PHYS: Bile Secretion and Gall Bladder Function

Question 1

Why is bile necessary?

Answer 1

Bile is necessary for the digestion and absorption of lipids in the small intestine

Question 2

What are the 4 major components of bile (and their relative percentages)?

Answer 2

Bile salts (50%)
Phospholipids (40%)
Cholesterol (4%)
Bile pigments (2%)

Question 3

What are bile salts?

Answer 3

bile acids + conjugated forms of bile acids

Question 4

What is the molecule used to make bile salts?

Answer 4

cholesterol

Question 5

What enzyme acts on cholesterol to form bile salts?

Answer 5

7-alpha-hydrozylase

Question 6

What is the most common bile acid (primary)?

Answer 6

cholic acid

Question 7

What happens when cholic acid (primary bile salts) are secreted into the lumen?

Answer 7

primary bile acids are dehydroxylated at C7 (by bacteria) to become secondary bile acids

Question 8

How do secondary bile acids become bile salts?

Answer 8

they get coupled to glycine or taurine

Question 9

What is the characteristic of bile salts that allows them to emulsify lipids and solubilize products of digestion into micelles?

Answer 9

amphipathic nature

Question 10

What is a micelle?

Answer 10

core of hydrophobic lipid products with a lining of phospholipids, lecithin, cholesterol, and bile salts

Question 11

What is the major role of bile salts?

Answer 11

osmotic driving force for water and electrolytes into the bile duct

Question 12

What is the major bile pigment? What is its color?

Answer 12

bilirubin (yellow pigment)

Question 13

How is bilirubin formed?

Answer 13

Hb metabolism

Question 14

What protein stimulates the secretion of HCO3-, Na+ and water into the bile?

Answer 14

secretin

Question 15

What organ synthesizes bile?

Answer 15

liver

Question 16

What is the roll of the gallbladder?

Answer 16

store bile
concentrate bile
eject bile

Question 17

What protein stimulates the gallbladder to contract?

Answer 17

CCK

Question 18

What does CCK do to cause the gallbladder to contract?

Answer 18

CCK triggers a vagovagal reflex→ Ach released to contract the gallbladder and relax the sphincter of Oddi

Question 19

Into what does the gallbladder secrete bile?

Answer 19

bile duct

Question 20

What is the name of the sphincter though which bile must pass to get into the duodenum?

Answer 20

sphinter of Oddi

Question 21

How do components of bile salts get reabsorbed?

Answer 21

• passively reabsorbed in dudenum

- actively transported in the ileum

Question 22

What characteristic of molecules determines if they will get passively reabsorbed out of the duodenum lumen?

Answer 22

lipophillic molecules (ex. unionized bile salts) get passively reabsorbed

Question 23

What characteristic of molecules determines if they will get actively transported into the duodenum lumen?

Answer 23

hydrophillic molecules (ex. cholic acid with tons of -OH groups or conjugated bile salts that are ionized) are more likely to go to the ileum before being absorbed

Question 24

What is responsible for the active transport of bile salts into the ileum?

Answer 24

sodium dependent active transporters

Question 25

What happens after bile salts are absorbed in the ileum?

Answer 25

recirculated to the liver via enterohepatic (portal) circulation

Question 26

How do hepatocytes reabsorb bile salts from the portal blood?

Answer 26

sodium dependent bile acid uptake that works to pull bile salts and sodium into the cell (along the concentration gradient set up by Na+/K+ ATPase)

Question 27

How do bile salts in hepatocytes get transported into the bile canaliculi?

Answer 27

facilitated diffusion (sets up osmotic gradient to pull electrolytes in)

Question 28

What is a major inhibitor of 7-alpha-hydroxylaase?

Answer 28

bile salts

Question 29

How often do bile salts travel via the enterohepatic circulation?

Answer 29

system is repeated around 12-15 times in a day

Question 30

Why is the enterohepatic circulation (and ileum) important?

Answer 30

and vastly decreases the amount of bile salts that the liver must replace in a day (only the 5% or 500mg lost in stool)

Question 31

Where is hemoglobin borken down?

Answer 31

reticuloendothelial system

Question 32

What is bilirubin bound to in blood?

Answer 32

albumin

Question 33

What does the liver do with bilirubin?

Answer 33

extracts it and conjugates to to glucoronic acid (forming bilirubin glucoronide)

Question 34

What happens to bilirubin glucoronide after formation?

Answer 34

bilirubin glucuronide is secreted into bile, and in the duodenum, bacteria can deconjugate it back to bilirubin.

Question 35

After bilirubin is re-formed int the duodneum, what is its fate?

Answer 35

reduced to urobilinogen

Question 36

What happens if urobilinogen stays in the intestine?

Answer 36

gets oxidized to stercobilin (give feces its brown color)

OR gets recirculated via the portal blood to the liver.

Question 37

What happens if urobilinogen enters the systemic blood?

Answer 37

travels to the kidney where it is converted to urobilin (gives urine its dark color)

Question 38

How does bile get concentrated in the gallbladder?

Answer 38

epithelial cells of gallbladder absorb ions and water in an isosmotic fashion (micelles are negatively charged and bind up excess Na+ in bile to keep it isosmotic–even though it is concentrated)

Question 39

When does ejection of bile occur?

Answer 39

around 30 minutes after ingestion of a meal

Question 40

What cells release CCK?

Answer 40

I cells

Question 41

Does the gallbladder release all the bile in a continuous movement?

Answer 41

no, occurs in pulsatile “spurts”

Question 42

True or false: all bile produced is supersaturated with cholesterol.

Answer 42

TRUE

Question 43

Why are obese people more susceptible to cholesterol stones?

Answer 43

high cholesterol levels

Question 44

What acts as the nidus for crystal formation and precipitation of cholesterol stones?

Answer 44

bilirubin

Question 45

What is the cause of pigment stones?

Answer 45

bile is saturated with unconjugated bilirubin→ not water soluble→ becomes stones

Question 46

Why would you get increased levels of unconjugated bilirubin (which leads to pigment stones)?

Answer 46

Gall bladder wall is damaged by bacteria → leads to the increased beta glucuronidase (enzyme that deconjugates bilirubin glucuronide back to unconjugated bilirubin)