LECTURE 6
Dr. Zahoor Ali Shaikh
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 Bile is formed in the liver, emptied in the duodenum
via bile duct.
 Biliary system includes the liver, gallbladder, and
ducts.
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 Metabolism of carbohydrate, protein, and fat, after
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their absorption from the digestive tract.
Detoxification of drugs, hormones, body waste
products.
Plasma Protein Synthesis.
Blood clotting factors Synthesis.
Storing Glycogen, fat, iron, copper.
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 Storing vitamin A,D, Vit B12.
 Activating vitamin D.
 Removing bacteria and old red blood cell by
macrophages.
 Secreting hormones e.g. insulin like growth factor 1
[stimulates growth], thrombopietin [stimulates
platelet production].
 Excreting cholesterol and bilirubin [bilirubin is
breakdown product of RBC].
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 Liver cell is called HEPATOCYTE.
‘HEPATO’ means liver, ‘CYTE’ means cell.
 HEPATOCYTE performs metabolic and secretary
functions.
 HEPATOCYTE does not do Phagocytosis.
 Phagocytosis is done by macrophages present in the
liver called KUPFFER cells.
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 Two sources
1. Hepatic Artery – supplies arterial blood
2. Portal Vein – from GIT
 Blood leaves the liver via hepatic vein.
 NOTE – Portal Vein breaks in sinusoids which
exchange with hepatic cells before draining into
hepatic vein which joins inferior venaceva.
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 Liver has functional units called lobules, they are
hexagonal with central vein.
 Each lobule has three vessels:
- Branch of Hepatic Artery,
- Branch of Portal Vein
- Bile Duct
 From Hepatic artery and Portal vein blood goes to
expended capillary space called SINUSOIDS which
runs to central vein.
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 The Kupffer cells line the sinusoids and destroy old
RBC and bacteria that pass through them.
 Central veins of all liver lobules converge to form
hepatic vein, which carries blood away from the liver.
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 The bile is formed and continuously secreted by liver
cells [Hepatocyte].
 Bile goes to bile duct.
 Bile ducts from different lobules form Right and Left
hepatic duct, then common hepatic duct is formed
which combines with Cystic duct (from Gall bladder)
to form Common bile duct.
 Common bile duct transports bile to the duodenum.
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 Bile is continuously secreted by liver and sent to the
Gallbladder between meals.
 Opening of the bile duct in the duodenum is guarded
by the sphincter of Oddi. It allows the bile to pass in
the duodenum during meals.
 When food is not taken sphincter of Oddi is closed ,
therefore bile secreted by the liver goes to the
gallbladder
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 In the gallbladder bile is stored and concentrated
between the meals.
BILE
 Bile secreted per day --- 500 ml
 Bile is alkaline fluid PH 8 (it has NaHco3- from bile
ducts)
 Bile contains
Bile salts, cholesterol, lecithin (phospholipid) and
Bilirubin (all derived from Hepatocyte activity )
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 Bile does not contain any enzyme
 Bile is important for Emulsification [breaking fat into
small molecules] therefore helping in digestion and
absorption if Fats
BILE SALTS AND THEIR ENTROHEPATIC
CIRCULATION
 Bile salts are derivates of cholesterol. They are actively
secreted in bile.
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 Most of the bile salts [95%] are reabsorbed from
terminal ileum [small intestine] into the blood by
active transport.
 Bile salt are returned to liver by hepatic portal system.
 Liver re-secretes them into the bile. This recycling of
bile salt between small intestine and liver is called
‘ENTROHEPATIC CIRCULATION’ [‘Entro’ means
intestine, ‘hepatic’ means liver].
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 On average bile salts cycle between liver and small
intestine twice during one meal.
 Only 5% of bile salt are lost in the feces per day.
 Last bile salts are replaced by new bile salts
synthesized by liver.
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 Bile salts cause lipid emulsification [breaking fat into
small molecules], therefore, increasing the surface
area, so that pancreatic lipase can act.
 These fat globules are triglyceride molecules.
 To digest fat globules, lipase must act on them.
 NOTE – If no bile salt, it will take long time for lipase
to do fat digestion.
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 MICELLAR FORMATION
 Micelle is small lipid particle 3-10 nm [emulsified fat
droplet is 1000 nm].
 bile salt, cholesterol and lecithin help in Micelle
formation.
 Micelle carry Monoglycerides and free fatty acids.
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 Gall Stones
- Cholesterol Gall Stone – 75%
- Bilirubin Gall Stone – 25%
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 Bilirubin is waste product excreted in bile.
 It is bile pigment, derived from the breakdown of RBC.
 It does not play any role in Digestion.
 Bilirubin is taken from the blood by Hepatocyte and
actively excreted into the bile.
 Bilirubin is yellow pigment, therefore, gives yellow
color to bile.
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 In intestine, bilirubin is acted by bacteria and
converted to urobilinogen and stercobilinogen.
 Stercobilinogen is excreted in feces and gives brown
color to feces.
 If bile duct is obstructed by stone, color of feces turns
to grey white.
 Small amount of urobilinogen is reabsorbed in the
intestine in the blood and excreted in the urine and
gives yellow color to urine.
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 If increased amount of bilirubin in the blood, it causes
Jaundice [yellow coloration of eyes].
 Normal bilirubin is less than 2mg /dl.
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 Three Mechanism
1. Chemical
2. Hormonal
3. Neural
 1. Chemical Mechanism
 By bile salt, they are most potent stimulus for
increasing bile secretion.
 Any substance which increases bile secretion is called
‘CHOLERETIC’.
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 2. Hormonal Mechanism
 Secretin hormone stimulates watery alkaline bile
secretion from the bile ducts.
 3. Neural Mechanism
 Vagal stimulation plays minor role in bile secretion
during cephalic phase of digestion.
 IMPORTANT – Food in duodenum [fat] causes
release of CCK. This hormone causes contraction of
gallbladder and relaxation of sphincter of ODDI.
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 It stores and concentrates bile between meals and
empties bile into the duodenum during meals.
 As bile secretion occurs continuously in liver,
therefore, bile secreted between the meals is send to
the gall bladder, where it is stored and concentrated.
 In gall bladder, bile is concentrated 5-10 times due to
absorption of bile salt and water.
 Gall bladder can hold 50ml of bile.
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 Jaundice
 When bilirubin increases more than 2mg/dL jaundice
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occurs.
Causes of Jaundice
Pre-hepatic [problem before liver] or Hemolytic
Jaundice – due to increased breakdown of RBC.
Hepatic [problem in liver] e.g. Viral Hepatitis
Post-hepatic [problem after the liver] or Obstructive
Jaundice e.g. stone in the bile duct.
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 Functions of Liver
 Blood supply to Liver
 Bile Secretion
 Bile Salts and their Entrohepatic Circulation
 Role of Bile Salt in Lipid Emulsification, Fat Digestion
and Absorption
 Bilirubin – Source & Excretion
 Control of Bile Secretion
 Jaundice
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