GIT Secretions

Question 1

What are the different gastric cells? (Stomach) (5)

Answer 1

• G cells
• D cells
• ECL cells
• Chief cells
• Parietal cells

Question 2

What do parietal cells secrete?

Answer 2

Acid

Question 3

What do G cells secrete?

Answer 3

Gastrin

Question 4

What do D cells secrete?

Answer 4

Somatostatin

Question 5

What do ECL cells secrete?

Answer 5

Histamine

Question 6

What are secretory glands in the intestine called?

Answer 6

Crypts of Liberkün

Question 7

What do chief cells secrete?

Answer 7

Pepsinogen

Question 8

How does the control of gastric secretion work in the cephalic phase?

Answer 8

• ACh is a strong stimulant for the release of acid and pepsinogen (parietal and chief cells)
• ACh also activates ECL cells which release histamine to act on the parietal cell
• ACh turns off D cells which normally produce somatostatin to inhibit gastrin production
• ACh turns on G cells, gastrin activates ECL cell, parietal cell and D cell

Question 9

What is the main stimulant for acid release?

Answer 9

Histamine

Question 10

What happens to secretions in the gastric phase?

Answer 10

• stretch of the stomach stimulates enteric NS - increases release of ACh
• presence of food actively stimulates G-cells as well

Question 11

Control of acid release: ACh

Answer 11

….

Question 12

Somatostatin acts on parietal/chief cells through…….

Answer 12

Gi linked receptor, inhibits cAMP and PKA

Question 13

What are the intestinal glands? (4)

Answer 13

• goblet cells
• S-cells
• I-cells
• Paneth cells

Question 14

What do globlet cells produce?

Answer 14

Mucous

Question 15

What do S-cells secrete?

Answer 15

Secretin

Question 16

What do I-cells secrete?

Answer 16

Cholecystokinin

Question 17

What is the only intestinal enzyme?

Answer 17

Enteropeptidase: activates trypsinogen to trypsin

Question 18

Chyme is …….

Answer 18

Hypertonicity and pulls water out of intestinal cells

Question 19

What are the exocrine pancreatic cells?

Answer 19

Acinar cells

Question 20

Where do pancreatic enzymes enter the intestine?

Answer 20

Sphincter of Oddi

Question 21

What are the pro-enzymes secreted by the pancreas?

Answer 21

• chymotrypsin
• elastase
• carboxypeptidase

Cleaved and activated by trypsin

Question 22

What are the active enzymes secreted by the pancreas? (5)

Answer 22

• amylase
• lipase
• carboxyl lipase (cholesterol)
• DNase
• RNase

Question 23

How are pancreatic enzymes secreted?

Answer 23

• zymogens stored in secretory vesicles
• exocytosis - uses SNARE proteins
• triggered by PKC and PKA calcium sensitisation of SNARE proteins

Question 24

How are pancreatic secretions inhibited?

Answer 24

• somatostatin
• cAMP
• decreases PKA (Gi linked)
• decreases calcium sensitisation

Question 25

What does PKC do in pancreatic secretion?

Answer 25

Phosphorylates SNARE proteins and reduces the conc. of calcium needed to activate exocytosis

Question 26

How is pancreatic fluid secreted? (5)

Answer 26

1. Na/K ATPase creates sodium gradient (3 Na out, 2 K+ in) 2. pump pumps Na(3), Cl(6) and K(3) in to cells 3. K has channels so K does bog laps as usual 4. Cl- diffuses our through apical membrane 5. Pulls Na+ - para cellular route (+water)

Question 27

Pancreatic fluid cells have an unusually high concentration of.......

Answer 27

Chloride

Question 28

What stimulates pancreatic fluid release?

Answer 28

ACh, CCK - increase intracellular Ca2+ which opens apical chloride channel

Question 29

Pancreatic bicarbonate is made by the ......

Answer 29

Epithelial cells of pancreatic duct

Question 30

How is pancreatic bicarbonate secreted?

Answer 30

1. CO2 moves in from basolateral surface 2. Carbonic anhydrase makes bicarbonate and acid 3. Acid is moved back across basolateral membrane through H+ ATPase pump and Na+/H+ antiport 4. Bicarbonate is also transported directly in the cell with a bicarbonate/Na+ symport 5. Bicarbonate leaves the cell using a Cl-/HCO3- antiport 6. Chloride has transporters so it does bog laps on the apical membrane (cystic fibrosis transmembrane regulator CFTR)

Question 31

What is the regulated part of pancreatic bicarbonate release?

Answer 31

CFTR channel - secretin acts through Gs, ACh also has some effect (PKC, calcium...)

Question 32

What happens with pancreatic releases in the cephalic phase?

Answer 32

ACh stimulates release, gastrin release

Question 33

How does CCK affect pancreatic secretions in the intestinal phase?

Answer 33

Acts on acinar cells, also acts on nerves | Secretin acts only on bicarbonate receptors, no nerves

Question 34

What are the characteristics of bile?

Answer 34

- made in liver - secreted into bile ducts - stored in gallbladder - primary bile salts made in gallbladder from cholesterol - secondary bile salts altered by bacteria in gut

Question 35

Where are bile salts reabsorbed?

Answer 35

Ilium

Question 36

What is the bile salts reuptake pathway?

Answer 36

Hepatocytes use Na+ bile salt symport and ATP powered organic anointed transporter, exported by bile salt export protein (BSEP)

Question 37

What controls release of bile salts?

Answer 37

- cephalic and gastric: ACh and gastrin - intestinal: CCK Causes contraction of gallbladder and relaxation of sphincter of Oddi

Question 38

How are bile salts concentrated?

Answer 38

1. Na+/K+ pumps ions from apical membrane, through the cell and across the basal membrane 2. Cl- moves across by osmosis 3. Water follows 4. Bile salts are concentrated