Gastric secretions

Question 1

function of stomach

Answer 1

secretes hydrogen, pepsinogen, mucus, bicarbonate and intrinsic factor

muscular contractions to mix contents

releases humoral factors

Question 2

function of acid secreted

Answer 2

denature proteins, aid digestion

promotes truncation of pepsinogen to form active enzyme pepsin

Question 3

which cells secrete HCL?

Answer 3

Parietal cells

Question 4

intrinsic factor function

Answer 4

aids B12 absorption

Question 5

mechanism of acid secretion

Answer 5

1. intracellular carbonic anhydrase catalyses the hydration of carbon dioxide to yield carbonic acid that then dissociates into hydrogen and bicarbonate ions
2. hydrogen potassium ATPase pumps out hydrogen ions at apical membrane in exchange for potassium
3. potassium recycles out of the cell through apical potassium channels
4. bicarbonate ions exit basolateral membrane then enter blood to act as a buffer
5. chloride diffuses through apical channel to form HCL in lumen
6. water follows via aquaporins

Question 6

alkaline tide definition

Answer 6

alkalinisation of blood during acid secretion

Question 7

Where is the ATPase located in inactive cells?

Answer 7

within vesicles

ATPase is inside out, pumping hydrogen ions to the lumen and potassium out

Question 8

three molecules that induce acid secretion

Answer 8

ACh, gastrin and histamine

Question 9

explain stimulation of ACh and actions

Answer 9

1. vagus releases ACh that binds to M3 receptors
2. activate PLC which conerts PIP2 to IP3 and DAG
3. IP3 releases calcium, DAG activates PKC
4. PKC phosphorylates parietal cell proteins, including H/K pump

Question 10

explain gastrin mechanism of action

Answer 10

1. Binds to CCKb receptors

2. GqPCR- PKC and IP3

Question 11

explain release of gastrin

Answer 11

1. vagus nerve/ protein digestion products in the lumen stimulate GRP-releasing neurones
2. GRP-releasing neurones release gastrin related peptide which binds to G cells
3. G cells then release gastrin

Question 12

histamine precursor

Answer 12

histamine

Question 13

where is histamine released from?

Answer 13

ECL cells in stomach

Question 14

Histamine mechanism of action

Answer 14

1. binds to H2 receptors
2. activate cAMP–> PKA
3. PKA phosphorylates H/K ATPase

Question 15

how is histamine released?

Answer 15

gastrin and ACh bind to M3 CCK receptors on the ECL cells to induce histamine release

Question 16

common mediator definition

Answer 16

gastrin and ACh affect histamine which induces gastric acid release

Question 17

evidence for common mediator

Answer 17

Ranitidine, a H2 antagonist, is a strong inhibitor of gastric acid secretion

Question 18

ulcer definition

Answer 18

an area of dead epithelium

Question 19

peptic ulcer definition

Answer 19

area of necrosed lining of the stomach, proximal duodenum or oesophagus caused by gastric secretions

Question 20

common causes of peptic ulcers

Answer 20

Helicobacter pylori bacteria or long term use of NSAIDS

Question 21

explain NSAID adverse action

Answer 21

acidic molecules directly irritate gastric mucosa and inhibit COX-1 and COX2, reducing levels of prostaglandins

increases gastric acid secretion, diminishes bicarbonate and mucus secretion

Question 22

common therapy for peptic ulcers

Answer 22

antacids

Question 23

what are antacids?

Answer 23

reduce the problem of too much acid by neutralising them with an alkali

Question 24

examples of antacids

Answer 24

aluminium hydroxide, magnesium hydroxide, trisilicate

Question 25

side effects of antacids

Answer 25

diarrhea

Question 26

two other treatments for peptic ulcer

Answer 26

H/K pump blocker, H2 antagonists

Question 27

example of H/K pump blocker

Answer 27

omeprazole

Question 28

prostaglandin functions

Answer 28

secretion of mucus is mediated by prostaglandins E and I-2

Question 29

evidence for H.pylori involvement

Answer 29

eradication of bacteria reduces the risk of peptic ulcer recurrence

Question 30

what is being used against H.pylori?

Answer 30

chemotherapy