti-histamine
- Proton Pump Inhibitor
How does Anti-histamine reduce gastric acid secretion? (2 steps)
- Inhibits histamine @ H2 receptors (on Parietal cells)
- Removes Gastrin / Ach signal amplification
How do Proton Pump Inhibitors reduce gastric acid secretion?
Prevent H+ from being pumped through Parietal cell Canaliculi
What are the properties of stomach mucus? (2 things)
- Sticky: stays on stomach lining
- Basic: buffers H+
What layer does mucus form in the stomach?
An “unstirred layer”
Where ions can’t move easily in
How does the “unstirred” layer of the stomach buffer H+? (3 steps)
- H+ ions diffuse into layer from stomach lumen
- HCO3- secreted into layer from Neck Cells (Gastric Pit Cells)
- Because layer is unstirred (ion can’t move easily in): HCO3- stays close to surface cells → surface pH stays above 6
What are HCO3- and Mucus secretions stimulated by?
Prostaglandins
- (Which are promoted by most factors that stimulate acid secretion)
What things can breach the stomachs defences? (3 things)
- Alcohol
- Helicobacter Pylori
- NSAIDs
How does alcohol breach the stomachs defences?
Dissolves mucus → acid attacks stomach
How does Helicobacter Pylori breach the stomachs defences?
Infects surface cells → No mucus / HCO3- produced
How do NSAIDS breach the stomachs defences?
Inhibit prostaglandins → no HCO3- / mucus produced
What can form if the stomach defences are breached?
Peptic ulcers
What is the treatment for breached stomach defences / peptic ulcers? (2 things)
- Reduce acid secretion (anti-histamine / proton pump inhibitors)
- Abx to eliminate Helicobacter Pylori (if needed)
What reflex allows us to eat larger meals?
Receptive Relaxation
What is Receptive Relaxation?
Stomach reflex: Gastric fundus dilates when food passes down pharynx + oesophagus
How does Receptive Relaxation occur? (3 steps)
- Food goes down pharynx + oesophagus
- Neural reflex from Vagus nerve triggers stomach wall relaxtion → stomach pressure doesn’t increase
- Pressure not increasing limits reflux + allows us to eat larger meals
What happens if the Vagus nerve is damaged? (Receptive relaxation)
Stomach pressure increase NOT inhibited by Receptive Relaxation → Reflux + Can’t eat large meals
What are the rhythmic contractions of the stomach? (2 steps)
- Pacemaker in Cardiac region of Stomach → drives Longitudinal + Circular muscles contrctions
- Regular accelerating peristaltic contractions from Cardia → Pylorus
How is the stomach emptied?
- Chyme reaches Pyloric region
- Small squirt ejected into intestine before peristaltic wave comes and shuts it
* 3 persistaltic waves / min → 3 squirts / min
What are the squirts of gastric emptying affected by? (3 things)
- Rate of peristaltic wave acceleration
- Intestinal hormones
- Fat + low pH slows down emptying
What are some Gastric disordes? (4 things)
- Gastro-oesophageal Reflux Disease (GORD)
- Peptic Ulcer Disease (PUD)
- Helicobacter Pylori
- Gastrits
What are the clinical features of Gastro-oesophogeal Reflux Disease (GORD)?
Dyspepsia (heart burn)
- Worse @ lying down / bending / hot drinks
How is Gastro-oesophogeal Reflux Disease (GORD) diagnosed and investigated? (2 things)
- Clinical diagnosis done on symptoms alone
- If Hiatus Hernia suspected: investigate by Endoscopy
How is Gastro-oesophogeal Reflux Disease (GORD) managed? (6 things)
- Lifestyle
- Lose weight
- Reduce smoking / alcohol
- Reduce chocolate + fatty foods
- Medication
- Antacids
- Proton Pump Inhibitor → reduces acid secretion from Parietal cells
- Anti-histamines (H2 antagonists) → reduces acid secretion from Parietal cells
What happens to the stomach cells in Peptic Ulcer Disease (PUD)?
Break in superficial epithelial cells → Penetrates down to Muscularis Mucosa
What causes Peptic Ulcer Disease (PUD)?
NSAIDS
- Inhibit prostaglandin production → reduces mucus production
What are the clinical features of Peptic Ulcer Disease (PUD)? (2 things)
- Burning epigastric pain
- Persistant + severe pain: suggests ulcer penetration into other organs
- Back pain: suggests posterior penetration of ulcer
- Weight loss / anorexia
How is Peptic Ulcer Disease (PUD) investigated? (2 things)
- Investigate H. Pylori infections
- Endoscopy for older patients → rule out cancer
How is Peptic Ulcer Disease (PUD) managed? (2 things)
- If due to H. Pylori: Triple Therapy:
- Proton Pump Inhibitors
- Abx
- Anti-histamine (H2 antagonists)
- If taking NSAIDs: Stop + review
What are the complications of Peptic Ulcer Disease (PUD)? (2 things)
- Perforations of ulcer → into Peritoneal cavity
- Gastric outlet obstruction
What is Chronic Gastritis caused by?
Helicobacter Pylori
What are the features of Helicobacter Pylori? (3 things)
- Aerobic
- Produces urease enzyme
- Resides in stomach of infected person
How does Helicobacter Pylori survive in the stomach?
- Produces urease enzyme → produces ammonia
- Ammonia neutralised acid → allows H. Pylori to survive
How does Helicobacter Pylori damage the stomach? (2 things)
Damages epithelium by:
- Releasing enzymes
- Inducing apoptosis
How is Helicobacter Pylori diagnosed? (3 things)
- igG in serum
- Urea breath test
- Culture gastric sample (taken by endoscopy)
What is the treatment for Helicobacter Pylori?
Triple Therapy:
- Proton Pump Inhibitors
- Abx
- Anti-histamine (H2 antagonists)
What can chronic gastritis cause?
Ulceration
Endocrine cells (G cells) release gastrin (Hypergastrinaemia) → increases acid production → ulceration
What are the 5 parts of the stomach?
- Cardia
- Fundus
- Body
- Antrum
- Pylorus
What are the 2 stomach sphincters?
- Inferior Oesophageal Sphincter
- Pyloric Sphincter
What is the Z line of the GI system?
Where Squamous mucosa of oesophagus meets Columnar mucosa of stomach
What is superior to the Z line of the GI system?
Diaphragmatic musculature: forms LOWER OESOPHAGEAL SPHINCTER
What is the Lower Oesophageal sphincter coupled with to prevent stomach reflex?
Cardiac notch of stomach
What is the Pyloric sphincter made out of?
Thickened circular muscle coat
What does the Pyloric sphincter of the muscle control?
The squirts of the stomach into the duodenum
What is the gastric mucosa like when empty?
- Longitudinal folds (rugae)
- Gastric canal forms between folds along Lesser Curvature of stomah → allows saliva & small parts of food → Pylorus
How are the different parts of the stomach histologically different?
- Cardia:
* Neck cells → mucus - Fundus & Body
- Neck cells → mucus
- Parietal cells → acid
- Chief cells → pepsinogen
- Pylorus
- Neck cells → mucus
- Endocrine Cells (G cells) → Gastrin
What are the peritoneal folds around the stomach? (2 things)
- Greater Omentum
- Lesser Omentum
What is the Greater Omentum? (3 points)
- 4 layered peritoneal fold
- Hangs down from GREATER curvature of stomach
- Folds back up → attaches to anterior surface of transverse colon + its mesentry
What is the Lesser Omentum? (3 points)
- 2 layered peritoneal fold
- Connects LESSER curvature of stomach + proximal part of duodenum → liver
- Connects stomach to portal triad
What is the blood supply tree to the stomach?
What is the blood supply to the Lesser Curvature of the stomach?
L & R Gastric Arteries
L esse R
What is the blood supply to the Greater Curvature of the stomach?
L & R Gastro-omental Arteries
What is the blood supply to the Fundus & Body of the stomach?
Posterior Gastric arteries
What is the venous drainage of the stomach? (4 things)
- L & R Gastric → Hepatic portal vein (HPV)
- Short Gastric → Splenic vein → joins Superior Mesenteric Vein (SMV) → HPV
- L Gastro-omental → splenic vein → joins SMV → HPV
- R Gastro-omental → SMV → joins splenic vein → HPV
