Bile and Its Components Quiz

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Questions and Answers

What is the primary function of bile in fat digestion?

It emulsifies and solubilizes fats. (correct)

It acts as a solvent for sugars.

It provides an energy source.

It reduces the temperature of the food.

Which factor induces the release of bile from the gallbladder?

Insulin

Secretin

Gastrin

Cholecystokinin (CCK) (correct)

Which component is NOT a principal excretory product of bile?

Bile acids

Glucose (correct)

Bile pigments

Cholesterol

What is the typical daily production of bile in adults?

500 mL Signup and view all the answers

Jaundice can be classified based on which of the following criteria?

Location of the bilirubin-handling defect Signup and view all the answers

What role do bile acids play in the composition of bile?

They act as emulsifiers for fats. Signup and view all the answers

Which part of the digestive system is primarily responsible for inducing the release of cholecystokinin?

Duodenum Signup and view all the answers

Which type of bilirubin is primarily dealt with in the liver?

Conjugated bilirubin Signup and view all the answers

What is the function of bile acids during digestion?

To facilitate fat digestion and absorption Signup and view all the answers

Where are primary bile acids synthesized in the body?

Liver Signup and view all the answers

What percentage of bile acids are reabsorbed in the ileum?

95% Signup and view all the answers

What leads to the conversion of primary bile acids into secondary bile acids?

Bacterial metabolism in the colon Signup and view all the answers

How are most senescent red blood cells (RBCs) destroyed in the body?

Through phagocytosis and/or lysis Signup and view all the answers

What is the primary characteristic of pre-hepatic jaundice?

Excess bilirubin production from haemolysis Signup and view all the answers

Which condition is associated with intra-hepatic jaundice?

Generalized liver dysfunction Signup and view all the answers

Which of the following could cause post-hepatic jaundice?

Biliary tract obstruction Signup and view all the answers

What type of bilirubin is typically elevated in pre-hepatic jaundice?

Unconjugated bilirubin Signup and view all the answers

Which biochemical markers are typically elevated in intra-hepatic jaundice?

AST and ALT Signup and view all the answers

What is the primary consequence of free iron ($Fe^{2+}$) being released during hemolysis?

It promotes tissue damage and inflammation. Signup and view all the answers

Which two enzymes are primarily involved in the degradation of hemoglobin to bilirubin?

Heme Oxygenase and Biliverdin reductase Signup and view all the answers

Which protein binds free hemoglobin in the blood to prevent iron loss through urine?

Haptoglobin Signup and view all the answers

What percentage of bilirubin in the body is derived from the breakdown of red blood cells?

75% Signup and view all the answers

What is the role of UDP-glucuronyl transferase in bilirubin metabolism?

To make bilirubin water-soluble Signup and view all the answers

What happens to conjugated bilirubin after it is synthesized in the liver?

It is secreted into bile ducts and excreted into the gut. Signup and view all the answers

Which of the following statements is true regarding jaundice?

It is characterized by hyperbilirubinemia. Signup and view all the answers

What is a common symptom associated with jaundice?

Pale feces Signup and view all the answers

How is excess bilirubin typically excreted from the body?

Through bile as stercobilin and via urine as urobilin Signup and view all the answers

What is the implication of high levels of bilirubin (> 35 µM/L) in the body?

It signifies potential hemolytic disease or liver dysfunction. Signup and view all the answers

What is a common consequence of complete bile duct obstruction?

Dark urine due to increased conjugated bilirubin Signup and view all the answers

Which condition is characterized by mild, fluctuating unconjugated hyperbilirubinaemia?

Gilbert's Syndrome Signup and view all the answers

What factor can aggravate jaundice in patients with Dubin-Johnson Syndrome?

Dehydration Signup and view all the answers

What is the typical treatment for Type I Crigler-Najjar Syndrome?

Liver transplant Signup and view all the answers

What is a typical complication of severe unconjugated hyperbilirubinaemia in newborns?

Kernicterus Signup and view all the answers

Which type of bilirubin is primarily increased in post-hepatic jaundice?

Conjugated bilirubin Signup and view all the answers

What is the typical timeframe for newborn jaundice to resolve without treatment?

Within 10 days Signup and view all the answers

What laboratory finding is typically normal in pre-hepatic jaundice?

Conjugated bilirubin levels Signup and view all the answers

Which medication can induce synthesis of UDP-glucuronyl transferase in Gilbert's Syndrome?

Phenobarbitone Signup and view all the answers

What is a key difference in the urine findings between intra-hepatic and post-hepatic jaundice?

Urine urobilinogen is absent in intra-hepatic jaundice Signup and view all the answers

Which statement accurately describes the pathway of bile acids in the body?

Primary bile acids are synthesized in the liver and conjugated before storage. Signup and view all the answers

What role does CCK play in bile acid metabolism?

It stimulates the release of bile from the gallbladder after a meal. Signup and view all the answers

How are primary bile acids modified before they are stored in the gallbladder?

They are conjugated to taurine or glycine. Signup and view all the answers

Which of the following accurately describes bilirubin's origin?

Bilirubin is a breakdown product of the degradation of hemoglobin from senescent erythrocytes. Signup and view all the answers

What occurs to bile acids following their initial release into the intestine?

They are mostly reabsorbed in the ileum and returned to the liver. Signup and view all the answers

What distinguishes intra-hepatic jaundice from the other forms of jaundice?

It is characterized by impairment in bilirubin uptake and conjugation. Signup and view all the answers

Which condition is most commonly associated with pre-hepatic jaundice?

Hemolytic disease of the newborn. Signup and view all the answers

What is a hallmark biochemistry finding in post-hepatic jaundice?

High levels of conjugated bilirubin in the plasma. Signup and view all the answers

Which of the following conditions might lead to intra-hepatic jaundice?

Genetic liver disorders. Signup and view all the answers

What plasma bilirubin level is considered normal, and how does this relate to conditions associated with excessive bilirubin?

Normal level is ~17μmol/L, but levels can rise in hemolytic conditions. Signup and view all the answers

What is the primary alkaline pH range of bile produced by adults?

7.5 – 8 Signup and view all the answers

Which of the following is NOT a principal function of bile?

Storage of bile salts Signup and view all the answers

What initiates the release of bile from the gallbladder?

Cholecystokinin (CCK) Signup and view all the answers

Which component is directly responsible for the emulsification of fats in bile?

Bile acids Signup and view all the answers

Which type of bilirubin is primarily formed from the breakdown of hemoglobin?

Unconjugated bilirubin Signup and view all the answers

What term describes the clinical condition with yellowing of the skin due to excess bilirubin?

Jaundice Signup and view all the answers

What is a common cause of post-hepatic jaundice?

Bile duct obstruction Signup and view all the answers

Which organ is primarily responsible for the removal of particulate matter from the bloodstream as part of bile function?

Liver Signup and view all the answers

What is the primary consequence of the detoxification process of free haem in the blood?

Formation of bilirubin and preventing iron loss Signup and view all the answers

Which enzyme is responsible for the conversion of haem to biliverdin during bilirubin formation?

Heme Oxygenase Signup and view all the answers

How is unconjugated bilirubin made water-soluble in the liver?

By conjugation with glucuronic acid Signup and view all the answers

What initiates the process of bilirubin metabolism in the liver?

Facilitated diffusion by OATP transporter Signup and view all the answers

What primarily distinguishes post-hepatic jaundice from other forms of jaundice?

Obstruction in the biliary tract Signup and view all the answers

Why is free haem in the blood considered toxic?

It causes tissue damage and inflammation Signup and view all the answers

What percentage of bilirubin is derived from heme-containing proteins other than RBCs?

25% Signup and view all the answers

How does the liver handle free haem in the blood?

Via binding to hemopexin and haptoglobin Signup and view all the answers

What is a common associated symptom of jaundice?

Abdominal pain Signup and view all the answers

Which protein is crucial for the secretion of conjugated bilirubin into bile?

MRP-3 Signup and view all the answers

What is the primary genetic cause of Crigler-Najjar Syndrome?

Mutation in the gene coding for UDP-glucuronyl transferase Signup and view all the answers

Which laboratory finding is distinctively absent in post-hepatic jaundice?

Urinary urobilinogen Signup and view all the answers

What characterizes Gilbert’s Syndrome?

Mild, fluctuating unconjugated hyperbilirubinaemia Signup and view all the answers

Which treatment option is specifically indicated for Type I Crigler-Najjar Syndrome?

Liver transplant Signup and view all the answers

What is a common consequence of severe jaundice in newborns?

Kernicterus Signup and view all the answers

Which of the following conditions is typically associated with conjugated hyperbilirubinaemia?

Dubin-Johnson Syndrome Signup and view all the answers

Which aggravating factor can lead to worsening of jaundice in patients with Dubin-Johnson Syndrome?

Dehydration Signup and view all the answers

What is the usual course of treatment for newborn jaundice that is transient?

No treatment required Signup and view all the answers

What enzyme is primarily affected in Gilbert’s Syndrome?

UDP-glucuronyl transferase Signup and view all the answers

In which type of jaundice is urine bilirubin typically absent?

Pre-hepatic jaundice Signup and view all the answers

Study Notes

Bile

Produced by the liver (~500mL daily in adults)
Yellow-green in colour
Alkaline pH (7.5-8)
Stored in the gall bladder
Released by cholecystokinin (CCK) after eating
Principal functions:
- Fat digestion and absorption
- Excretion of excess cholesterol and metabolites
- Neutralisation of stomach acid

Components of Bile

Bile acids
Bile pigments
Cholesterol
Drugs and metabolites
Particulate matter

Bile Acids

Primary bile acids are synthesised in the liver from cholesterol
Conjugated with glycine or taurine
Stored in the gall bladder
Released in response to a meal to facilitate fat digestion and absorption
Primary bile acids are converted to secondary bile acids by bacteria in the colon
Excreted in faeces

Bilirubin

Natural degradation product of haem
Erythrocytes (RBCs) have a finite lifespan (~60-120 days)
Senescent RBCs destroyed by phagocytosis/lysis
Haem is toxic and must be metabolised to bilirubin in a 2-step process
Most bilirubin in the body is derived from RBCs

Bilirubin Formation

Haem is converted to biliverdin by Heme Oxygenase
Biliverdin is converted to bilirubin by Biliverdin reductase
Bilirubin binds to albumin and is transported to the liver
Bilirubin is conjugated with glucuronic acid by UDP-glucuronyl transferase (UDP-glucuronosyltransferase) to make it water-soluble
Conjugated bilirubin is secreted into bile ducts and excreted

Causes of Jaundice

Pre-hepatic jaundice
- High bilirubin production
- Haemolytic disease of newborn
- Structurally abnormal RBCs
- Breakdown of extravasated blood
Intra-hepatic jaundice
- Impaired uptake, conjugation or secretion of bilirubin
- Liver disease
- Neonatal jaundice
Post-hepatic jaundice
- Obstruction of biliary flow
- Gallstones
- Cancer
- Pale stools
- Dark urine

Newborn Jaundice

Common, particularly in premature infants
Occurs 2-4 days after birth
Caused by immaturity of enzymes involved in bilirubin conjugation
Usually transient, resolving within first 10 days of life
Complications:
- Kernicterus
Treatment:
- Phototherapy
- Phenobarbitone administration
- Exchange blood transfusion

Gilbert's Syndrome

Most common inherited disorder of bilirubin conjugation
Mild, fluctuating unconjugated hyperbilirubinaemia
Onset typically during adolescence
Reduced activity of UDP-glucuronyl transferase
Can be treated with phenobarbitone

Crigler-Najjar Syndrome

Rare autosomal recessive disorder
Severe unconjugated hyperbilirubinaemia
Mutation in gene coding for UDP-glucuronyl transferase
Type l - complete absence of enzyme
Type ll - marked reduction in enzyme activity
Affected individuals at high risk for kernicterus
Treatment:
- Type l - Liver transplant
- Type ll - Phenobarbitone or phototherapy

Dubin-Johnson Syndrome

Benign genetic disorder
Impaired biliary secretion of conjugated bilirubin
Mutation in gene coding for MRP-2
Jaundice may worsen with aggravating factors
Treatment not usually necessary

Bile

Complex fluid produced by the liver
~500mL produced daily by adults
Yellow-green color
Alkaline pH (7.5 – 8)
Stored in the gallbladder
Released into the duodenum in response to cholecystokinin (CCK)
CCK is released from I cells in the duodenum after eating a meal
CCK induces gallbladder contraction

Bile Functions

Facilitates fat digestion and absorption
Excretes excess cholesterol and metabolites
Neutralizes stomach acid

Bile Composition

Bile acids
Bile pigments (from haem degradation)
Cholesterol
Drugs and their metabolites
Particulate matter (removed from the bloodstream by Kupffer cells in the liver)

Bile Acids

Amphipathic molecules - charged (hydrophilic) on one side, uncharged (hydrophobic) on the other
Primary bile acids are synthesized in the liver from cholesterol
Conjugated to glycine or taurine
Stored in the gallbladder
Released in response to a meal to facilitate fat digestion and absorption
Primary bile acids are converted to secondary bile acids by bacteria in the colon
Provide a pathway for excess cholesterol excretion from the body

Bilirubin

A natural degradation product of haem
Released from senescent red blood cells (RBCs)
RBCs have a finite lifespan (~60-120 days)
Most RBCs are destroyed extravascularly (in the liver, spleen, or bone marrow)
Intravascular haemolysis also occurs, usually as a consequence of disease
Free haem is toxic and must be metabolised
75% of the bilirubin in the body is derived from RBCs
The remainder comes from other heme-containing proteins (e.g., myoglobin, cytochromes)
Bilirubin metabolism is a 2-step detoxification process

Handling of Free Haemoglobin

Free haem is toxic and must be bound to serum proteins for detoxification
Haptoglobin binds to haemoglobin, forming a complex that is metabolized in the liver and spleen
Haemopexin binds to free haem, forming a complex that is taken up by the liver
Albumin binds to oxidized haem, forming Met-haemalbumin

Degradation of Haem to Bilirubin

Occurs mostly in the spleen
Requires 2 enzymes:
- Heme oxygenase (primarily in the spleen)
- Biliverdin reductase

Metabolism of Bilirubin

Taken up by the liver by carrier-mediated facilitated diffusion (transporters OATP)
Binds to cytoplasmic proteins in hepatocytes (e.g., Ligandin, Protein Y)
Bilirubin is conjugated with glucuronic acid by UDP-glucuronyl transferase (UDP-glucuronosyltransferase), making it water-soluble
Conjugated bilirubin is secreted into the bile ducts (active transport via MRP-3)
Bile is excreted from the liver into the gut
Glucoronidases in colonic bacteria de-conjugate bilirubin to urobilinogen (colorless)
Urobilinogen is oxidized by bacteria to stercobilin (brown pigment)
Most stercobilin is excreted in feces
Some urobilinogen is reabsorbed into the portal blood
Some urobilinogen is excreted into the urine as urobilin.

Jaundice

Yellowing of the skin, whites of the eyes, and mucous membranes due to high bilirubin levels (hyperbilirubinemia)
Indicates underlying disease involving abnormal heme metabolism, liver dysfunction, or biliary tract obstruction
Typically occurs when serum bilirubin levels are > 35µM/L (normal = 17uM/L)
Common in newborns
Can lead to neurological damage (kernicterus) in severe cases
Treatment depends on the underlying cause

### Classification of Jaundice

Pre-hepatic (haemolytic) jaundice: Bilirubin production exceeds the uptake capacity of the liver.
Intra-hepatic (hepatocellular) jaundice: Bilirubin cannot be taken up, conjugated, and/or excreted due to hepatocellular damage.
Post-hepatic (cholestatic) jaundice: Obstruction to biliary flow.

Pre-hepatic Jaundice

Also called haemolytic jaundice
Excess production of bilirubin following massive hemolysis
Excess RBC lysis is often due to:
- Autoimmune disease (e.g., haemolytic disease of the newborn)
- Structurally abnormal RBCs (e.g., sickle cell disease)
- Breakdown of extravasated blood
Characterized by high plasma levels of unconjugated bilirubin

Intra-hepatic Jaundice

Also called hepatocellular jaundice
Impaired uptake, conjugation, or secretion of bilirubin
Reflects generalized liver cell dysfunction (e.g., hepatitis, cirrhosis, genetic abnormalities)
Hyperbilirubinaemia usually accompanied by other abnormal biochemical markers of liver function (e.g., elevated AST, ALT)

Post-hepatic Jaundice

Also called obstructive jaundice or cholestatic jaundice
Caused by obstruction to the biliary tract (e.g., gallstones, cancer)
Plasma bilirubin is primarily conjugated
Other bile constituents (e.g., bile acids) also accumulate in plasma
Characterized by
- Pale stools (absence of faecal bilirubin or stercobilin)
- Dark urine (increased conjugated bilirubin)

Differential Diagnosis of Jaundice

Pre-hepatic: Elevated unconjugated bilirubin; normal ALT, AST, and ALP; absent urine bilirubin; present urine urobilinogen.
Intra-hepatic: Elevated conjugated and unconjugated bilirubin; increased ALT, AST, and ALP; present urine bilirubin; present urine urobilinogen.
Post-hepatic: Elevated conjugated bilirubin; normal ALT, AST; increased ALP; present urine bilirubin; absent urine urobilinogen.

Newborn Jaundice

Common, particularly in premature infants
Occurs 2-4 days after birth
Due to immaturity of enzymes involved in bilirubin conjugation (e.g., UDP-glucuronyl transferase)
Usually transient, resolving within the first 10 days of life

### Newborn Jaundice Complications

Unconjugated bilirubin can deposit in the brain, leading to kernicterus (rare form of brain damage)
Aggravating factors
- Haemolysis (infants have increased RBC turnover)
- Breastfeeding (dehydration can increase RBC lysis)
- Sulphonamides (displace bilirubin from albumin)
- Antibiotics (can inhibit glucuronyltransferase)

Newborn Jaundice Treatment

Usually resolves on its own within 10 days
Phototherapy (UV light) converts bilirubin to a water-soluble, non-toxic form.
Phenobarbital administration (induces synthesis of UDP-glucuronyl transferase)
Exchange blood transfusion to remove excess bilirubin
Jaundice within the first 24 hours of birth or that persists beyond 10 days is usually pathological

Gilbert's Syndrome

Most common inherited disorder of bilirubin conjugation
Characterized by mild, fluctuating unconjugated hyperbilirubinaemia
Onset of symptoms is typically during adolescence
Caused by reduced activity of UDP-glucuronyl transferase (UDP-glucuronosyltransferase), preventing bilirubin conjugation in the liver
Can be treated with phenobarbital to stimulate UDP– glucuronyl transferase

Crigler-Najjar Syndrome

Extremely rare autosomal recessive disorder presenting with severe unconjugated hyperbilirubinaemia
Caused by a mutation in the gene coding for UDP-glucuronyl transferase (UDP-glucuronosyltransferase)
- Type I: complete absence
- Type II: marked reduction in enzyme activity
Affected individuals are at high risk for kernicterus
Treatment:
- Type I: by liver transplant in some cases (by 5 years old)
- Type II: with phenobarbital or phototherapy (10-12 hours per day)

Dubin-Johnson Syndrome

Benign genetic disorder presenting with conjugated hyperbilirubinaemia
Most patients have lifelong, recurrent mild symptoms of jaundice
Characterized by impaired biliary secretion of conjugated bilirubin (intrahepatic jaundice)
Mutation in the gene coding for MRP-2
Jaundice may worsen with aggravating factors (e.g., pregnancy, oral contraceptives)
Treatment is not usually necessary

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Description

Test your knowledge on bile, its production, components, and functions in the digestive system. This quiz covers the role of bile acids, bilirubin metabolism, and the significance of bile in fat digestion and cholesterol excretion.