Bile and Biliary system Flashcards
Bile Functions
Bile salts aid digestive enzymes by:
breaking the fat globules into droplets- EMULSIFICATION, increasing the SA of the fatty substance; the lipase can digest the fat molecules more effectively.
Bile salts also increase the absorption of fatty acids by forming complexes called misceles - soluble in chyme and easily absorbed by the epithelial cells
It also aids the absorption of fat soluble vitamins
Mucous membrane of the SI membrane reabsorbs all of the bile salts, is brought back to the liver ( by the enterohepatic circulation) for it to be resecreted to the bile duct OR live can resynthesise it
Synthesis of bile
In the liver
From cholesterol, chalice, chenoxexycholic, deoxycholic, lithocholic
Bile is nearly isotonic with plasma but Na+ is higher in bile salts as the bile salts form osmotically inactive micelles
Controlling of bile salts
- Serotonin- inhibits net fluid and electrolyte reabsorption
-Vagus-stimulation causes 2-4 fold increase in bile secretion
Bilateral vagatory nerves abolishes feed induced stimulation of bile flow
Splanchnic nerve stimulation causes vasoconstriction which decreases bile secretion
- Chemical- bile salts are a powerful choleretic
- Secretin- Increases bile flow without increasing bile secretion
Mechanisms underling bile secretion
With oxygen, there is increased bile flow at low blood flow—> This means that it is an oxygen requiring process which means that it is a metabolic process which requires energy
Secretion of bile can occur against the pressure gradient-
which means that it is not the result of hydorstartic pressure directed from the blood to bile duct
Describe how bile is drained from the cells
Bile drained by canaliculi—> terminal bile ducts—> perilobular ducts–> interlobular ducts
How are are concentrations of bile salts in the gall bladder controlled
Exchange ( both active and passive) of ions –> see notes
Organic Constituents and electrolytes in hepatic bile
water
electrolytes
cholesterol
bile salts
Bile pigments- no digestive function eg. bilirubin
Billirubin
metabolic product of haemoglobin + TOXIC
Major product of bile
In blood bound to albumin but its free form is taken up by the liver where its conjugates with glucuronic acid- to form bilirubin glucuronide. This is secreted into the canaliculi
Thos is then degraded into reticuloendothelial system- secreted into bile at 1000 times plasma concentration
Pathophysiology- biliary disease
Caused by abnormalities in bile composition, biliary antatomy, function
NB the liver determines the chemical composition of the bile
The gall bladder and the biliary epithelium modifies it
Key to bile secretion
Bile secretion = bile lost
Lipid Absorption
1) LCFA and other products of lipids digestion converted to TGA , phosholipids and esters of cholesterol in the SER
2) In the RER, apoproteins are synthesised and transferred to the SER. The apoproteins associate with the lipid droplets
3) nascent chylomicrons and VLDLs arrive at the cis face of the golgi. Apoproteins are glycosylated
4) Vesicles carrying the chylomicrons bud of from the trans face of the golgi. They move to the basolateral membrane in transport vesicles
5) Transport vesicles fuse with the basolateral membrane of enterocyte releasing chylomicrons
6) Chylomicrons/VLDLs are too large to enter the fenestrated capillaries they enter the lymph through larger interendothelial channels of the lymphatic capillaries
OR
- glycerol and short chained FA move straight through the cell intro the interstitial fluid into blood capillary
Causes and consequences of gallstone
Causes–> too much absorption of water/bile salts/cholesterol from bile OR Inflammation of epithelium
Consequences—> gather in gall bladder or even papilla of water blocking pro enzymes and bile salts
