3. Secretory processes control systems which regulate motility secretion and secretion

Question 1

List the 5 components of gastric secretions in the stomach and their functions

Answer 1

1. Hydrogen ions - produced by parietal cells - converts pepsinogen into pepsin
2. Pepsin - produced by chief cells as pepsinogen - breaks down protein
3. Intrinsic factor - forms a complex with vitamin B12 for absorption in terminal ileum
4. Mucus - lubrication and protection of mucosa from being digested by pepsin
5. Water

Question 2

Describe the 2 functions of gastric acid.

Answer 2

1. Converts inactive pepsinogen into the active enzyme pepsin
2. Kills a large number of bacteria that enter the stomach

Question 3

What is the pH of blood?

Answer 3

7.4

Question 4

What pH level can the stomach reach with high rates of gastric acid secretions?

Answer 4

Approx pH 1

Question 5

Why do parietal cells expend a lot of energy?

Answer 5

Because they produce HCl which requires a lot of energy - parietal cells would therefore have lots of mitochondria

Question 6

Where are oxyntic glands found?

Answer 6

In the fundus of the stomach

Question 7

What cells are found in oxyntic glands?

Answer 7

(Lumen)
Epithelial cells
Parietal cells
Chief cells
(Muscularis mucosae)

Question 8

By what mechanism is hydrogen actively “pumped” into the gastric lumen?

Answer 8

H+, K+ -ATPase

Question 9

What catalyses the production of bicarbonate from OH- and CO2 in parietal cells to then enter the bloodstream?

Answer 9

Carbonic anhydrase (CA)

Question 10

What are the 3 stimulants for acid secretion and what receptors do they act on (parietal cells)?

Answer 10

1. Gastrin - CCK2-R (cholecystokinin-2)
2. Histamine -H2
3. Acetylcholine - Ach-R (parasympathetic neurotransmitter of vagus nerve)

Question 11

What cells produce histamine and where can they be found?

Answer 11

Enterochromaffin-like cells (ECL cells)

Found near parietal cells

Question 12

Outline the cephalic phase in gastric secretion.

Answer 12

1st phase
Starts with the sight, smell, taste of food
Vagus nerve activates parietal and gastrin cells
Leads to moderate stimulation of HCl/pepsinogen release

Question 13

Outline the gastric phase of secretion

Answer 13

2nd phase
Caused by proteins in antrum/distention of stomach
Vaso-vagal reflex & gastrin (& histamine)
Strong stimulation of HCl/pepsinogen

Question 14

What foods directly stimulate gastrin release?

Answer 14

Coffee
Protein/peptides
Calcium rich foods
(Alcohol DOES NOT affect release)

Question 15

Outline the intestinal phase

Answer 15

3rd phase
Proteins entering duodenum -> gastrin release (excitatory)
HCl in duodenum -> secretin release (inhibitory)
Lipids in duodenum -> peptide YY (inhibitory)

Question 16

What 3 things are secreted by the crypts of the small intestine and what are their functions?

Answer 16

1. NaCl/ NaHCO3 - neutralises gastric pH
2. Amylase - starch digestion
3. Enteropeptidase - activates trypsinogen

Question 17

What are found on villus tips of the small intestine to aid digestion?

Answer 17

Brush border enzymes

Question 18

What interventions can be used to reduce gastric secretions by targeting histamine release?

Answer 18

Antihistamines

Cimetidine

Question 19

What are generally used to reduce gastric acid secretions?

List 3 examples.

Answer 19

Proton pump inhibitors (PPIs)

Omeprazole, lansoprazole, esomeprazole

Question 20

Gastric acid plays a role in fighting bacteria. What does the use of PPIs put the patient at higher risk of?

Answer 20

Nosocomial infections (originate in hospitals)
e.g. Clostridium difficile

Question 21

When is gastric acid secretion at its peak?

Answer 21

1 hour post-ingestion

Question 22

At what pH is gastrin inhibited?

Answer 22

pH < 3

Question 23

What inhibitory hormone is released in response to low pH?

Answer 23

Somatostatin

Question 24

What are the 3 enterogastrones (hormones) released by the duodenum in response to low pH?

Answer 24

1. CCK
2. Gastric inhibitory polypeptide (GIP)
3. Secretin

Question 25

What is secreted by the pancreatic duct and what causes its release?

Answer 25

Bicarbonate | Release from duct cells stimulated by secretin release, which is stimulated by HCl in the duodenum

Question 26

What are released by the acinar cells of the pancreas and what stimulates their release?

Answer 26

Pro-enzymes. Their release is stimulated by CCK which is released in the presence of proteins/lipids. NaCl also released