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Semester 3 - Gastrointestinal > 7. Intro to the Stomach > Flashcards

7. Intro to the Stomach Flashcards

1
Q

What are the basic functions of the stomach?

A

• Short term storage facility
• Disrupt food
o Vigorous contractions of the smooth muscle
• Continue/commence digestion - fat and carbs
o Mainly proteins
• DisinfecT

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2
Q

Where is the stomach?

A

left upper quadrant, between liver and spleen

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3
Q

What are the different parts of the stomach?

A

Cardia, fundus, body, antrum, pylorus

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4
Q

What is the cardia of the stomach?

A

Surrounds the superior opening of the stomach at the T11 level.

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5
Q

What type of epithelium is present in the stomach?

A

Columnar

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6
Q

what is the transition of epithelium from oesophagus to stomach and why?

A

Abrupt transition of stratified squamous to columnar

o This is about secretion

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7
Q

What are the stomach folds called?

A

Rugae

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8
Q

What are the different secretory cells of the stomach and where do they exist?

A

Mucous cells, Parietal cells, Chief cells, G cells. Found • Cover surface and extend into pits/glands

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9
Q

What are the layers of smooth muscle in stomach?

A

Internal oblique, circular, outer longitudinal

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10
Q

Why does stomach have extra layer of smooth muscle?

A

Mix/grind contents, aid digestion, Move contents along

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11
Q

What is the difference in contractions between the upper and lower stomach?

A

Upper: sustained contractions, creates basal tone

Lower: strong peristalsis mixes stomach content, coordinated, contracts every 20 sec, proximal to distal

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12
Q

How does shape of stomach aids flow of contents?

A

Larger proximally and smaller distally
Distal stomach walls thicker + more muscular than proximal.

When stomach contracts, food moves faster as it moves distally. This helps accelerate smaller particles towards pyloric sphincter first, and leave larger particles, that need to be broken down further in stomach till they’re smaller.

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13
Q

Forceful contractions of the stomach serve 3 purposes - which are?

A

1) MOVEMENT through stomach
2) BREAKDOWN/mech digestion
3) SEPARATION of large + small molecules

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14
Q

How often is chyme ejected into duodenum?

A

3 times a minute (every 20 seconds)

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15
Q

Name three ways the stomach prevents gastric reflux?

A

> Angle of entry
LOS + its components - smooth muscle
- crural diaphragm
Receptive relaxation

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16
Q

Explain how RECEPTIVE RELAXATION prevents gastric reflux?

A

peristalsis of oesophagus causes reflex relaxation of proximal stomach so fundus distends and stomach expands so that it can fill without significant rise in pressure

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17
Q

Explain how angle of entry of stomach prevents gastric reflux?

A

Angle of entry is acute so harder for fluid to move backwards

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18
Q

What is the difference between the function of the PYLORIC SPHINCTER + LOS?

A

Pyloric - controls release of chyme out of stomach

LOS - prevents gastric reflux

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19
Q

Name the muscles that make up the LOS.

A

Intrinsic Smooth muscle of stomach

Crural muscles of diaphragm

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20
Q

Where is the splenic artery relative to the stomach?

A

Behind

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21
Q

What branch of the splenic artery supplies the what part of the stomach?

A

Left gastric epiploic artery, supplies left side of greater curvature of stomach

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22
Q

what are the branches of the splenic artery?

A

Left gastro-epiploic artery

short gastric artery

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23
Q

when does common hepatic artery become proper hepatic artery

A

After giving off the gastrodudenal artery

24
Q

What branch of the gastroduodenal artery supplies what part of the stomach?

A

right gastric epiploic artery, supplies right side of greater curvature of stomach

25
Q

what does the right gastro-epiploic artery anastomose with?

A

left gastro-epiploic artery from splenic artery

26
Q

what does the short gastric artery from teh splenic artery supply?

A

fundus of stomach

27
Q

What is the first branch of the proper hepatic artery and what does it supply?

A

Right gastric artery supplies the lesser curvature of the stomach

28
Q

What does the left gastric artery supply?

A

lesser curvature of stomach

29
Q

Where is the gastrodudenal artery relative to the stomach and what is the clinical significance of this?

A

Travels behind pylorus/duodenum. Ulceration in antrum can perforate this vessel and cause bleeding into the stomach

30
Q

what are the branches of the proper hepatic artery after giving of gastro duodenal?

A

right hepatic
left hepatic
cystic

31
Q

Where does venous drainage of stomach go?

A

Hepatic portal vein

32
Q

Why does stomach relax when receiving food and what is it mediated by?

A

Vagally mediated,

  • allows food to enter stomach without raising intra-gastric pressure too much
  • Prevents reflux of stomach contents during swallow
33
Q

How does the acidity of the stomach aid digestion?

A

◦ Helps unravel proteins

◦ Activates proteases (Pepsinogen to Pepsin)

34
Q

Where are chief cells found? Function?

A

In gastric gland within gastric pit. Secretes pepsinogen. Uses HCL from parietal cells to convert pepsinogen to pepsin to breakdown proteins.

35
Q

Why isn’t stomach acid produced 24/7?

A

Stomach enviroment would be hostile

Also requires energy (H+/K+ ATPase) so would be energy inefficent to have it going all the time.

36
Q

How does the stomach produced stomach acid?

A

Parietal cells contain tubulovesicles, which contain proton pumps (H+/K+ ATPases), which move H+ into stomach lumen.

37
Q

how is acid production prevented in resting phase and activated in stimulated phase in the parietal cell?

A

in the resting phase, tubulovesicles containing proton pumps are not associated with the apical (containing K+ channels) and tubulovesicles lack K+ permeability so no acid production as K+ needed for H+/K+ATPase to work.

when stimulated, tubulovesicles move towards the apical membrane so the K+ channels and proton pumps brought together

38
Q

What is the distribution of secretory cells in the stomach?

A

Cardia - predominantly mucus secretion
Fundus/body - Mucus, HCL, pepsinogen
Antrum/Pylorus - Gastrin, somatostatin

39
Q

what stimulates acid production?

A

◦ sensory trigger - smell, sight, taste
◦ gastric triggers - stretch, presence of amino acids and small peptides, food acts as a buffer (Ph increases and inhibition on acid production remove)
◦ intestinal triggers - chyme in duodenum

40
Q

What are the 3 phases of digestion? Which produces the most HCL?

A

Cephalic - 30%
Gastric - most (60%)
Intestinal - least (10%)

41
Q

What are the parietal cells stimulated by?

A

◦ Gastrin
◦ Histamine
◦ Ach (vagal stimulation)

42
Q

What area G cells stimulated by?

A

◦ Peptides/amino acids in stomach lumen

◦ Vagal stimulation (Acetylcholine & Gastrin-releasing peptide (GRP))

43
Q

What is gastrin secreted into?

A

Blood stream

44
Q

what is the action of gastrin?

A

◦ binds to and stimulates CCK receptors on parietal cells to increase acids production
◦ stimulates CCK receptors on enterochromaffin like cell (ECL) which produce histamine

45
Q

what is the action of histamine?

A

acts on histamine receptors on parietal cells to stimulate acid production

46
Q

other than gastrin, what stimulates ECL?

A

vagal stimulation - muscarinic receptor on ECl stimulated by ACh

47
Q

what are the effects of vagal stimulation?

A
  1. activates muscarinic receptors on parietal cells
  2. activate muscarinic receptors on ECL stimulating histamine release which act on histamine receptors on parietal cells
  3. activate muscarinic receptor on G cell, stimulating gastrin release

1-3 = release of ACh

  1. causes release of GRP which activate G cells to release gastrin
48
Q

How is HCL production inhibited?

A 
• Essentially an inhibition of G cells
• When food leaves stomach pH drops
o Food is a buffer
• Low pH activates D cells
• D cells release somatostatin
o Somatostatin inhibits G cells (and ECL cells)

• Stomach distension reduces
o Reduced vagal activity

49
Q

what are the 3 phases?

A
  • Cephalic
  • Gastric
  • Intestinal
50
Q

What happens during cephalic phase of digestion and how much HCL is produced?

A

Vagus nerve stimulates gastric secretion even before food is swallowed.
• Parasympathetic stimuli
o Smelling, tasting, chewing, swallowing
• Direct stimulation of parietal cell by vagus nerve
• Stimulation of G cells by vagus (GRP released)

51
Q

What happens during gastric phase of digestion and how much HCL is produced?

A

• Distension of stomach stimulates vagus
o Which then stimulates Parietal cells and G cells (+ECL)
• Presence of amino acids and small peptides
o Stimulate G cells
• Food acts as a buffer in stomach
o Removes inhibition on Gastrin production

52
Q

What happens during intestinal phase of digestion and how much HCL is produced?

A

• Chyme initially stimulates Gastrin secretion
• Partially digested proteins detected in duodenum
o Short phase
• Soon overtaken by inhibition of G cells
• Presence of lipids activate enterogastric reflex
o Reduces vagal stimulation
• Chyme stimulates CCK and secretin (help suppress secretion)

53
Q

Explain how HCL is produced in parietal cells

A
  • water and CO2 combine to form H2CO3 which splits into H+ and HCO3- in the presence of carbonic anhydrase.
  • HCO3- remved from basal surface of parietal cell into venous blood via Cl-/HCO3- antiporter - alkaline tide
  • Cl- channel on apical surface allow Cl- to leave cell
  • H+ leaves apical surface via H+/K+ ATPase
  • H+ combines with Cl- outside of parietal cell to form HCl
54
Q

What maintains potassium levels in the lumen of the stomach/

A

Apical K+ channel protein (moves K+ out of parietal cells and H+/K+ ATPase moves K+ into the cell)

55
Q

How is the lining of the stomach protected from the acidity?

A
  1. Mucin is secreted by the foveolar cells
    o Forms viscous mucus layer that adheres to epithelium and helps prevent physical damage from food
  2. HCO3 ions are secreted into mucus layer to provide a (pH neutral) barrier against the stomach acid
  3. Rich blood supply to gastric mucosa can remove and buffer acid that has breached mucus layer
  4. Prostaglandins are released that promote the above processes
  5. High turnover of epithelial cells
    o Helps keep epithelia intact
56
Q

What effect do prostaglandins have on the mucus lining in the stomach and what effects prostaglandin release?

A
  1. increase mucosal blood flow
  2. support mucus layer
  3. generally protective
    - NSAIDs decrease prostaglandins
57
Q

what things breach stomach defences?

A 
• Alcohol
o Dissolves mucus layer
• Helicobacter pylori
o Chronic active gastritis
• NSAIDS
o Inhibits prostaglandin

Semester 3 - Gastrointestinal (17 decks)

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