Acid secretion in stomach

Question 1

Where are oxyntic glands located

Answer 1

Inside surfaces of body and fundus of stomach

Question 2

Where are pyloric glands located

Answer 2

Antral portion of stomach

Question 3

What do oxyntic glands secrete

Answer 3

HCl
Pepsinogen
Intrinsic factor
Mucus

Question 4

What do pyloric glands secrete

Answer 4

Mucus

Gastrin

Question 5

What is an oxyntic gland composed of

Answer 5

(top to bottom)

• Mucus neck cells (secrete mucus and HCO3-)
• Parietal cells (secrete HCl and IF)
• Chief cells (secrete pepsinogen and gastric lipase)

Question 6

What pH is the HCl that parietal cells secrete

Answer 6

0.8

Question 7

How is the parietal cell arranged

Answer 7

At rest have numberous tubulovesicles derived from smooth endoplasmic reticulum. These contain H+ pumps and aren’t connected to apical memb.
When acid secretion stimulated they merge and become deep invaginations, secretory canaliculi. Pump HCl out into lumen. canaliculi have to be damaged from the acid and recycled

Question 8

What is the function of HCO3- secreted by epitelial cells

Answer 8

Diffuses into blood, making gastric venous blood have a higher pH

Question 9

Formation and secretion of HCl

Answer 9

CO2 from blood + H20 is the source of H+
On apical membrane of canaliculi, H+ actively secreted via H+/K+/ATPase pump (K+ in, H+ out)
K+ and Cl - recylced out through leaky channels

Question 10

Basolateral HCO- efflux

Answer 10

HCO3- formed with H+ leaves cell passively through basolateral membrane
Via HCO3-/ Cl- exchanger (Cl- moves in)
This Cl- influx is directly balanced through Cl- efflux in apical membrane

Question 11

Pepsin production

Answer 11

Pepsinogen secreted by chief cells

HCl activates pepsinogen to form pepsin

Question 12

Pepsin action

Answer 12

Works best at pH 1.8-3.5
Proteolytic enzyme that acts on proteins and polypeptides
Can degrade mucus but is made less active by alkaline pH caused by HCO- secretion

Question 13

How is secretion of oxylitic glands stimulated?

Answer 13

Ach released by parasympathetic stimulation of vagus nerve/ enteric nerves plexus
Stimulates pepsinogen, HCl and mucus release

Question 14

Intrinsic factor actions

Answer 14

essential for vitamin B12 absorbtion in ileum (as a Vit B12 binding protein)
secreted by parietal cells along with HCl

Question 15

What stimulates HCl secretion?

Answer 15

Histamine
Gastrin
Acetylcholine
ALL ACT ON PARIETAL CELL

Question 16

Pyloric gland

Answer 16

Mostly mucus cells
Secrete mucus for lubrication and protect stomach wall from digestion
Also have enteroendocrine cells which secrete gastrin (G cells) and somatostatin (D cells)

Question 17

Surface mucus cells

Answer 17

Entire surface of stomach mucose has mucus cells in between glands. Protection as any irritation causes these to produce mucus

Question 18

Stimulation of gastric acid secretion (enterochromaffin-like cells)

Answer 18

ECLs secrete histamine when gastrin and Ach binds to it.

This histamine binds to H2R receptor on parietal cells

Question 19

3 phases of gastric secretion

Answer 19

1. cephalic phase
2. gastric phase
3. intestinal phase

Question 20

Cephalic phase

Answer 20

Begins before meal and lasts up to 30 mins into meal
shortest phase
30% of gastric secretion
parasymp - vagus nerve mediates via caeliac plexus
Ach acts directly on parietal, indirectly by causing release of gastrin from G cells, indirecly by causing ECL to release histamine

Question 21

Gastric phase

Answer 21

Longest phase, lasting up to 2.5 hours after start of meal
60% of gastric secretion
Trigger by food causing distention in stomach and presence of aa and peptides

Question 22

Gastric phase excites…?

Answer 22

Long vagal reflexes
local enteric reflexes
which stimulate gastrin release and nerves to increase Ach release

Question 23

Intestinal phase

Answer 23

Triggered by presence of food in duodenum.
Stimulatory; G-cells in duo release gastrin
Inhib (predominant)

Question 24

Inhibitory effects of intestinal phase

Answer 24

-Somatostatin released from D cells in duo
- Acid mediates secretin release into blood, inhibiting release of gastrin and reducing parietal response to gastrin
- fatty acids in duo causes the release of gastric inhibitory polypeptide (GIP) and cholecystokin (CKK) which inhibit parietal acid secretion
Secretin, CCK and GIP are entrogastrones

Question 25

PANCREATIC DUCT SECRETION

Answer 25

A little NaCl and H2O is secreted by acinus into lumen under influence of CCK
NaHCO3 and H2O secreted by duct epithelial cels under influence of secretin

Question 26

How is HCO3- made in pancreatic duct?

Answer 26

Same way as parietal cells (CO2 from blood + H2O) to form H+ and HCO3- with the catalyst carbonic anhydrase

Question 27

How much HCO3- is made in pancreatic ducts?

Answer 27

140 mM

Question 28

How does H+ leave cell

Answer 28

Through basolateral membrane via Na+/H+ housekeeping pump

grad of Na+ kept by K+/Na+ pump

Question 29

How does HCO3- leave cell?

Answer 29

Thorugh apical membrane into lumen.Using HCO3-/Cl- exchanger. This results in lots of Cl- in the cell, so has to leave through apical membrane via CFTR channel

Question 30

Effect of secretin on these cells

Answer 30

Secretin stimulates cAMP in cell, which opens the CFTR channels. So more Cl- can pass through, driving the HCO3- pump

Question 31

How does Na get into lumen to form NaHCO3

Answer 31

Diffuses from blood through tight juntions via parracellular pathway

Question 32

What happens when lumen HCO3- conc gets very high?

Answer 32

The HCO3-/Cl- transporter doesnt work .

So HCO3- leaves cell through the CFTR channel also

Question 33

Na+/H+ exchanger name

Answer 33

NHE family

Question 34

HCO3-/Cl- exchanger name

Answer 34

AE and SLC26 family

Question 35

Na+-HCO3- contransporter

Answer 35

NBC family

Question 36

H+ pumps

Answer 36

P-type and V-type ATPases