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13. Gastrointestinal > 4. The Stomach > Flashcards

4. The Stomach Flashcards

1
Q

What are the key functions of the stomach?

A

Stores food, disinfect food, and breaks food down into chyme.

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2
Q

What are gastric pits?

A

Indentations in the stomach mucosa that are the openings to gastric glands.

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3
Q

Where do stomach secretions come from?

A

Gastric pits.

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4
Q

What cells do gastric pits contain?

A

Neck cells.

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5
Q

Which cells do gastric glands contain?

A

Parietal, chief, G-cells, and smooth muscle cells.

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6
Q

Which cell secretes hydrochloric acid?

A

Parietal cells.

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7
Q

Which cell secretes proteolytic enzymes?

A

Chief cells.

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8
Q

Which cell secretes mucus?

A

Neck/surface cells.

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9
Q

Which cell secretes HCO3-?

A

Neck/ surface cells.

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10
Q

Which cell secretes gastrin?

A

G-cells.

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11
Q

How is H+ made in large quantities?

A

In the mitochondria of parietal cells by splitting water into H+ and OH- ions.

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12
Q

For every mol of H+ secreted into the stomach, how much HCO3- enters the blood?

A

1 mol.

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13
Q

How is HCO3- added to the blood from water split in the mitochondria?

A

The OH- generated combines with CO2 to form HCO3- which is exported into the blood.

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14
Q

Why can parietal cells produce H+ at a high rate?

A

They have lots of mitochondria.

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15
Q

How do parietal cells avoid accumulation of H+ ions in the cells?

A

They have invaginations in their cell walls, canaliculi. These have proton pumps to expel H+ from the parietal cells up a concentration gradient.

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16
Q

What are parietal cells stimulated by?

A

Acetylcholine, gastrin, and histamine.

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17
Q

How does acetylcholine affect parietal cells?

A

It acts on muscarinic receptors.

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18
Q

What is ACh released from?

A

Postganglionic parasympathetic neurones.

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19
Q

What stimulates ACh release?

A

Gastric distension as food arrives.

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20
Q

What is the basic structure of gastrin?

A

17-amino acid polypeptide.

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21
Q

What stimulates gastrin secretion?

A

The presence of peptides and ACh from intrinsic neurones.

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22
Q

What inhibits gastrin secretion?

A

Low pH in the stomach.

23
Q

What is histamine released from?

A

Mast cells.

24
Q

What does histamine bind to on parietal cells?

A

H2 surface receptors.

25
Q

In what way does histamine act as an amplifier?

A

Gastrin and ACh stimulate mast cells, which releases histamine so more acid is secreted - the purpose of gastrin and ACh is amplified.

26
Q

What are the three phases of gastric secretion control?

A

Cephalic phase, gastric phase, and intestinal phase.

27
Q

What is the cephalic phase of gastric secretion control?

A

At the sight and smell of food, and the act of swallowing, parasympathetic nervous system is activated. This stimulated ACh release, which stimulates parietal cells directly and via histamine so more acid release.

28
Q

What is the gastric phase of gastric secretion control?

A

When food reached the stomach, it causes distension which stimulates ACh release and therefore parietal cells. Gastrin is disinhibited and peptides are produced so more acid is made.

29
Q

How does food acting as a buffer affect acid release?

A

It causes luminal pH to rise so gastrin is disinhibited and more acid is made. The acid act on proteins to produce peptides which further stimulate gastrin and pH falls further.

30
Q

What is the intestinal phase of gastric secretion control?

A

As chyme leaves the stomach, the release of cholecystokinin and gastric inhibitory polypeptide is stimulated from the intestines. These antagonise gastrin so less is released. The small amount of food has less of a buffering effect so lower pH inhibits gastrin.

31
Q

Why is stomach ulcer pain worse at night?

A

Because between meals, the stomach has a lower pH, which aggravates the ulcers.

32
Q

Which two types of drug can reduce gastric acid secretion?

A

Histamine blockers and proton pump inhibitors.

33
Q

How do histamine blockers reduce gastric acid secretion?

A

They remove the amplification of gastrin and ACh signals.

34
Q

How do proton pump inhibitors reduce gastric acid secretion?

A

It prevents H+ ions being pumped into parietal cell canaliculi.

35
Q

What is an example of a histamine blocker drug?

A

Cimetidine.

36
Q

What is an example of a proton pump inhibitor?

A

Omeprazole.

37
Q

How does the stomach protect itself from it’s own low pH?

A

Mucus secreted by neck cells that protects the mucosa.

38
Q

How does mucus protect the stomach?

A

It is sticky and basic so it forms an unstirred layer that ions can’t move through. The H+ ions react with the HCO3- of the mucus and bring the surface pH to above 6.

39
Q

What stimulates mucus and HCO3- secretion from neck cells and surface cells?

A

Prostaglandins.

40
Q

What can the stomach’s defences by breached by?

A

Alcohol, Helicobacter pylori, NSAIDS.

41
Q

How does alcohol breach the stomach’s defences?

A

Dissolves the mucus, allowing the acid to attack the stomach.

42
Q

How does helicobacter pylori breach the stomach’s defences?

A

Surface cells become infected, inhibiting mucus/ HCO3- production.

43
Q

How do NSAIDS breach the stomach’s defences?

A

Inhibit prostaglandins so reduce defences.

44
Q

What is the result of the stomach’s defences being breached?

A

Peptic ulcers.

45
Q

How can peptic ulcers be treated?

A

Reduce acid secretion and, if present, eliminate H. pylori with antibiotics.

46
Q

What is receptive relaxation?

A

As food travels down the oesophagus, relaxation of the muscle in the stomach’s wall is triggered so pressure doesn’t increase.

47
Q

How does receptive relaxation limit reflux?

A

It means the pressure in the stomach doesn’t increase as it fills.

48
Q

What are the rhythmic contractions of the stomach?

A

The longitudinal and circular muscles of the stomach contract according to the pacemaker in the cardiac region.

49
Q

How often does the stomach pacemaker fire?

A

About three time a minute.

50
Q

What is the result of the stomach pacemaker?

A

Regular, accelerating peristaltic contraction from the cardia to the pylorus.

51
Q

How is liquid chyme allowed into the duodenum?

A

Accelerating, rhythmic, peristaltic contraction moves solid lumps backwards into the fundus of the stomach but lets liquid chyme through.

52
Q

How is gastric emptying controlled?

A

Emptying happens gradually according to the peristaltic waves and rate of their acceleration. It also depends on hormones from the intestine.

53
Q

What is gastric emptying slowed by?

A

Fat, low pH, and hypertonicity in the duodenum.

13. Gastrointestinal (17 decks)

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