Lecture 2 - Stomach Secretions

Question 1

The stomach produces _____ factor, which is secreted by ______ cells and is necessary for intestinal absorption of vit B-12.

Answer 1

Intrinsic factor

Parietal cells

Question 2

_______ is a zymogen secreted by Chief cells in the stomach. It is converted to the active enzyme, _____, at pH < ____. _____ is most highly active in a pH ranging from ____-____.

Answer 2

Pepsinogen

Pepsin

5

Pepsin

1-3

Question 3

Mucus is secreted in the stomach by _____ and epithelial cells. Keep in mind these cells act as ____ cells for the gastric pits.

Answer 3

Neck

Stem cells

Question 4

While gastric pits in the Fundus and Antrum have Epithelial and mucus Neck cells in common, how do they differ in cell-types/composition?

Answer 4

Acid and Intrinsic factor-secreting Parietal cells, Histamine secreting ECL cells, and Pepsinogen-secreting Chief cells comprise the FUNDUS.

Somatostatin-secreting D cells, Gastrin secreting G cells, and Prostaglandin secreting cells comprise the ANTRUM.

Question 5

X/A cells are responsible for secreting _______ when the stomach is empty, which signals hunger.

Answer 5

Ghrelin

Question 6

At basal rates of secretion, how do concentrations of Na+, Cl-, and K+ in aqueous stomach secretion compare to their plasma concentrations?

Answer 6

Na+ is < in plasma

Cl- is > in plasma

K+ is > in plasma

Question 7

How does the ion concentration and composition of stomach secretions change with increased rate of secretion?

Answer 7

Na+ decreases rapidly, Cl+ increases, and H+ increases rapidly –> this leads to acidic (high HCl concentration) environment, favorable for digestion.

Question 8

Parietal cells take up _____ via diffusion, which is acted on by _____ _____ to produce H2CO3 –> this is broken down to HCO3- + H+ –> the HCO3- is exchanged with _____ on the basolateral side of the cell, and H+ is moved to the lumen via H+/___ ATPase. _____ moves into the lumen via a CLC channel –> there it can combine with H+ to form stomach acid.

Answer 8

CO2

Carbonic Anhydrase

Cl-

H+/K+ ATPase

Cl-

Question 9

What does Alkaline Tide refer to?

Answer 9

Postprandial high pH in gastric veins due to HCO3-/Cl- exchange.

Question 10

The ____-subunit of the the Parietal cell proton pump has catalytic activity and is the site for proton pump inhibitor binding –> Specifically, proton pump inhibitors form irreversible ______ bridges with _____ residues on the luminal surface of the pumps.

The ___-subunit of the proton pump helps facilitate its upregulation from ______-vesicles to the ______ surface of the Parietal cells in response to secretory signals.

Answer 10

Alpha-subunit

Disulfide bridges

Cysteine residues

Beta-subunit

Tubulo-vesicles

Apical surface

Question 11

Neurocrine signaling via the ____ nerve stimulates Parietal cells’ secretion of _____ –> ACh released from the nerve binds _____ receptors and acts via _____ as a second messenger –> _____ is a drug that blocks these receptors.

Answer 11

Vagus

HCl

M3 receptor

Ca++

Atropine

Question 12

Endocrine signaling via ______ from G-cells binding to _____ receptors stimulates Parietal cells’ secretion of HCl –> _____ is the second messenger in this pathway. ______ is a drug that blocks these receptors.

Answer 12

Gastrin

CCK-2

Ca++

Proglumide

Question 13

Paracrine signaling via _______ from ECL cells binding to _____ receptors stimulates Parietal cells’ secretion of HCl –> ______ is the major second messenger of this pathway. _____ is a drug that blocks the receptor in this pathway.

Answer 13

Histamine

H2

cAMP

Cimetidine

Question 14

_____ secreted from D-cells, PGE2, and EGF are all endocrine factors that _____ (stimulate or inhibit?) HCl secretion from Parietal cells by ______ (increasing or decreasing?) intracellular cAMP.

Answer 14

Somatostatin (SST)

Inhibit

Decreasing

Question 15

How does ACh affect ECL, G, and D cells?

Answer 15

Stimulates ECL and G to produce Histamine and Gastrin, respectively.

Inhibits production of SST from D-cells.

Question 16

How does Gastrin affect ECL and D-cells?

Answer 16

Gastrin has greatest effect on ECL cells –> stimulates production and secretion of Histamine from ECL cells more so than it directly stimulates HCl secretion from Parietal cells. Gastrin INHIBITS D-cells.

Question 17

______ is the most potent activator of HCl secretion from Parietal cells.

Answer 17

Histamine

Question 18

The viscous mucus layer traps _____ secreted from surface epithelial cells –> this helps protect the cells lining the lumen of the stomach from HCl.

Answer 18

HCO3-

Question 19

H. pylori cannot survive in pH < 4 without _____ and its transporter _____.

Answer 19

Urea

Ure I

Question 20

Aspirin irreversibly inhibits COX-1 and 2. Which one is required for PG and Thromboxane synthesis, and why would inhibiting these lead to ulcers?

Answer 20

COX-1 is needed for PG and Thromboxane synth.

PGE2 inhibits HCl secretion from Parietal cells, and Thromboxanes are required for clotting, thus, inhibiting both would lead to acidic erosion of the stomach lining with subsequent bleeding and inability to clot.