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+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction > Stomach > Flashcards

Stomach Flashcards

1
Q

What is the stomach?

A

highly involuted sac-like pouch that is divided into three main sections

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2
Q

What are the three parts of the stomach?

A
  • fundus
  • body
  • antrum
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3
Q

What is the fundus section of the stomach?

A

portion lying above gastroesophageal sphincter

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4
Q

What is the body section of the stomach?

A

middle portion

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5
Q

What is the antrum section of the stomach?

A

most distal region, characterized by thickening of muscularis externa

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6
Q

What GI processing differences are there between the different regions of the stomach?

A

differences in motility and secretions

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7
Q

What are the 3 primary roles of the stomach?

A
  • mixing and mechanical breakdown of stomach contents
  • storage of ingested food, and regulated delivery of processed stomach contents to duodenum
  • secretion of HCl and enzymes involved in protein digestion
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8
Q

Gastric Motility

What are the 4 categories of motility associated with the stomach?

A
  • filling
  • storage
  • mixing
  • emptying
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9
Q

Gastric Motility

Filling – What is receptive relaxation?

A

stomach reflexively relaxed upon food entry

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10
Q

Gastric Motility

What is filling mediated by?

A

via short loop ENS inhibition of muscularis externa

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11
Q

Gastric Motility

What happens to stomach structure during filling?

A

stomach can expand from volume of ~50 ml to ~1000 ml with little change in tension in gastric wall

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12
Q

Gastric Motility

Where is food stored?

A

in stomach body

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13
Q

Gastric Motility

What movement occurs during storage?

A

periodic (3/minute) weak peristaltic contractions occur, propagating from fundus toward antrum

these contractions result from fundal pacemaker cell activity – do little to move stomach body contents

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14
Q

Gastric Motility

What occurs during mixing?

A
  • rhythmic slow wave propagation and associated muscularis externa contractions generate powerful antral peristaltic waves
  • force antral contents toward pyloric sphincter – these are responsible for gastric mixing
  • pyloric sphincter is only open enough to let small amounts of liquid through with each peristaltic contraction
  • this wave of contraction also contracts sphincter so that solid luminal contents are diverted backward
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15
Q

Gastric Motility

Emptying – What does the volume of chyme that enters the duodenum dependent on? (2)

A
  • strength of contraction of pyloric sphincter

- number of peristaltic waves per unit time

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16
Q

Gastric Motility

Emptying – What are the two apparent problems that the body must overcome?

A
  • stomach receives variable input in terms of frequency, quantity and consistency of food, whereas duodenum requires stable environment
  • gastric contents are highly acidic, while duodenum requires basic environment
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17
Q

Gastric Motility

Emptying – How does gastric emptying solve the two apparent problems (see previous question)?

A

gastric emptying is under tight regulation – emptying is influenced by both gastric and duodenal factors to control:

  • strength of contraction of pyloric sphincter
  • rate of gastric peristaltic contractions
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18
Q

Gastric Motility

What factors regulate gastric emptying?

A
  • gastric factors – minor

- duodenal factors – major

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19
Q

Gastric Motility

What are the gastric factors that regulate gastric emptying? (2)

A
  • amount of chyme in stomach

- degree of fluidity of gastric contents

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20
Q

Gastric Motility

What are duodenal factors that regulate gastric emptying? (4)

A
  • acid
  • fat
  • peptides and amino acids
  • osmotic pressure
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21
Q

Gastric Motility

What is the neuronal response to duodenal factors that regulate gastric emptying?

A

enterogastric reflexes

  • short-loop reflexes (ENS)
  • long-loop reflexes (ANS)
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22
Q

Gastric Motility

What is the hormonal response to duodenal factors that regulate gastric emptying?

A

enterogastrones

include cholecystokinin (CCK), gastrin, and secretin

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23
Q

Gastric Motility

How does acid regulate gastric emptying?

A

(pH < 3.5)

  • neuronal reflex
  • release of hormone secretin
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24
Q

Gastric Motility

How does fat regulate gastric emptying?

A

(monoglycerides or fatty acids)

  • release of hormone CCK
  • neuronal reflex
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25
Q

Gastric Motility

How do peptides and amino acids regulate gastric emptying?

A

release of hormone gastrin

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26
Q

Gastric Motility

How does osmotic pressure regulate gastric emptying?

A

(hypertonic chyme)

  • unidentified hormone
  • neuronal response
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27
Q

Gastric Secretion

What are the specialized infoldings of the gastric mucosa functionally divided into?

A
  • oxyntic mucosa: lines fundus and body

- pyloric gland area (PGA): lines antrum

28
Q

Gastric Secretion

What are the exocrine secretions? (3)

A
  • mucus
  • HCl and intrinsic factor
  • pepsinogen
29
Q

Gastric Secretion

What are the endocrine and paracrine secretions? (3)

A
  • histamine
  • gastrin
  • somatostatin
30
Q

Gastric Secretion

Where is mucus secreted from?

A

mucous cells in gastric pits and on epithelial surface of stomach lining

31
Q

Gastric Secretion

Where is HCl and intrinsic factor secreted from?

A

parietal cells in gastric glands of oxyntic mucosa

32
Q

Gastric Secretion

Where is pepsinogen secreted from?

A

chief cells in gastric glands of oxyntic mucosa

33
Q

Gastric Secretion

Where is histamine secreted from?

A

enterochromaffin-like (ECL) cells in gastric glands of oxyntic mucosa

34
Q

Gastric Secretion

Where is gastrin secreted from?

A

G cells in gastric glands of PGA

35
Q

Gastric Secretion

Where is somatostatin secreted from?

A

D cells in gastric glands of PGA

36
Q

Gastric Secretion

How is HCl secreted?

A
  • parietal cells actively secrete HCl
  • ionic pumps move H+ and Cl- ions against their concentration gradients
  • biochemical neutrality maintained
37
Q

Gastric Secretion

What are the 4 functions that HCl performs that assists GI activity?

A
  • converts pepsinogen into active pepsin
  • breakdown of connective tissue and muscle fibres
  • breaks tertiary structure of proteins
  • kills some ingested microorganisms
38
Q

Gastric Secretion

What is pepsinogen?

A

inactive form of pepsin

39
Q

Gastric Secretion

What is autocatalysis of pepsinogen?

A
  • HCl activates
  • pepsin cleaves peptide bonds between certain amino acids
  • stored inactive in zymogen granules within chief cells
40
Q

Gastric Secretion

What are the functions of mucus?

A

protective

  • lubrication
  • inhibits pepsin to protect against auto-digestion
  • neutralizes gastric acid at epithelial surface
41
Q

Gastric Secretion

How are ulcers formed?

A
  • H. pylori secretes toxin that weakens mucosal barrier
  • acid and pepsin penetrate mucosal barrier
  • histamine release enhances gastric acid and pepsin production
  • other contributing factors include chronic alcohol, NSAIDs and stress
42
Q

Gastric Secretion

Is ulcer formation multifactorial?

A

yes

43
Q

Gastric Secretion

What is intrinsic factor required for?

A

absorption of vitamin B12 red blood cell formation

44
Q

Gastric Secretion

What happens if there is a failure to produce intrinsic factor?

A

pernicious anaemia

45
Q

Gastric Secretion

What are the 4 chemical messengers that regulate secretion of gastric juices?

A
  • acetylcholine
  • gastrin
  • histamine
  • somatostatin
46
Q

Gastric Secretion

What does acetylcholine stimulate? (4)

A
  • parietal (H+) cell secretions
  • chief (pepsinogen) cell secretions
  • ECL (histamine) cell secretions
  • G (gastrin) cell secretions
47
Q

Gastric Secretion

What is gastrin secreted into the blood by? When?

A

secreted into blood by G cells in PGA gastric glands, in presence of protein products in stomach lumen

48
Q

Gastric Secretion

What does gastrin stimulate? (3)

A
  • parietal cell secretions
  • chief cell secretions
  • ECL cell secretions
49
Q

Gastric Secretion

What is the primary factor responsible for increasing gastric secretions during the ingestion of a meal?

A

gastrin

50
Q

Gastric Secretion

What does gastrin promote growth (trophic) of?

A

gastric and duodenal mucosa – maintains their functionality

51
Q

Gastric Secretion

What is histamine?

A

paracrine substance released from ECL cells in oxyntic gastric glands in response to both gastrin and Ach

52
Q

Gastric Secretion

What does histamine stimulate?

A

acts locally to stimulate parietal cell H+ production

53
Q

Gastric Secretion

What does somatostatin do?

A

inhibits and acts in negative-feedback manner to turn off gastric H+, pepsinogen and histamine production

54
Q

Gastric Secretion

What are the 3 phases of secretion of gastric juice during ingestion of a meal?

A
  • cephalic phase
  • gastric phase
  • intestinal phase
55
Q

Gastric Secretion

What occurs during the cephalic phase?

A
  • secretion of pepsinogen and H+ in response to sight, smell or thought of food and process of swallowing
  • initiated in hypothalamus and mediated by vagal efferents
  • vagal input also stimulates G cell production of gastrin
56
Q

Gastric Secretion

When does gastric phase begin?

A

when food actually enters stomach

57
Q

Gastric Secretion

What occurs during the gastric phase?

A
  • proteins and peptides within lumen are the most potent stimuli
  • receptors in ENS initiate short reflexes resulting in gastrin release from G cells
  • long reflex loop also activates H+, and gastrin secretion via vagal and ENS activity
  • histamine release is also stimulated, augmenting H+ secretion
  • distension/caffeine/alcohol can also stimulate gastric juice production
58
Q

Gastric Secretion

When does the intestinal phase begin?

A

when chyme empties into duodenum

59
Q

Gastric Secretion

What type of phase is the intestinal phase?

A

inhibitory

60
Q

Gastric Secretion

What happens during the intestinal phase?

A
  • as meal leaves stomach, protein is removed
  • somatostatin is released from D cells in PGA gastric glands in response to drop in pH – inhibits parietal, chief, and HCl cell activity
  • negative feedback influence on gastric secretions via enterogastric reflexes and enterogastrones CCK and secretin
  • these factors also decrease gastric emptying
61
Q

Gastric Digestion

What types of digestion occur?

A
  • carbohydrate
  • protein
  • iron*
62
Q

Gastric Digestion

What occurs during carbohydrate digestion?

A
  • initiated in mouth from salivary amylase
  • continues to occur in food bolus as it is stored in body of stomach
  • no further amylase is secreted by stomach
63
Q

Gastric Digestion

What causes protein digestion?

A

resulting from pepsinogen and acid exposure

64
Q

Gastric Digestion

Where does protein digestion occur?

A

in antrum of stomach where ingested food is thoroughly mixed with gastric juice

65
Q

Gastric Absorption

What does stomach absorb (2)?

A
  • (ethyl) alcohol

- aspirin

66
Q

Gastric Absorption

What is aspirin?

A

acetylsalicylic acid – weak acid that remains un-ionized in strongly acidic gastric juice

un-ionized → acids are lipid soluble and cross gastric epithelium, rapidly producing its effects

+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction (32 decks)

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