Flashcards in Lecture 8 - Functional Hepatic Anatomy/bile formation (Freeman) Deck (34):
bile formation provides three things
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
what are the 3 different situations regarding gall bladder function seen in domestic animals?
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.
how is bile stored in the gall bladder?
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.
what is the main stimulus for gall bladder emptying?
food entering the duodenum
what are the two processes required to empty the gall bladder?
contraction of the gall bladder and relaxation of the sphincter of oddi
what stimulates the release of cholecystokinin (CCK) and where is it released from?
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
what inhibits the release of cholecystokinin (CCK)?
its release is inhibited by high luminal concentrations of bile acids
what does CCK do in response to lipid and protein digestion products in the lumen?
1. contracts the gall bladder
2. relaxes the sphincter and delivers a high concentration of bile salts for small bowel digestive processes
describe the concentration of bile
- 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
what is precursor of bile salts?
how are bile salts formed from cholesterol?
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
what does conjugation of bile salts do?
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.
what do humans conjugate bile salts with?
glycine and taurine
what do dogs and cats conjugate bile salts with?
can dogs and cats convert to glycine concentration if taurine is deficient?
dogs can, cats CANNOT
Bile salts are amphiphathic molecules. define this term
they have polar and nonpolar functional groups and therefore function as detergents
what are two important functions of bile salts as amphipathic molecules
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.
how do bile salts help absorb fatty acids ?
by forming minute complexes with lipids called micelles. they can be transferred across the unstirred layer to the mucosa where their contents are absorbed.
when are micelles formed?
when bile salts reach a particular concentration in the intestine, called the critical micellar concentration (CMC)
where is the fat soluble vitamin K stored in the body?
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
what are two components of bile secretion?
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
what concentration of bile salts is typically reabsorbed?
bile-salt dependent flow
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
when is the bile salt-dependent flow greatest?
bile salt-dependent flow is greatest when bile salts are reabsorbed from the intestine and transported back to the liver to be secreted again.
what are transported from the hepatocytes in addition to bile salts?
lechithin and cholesterol are also transported from the hepatocytes
how are secondary bile salts produced?
name two examples of secondary bile salts
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
where does conversion to secondary bile salts predominantly take place?
where does the main system for bile absorption in the intestine take place?
active transport by the ileum
the jejunum can recover a portion by passive uptake
what does bile secretion represent mainly? secreted by what?
a watery solution of NaHCO3 and NaCl
secreted by epithelial cells of the bile ductules and ducts that is influenced by secretin
secretin feedback mechanism
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
what is the unstirred layer
a thin layer of lumen contents in water on the surface of epithelial cells that is poorly mixed, or not mixed at all.
can free fatty acids and 2-monoglycerides diffuse through the unstirred layer?
how do free fatty acids and monoglycerides diffuse through the unstirred layer?