Stomach Flashcards by Sarah L

What is the stomach?

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

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What are the three parts of the stomach?

fundus
body
antrum

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What is the fundus section of the stomach?

portion lying above gastroesophageal sphincter

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What is the body section of the stomach?

middle portion

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What is the antrum section of the stomach?

most distal region, characterized by thickening of muscularis externa

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

differences in motility and secretions

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What are the 3 primary roles of the stomach?

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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Gastric Motility

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

filling
storage
mixing
emptying

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Gastric Motility

Filling – What is receptive relaxation?

stomach reflexively relaxed upon food entry

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Gastric Motility

What is filling mediated by?

via short loop ENS inhibition of muscularis externa

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Gastric Motility

What happens to stomach structure during filling?

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

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Gastric Motility

Where is food stored?

in stomach body

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Gastric Motility

What movement occurs during storage?

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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Gastric Motility

What occurs during mixing?

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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Gastric Motility

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

strength of contraction of pyloric sphincter

- number of peristaltic waves per unit time

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Gastric Motility

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

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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Gastric Motility

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

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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Gastric Motility

What factors regulate gastric emptying?

gastric factors – minor

- duodenal factors – major

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Gastric Motility

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

amount of chyme in stomach

- degree of fluidity of gastric contents

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Gastric Motility

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

acid
fat
peptides and amino acids
osmotic pressure

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Gastric Motility

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

enterogastric reflexes

short-loop reflexes (ENS)
long-loop reflexes (ANS)

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Gastric Motility

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

enterogastrones

include cholecystokinin (CCK), gastrin, and secretin

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Gastric Motility

How does acid regulate gastric emptying?

(pH < 3.5)

neuronal reflex
release of hormone secretin

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Gastric Motility

How does fat regulate gastric emptying?

(monoglycerides or fatty acids)

release of hormone CCK
neuronal reflex

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Gastric Motility How do peptides and amino acids regulate gastric emptying?

release of hormone gastrin

Gastric Motility How does osmotic pressure regulate gastric emptying?

(hypertonic chyme) - unidentified hormone - neuronal response

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

- oxyntic mucosa: lines fundus and body | - pyloric gland area (PGA): lines antrum

Gastric Secretion What are the exocrine secretions? (3)

- mucus - HCl and intrinsic factor - pepsinogen

Gastric Secretion What are the endocrine and paracrine secretions? (3)

- histamine - gastrin - somatostatin

Gastric Secretion Where is mucus secreted from?

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

Gastric Secretion Where is HCl and intrinsic factor secreted from?

parietal cells in gastric glands of oxyntic mucosa

Gastric Secretion Where is pepsinogen secreted from?

chief cells in gastric glands of oxyntic mucosa

Gastric Secretion Where is histamine secreted from?

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

Gastric Secretion Where is gastrin secreted from?

G cells in gastric glands of PGA

Gastric Secretion Where is somatostatin secreted from?

D cells in gastric glands of PGA

Gastric Secretion How is HCl secreted?

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

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

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

Gastric Secretion What is pepsinogen?

inactive form of pepsin

Gastric Secretion What is autocatalysis of pepsinogen?

- HCl activates - pepsin cleaves peptide bonds between certain amino acids - stored inactive in zymogen granules within chief cells

Gastric Secretion What are the functions of mucus?

protective - lubrication - inhibits pepsin to protect against auto-digestion - neutralizes gastric acid at epithelial surface

Gastric Secretion How are ulcers formed?

- 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

Gastric Secretion Is ulcer formation multifactorial?

yes

Gastric Secretion What is intrinsic factor required for?

absorption of vitamin B12 red blood cell formation

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

pernicious anaemia

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

- acetylcholine - gastrin - histamine - somatostatin

Gastric Secretion What does acetylcholine stimulate? (4)

- parietal (H+) cell secretions - chief (pepsinogen) cell secretions - ECL (histamine) cell secretions - G (gastrin) cell secretions

Gastric Secretion What is gastrin secreted into the blood by? When?

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

Gastric Secretion What does gastrin stimulate? (3)

- parietal cell secretions - chief cell secretions - ECL cell secretions

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

gastrin

Gastric Secretion What does gastrin promote growth (trophic) of?

gastric and duodenal mucosa – maintains their functionality

Gastric Secretion What is histamine?

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

Gastric Secretion What does histamine stimulate?

acts locally to stimulate parietal cell H+ production

Gastric Secretion What does somatostatin do?

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

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

- cephalic phase - gastric phase - intestinal phase

Gastric Secretion What occurs during the cephalic phase?

- 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

Gastric Secretion When does gastric phase begin?

when food actually enters stomach

Gastric Secretion What occurs during the gastric phase?

- 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

Gastric Secretion When does the intestinal phase begin?

when chyme empties into duodenum

Gastric Secretion What type of phase is the intestinal phase?

inhibitory

Gastric Secretion What happens during the intestinal phase?

- 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

Gastric Digestion What types of digestion occur?

- carbohydrate - protein - iron*

Gastric Digestion What occurs during carbohydrate digestion?

- 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

Gastric Digestion What causes protein digestion?

resulting from pepsinogen and acid exposure

Gastric Digestion Where does protein digestion occur?

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

Gastric Absorption What does stomach absorb (2)?

- (ethyl) alcohol | - aspirin

Gastric Absorption What is aspirin?

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

Stomach Flashcards

(66 cards)