2. INTRODUCTION
• Bile is a digestive juice, formed continuously in the liver by the
hepatocytes and epithelial cells lining the bile ducts.
• Bile is secreted by the liver, stored in gall bladder and emptied into
the small intestine.
• In the gall bladder, while being stored, it also undergo some
alterations.
3. FUNCTIONALANATOMY OF LIVER
• The functional unit of liver is the hepatocyte.
• Hepatocytes are arranged around the central vein in layers.
• Only one layer of hepatocytes will be there between two sinusoids.
• Bile canaliculi of hepatocytes are the invaginations into which the
secretions of the hepatocytes are drained, which in turn drains
into the sinusoids.
4.
5. FUNCTIONALANATOMY OF LIVER
• Portal space has the triad of
• Bile duct, entering it from sinusoids,
• Portal vein leaving it and
• Hepatic artery leaving it
• Portal vein(blood with absorbed nutrients) and
hepatic artery (blood with oxygenated blood)
supply hepatocytes and drain into central vein.
• Many terminal bile ducts join to form larger bile
ducts, many of which join to form hepatic duct.
• Hepatic duct joins with the cystic duct to form
common bile duct which empties into duodenum
through the Sphincter of Oddi.
6.
7. GALL BLADDER
• Gall bladder is the hollow organ meant for storage of bile.
• The volume of gall bladder is 30 to 60 ml.
• But it can store bile from liver over a duration of 12 hours (about
450 ml) due to its concentrating property.
• Usually bile is concentrated to 5 folds.
• Maximum concentrating capacity is 20 folds.
8. BILE
• Volume: 500 ml/day
• Consists of
oWater
oBile salts, most abundant
(sodium and potassium salts of bile acids)
oBile pigments
oCholesterol
oLecithin and
oElectrolytes
9. BILE
• In the gall bladder, the following substances are reabsorbed:
Water and
Electrolytes (except calcium)
• The substances which are not reabsorbed include:
Calcium
Bile salts
Cholesterol and
Lecithin
10. BILE PIGMENTS
• Bile pigments gives the golden yellow colour to the bile.
• They are, (mainly) bilirubin and biliverdin.
In detail:
Bilirubin from Hb binds with albumin.
In liver, it dissociates and free bilirubin enters liver cells.
11. BILE PIGMENTS
In liver cells, bilirubin reacts with uridine diphospho
glucuronic acid, in the presence of glucuronyl transferase
and forms bilirubin mono and di glucuronides – the
conjugated bilirubin.
This conjugated bilirubin is secreted into the intestine.
This conjugated bilirubin, as such is impermeable to
intestinal mucosa; but some conjugated bilirubin gets
converted to urobilinogen (also called as stercobilinogen)
which is permeable to intestinal mucosa.
Some of this urobilinogen enters the blood and is excreted
in urine.
12.
13. BILE SALTS AND BILE ACIDS
• Bile salts are sodium and potassium salts of bile acids, (i.e. sodium
taurocholate, sodium glycocholate, potassium taurocholate and
potassium glycocholate).
• BILE ACIDS:
Bile acids are synthesized from cholesterol.
The principal bile acids are cholic acids and chenodeoxycholic
acid.
These bile acids combine with taurine and glycine to form tauro
and glyco conjugated bile acids.
14. BILE SALTS AND BILE ACIDS
Secondary bile acids:
In colon, the bacteria converts
Cholic acid to deoxycholic acid and
Chenodeoxycholic acid to lithocholic acid.
15. GALL BLADDER EMPTYING
• Contraction of gall bladder with simultaneous relaxation of
sphincter of Oddi empties the gall bladder.
• Fatty meal stimulates CCK secretion which in turn causes gall
bladder contraction.
• Gall bladder emptying starts 30 minutes after a meal and is
completely emptied within one hour with a fatty meal.
• Vagus and ENS also stimulates gall bladder emptying, to a lesser
extent by Acetylcholine.
16. REGULATION OF BILE SECRETION AND GALL
BLADDER EMPTYING
• Chologogues are substances that cause contraction of gall
bladder. Cholecystokinin is the chief chologogue, it is a
potent stimulant of gall bladder contraction; it also
relaxes the sphincter of Oddi.
• Vagal stimulation and ENS stimulation causes weak
contraction of gall bladder.
• Choleretics are substances which increases bile secretion.
Secretin is a choleretic, which causes ductal secretion of
bicarbonate ions.
• Bile salts themselves are the chief choleretics, and they
increase the parenchymal secretion.
17. ENTEROHEPATIC CIRCULATION OF BILE SALTS
• 95% of the bile salts in the small intestine are reabsorbed.
They enter the portal blood.
• From the portal blood, the hepatic cells absorbs the bile salts
and secretes it again into the bile, this cycle continues.
• Bile salts are recircuited 18 times before excreted in the
feces.
• The lost 5% is compensated (replaced) by new amounts
formed by the liver.
• Thus bile salts in enterohepatic circulation increases the
secretion of bile – the choleretic action of bile salts.
18.
19. FUNCTIONS OF BILE
• Digestive function
It helps in the digestion of fats by emulsifying fat drops
• Absorptive function
It helps in the absorption of fats (by micelle formation) and fat soluble
vitamins
• Excretory function
Bile pigments are the major excretory products of the bile. The other
substances excreted in the bile are, heavy metals (e.g. copper, and iron),
some toxins and some bacteria; cholesterol, lecithin and alkaline
phosphatase too.
20. FUNCTIONS OF BILE
• Laxative function
Bile salts increase the gastrointestinal motility and act as a laxative.
• Choleretic function
Bile salts stimulates the liver to secrete bile.
• Maintenance of pH in the GIT
Being highly alkaline, the bile juice neutralizes the gastric HCl present
in the chyme entering the small intestine. Thus an optimum pH is
maintained for the action of digestive enzymes.
21. FUNCTIONS OF BILE
• Prevention of gall stone formation
Bile salts keep the cholesterol and lecithin in solution and thus prevents
the formation of gall stones. In the absence of bile salts, the cholesterol
precipitates along with lecithin and may form gall stones.
• Lubricating function
Mucin secreted by gall bladder mucosa into the bile lubricates the
chyme in the intestine
• Cholagogue function
Cholagogue is an agent which increases the release of bile from the gall
bladder into the intestine. The bile salts perform this function indirectly.
The bile salts stimulate the release of the hormone CCK which has got
cholagogue action.
22. BILE SALTS IN FAT DIGESTION
• Fat has increased surface tension which prevents the breaking
down of fat globules into minute sizes by internal agitation.
(Remember, digestive enzymes act on the surface).
• Bile salts, along with lecithin decreases surface tension and
favours digestion of fat.
• Bile salts and lecithin have a water-soluble end and also a fat
soluble end, with which it decreases the surface tension and causes
more surface of fat to be exposed for the action of digestive
enzymes. Thus they cause emulsification of fats.
23.
24. GALL STONE FORMATION
• Bile has cholesterol as a by-product of bile salt
formation.
• This cholesterol is maintained in the form of
colloidal solution by the action of bile salts and
lecithin. So, normally they won’t precipitate.
• They precipitate when there is,
Too much absorption of water
Increased cholesterol secretion (as in high fat diet for a
long period)
Inflammation of gall bladder epithelium – chronic low
grade infection alters the characteristic of gall bladder
mucosa and increases absorption of water and bile salts
but leaves cholesterol.
25. JAUNDICE
• Jaundice is the yellow discolouration of the skin,
conjunctivae, and other tissues caused by the
presence of an excess of bilirubin in plasma and
tissue fluids. The normal adult range of plasma
bilirubin is 0.3 to 1.0 mg/100ml.
• An excess of bilirubin can result from:
Excess breakdown of RBCs – hemolytic (pre hepatic)
jaundice
Infective of toxic damage to the liver cells – hepatic
jaundice
Obstruction of bile ducts – obstructive (post hepatic)
jaundice.
