Gastric Motility & Secretion Flashcards
Outline the functions of the stomach
Store food
Minimise ingestion of bacteria
Dissolve and partially digest macromolecules
Regulates rate at which contents emptied into SI
Secretes intrinsic factor, allowing body to absorb vitamin B12
How does the stomach function as a reservoir for large volume of food? (Receptive relaxation)
Submucosa highly folded into rugae = can increase in volume with little change in pressure as unfolding rather than unstrecthing
Describe the movements of the stomach - what’s their role?
Fragment food into smaller particles to mix with gastric secretions and them empty into duodenum
Peristaltic waves towards antrum = mix
PLS shut and antrum forces food back to body of stomach = retropulsion
How is receptive relaxation controlled?
PNS, vagus nerve
ENS release NO and 5-HT to relax smooth muscle wall
= allows stomach to unfold and store food
How is gastric motility controlled?
Slow waves and action potentials
ANS and ENS
Outline the function and anatomy of the pyloric sphincter
Ring of smooth muscle between gastric antrum and duodenum
ANS control (vagus) and hormones (CCK, gastrin, GIP, secretin)
Allows regulated emptying of gastric contents and prevents regurgitation of duodenal products
Receptors on the mucosae of duodenum and jejunum sense acidity/osmotic pressure/fats to release hormones which control gastric emptying.
When is the rate of gastric emptying reduced?
High fat digestion products
Highly acidic
Very hypertonic
What makes up gastric juice (gastric secretions)?
HCL
Mucous
Enzymes (pepsinogens, gastric lipase)
Intrinsic factor
3 gastric hormones: gastrin, histamine and somatostatin. What are their roles?
Gastrin = inhibits emptying and stimulates motility and acid secretion
Histamine = paracrine agent secreted by ECL cells to stimulate secretion and local blood flow for metabolism and contraction
Somatostatin = inhibits gastrin release and acid secretion
What stimulates and inhibits gastric acid secretion?
Gastrin, histamine and ACh stimulate
Somatostatin, prostaglandins and intestinal hormones inhibit
Outline the structure of gastric glands
Gastric pits extend into the mucosa, lined with 4 types of secretory epithelial cells
Surface and neck mucous cells
Parietal cells - HCL and IF
Chief cells - pepsinogen
G cells - gastrin
What’s the mechanism of HCL secretion by parietal cells?
H+ secreted into lumen by H+/K+ ATPase pump
HCO3- moves out of cell via anti port with Cl-
Cl- diffuses passively into lumen via Cl- channel
=HCL formed
What’s mucous composed of and where is it secreted from?
Glycoproteins and glycopolysaccharides
Necks of gastric glands by epithelial cells
How is the stomach protected against autodigestion?
Gastric mucosal barrier requires both mucous and HCO3- to form a gel on luminal surface to protect stomach wall against acid/mechano damage
What effect do prostaglandins have on mucosal barrier?
Why can NSAIDs lead to stomach ulcers?
Local irritation to mucosa stimulates prostaglandins to increase mucous and HCO3- secretion to renew the barrier and promote local healing
What drug classes are used to treat gastric acid disorders?
Antacids and Alginates
Proton pump inhibitors
H2 Histamine Receptor Antagonists
What’s the prescribed drug of choice for reflux oesophagitis?
Proton pump inhibitors (omeprazole/lansoprazole)
What’s the role of Helicobacter Pylori with regards to peptic ulcers?
How is it treated?
Spiral shaped gram negative bacterium that damages stomach and duodenal tissue - penetrates mucosal barrier facilitating acid penetration
Treated with combination of antibiotics and proton pump inhibitors
What’s A/Hypochlorhydria?
Absence/deficiency of HCL in gastric juice = impaired ability to absorb and digest certain nutrients (iron and vitamin Bs) and increased susceptibility of GI tract to bacterial infections
What are the 4 layers of the GI tract that are the same form the lower oesophagus -> anal canal
Mucosa -> Submucosa -> Muscularis -> Serosa
Where’s intrinsic factor released from and what’s its role?
Parietal cells -> necessary for vitamin B12 absorption
