Physiology: Bile

Bile acids/salts are made in the ____ and are important in…?

liver

fat digestion

Bile components concentrations are modified by the…?

gallbladder and bile ducts

___ is a unique and vital aqueous secretion of the liver that is formed by the hepatocyte and modified down stream by absorptive and secretory properties of the bile duct epithelial cells

Bile

Most of the components that make up bile are synthesized by the _____ and secreted into the _____

liver

bile ducts

t/f: bilirubin is cleared and produced by the liver

false. Bilirubin is cleared by the liver but not produced by the liver

what are the components of bile? what is the major component?

bile salts are the major component (61%)

how is bilirubin produced?

produced from the degradation of hemoglobin from erythrocytes undergoing normal senescence

High bilirubin levels are seen in adults, but the disorder is more common in newborn infants. Why?

This is because it takes some time after birth for an infant to start efficiently metabolizing bilirubin and excreting it in their stool. (normal for newborns to have jaundice)

what is the life span of RBCs?

120 days

jaundice is an indication of what?

too much conjugated bilirubin circulating in blood (not exiting body via feces)

why does the liver convert cholesterol to cholic acid?

Cholic Acid has 5 charged groups and is 7253X more soluble in aqueous solution than cholesterol

Cholic and Chenodeoxycholic bile acids are synthesized in the liver from …?

cholesterol (primary bile acids)

Primary bile acids can be modified in the gut by bacteria to form the secondary bile acids:

Deoxycholic and Lithocholic acid

Secondary bile acids are conjugated with ________ and are considered to be functionally equivalent to primary bile acids.

glycine or taurine

the amphipathic property of bile acids allows what?

allows bile acids to facilitate emulsifying fats and the formation of micelles

what is essential for the efficient absorption of lipids?

micellar solubilization

Micellar solubilization of polar lipids greatly increases their rate of diffusion to the epithelial surface of the small intestine.

desribe the process of bile acid function in digestion

1. emulsification of fat droplets by bile salts

2. hydrolysis of TGs in emulsified fat dropelets into fatty acids and MGs

3. dissolving of FAs and monogylcerides into micelles to produce “mixed micelles”

Bile salts are synthesized from __________ in the liver

cholesterol

The bile salt pool is how many grams and circulates how many times a day?

2-4 grams

6-10 times a day

Only % of bile salt pool are lost each day to excretion

15-30%

describe how bile salts are recycled in the body?

the liver removes bile salts from circulation (from ileum, travels through portal vein to be reused in liver) and secretes them back into the bile

In the distal ileum bile acids are taken up by the enterocytes by 2 methods:

1. Na+ dependent symporter

2. Diffusion across the cell membrane using the hydrophobic surface of the bile acid to fuse with the lipid of the cell membrane

Between meals most bile secreted by the liver is stored and concentrated in the…?

gallbladder

how does ingestion of food affect bile flow?

Eating causes contraction of the gallbladder (CCK and neural stimulation) and relaxation of the sphincter of Oddi

what molecule controls gallbladder contraction and sphincter of Oddi relaxation?

CCK

As the concentration of ions in the interstitial space increases, what happens to H2O?

H2O flows out of the bile following the ion concentration gradient passively.

Basically, ions are removed from the bile in the gall bladder and are secreted into the interstitial space.

As the concentration of ions in the interstitial space increases H2O flows out of the bile following the ion concentration gradient passively.

This process concentrates gall bladder bile ____ times.

10X to 20X

what cells are responsible for secretion of bicarbonate rich fluid via transporters that create osmotic gradients within the bile canalicular lumen?

Cholangiocytes (help neutralize low pH of chyme)

where do gallstones form?

Stones can develop anywhere in the biliary tract where there is bile: within the liver, gallbladder and common bile duct.

The process of gallstone formation is referred to as

cholelithiasis

what are gallstones formed from? (aka what are the 2 types of gallstones)

cholesterol (70%)

pigment - black or brown (30%)

(pts can have a mixture of the 2 gallstone types)

characteristics of cholelithiasis

• slow process,

• usually causes no pain or other symptoms.

• majority of gallstones are either the cholesterol or mixed type

• can range in size from a few millimeters to several centimeters in diameter

t/f: Most people with gallstones (about 80%) never have symptoms

true

A blocked bile duct may result in…?

inflammation of the gallbladder

A gallstone or bile stone in the common bile duct may block the …?

pancreatic duct, causing painful inflammation of the pancreas or pancreatitis (most common symptom)

Bile stones can occur throughout the bilary tree and if the stone is large enough it can block …?

bile flow

gallbladder with mixed stones

Bile acids are synthesized from cholesterol by …?

hepatocytes

describe the structure of bile acids?

amphipathic having one surface be hydrophobic and the other hydrophilic

bile acids play an important role in what processes?

• fat emulsification

• micelle formation

The liver takes up _____ from the circulation and secretes it into the bile and it is eliminated from the body through the urine and feces

bilirubin (this is why our pee and poop is the color)