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Block 1 Week 2 > Gastric Motility and Secretion > Flashcards

Gastric Motility and Secretion Flashcards

1
Q

Name 5 functions of the stomach.

A
  1. To store food
  2. To minimize ingestion of bacteria
  3. To dissolve and partially digest the macromolecules in food
  4. To regulate the rate at which the contents of the stomach empty into the small intestine.
  5. To secrete intrinsic factor
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2
Q

What 3 different things does gastric motility allow the stomach to do?

A
  1. Serve as a reservoir for a large volume of food
  2. Fragment the food into smaller particles and mix it with gastric secretions
  3. Empty gastric contents into the duodenum at a controlled rate
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3
Q

What comprises the Orad region of the stomach?

A

The top half of the body of the stomach and the Fundus.

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4
Q

What comprises the Caudad region of the stomach?

A

The bottom half of the body of the stomach and the Antrum.

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5
Q

What are the folds of the mucosa and submucosa in the stomach called?

A

Rugae

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6
Q

What is the mechanism called through which the stomach increases its volume to receive food?

A

Receptive relaxation

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7
Q

What is the approximate volume of an empty stomach of an adult?

A

50ml.

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8
Q

What are the 4 layers of the wall of the GI tract, going from the lumen outwards?

A
  1. Mucosa
  2. Submucosa
  3. Muscularis
  4. Serosa
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9
Q

Contractions of what create the rugae in the stomach?

A

Muscularis mucosae

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10
Q

In which layer of the GI tract wall is the muscularis mucosae found?

A

Mucosa

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11
Q

What are the 2 branches of the enteric nervous system?

A
  1. Myenteric plexus

2. Submucosal plexus

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12
Q

What does the submucosal plexus of the stomach influence?

A

Secretion

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13
Q

What does the myenteric plexus of the stomach influence?

A

Smooth muscle cell activity

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14
Q

Which nerve co-ordinates with the stomach’s enteric nerve plexuses to bring about receptive relaxation?

A

Vagus nerve.

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15
Q

What do the enteric neurons release which mediates the relaxation of the smooth muscle cells of the muscularis mucosae?

A

Nitric oxide (NO) and Serotonin.

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16
Q

What is chyme?

A

Chyme is a thick semifluid mass of partially digested food and digestive secretions.

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17
Q

How many layers of smooth muscle does the muscularis of the stomach consist of? What are they?

A

3 layers:

  1. Inner oblique layer.
  2. Middle layer of circular muscle.
  3. Outer layer of longitudinal muscle.
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18
Q

What are the different patterns of electrical activity which cross the membranes of smooth muscle cells to coordinate contractions of smooth muscle?

A
  1. Slow waves

2. Action potentials

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19
Q

What is another name for the basic electrical rhythm of the GI tract?

A

Slow waves

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20
Q

What is another name for the slow waves of the GI tract?

A

Basic electrical rhythm.

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21
Q

What is the frequency of gastric slow waves?

A

Approximately 3 per minute.

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22
Q

Where in the stomach is the rhythm of gastric slow waves generated?

A

The pacemaker zone.

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23
Q

What do slow waves do and not do in relation to contractions?

A

Slow waves do not elicit contractions. They co-ordinate contractions by controlling the appearance of action potentials.

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24
Q

How do hormones and neurotransmitters help to fire action potentials in the stomach?

A

They further depolarize the cell, thereby increasing the amplitude of slow waves.

25
Q

What determines the number of action potentials fired at the peak of the slow waves?

A

The concentration of the hormones and neurotransmitters.

26
Q

What does the number of action potentials occurring at the peak of a slow wave determine in terms of contractions?

A

The strength of the muscle contraction.

27
Q

What is the pyloric sphincter?

A

A ring of smooth muscle and connective tissue between the gastric antrum and the duodenum.

28
Q

In what way do the sympathetic nerve fibres affect the pyloric sphincter?

A

Increase the constriction of the sphincter.

29
Q

In what way do the parasympathetic nerve fibres affect the pyloric sphincter?

A
  1. Inhibitory vagal fibres relax the sphincter.

2. Excitatory vagal fibres constrict the sphincter.

30
Q

Which 4 hormones affect the pyloric sphincter and in what way?

A
  1. Gastrin
  2. Cholecystokinin
  3. Gastric inhibitory peptide
  4. Secretin

They all elicit constriction of the sphincter.

31
Q

Receptors in the duodenum sense what 3 types of materials which decrease the rate of gastric emptying?

A
  1. High in fat digestion products
  2. Highly acidic
  3. Very hypertonic
32
Q

What are the 4 main components of gastric juice?

A
  1. Enzymes: pepsinogens, gastric lipase
  2. Intrinsic factor
  3. Hydrochloric acid
  4. Mucus
33
Q

What is secreted by the parietal cells of the stomach?

A

Intrinsic factor and hydrochloric acid.

34
Q

What is secreted by the G cells of the stomach?

A

Gastrin

35
Q

What is secreted by the chief cells of the stomach?

A

Pepsinogen

36
Q

Which cells are predominant in the oxyntic gland area of the stomach?

A

Parietal cells.

37
Q

What are the 3 primary gastric effects of Gastrin?

A
  1. Stimulation of the secretion of acid, pepsinogens, mucus and bicarbonate.
  2. Stimulation of gastric motility.
  3. Inhibition of gastric emptying.
38
Q

What are the 2 gastric effects of Histamine?

A
  1. Stimulation of acid secretion.

2. Increased local blood flow, which supports the increase in metabolism associated with acid secretion.

39
Q

In the stomach, from which cells is histamine secreted?

A

Enterochromaffin-like cells (ECL).

40
Q

In the stomach which cells produce somatostatin?

A

D cells.

41
Q

What are the 2 gastric effects of somatostatin?

A
  1. Inhibition of gastrin release.

2. Inhibition of acid secretion.

42
Q

What causes the conversion of pepsinogen to pepsin?

A

Exposure to low pH in the gastric lumen.

43
Q

Pepsin accelerates the digestion of what?

A

Proteins.

44
Q

What type of molecular structure is intrinsic factor?

A

Glycoprotein.

45
Q

What is intrinsic factor essential for the absorption of?

A

Vitamin B12.

46
Q

How much HCl does the stomach secrete per day?

A

Approximately 2-3 litres.

47
Q

What is the pH of the gastric lumen?

A

Between 1 and 2.

48
Q

What is the general shape of a parietal cell?

A

Pyramid/triangular.

49
Q

What do the extensive invaginations of the luminal membrane of parietal cells form?

A

Canaliculi.

50
Q

Why do parietal cells require a high content of mitochondria?

A

Because parietal cells have many proton pumps. Proton pumps are active transporters which use energy derived from the hydrolysis of ATP. Mitochondria synthesize ATP molecules.

51
Q

What are the 4 steps of the mechanism of acid secretion by parietal cells?

A
  1. H+ and HCO3- are produced from CO2 and H2O.
  2. H+ is secreted into the lumen by a H+/K+-ATPase pump (proton pump).
  3. HCO3- moves out of the cell, across the basolateral membrane via an antiport with Cl-.
  4. Cl- diffuses passively into the lumen via a Cl- channel.
52
Q

Which 3 things stimulate gastric acid secretion?

A
  1. Gastrin
  2. Acetylcholine
  3. Histamine
53
Q

Which 3 things inhibit gastric acid secretion?

A
  1. Somatostatin
  2. Prostaglandins E2 and I2.
  3. Intestinal hormones.
54
Q

Which neurotransmitter and hormone stimulate the release of histamine from ECL cells in the stomach?

A

Acetylcholine and Gastrin.

55
Q

What molecule type are prostaglandins?

A

Lipids

56
Q

What substance are prostaglandins derived from?

A

Arachidonic acid.

57
Q

The gastric mucosal barrier requires which 2 things?

A

Mucus and bicarbonate.

58
Q

What is a gastric ulcer?

A

A lesion in the gastric mucosa.

Block 1 Week 2 (10 decks)

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