Lecture 8 - Functional Hepatic Anatomy/bile formation (Freeman)

Question 1

bile formation provides three things

Answer 1

1. provides a source of bile acids for fat digestion and absorption
2. provides an excretory route for drugs and metabolites
3. provides additional buffer for neutralization of H ion in the duodenum

Question 2

what are the 3 different situations regarding gall bladder function seen in domestic animals?

Answer 2

1. in the ruminant and pig, the sphincter of oddi is poorly defined so there is relatively continuous secretion of hepatic bile into the intestine
2. the horse does not have a gall bladder so the secretion of bile is continuous
3. in the dog and cat, they are typically only fed once a day so bile is stored in the gall bladder and during interdigestive periods, the sphincter of oddi is closed.

Question 3

how is bile stored in the gall bladder?

Answer 3

different absorptive processes for electrolytes and water in gall bladder mucosa modify the concentration and relative composition of hepatic bile, concentrating bile 5 to 20 times its original concentration. this allows a large concentration of bile to be stored in a small capacity.

Question 4

what is the main stimulus for gall bladder emptying?

Answer 4

food entering the duodenum

Question 5

what are the two processes required to empty the gall bladder?

Answer 5

contraction of the gall bladder and relaxation of the sphincter of oddi

Question 6

what stimulates the release of cholecystokinin (CCK) and where is it released from?

Answer 6

CCK is found in the I cell of proximal small intestinal mucosa.
it is released in response to increasing loads of fatty acids in the intestinal lumen

Question 7

what inhibits the release of cholecystokinin (CCK)?

Answer 7

its release is inhibited by high luminal concentrations of bile acids

Question 8

what does CCK do in response to lipid and protein digestion products in the lumen?

Answer 8

1. contracts the gall bladder

2. relaxes the sphincter and delivers a high concentration of bile salts for small bowel digestive processes

Question 9

describe the concentration of bile

Answer 9

• bile salts account for about half of the total solutes of bile
• bilirubin, cholesterol, lechithin, and electorlytes of plasma are also secreted in large quantities

Question 10

what is precursor of bile salts?

Answer 10

cholesterol

Question 11

how are bile salts formed from cholesterol?

Answer 11

choleserol is converted to colic acid or chenodeoxycholic acid. these acids then combine with glycine and sometimes taurine to form glyco- and tauro-conjugated bile salts

Question 12

what does conjugation of bile salts do?

Answer 12

conjugation lowers the pKa to well below the physiologic range of biliary and intestinal pH, so conjugated bile acids become ionized anions (called bile salts) rather than undissociated bile acids.

in the ionized form, they are less likely to be absorbed by small intestine and so maintain a high intraluminal concentration. they are also more soluble when conjugated, which facilitates dispersal in the lumen.

Question 13

what do humans conjugate bile salts with?

Answer 13

glycine and taurine

Question 14

what do dogs and cats conjugate bile salts with?

Answer 14

primarily taurine

Question 15

can dogs and cats convert to glycine concentration if taurine is deficient?

Answer 15

dogs can, cats CANNOT

Question 16

Bile salts are amphiphathic molecules. define this term

Answer 16

they have polar and nonpolar functional groups and therefore function as detergents

Question 17

what are two important functions of bile salts as amphipathic molecules

Answer 17

1. the have a detergent action on fat particles in the food which allow the intestine to break the fat globules into minute sizes by agitation. this is called the emulsifying or detergent function of bile salts
2. bile salts help in absorption of fatty acids, monoglycerides, cholesterol, and other lipids from the intestinal tract.

Question 18

how do bile salts help absorb fatty acids ?

Answer 18

by forming minute complexes with lipids called micelles. they can be transferred across the unstirred layer to the mucosa where their contents are absorbed.

Question 19

when are micelles formed?

Answer 19

when bile salts reach a particular concentration in the intestine, called the critical micellar concentration (CMC)

Question 20

where is the fat soluble vitamin K stored in the body?

Answer 20

it is not stored anywhere in the body! therefore if bile secretion stops, a deficiency of vitamin K develops and this results in deficient formation of several blood coagulation factors

Question 21

what are two components of bile secretion?

Answer 21

1. bile salt recovery through the enterohepatic circulation

2. water and electrolyte component of bile that is dependent on the effects of secretin in the bile ductules and ducts

Question 22

what concentration of bile salts is typically reabsorbed?

Answer 22

~ 94%

Question 23

bile-salt dependent flow

Answer 23

this is how bile salts are transported. they are actively transported from the hepatocyte into the bile canaliculi by an energy dependent process where cations and water ollow passively so that bile becomes iso-osmotic.

bile-salt dependent flow depends upon the recirculation of bile salts from the intestine

Question 24

when is the bile salt-dependent flow greatest?

Answer 24

bile salt-dependent flow is greatest when bile salts are reabsorbed from the intestine and transported back to the liver to be secreted again.

Question 25

what are transported from the hepatocytes in addition to bile salts?

Answer 25

lechithin and cholesterol are also transported from the hepatocytes

Question 26

how are secondary bile salts produced?

name two examples of secondary bile salts

Answer 26

produced from bacterial conjugation and dehydroxylation of bile salts that are not absorbed in the small intestine and enter the colon

2 examples of secondary bile salts: deoxycholic acid and lithocholic acid

Question 27

where does conversion to secondary bile salts predominantly take place?

Answer 27

colon

Question 28

where does the main system for bile absorption in the intestine take place?

Answer 28

active transport by the ileum

the jejunum can recover a portion by passive uptake

Question 29

what does bile secretion represent mainly? secreted by what?

Answer 29

a watery solution of NaHCO3 and NaCl

secreted by epithelial cells of the bile ductules and ducts that is influenced by secretin

Question 30

secretin feedback mechanism

Answer 30

bicarbonate passes into the small intestine and combines with bicarbonate from the pancreas in neutralizing acid from the stomach.

the secretin feedback mechanism for neutralizing duodenal acid operates thorugh the liver ductules and ducts in the same manner as the pancreas

Question 31

what is the unstirred layer

Answer 31

a thin layer of lumen contents in water on the surface of epithelial cells that is poorly mixed, or not mixed at all.

Question 32

can free fatty acids and 2-monoglycerides diffuse through the unstirred layer?

Answer 32

no!

Question 33

how do free fatty acids and monoglycerides diffuse through the unstirred layer?

Answer 33

in micelles.

Question 34

what are micelles the products of?

what do micelles prevent?

Answer 34

triglyceride hydrolysis
.
they prevent segregation of hydrolysis products