15 - Gastric Physiology, Acid Secretion, and Digestion Flashcards Preview

GI / Hepatology > 15 - Gastric Physiology, Acid Secretion, and Digestion > Flashcards

Flashcards in 15 - Gastric Physiology, Acid Secretion, and Digestion Deck (63)
Loading flashcards...
1

Pancreas

Mixed endocrine-exocrine organ
Primarily exocrine
Acini = 84% Ducts, 5% of pancreatic mass
Islets (endocrine pancreas) = 1% of pancreatic mass
Both ducts and acini of the exocrine pancreas are secretory

2

Exocrine cells of the pancreas

Polarized
Secrete from apical surfaces
Respond to signals delivered to basolateral surfaces

3

Acinar cells

Secrete enzymes

4

Duct Cells

Secrete water, bicarb, sodium

5

Centroacinar cells

Cells that project back into the acini

6

Mechanism for creating bicarb that is eventually shuttled into the lumen of the duct

CO2 + H2O = HCO3- and H+

H+ moves into bloodstream in exchange for sodium
Sodium moves into the bloodstream in exchange for potassium via the Sodium/Potassium pump (sodium is kind of just a middle man)
Bicarb moves into the lumen in exchange for chloride.

7

Secretin

H+ stimulates secretin's production.
Produced by S Cells
Stimulates cAMP (works with nerves, works without nerves)
Duct cells put out a lot of water and bicarb.

8

Cholecystokinin (CKK)

Produced by I cells
Stimulates duct cells to release intracellular calcium (via IP3 cascade, working together with nerves)
Calcium is the signal for pancreatic enzyme release.

9

What is the ideal pH fro pancreatic enzymes to work?

Neutral!

This means the pancreas has to secrete bicarb along with its enzymes so that the acidic pH of the gut can be combatted!

10

Secretin response to acid

Acid induces secretin-releasing peptides (S-RPs) to be released.
Vagal stimulation also induces this.
S-RPs stimulate S cells
S cells release secretin

11

Secretin's effect on the duct

Secretin stimulates receptors on the duct cells.
Duct cells increase cAMP production.

Carbonic anhydrase catalyzes the production of H+ and HCO3- from CO2 and H2O
Luminal Cl- channel (CTFR) opens, and is coupled to a Cl-/HCO3- antiport channel.
Basolateral Na+/H+ antiport, Na+/K+ ATPase & H+ ATPase (exporting H+

12

Overal trend. When the gut gets more acidic (via parietal cells), the blood

Gets more alkaline

13

When the gut gets more basic (via pancreatic secretion), the blood

Gets more acidic

14

What amplifies the absorptive surface of the gut?!

Length
Plicae
Villi
Microvilli
Glycocalyx

15

How big is the surface area of the intestines?

A tennis court!!!
300 square meters

16

Small intestinal mucosa crypt-villus organization

Crypt-villus axis is continuous (Cores of villi contain lamina propria)
Stem cells are found near the base of the crypts (generate crypt epithelial cells that line the villi)
Enterocytes mature at the crypt-villus junction
Old cells are extruded from villus tips.
It's like an escalator.

17

Core of microvilli

Microfilaments

18

External plasma membrane surface of microvilli

Studded
Studs are clathrin, enzymes and transporters.

19

Terminal Web

Microfilaments in microvilli enter the cells and are linked by myosin. This is called the terminal web.

20

Beneath the terminal web

Intermediate Filaments (providing structure)

21

Celiac Pathogenesis

Gluten triggers a hypersensitivity reaction against the gut.
Crypt cells turn over crazy quicksies.
The intestines are now lined with crypt cells without the microvilli and junk!!!!!! Can't absorb!!!!!!!!

Steatorrhea
Fat-soluble vitamin deficiencies!

22

5 patterns of digestion-absorption

No digestion (glucose transport)

Luminal hydrolysis of polymer to monomers (protein to AA, AA transport)

Brush border hydrolysis of oligomer to monomer (Sucrose to fructose & glucose, glucose & fructose transport)

Intracellular hydrolysis (peptide uptake, breakdown to AA, AA export)

Luminal hydrolysis followed by intracellular resynthesis (triglyceride to glycerol & fatty acids, uptake of those components, triglyceride resynthesis, triglyceride export)

23

Where are carbohydrates, proteins & lipids maximally absorbed?

Duodenum

Less absorbed further downstream, no more absorption once you hit the ileum.

24

Where are calcium, iron and folate actively absorbed?

Duodenum

Calcium also continues to be absorbed throughout small intestine.

25

Where are bile acids maximally absorbed?

Ileum

Less-so in the jejunum and the ascending colon

26

Where is B12 (cobalamin) absorbed?

ONLY IN THE ILEUM

27

What MUST you do (nutritionally) if you've had to remove your ileum?

B12 injections. Can't absorb it anymore.

28

Carbohydrate digestion

Luminal & Surface enzymes & transporters

Luminal digestion, terminating on the microvilli with immediate capture.

29

Carbohydrate Digestion - Luminal Enzymes

Amylase

30

Carbohydrate Digestion - Brush Border Enzymes

Glucoamylase
Lactase
Sucrase-Isomaltase