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Block 1 AR > Stomach > Flashcards

Stomach Flashcards

1
Q

Which structure related to the stomach can limit the spread of infection?

A

Greater omentum as it can adhere to infected sites

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2
Q

Where is the lesser omentum?

A

Between liver and stomach

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3
Q

What is special about the splenic artery?

A

Tortuous so can stretch

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4
Q

What does free border of lesser omentum become?

A

Hepatoduodenal ligament

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5
Q

What is the pringle manoeuvre?

A

Clamping of hepatoduodenal ligement during surgery to prevent excessive bleeding from liver

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6
Q

What are the 3 phases of gastric motility?

A

Receptive relaxation
Mixing
Emptying

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7
Q

Which 2 electrical modalities contribute to the coordinated contraction of smooth muscle in the stomach?

A

Slow waves

Action potentials

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8
Q

Which phase of gastric motility occurs in the orad region?

A

Receptive relaxation

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9
Q

How does the stomach expand to accommodate food?

A

Unfolding of rugae

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10
Q

Describe the mixing process in the stomach

A

Peristaltic waves move food towards antrum
When approaching antrum, contraction force increases and pyloric sphincter shuts
This forces most of the food back into the stomach - retropulsion

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11
Q

List 5 functions of the stomach

A 
Storage of food
Minimise ingestion of bacteria
Dissolve and partly digest macromolecules
Regulate rate of gastric emptying
Secrete intrinsic factor
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12
Q

Which reflex is activated when food enters digestive system?

A

Vagovagal

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13
Q

List 3 things which stimulate acid production in the stomach

A

ACh
Histamine
Gastrin

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14
Q

List 3 things which inhibit gastric acid secretion

A

Somatostatin
Prostaglandin
Enteric hormones

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15
Q

What disruption of acid base balance can excessive vomiting cause?

A

Metabolic alkalosis

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16
Q

What 2 problems can be caused by hypochlorhydia?

A

Increased vulnerability to GI bacterial infection

Impaired ability to digest and absorb certain nutrients and B vitamins

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17
Q

What does carbonic anhydrase do?

A

Catalyses reaction producing H+ and HCO3 from H2O and CO2

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18
Q

Give 2 functions of the pyloric sphincter

A

Prevent regurgitation

Allow regulated emptying of stomach

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19
Q

What effect does CCK have on the pyloric sphincter?

A

Constriction

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20
Q

How is gastric emptying regulated?

A

By duodenal contents. Receptors on duodenal and jejunal mucosa detect acidity, osmotic pressure, fats, amino acids, peptides etc.
A high fat meal, high acidity or very hypertonic would all decrease the rate of gastric emptying

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21
Q

What needs to contract to bring about emptying of the stomach?

A

Contraction of stomach, pylorus and proximal small intestine

Relaxation of pyloric sphincter

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22
Q

Name the 4 parts of the stomach

A

Fundus
Body
Pyloric antrum
Pyloric canal

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23
Q

What is a mesentery?

A

Mesenteries are double-layered folds of peritoneum attaching the gut tube to the body wall

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24
Q

What does the free edge of the lesser omentum contain?

A

Contains common bile duct, hepatic artery, portal vein

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25
What does the greater omentum contain?
Blood vessels and fat
26
Describe the blood supply to the stomach
Coeliac trunk derived. Left and right gastric form anastamotic loop which supplies lesser curvature. Splenic artery branches to the short gastric which supplies fundus. Spenic artery also branches to form left gastro-epiploic/omental which forms anastamotic loop on greater curvature with right gastro-epiploic/omental which comes from gastroduodenal. Gastroduodenal also branches to form superior pacreaticoduodenal.
27
What does gastric motility allow the stomach to do?
Serve as reservoir for large volume Fragment food into smaller particles and mix it with gastric secretions Empty gastric contents at a controlled rate
28
What is the volume of the empty stomach?
50ml
29
Describe receptive relaxation
Food is swallowed, smooth muscle in stomach wall orad region relaxes Enables stomach to increase volume to 1.5L with little increase in pressure
30
Which nerve mediates receptive relaxation?
Vagus coordinating with enteric nerve plexuses | Enteric nerves release NO and serotonin to mediate smooth muscle relaxation
31
What is the predominant motor activity of the orad region?
Accommodation of ingested food | Muscle layers are thin so contractions here are weak
32
What is the basic electric rhythm of the GI tract?
Smooth muscle cells undergo spontaneous cycles of depolarisation and repolarisation
33
What are slow waves?
Fluctuations in membrane potential spreading from adjacent sections of muscle Gastric slow waves at 3/min Rhythm generated in pacemaker zone Coordinate contractions by controlling appearance of action potentials
34
What is the pyloric sphincter?
Ring of smooth muscle and connective tissue between gastric antrum and duodenum
35
Which hormones cause constriction of the pyloric sphincter?
CCK, gastrin, GIP, secretin
36
What effect do enteric hormones have on gastric emptying?
Inhibit antral contractions Constriction of pyloric sphincter Decrease gastric emptying
37
How much gastric juice is released per day?
3L
38
What are the main components of gastric juice?
Hydrochloric acid Mucus Enzymes - pepsinogens, gastric lipase Intrinsic factor
39
What are the 5 cell types in gastric pits?
``` Surface mucus cells Mucus neck cells Parietal cells - HCl and intrinsic factor Chief cells - pepsinogen G cells - gastrin ```
40
Where are parietal cells located?
Proximal 80% of stomach, oxyntic gland area
41
Where are G cells located?
Antrum, pyloric gland area
42
What are gastric hormones?
Gastrin Histamine Somatostatin
43
What is gastrin?
Principal hormone secreted from gastric epithelium Polypeptide secreted by G cells Stimulates acid secretion, pepsinogens, mucus, HCO3 Stimulates gastric motility Inhibits gastric emptying Stimulates pancreatic secretions, insulin release, intestinal motility
44
What effect does histamine have on GI tract?
Paracrine agent Secreted by enterochromaffin like cells (ECL cells) close to parietal cells Stimulation of acid secretion Increased local blood flow
45
What effects does somatostatin have on GI tract?
Polypeptide synthesised by D cells in antrum and body of stomach Inhibits gastrin release Inhibits acid secretion
46
What is special about the shape of parietal cells?
Truncated pyramidal, apex oriented towards gastric lumen Extensive invaginations of luminal membranes forming canaliculi lined with ion pumps High mitochondrial content
47
How is gastric acid produced?
H+ and HCO3 produced from H20 and CO2 H+ secreted into lumen by H/K ATPase HCO3 moves out of basolateral membrane via antiport with Cl- Cl- diffuses passively into lumen via Cl channel
48
How does prostaglandin inhibit gastric acid secretion?
Blocks activity of histamine on parietal cells
49
How does somatostatin inhibit gastric acid secretion?
Acts on ECL cell to reduce histamine release | Acts on parietal cell to block effects of gastrin
50
What is mucus?
Mixture of glycoproteins and glycopolysaccharides Forms a viscous gel on luminal surface with alkaline secretions trapped in it Gastric mucosal barrier to protect against acid, enzymes and mechanical damage Allows cells to be kept at near neutral pH despite low pH of stomach
51
Describe renewal of the gastric mucosal barrier
Local irritation to mucosa stimulates production of prostaglandins which increase mucus and HCO3 production and inhibit acid secretion. Also promote healing Stimuli of acid secretion also promote mucus and HCO3 production
52
Why can excessive use of NSAIDs cause stomach damage?
Blocks production of prostaglandins which act to reduce acid secretion, increase mucus and HCO3 production and promote healing
53
What are antacids?
Base, counteracts stomach acidity by buffering, so raise pH
54
What are alginates?
Anionic polysaccharides that form a viscous gel on binding water Increase viscosity of stomach contents so protect from acid reflux Gel raft floats on stomach contents
55
What is Misoprostol?
Stable analogue of prostaglandin 1 Inhibits acid secretion and mucosal blood flow Augments secretion of mucus and HCO3 Given to prevent gastric damage that can occur with chronic use of NSAIDs
56
Give examples of histamine receptor antagonists
Cimetidine Ranitidine Famotidine Nizatidine
57
How effective are histamine receptor antagonists at reducing acid secretion?
Decrease basal and stimulated secretion by 90%
58
In which patients should caution be used with H2 antagonists?
Hepatic and renal failure | Pregnancy and breast feeding
59
Give examples of PPIs
``` Omeprazole Lansoprazole Esomeprazole Pantoprazole Rabeprazole ```
60
What are advantages of PPIs over H2 antagonists?
Inactive at neutral pH so activated where required in acidic stomach Accumulate in canaliculi of parietal cells
61
What is pepsin?
``` Secreted as Pepsinogen by chief cells Exposure to low pH causes conversion to pepsin It's secretion parallels acid secretion Active only at low pH Accelerates protein digestion ```
62
What is intrinsic factor?
Glycoprotein Secreted by parietal cells Essential for Vit B12 absorption in small intestine
63
What part of the stomach will you likely be able to see on a radiograph when the patient is standing?
Fundus because it is filled with air

Block 1 AR (19 decks)

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