Gastric motility and secretion

Question 1

What are the 3 anatomical divisions of the stomach?

Answer 1

Fundus
Body
Antrum

Question 2

What are the 2 motility divisions of the stomach?

Answer 2

Orad region
Caudad region

Question 3

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

Answer 3

Mucosa
Submucosa
Muscularis
Serosa

Question 4

What are the 3 muscle layers of the stomach wall?

Answer 4

Longitudinal
Circular
Oblique

Question 5

What is chyme?

Answer 5

A thick, semi-liquid mass of partially digested food mixed with gastric secretions

Question 6

What is the effect of the sympathetic nervous system on GI motility and secretion?

Answer 6

The sympathetic nervous system inhibits gastric motility + secretion

Question 7

What is the effect of the parasympathetic nervous system on GI motility and secretion?

Answer 7

The parasympathetic nervous system increases gastric motility + secretion

Question 8

What are the 2 plexuses of the enteric nervous system?

Answer 8

Submucosal plexus
Myenteric plexus

Question 9

What is the location + function of the submucosal plexus?

Answer 9

Between the submucosa and muscularis

Gastric secretion + blood flow

Question 10

What is the location + function of the myenteric plexus?

Answer 10

Between the circular and longitudinal muscle layer

Contraction

Question 11

Parasympathetic innervation to the GI tract is provided by which nerves?

Answer 11

Vagus nerve
Pelvic nerves

Question 12

Which type of cell junction allows the smooth muscle of the GI tract to act as unitary smooth muscle?

Answer 12

Gap junctions

Question 13

What are the 2 types of contractions of the stomach?

Answer 13

Phasic
Tonic

Question 14

What are slow waves?

Answer 14

Oscillating depolarisations and repolarisations of the membrane potential of smooth muscle cells

Question 15

What is the frequency of slow waves in the stomach per minute?

Answer 15

3 per minute (slowest)

Question 16

Slow waves are generated by which cells?

Answer 16

Interstitial cells of Cajal

Question 17

What is the function of the interstitial cells of Cajal?

Answer 17

Generate slow waves

Question 18

Describe how slow waves trigger action potentials.

Answer 18

1. Opening of voltage-gated Ca2+ channels, causing calcium influx and depolarisation
2. Action potential triggered by depolarisation
3. Opening of Ca2+-dependent K+ channels
4. K+ leaves the cell, causing slow repolarisation / hyperpolarisation

Question 19

How many litres of food can the stomach hold?

Answer 19

1.5 litres

Question 20

When food enters the stomach, which structures unfold to increase volume?

Answer 20

Rugae

Question 21

Enteric neurons release which 2 substances to mediate the relaxation of the muscularis mucosae?

Answer 21

Nitric oxide
Serotonin

Question 22

What is the term for when food is forced backwards into the stomach by the closed pyloric sphincter?

Answer 22

Retropulsion

Question 23

Emptying the stomach into the duodenum takes approximately how long?

Answer 23

3 hours

Question 24

What effect does the sympathetic nervous system have on the pyloric sphincter?

Answer 24

Increases constriction

Question 25

What effect does the parasympathetic nervous system have on the pyloric sphincter?

Answer 25

Inhibitory vagal fibres - relax pyloric sphincter Excitatory vagal fibres - constrict pyloric sphincter

Question 26

The stomach secretes up to how many litres of gastric juice per day?

Answer 26

3 litres

Question 27

What type of molecule is intrinsic factor?

Answer 27

Glycoprotein

Question 28

Intrinsic factor is essential for the absorption of what?

Answer 28

Vitamin B12

Question 29

What causes the conversion of pepsinogen to pepsin?

Answer 29

Low pH in the stomach

Question 30

Pepsin plays a key role in the digestion of what?

Answer 30

Proteins

Question 31

Where in the GI tract is vitamin B12 absorbed?

Answer 31

Ileum

Question 32

What is the only essential secretion of the stomach?

Answer 32

Intrinsic factor

Question 33

Intrinsic factor is secreted by which cell?

Answer 33

Parietal cells

Question 34

Hydrochloric acid is secreted by which cell?

Answer 34

Parietal cells

Question 35

Which cells in the stomach secrete histamine?

Answer 35

Enterochromaffin-like cells

Question 36

D cells of the stomach secrete what?

Answer 36

Somatostatin

Question 37

G cells of the stomach secrete what?

Answer 37

Gastrin

Question 38

Which anatomical region of the stomach are G cells found in?

Answer 38

Antrum

Question 39

Which anatomical regions of the stomach are D cells found in?

Answer 39

Antrum and body

Question 40

What is the effect of gastrin on acid secretion?

Answer 40

Stimulates acid secretion

Question 41

What is the effect of somatostatin on acid secretion?

Answer 41

Inhibits acid secretion

Question 42

Which cell is very low in numbers in the pyloric glands of the antrum?

Answer 42

Parietal cells

Question 43

Which system found in parietal cells is involved in the secretion of HCl?

Answer 43

Tubulovesicular system

Question 44

Describe how HCl is secreted from parietal cells.

Answer 44

Water combines with carbon dioxide to form carbonic acid. Carbonic acid becomes hydrogen and bicarbonate. Hydrogen is transported out of the cell via H+/K+ATPase pump. Chloride ions diffuse through chloride channels.

Question 45

Water combining with carbon dioxide to form carbonic acid is catalyzed by which enzyme?

Answer 45

Carbonic anhydrase

Question 46

How is bicarbonate transported across the basolateral membrane of parietal cells?

Answer 46

Bicarbonate-chloride exchanger

Question 47

Describe the neurocrine signalling of gastric acid secretion.

Answer 47

ACh secreted by the vagus nerve

Question 48

Describe the endocrine signalling of gastric acid secretion.

Answer 48

Gastrin secreted into the bloodstream by G cells

Question 49

What are the 3 phases of gastric acid secretion and the percentage of total HCl produced in each phase?

Answer 49

Cephalic - 30% Gastric - 60% Intestinal - 10%

Question 50

Describe the 2 mechanisms by which gastric acid is stimulated in the cephalic phase.

Answer 50

Vagus nerve secretes ACh Vagus nerve secretes gastrin-releasing peptide (GRP) which triggers the release of gastrin from G cells

Question 51

The cephalic phase of gastric acid secretion is mediated by what?

Answer 51

Sensory stimuli

Question 52

The gastric phase of gastric acid secretion is mediated by what?

Answer 52

Stomach distension

Question 53

The intestinal phase of gastric acid secretion is mediated by what?

Answer 53

Products of protein digestion

Question 54

Where in the GI tract is secretin released from and what is it's effect on gastric acid secretion?

Answer 54

Duodenum Inhibits gastric acid secretion