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2.4 Physiology > Control of Gastric Acid Secretion > Flashcards

Control of Gastric Acid Secretion Flashcards

1
Q

What is gastric acid?

A

It is a pale-yellow, acidic, watery, digestive fluid produced by the stomach.

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2
Q

Which cells produce mucus, what is the stimulus for release and what are its functions?

A

Mucous neck cells
Tonic secretion and with irritation of the mucosa
Physical barrier between lumen and epithelium

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3
Q

Which cells produce bicarbonate, what is the stimulus for release and what are its functions?

A

Mucous neck cells
Secreted with mucous
Buffers gastric acid to prevent damage to epithelium

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4
Q

Which cells produce gastric acid, what is the stimulus for release and what are its functions?

A

Parietal cells
Acetylcholine, gastrin, histamine
Activates pepsin and kills bacteria

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5
Q

Which cells produce intrinsic factor, what is the stimulus for release and what are its functions?

A

Parietal cells
Acetylcholine, gastrin, histamine
Complexes with vitamin B12 to permit absorption

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6
Q

Which cells produce histamine, what is the stimulus for release and what are its functions?

A

EC-like cells
Acetylcholine and gastrin
Stimulates gastric acid secretion

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7
Q

Which cells produce pepsin, what is the stimulus for release and what are its functions?

A

Chief cells
Acetylcholine and gastric acid secretion
Digests proteins

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8
Q

Which cells produce gastric lipase, what is the stimulus for release and what are its functions?

A

Chief cells
Acetylcholine and acid secretion
Digests fats

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9
Q

Which cells produce somatostatin, what is the stimulus for release and what are its functions?

A

D cells
Acid in the stomach
Inhibits gastric acid release

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10
Q

Which cells produce gastrin, what is the stimulus for release and what are its functions?

A

G cells
Acetylcholine, peptidase and amino acids
Stimulates gastric acid secretion

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11
Q

What is the function of HCl?

A

Food digestion in the stomach
Destroys microbes that enter into the stomach with food

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12
Q

Describe the process of HCl production?

A

H2O and CO2 combine within the parietal cell cytoplasm to form H2CO3 under the catalysis of carbonic anhydrase
H2CO3 spontaneously dissociates into H+ and HCO3-
H+ is transported into the stomach via the H+/K+ ATPase ion pump
HCO3- is transported into the blood via an anion exchanger, which exchanges it for Cl-
Cl- is then transported into the stomach lumen via a chloride ion
The opposing charges of H+ and Cl- within the lumen cause them to associate with each other to form HCl-

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13
Q

What is the pH of an empty stomach?

A

1.0 - 1.5

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14
Q

What occurs within the parietal cell at rest?

A

The H+/K+ ATPases present within the cell membrane is minimal, while the rest are sequestered into tubulovesicles in the cell

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15
Q

What happens to the tubulovesicles upon stimulation and why?

A

The vesicles fuse with the parietal cell membrane, leading to an increased insertion of H+/K+ ATPases on the cell membrane. This increases the movement of H+ ions, increasing acid production

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16
Q

What are the stimuli for increased gastric acid production?

A

Acetylcholine
Gastrin
Histamine

17
Q

How does acetylcholine increase HCl production?

A

It is released from CN X, which has a direct stimulatory effect on the parietal cell

18
Q

How does gastrin increase HCl production?

A

Gastrin is produced by the G cells and travels through the blood until it reaches the parietal cells.
Here, it binds to CCK receptors on the parietal cells to elevate calcium levels causing increased vesicular fusion

19
Q

How does histamine increase HCl production?

A

Secreted by ECL cells, it binds to the H2 receptor on the parietal cell
This also increases vesicular fusion, but through the second messenger cAMP

20
Q

What are the stimuli for decreased gastric acid production?

A

Somatostatin
Enterogastric reflex
Cholescystokinin and secretin

21
Q

How does the enterogastric reflex work to decrease HCl production?

A

It is activated by chyme and distention of the duodenum to send inhibitory signals to the stomach via reduced vagal stimulation

22
Q

What are the phases of acid secretion?

A

Cephalic, gastric, intestinal

23
Q

When does the cephalic phase occur?

A

Before food enters the stomach, especially when it is eaten

24
Q

What stimulates the cephalic phase of HCl secretion?

A

Sight, smell, taste or thought of food

25
Q

What initiates the cephalic phase?

A

Neurogenic signals that originate from the cerebral cortex and in the appetite centres of the amygdala and hypothalamus

26
Q

Where are the neurogenic signals initiated in the cephalic phase transmitted to?

A

Through the dorsal motor nuclei of the vagi, and then through CN X to the stomach

27
Q

What does the activation of CN X in the cephalic phase result in?

A

Chief cells to secrete pepsinogen
G cells to secrete gastrin
ECL cells to secrete histamine
Parietal cells to secrete HCl

28
Q

How much of gastric acid is produced during the cephalic phase?

A

20%

29
Q

When does the gastric phase of gastric acid secretion occur?

A

It occurs upon arrival of food in the stomach, which stimulates gastric activity

30
Q

How much of gastric acid is produced during the gastric phase?

A

2/3

31
Q

What stimulates the gastric phase?

A

Distention of the stomach and chyme

32
Q

What occurs if the pH of the stomach is <2?

A

The stomach inhibits the parietal cells and G cells, as the need for pepsin and HCl declines

33
Q

When does the intestinal phase occur?

A

It occurs in the duodenum as a response to the arrival of chyme

34
Q

What is the effect of the acid and semi-digested fats in the duodenum?

A

Trigger the enterogastric reflex, which sends inhibitory signals to the stomach
Suppresses gastric secretion by causing the release of compounds such as somatostatin, CCK and gastric inhibitory peptide

2.4 Physiology (7 decks)

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