27 Gi Secretions - Ii: Hepatobiliary, Intestinal Absorption And Secretion

Front 1

Heres a picture of GI circulation

Back 1

Front 2

Liver functions

Back 2

1. Carb, protein, and lipid metabolism

2. Hormone metabolism

3. Detoxification

4. Storage

5. Bile production

6. Immune function

Front 3

What is the biliary tract?

Back 3

The organs and ducts that make and store bile and deliver it to the SI

Front 4

What are some species differences in the Biliary tract?

Back 4

Ruminants/pigs: sphincter of Oddi is less defined = continuous secretion of bile

Horses: no gull bladder = continuous secretion of bile

Dogs/cats: intermittent secretion = meal dependent

Front 5

What are the 3 'tubes' that make up the portal triad?

Back 5

Hepatic artery

Portal Vein

Bile duct

**hepatic and portal vessels go towards central vein, bile dict is the opposite way

Front 6

Hepatobiliary tract - What do hepatocytes do?

Back 6

Bile synthesis from cholesterol

Front 7

Hepatobiliary tract - What does the Canaliculus do?

Back 7

Bile formation

Front 8

Hepatobiliary tract - What does the ductules and ducts do?

Back 8

Modification of bile

Absorption and secretion

Front 9

Hepatobiliary tract - What does the gallbladder do?

Back 9

Concentration

Storage

Delivery

Front 10

Hepatobiliary tract - What does the sphincter of Oddi do?

Back 10

Regulated delivery of bile to duodenum

Prevention of reflux

Front 11

Explain the regulation of bile secretion...

Back 11

1. nutrients in SI cause release of Secretin from S cells (H+) and CCK from I cells (FA, peptides)

2. CCK can...

-neuro root stimulate the vagus to DVC to vagal efferents to release bile (via Ach)

-blood to DVC to vagal efferents to release bile (via Ach)

-blood to gall bladder

3. Secretin can act on liver to release bile?

Front 12

What are the 3 types of bile acids?

Back 12

1. Primary (pH=6)

2. Conjugated (pK=2-4)

3. Secondary (products of bacterial metabolism)

Front 13

What are primary bile acids composed of?

Back 13

-cholic acid, chenodeoxycholic acid (high hyocholic in pigs)

-Hepatic synthesis from cholesterol

Front 14

What are the 2 ways that Primary bile acids can be formed through hepatic synthesis from cholesterol?

Back 14

1. Classical (neutral) pathway (75-90%): in microsomes

2. Alternate (acidic) pathway: in mitochondria

**both have rate limiting enzymes

Front 15

hat is the importance of conjugated bile acids?

Back 15

-Decrease pK of bile acids = charged complexes (bile salts) in intestinal lumen (pH=6)

-Bile salts cannot be absorbed passively in upper intestine

-retained in intestinal lumen for fat digestion/absorption

Front 16

What are the 2 conjugated bile acids?

Back 16

Taurocholic (pK = 2) conjugated to taurine

Glycocholic (pK = 4) conjugated to glycine

Front 17

Conjugated acids are actively absorbed in the ileum via what?

Back 17

ASBT (Apical Sodium dependent Bile acid Transporter)

OST (Organic Solute Transporter - basolateral)

Front 18

What are secondary bile acids?

Back 18

Deoxycholic acid, ursodexoycholic and lithocholic acid

-formed in the colon by bacterial dehydroxylation

(some absorbed in colon BUT more excreted)

Front 19

Function of bile acids with lipid and fat soluble vitamin digestion?

Back 19

-lipid emulsification

-micelle formation

-lipid absorption

Front 20

Function of bile acids with Cholesterol metabolism?

Back 20

Bile acid synthesis and excretion

**eliminate cholesterol

Front 21

Function of bile acids with protein digestion

Back 21

Bile acids denature proteins

-accelerate digestion by pancreatic proteases

Front 22

Function of bile acids with Antimicrobial effects

Back 22

-Cholic acid and deoxycholic acid disturb membrane integrity

-leakage of H+ K+ into bacterial cell

==== CELL DEATH

Front 23

Function of bile acids with Metabolic signalling molecules

Back 23

improve glucose tolerance and diabetic control

Front 24

Entero-hepatic circulation of bile...

Back 24

-95% of bile acids are recycled via portal vein at distal ileum

-recirculated back to liver to negatively feed back to bile synthesis (inhibit)

Front 25

Entero-hepatic circulation of bile - what do hepatocytes do?

Back 25

1. take up conjugated and unconjugated bile acids into the blood (portal vein)

2. synthesize new bile acids from cholesterol

-unconjugated are conjugated with taurine or glycine

-conjugated transported across apical plasma membrane (canalicular) into bile duct

Front 26

Entero-hepatic circulation of bile - what does the gull bladder do?

Back 26

1. Stores bile between meals

2. Neuro-hormonal pathways cause contraction and relaxation of the sphincter of Oddi at the ampulla of Vater resulting in transfer of bile into intestines

Front 27

Entero-hepatic circulation of bile - what does the intestine do?

Back 27

1. Conjugated bile acids in SI are taken up by Apical Sodium dependent Bile salt Transporter (ASBT) in end ileum and Organic solute Transporter (OST)

2. Some bile acids are deconjugated in proximal SI by protease removal of glycine or taurine and absorbed passively

Front 28

Entero-hepatic circulation of bile - what is the total bile acids pool?

Back 28

-95% is recirculated from intestine

-5% lost in stool

Front 29

Since bile acid synthesis can be up or down regulated depending on requirements, how is bile acid synthesis affected by ileal resection and feeding bile salts?

Back 29

-Increased secretion usually increases rate of return of bile acids to the liver via portal blood (negative feed back on synthesis)

Front 30

How is bile acid synthesis affected by ileal resection SPECIFICALLY?

-interruption of enterohepatic circulation?

-Increased bacterial overgrowth and beconjugation?

-Loss of ileal brake?

Back 30

-interruption of enterohepatic circulation = increase in hepatic bile synthesis

-Increased bacterial overgrowth and beconjugation = bile acid malabsorption = bile and FA diarrhea

-Loss of ileal brake = increased motility

Front 31

How is bile acid synthesis affected by bile acid feeding SPECIFICALLY?

Back 31

Feeding bile acids suppresses the new synthesis of bile acids by hepatocytes

Front 32

What is pathway that bile is secreted?

Back 32

-hepatocytes in canaliculi

-Bile ducts

-hepatic duct

-common bile duct

Front 33

What is bile acid composition?

Back 33

-solutes 4-10%

-bile salts 64% = electrolytes, phospholipids, cholesterol, bile pigments, and protein

Front 34

What are chlorites and what do they stimulate?

Back 34

-secretin and CCK

-bile secretion