Gastric Motility & Secretion

Question 1

Outline the functions of the stomach

Answer 1

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

Question 2

How does the stomach function as a reservoir for large volume of food? (Receptive relaxation)

Answer 2

Submucosa highly folded into rugae = can increase in volume with little change in pressure as unfolding rather than unstrecthing

Question 3

Describe the movements of the stomach - what’s their role?

Answer 3

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

Question 4

How is receptive relaxation controlled?

Answer 4

PNS, vagus nerve

ENS release NO and 5-HT to relax smooth muscle wall

= allows stomach to unfold and store food

Question 5

How is gastric motility controlled?

Answer 5

Slow waves and action potentials

ANS and ENS

Question 6

Outline the function and anatomy of the pyloric sphincter

Answer 6

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

Question 7

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?

Answer 7

High fat digestion products
Highly acidic
Very hypertonic

Question 8

What makes up gastric juice (gastric secretions)?

Answer 8

HCL
Mucous
Enzymes (pepsinogens, gastric lipase)
Intrinsic factor

Question 9

3 gastric hormones: gastrin, histamine and somatostatin. What are their roles?

Answer 9

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

Question 10

What stimulates and inhibits gastric acid secretion?

Answer 10

Gastrin, histamine and ACh stimulate

Somatostatin, prostaglandins and intestinal hormones inhibit

Question 11

Outline the structure of gastric glands

Answer 11

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

Question 12

What’s the mechanism of HCL secretion by parietal cells?

Answer 12

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

Question 13

What’s mucous composed of and where is it secreted from?

Answer 13

Glycoproteins and glycopolysaccharides

Necks of gastric glands by epithelial cells

Question 14

How is the stomach protected against autodigestion?

Answer 14

Gastric mucosal barrier requires both mucous and HCO3- to form a gel on luminal surface to protect stomach wall against acid/mechano damage

Question 15

What effect do prostaglandins have on mucosal barrier?

Why can NSAIDs lead to stomach ulcers?

Answer 15

Local irritation to mucosa stimulates prostaglandins to increase mucous and HCO3- secretion to renew the barrier and promote local healing

Question 16

What drug classes are used to treat gastric acid disorders?

Answer 16

Antacids and Alginates
Proton pump inhibitors
H2 Histamine Receptor Antagonists

Question 17

What’s the prescribed drug of choice for reflux oesophagitis?

Answer 17

Proton pump inhibitors (omeprazole/lansoprazole)

Question 18

What’s the role of Helicobacter Pylori with regards to peptic ulcers?
How is it treated?

Answer 18

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

Question 19

What’s A/Hypochlorhydria?

Answer 19

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

Question 20

What are the 4 layers of the GI tract that are the same form the lower oesophagus -> anal canal

Answer 20

Mucosa -> Submucosa -> Muscularis -> Serosa

Question 21

Where’s intrinsic factor released from and what’s its role?

Answer 21

Parietal cells -> necessary for vitamin B12 absorption