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3A week 1 - upper GI tract > gastric secretory function > Flashcards

gastric secretory function Flashcards

1
Q

7 functions of the stomach

A
  1. reservoir
  2. mixing
  3. tituration
  4. secretion
  5. digestion
  6. defence
  7. absorption
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2
Q

what are the 3 sections to the stomach

A
  1. fundus
  2. body
  3. antum
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3
Q

what landmark signifies the end of the stomach

A

pyloric sphincter

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4
Q

what does the antrum produce (3)

A
  1. mucus
  2. pepsinogen
  3. gastrin
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5
Q

what does the stomach body produce(3)

A
  1. mucus
  2. pepsinogen
  3. HCl
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6
Q

what role does the stomach play in RBC production

A

secretes intrinsic factor which allows B12 to be absorbed -> recquired for haemaglobin formation

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7
Q

what are the exocrine gastric secretions (3)

A
  1. HCl (aka gastric acid)
  2. pepsinogen
  3. intrinsic factor
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8
Q

what are the endocrine gastric secretions (3)

A
  1. gastrin
  2. leptin
  3. ghrelin
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9
Q

what are the paracrine gastric secretions (2)

A
  1. somatostatin
  2. histamine
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10
Q

what are the 4 types of gastric control

A
  1. exocrine
  2. endocrine
  3. paracrine
  4. neurocrine
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11
Q

how does the body prevent itself from getting gastric ulcers due to HCl

A
  1. tight control system - acid only produced when needed
  2. defence and repair mechanisms - HCO3- for buffering, rapid repair
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12
Q

why is there a high energy requirement for HCl secretion

A

H+ must be actively pumped against its gradient which requires lots of ATP

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13
Q

what are the defensive forces of the stomach (against HCl/peptic enzymes - 6)

A
  1. surface mucus secretion
  2. bicarbonate secretion into mucus (buffer)
  3. mucosal blood flow
  4. apical surface membrane transport
  5. epithelial regenerative capacity
  6. elaboration of prostaglandins
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14
Q

what are the 7 main cell types of the stomach and what do they secrete

A
  1. parietal cell - HCl and intrinsic factor
  2. chief cell - pepsinogen, leptin
  3. enterochromaffin-like cell (ECL) - histamine
  4. G-cell - gastrin
  5. D-cell - somatostatin
  6. epithelial cell
  7. progenitor cell
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15
Q

what are the layers of the stomach wall (inner -> outer, 8)

A

Stomach Lining Must Surely Overcome Crappy Lunch Sandwiches
1. mucosa
-> Surface epithelium
-> Lamina propria
-> Muscularis mucosae
2. Submucosa
3. muscularis
-> Oblique layer
-> Circular layer
-> Longitudinal layer
4. serosa

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16
Q

what are the layers of the gastric glad (inner -> outer, 6)

A
  1. gastric lumen
  2. gastric pit (secretes HCO3-)
  3. gland region
    -> mucous neck cells
    -> chief cells
    -> parietal cells
  4. muscularis mucosa
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17
Q

what cells are found in corpus (body) glands of the stomach and what part of the gland are they found in (8)

A
  1. surface cells (pit)
  2. progenitor cells (isthmus)
  3. parietal cells (neck)
  4. D - cells (neck + some in base)
  5. ECL cells (neck + some in base)
  6. EC cells (neck) - secrete seratonin
  7. X cells (neck) - secrete ghrelin
  8. chief cells (base)
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18
Q

what cells are found in antral glands of the stomach and what part of the gland are they found in (7)

A
  1. surface cells (pit)
  2. G cells (pit + some in base)
  3. D cells (pit + some in base)
  4. ECL cells (pit + some in base)
  5. EC cells (pit)
  6. progenitor cells (progenitor zone)
  7. deep mucous gland cells (base)
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19
Q

what are the 3 conventional phases of gastric secretion and what stimulates them

A
  1. cephalic - vagus nerve mediated stimulation due to thought or oral ingestion of food
  2. gastric - food in stomach resulting in HCl secretion
  3. intestinal - food in small intestines, initially HCl secretion stimulated but later inhibited
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20
Q

what mediates the cephalic phase of gastric secretion

A

vagus nerve -> Ach

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21
Q

what mediates the gastric phase of gastric secretion (2)

A
  1. neural mediation -> both long nerve (vagus) and short reflexes (intramucosal) responding to stomach distension
  2. gastrin -> pH dependent mainly
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22
Q

what 4 factors affect gastrin function

A
  1. pH
  2. vagus nerve
  3. nutrient stimulation
  4. stomach distension
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23
Q

what mediates the intestinal phase of gastric secretion

A

hormones -> gastrin and enteric inhibitors (e.g. PYY, GLPs, enterogastrones)

24
Q

what are the different forms of gastrin (2)

A
  1. gastric antrum (G-17)
  2. duodenum (G17 and G-34)
25
Q

what is the main physiological stimulant of gastric acid (HCl)

A

gastrin

26
Q

how does pH level determine gastrin secretion

A

a rise in pH results in gastrin secretion, but a pH < 3 inhibits gastrin secretion -> works as -ve feedback loop

27
Q

what factors can directly stimulate gastrin secretion

A
  1. Ca2+
  2. amines
28
Q

what type of receptors does gastrin bind to?

A

CCK receptos - 7 transmembrane receptors

29
Q

what hormone can control gastrin secretion

A

somatostatin

30
Q

how do D cells aid in gastrin inhibition

A

D cells detect high levels of H+ (i.e. low pH) -> intracellular [Ca2+] levels raised -> somatostatin release (acts in paracrine manner) -> inhibits gastrin secretion

31
Q

what is the parietal-ECL-D cell unit

A

functional cellular unit of acid secretion located in the gastric body

32
Q

how does the parietal-ECL-D cell unit work

A
  1. gastrin + vagus nerve act on ECL cell
  2. ECL cell secretes histamine
  3. histamine activates parietal cell
  4. D cell inhibits gastrin secretion via SST release due to pH drop => inhibits parietal cell activation
33
Q

what are the 3 main stimulants of gastric acid secretion

A
  1. ACh
  2. Gastrin
  3. Histamine
34
Q

how does ACh cause gastric acid release (2)

A
  1. vagus nerve mediated stimulation of gastrin -> histamine stimulation -> parietal cell activation
  2. direct stimulation of parietal cell via M3 muscarinic receptor (elevates Ca2+)
35
Q

how does gastrin cause gastric acid release

A
  1. stimulates histamine release
  2. directly stimulates parietal cell (CCK2R)
36
Q

how does histamine cause gastric acid release

A

directly stimualtes parietal cell - histamine H2 receptor stimulates cAMP in parietal cell

37
Q

what are the main inhibitors of gastric acid secretion and how (2)

A
  1. somatostatin - inhibits gastrin and histamine secretion and inhibits the parietal cell directly
  2. PGE2 - inhibits parietal cell directly
38
Q

acute effect of gastrin on ECL cells

A

histamine release (raised Ca2+)

39
Q

intermediate effect of gastrin on ECL cells

A

histamine synthesis

40
Q

chronic effect of gastrin on ECL cells

A

growth response -> hyperplasia

41
Q

what happens to the canaliculus of parietal cells when they are active

A

it increases in size and resting pumps are inserted into the canaliculus membrane

42
Q

what pump is involved in HCl formation in the canaliculus of a parietal cell

A
  1. H+/K+ ATPase (H+ into canaliculus) -> lots of energy is required to move H+ in opposing its gradient

(2. Cl- moves in down its gradient)

43
Q

what are the 3 most important molecules that bind to parietal cells in the mucosa

A
  1. Ach
  2. gastrin
  3. histamine
44
Q

what is the ultimate goal of the ECL cell

A

to release histamine in order to bind to the basolateral membrane of parietal cells and cause the insertion of a K+/H+ pump into the apical membrane

45
Q

what is the main role of gastrin in secretion

A

to act on ECL cells causing them to secrete histamine

46
Q

what are the 3 main activators of gastric acid secretion and what triggers them

A
  1. vagus nerve (thought of food, food in mouth, food in stomach);
  2. gastrin secretion (pH dependent mostly, vagal control, direct control)
  3. histamine secretion (gastrin, vagal control)
47
Q

what is the bicarbonate tide

A

efflux of bicarbonate into the blood after acid secretion can be detected and is known as the alkaline tide -> neutralises the blood

48
Q

what cells amplify the pro-acid secretion signals

A

ECL cells

49
Q

what are the 3 main inhibitors of gastric acid secretion

A
  1. emptying of the stomach (less vagal reflex, less gastrin release)
  2. low stomach pH (inhibits the release of gastrin, -ve feedback mechanism)
  3. endocrine -ve feedback (somatostatin secretions)
50
Q

what diseases result in to too much gastric acid secretion (7)

A

excess gastrin:
1. gastrinoma (ZE syndrome - not a tumour, just hyperplasia)
2. short bowel syndrome
3. non-gastrin ZES
4. G cell hyperfunction
5. H. pylori

excess histamine:
6. systemic mastocytosis

  1. hypercalcaemia (calcium is important in gastric acid release)
51
Q

what is mastocytosis

A

a rare disorder characterized by abnormal accumulation and activation of mast cells in the skin, bone marrow and internal organs

52
Q

what diseases result in too little gastric acid secretion (6)

A
  1. autoimmune gastritis
  2. H.pylori gastritis
  3. drugs
  4. vagotomy
  5. infectious diarrhoea
  6. gastric adenocarcinoma (colonisation of stomach w bacteria + carcinogens)
53
Q

what upper GI diseases occur with normal acid secretion (4)

A
  1. GORD
  2. NSAID-induced disease
  3. functional dyspepsia
  4. stress ulcerations (cushing’s, curler’s)
54
Q

what is zollinger-ellison syndrome

A

a condition in which a gastrin-secreting tumour or hyperplasia of the islet cells in the pancreas causes overproduction of gastric acid, resulting in recurrent peptic ulcers

55
Q

what is atrophic gastritis and what can be sen on imaging

A

a chronic inflammation and thinning of your stomach lining accompanied by a change in your stomach lining cells to mimic intestinal cells -> absence of rugae is seen

56
Q
A

3A week 1 - upper GI tract (7 decks)

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