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GI > The Stomach > Flashcards

The Stomach Flashcards

1
Q

Describe functions of the stomach

A 
Store food
Disinfect it (low pH)
Break it down to chyme - chemical disruption with acids and enzymes, physical disruption by motility
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2
Q

What are the components of gastric secretions and what are their cellular origins?

A

HCl - parietal cells
Proteolytic enzymes eg pepsin - chief cells
Gastrin - G-cells
Mucus - neck cells

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3
Q

What is stomach pH kept below?

A

2

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4
Q

What happens to the alkali produced with the acid? (1 mole of alkali must be produced for every mole of acid)

A

Released into bloodstream - alkaline tide

OH- + CO2 -> HCO3-

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5
Q

How is stomach acid produced?

A

Cells split water into H+ and OH-
H+ produced by mitochondria in parietal cells at a high rate
Canaliculi have proton pumps to expel H+ against high concentration gradient
Requires lots of energy

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6
Q

What are the three main factors that control acid secretion?

A

Gastrin
Histamine
Acetylcholine

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7
Q

How does gastrin control acid secretion?

A

It is a polypeptide which binds to surface receptors on the cell
Stimulates acid and intrinsic factor secretion via second messenger pathway

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8
Q

How does histamine control acid secretion?

A

Released from mast cells
Binds to H2 surface receptor on parietal cells
Stimulates acid secretion via cAMP

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9
Q

How does Ach control acid secretion?

A

Released from post-ganglionic parasympathetic neurones
Acts on muscarinic receptors on the parietal cell
Stimulates acid secretion via second messenger pathway

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10
Q

What factors affect gastrin?

A

Stimulated by

  • peptides
  • Ach from intrinsic neurones released by distension of the stomach wall

Inhibited by

  • low stomach pH
  • negative feedback
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11
Q

What factors affect histamine secretion?

A

Mast cells stimulated by gastrin and Ach

Antagonists can be used to reduce acid secretion

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12
Q

What drugs can be used to reduce stomach secretion?

A

Antagonise action of histamine by being H2 antagonistseg cimetidine. Particularly good because H2 receptors are rare elsewhere in the body (mostly H1)
Proton pump inhibitors

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13
Q

How does the mucus layer protect the stomach wall?

A

Mucosa covered in mucus which is sticky and basic
Forms an unstirred layer - ions cannot move through this easily
H+ ions slowly diffuse in and react with basic groups on the mucus and HCO3- secreted by surface epithelial cells

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14
Q

What is the surface pH of the epithelial cells of the stomach

A

6

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15
Q

When are prostaglandins released in the stomach and what do they do?

A

Secreted with acid

Stimulate mucus and alkali secretion so that defences match the attack

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16
Q

What is receptive relaxation?

A

When the stomach relaxes to accommodate food

A neural reflex triggered by swallowing

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17
Q

Which nerve controls receptive relaxation?

A

Efferent pathway via vagus nerve

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18
Q

What does receptive relaxation allow?

A

Pressure in stomach doesn’t increase as you eat - limits reflux
Allows you to consume larger meals

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19
Q

What can inhibit receptive relaxation and consequences?

A

Damage to vagus nerve

Have to small meals

20
Q

What controls rhythmic contractions of the stomach? How often is an action potential fired?

A

Pacemaker cells in the cardiac region

3 times a minute

21
Q

How is food ejected from the stomach?

A

Peristaltic wave travels towards to antrum
Initially it drives all stomach contents ahead of it
It overtakes the larger lumps as it accelerates so chyme gets to the end while lumps are driven back into the fundus
Pylorus opens and a small squirt is ejected

22
Q

What closes the pylorus?

A

When the peristaltic wave reaches it

23
Q

What is the volume of each squirt controlled by?

A

Rate of acceleration of the peristaltic wave

Hormones from the intestine

24
Q

What is gastric emptying slowed by?

A

Fat in duodenum
Low pH in duodenum
Hypertonicity in the duodenum

25
Q

What is delivered to the duodenum from the stomach?

A

Hypertonic solution of acid and chyme at a controlled rate

26
Q

Which arteries is the greater curvature supplied by?

A

Short gastric arteries

Right and left gastro-omental arteries

27
Q

What is the layout of the mucosa when the stomach is empty?

A

Mucosa lies in floss called rugae

Become more prominent towards the pyloric part and greater curvature

28
Q

What happens to the mucosa during swallowing?

A

The rugae form a temporary groove along the lesser curvature, known as the gastric canal. Masticated food and fluid can drain along this canal to the pyloric canal when the stomach is empty.

29
Q

At what vertebral level is the lower oesophageal sphincter?

A

Left of T11 vertebra

30
Q

What is the epithelium of the stomach?

A

Gastric mucosa - simple columnar

31
Q

What muscle is contained in the pyloric sphincter?

A

Smooth muscle

32
Q

What does the pyloric sphincter do?

A

Controls the exit of chyme

Muscle thickens to control discharge of starch contents through the orifice

33
Q

When does emptying of the stomach occur?

A

Intermittently when intragastric pressure overcomes resistance of the pylorus

34
Q

In what state is the pyloric sphincter normally?

A

Tonically contracted so that the orifice is small and food stays in the stomach for a suitably long period

35
Q

Microscopic structure of gastric mucosa? (Three regions of the stomach and the cells each contain)

A

Cardia - contains neck cells

Fundus and body has neck cells, parietal cells and chief cells

Pyloric - neck cells and G cells

36
Q

What do neck cells secrete?

A

Soluble mucus to lubricate chyme

37
Q

What do parietal cells produce?

A

HCl and gastric intrinsic factor

38
Q

What precursor enzymes do chief cells produce?

A

Pepsinogen
Rennin
Lipase

39
Q

What does the greater omentum contain?

A

Lymph nodes which contain macrophages to help fight infections of the GI tract

40
Q

How can the epiploic foramen be located?

A

Running a finger along the gall bladder to the free edge of the lesser omentum

41
Q

Arterial supply to the greater curvature?

A

Coeliac trunk - splenic artery - left gastro-omental

Coeliac trunk - common hepatic - gastroduodenal - right gastro-omental

42
Q

Arterial supply to the lesser curvature?

A

Coeliac trunk - left gastric

Coeliac trunk - common hepatic - right gastric

43
Q

Blood supply to the fundus and body?

A

Coeliac trunk - splenic - posterior gastric and small gastric

44
Q

Venous drainage of the stomach?

A

Follows arteries
Right and left gastric veins drain into hepatic portal vein
Shirt gastric vein, left and right gastro-omental veins drain into the splenic vein - superior mesentric vein

45
Q

Lymph nodes of the stomach?

A

Drains into gastric and gastro-omental lymph nodes found at the curvatures. They’re connect to the celiac lymph nodes.

GI (21 decks)

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