Medical Biochemistry: Heme Catabolism and Bilirubin Metabolism

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Questions and Answers

What is the primary function of bile salts?

To neutralize acid in the stomach

To store vitamins and minerals

To facilitate fat digestion and absorption (correct)

To synthesize plasma proteins

What is the pH of bile?

8 (correct)

What is the primary organ responsible for uptake, conjugation, and secretion of bilirubin in bile?

Liver (correct)

Spleen

Kidney

Pancreas

What is the approximate amount of bile secreted by the liver per day?

500 ml Signup and view all the answers

What is the role of the gallbladder in bile secretion?

To store and concentrate bile between meals Signup and view all the answers

What is the biochemical nature of jaundice?

An accumulation of bilirubin in the blood Signup and view all the answers

What is the function of UDP-bilirubin glucuronosyl transferase in bilirubin metabolism?

To conjugate bilirubin with glucuronic acid Signup and view all the answers

What is the primary source of bile acids?

Cholesterol Signup and view all the answers

What is the primary function of bile salts in the digestion of fats?

To emulsify large fat particles into smaller ones Signup and view all the answers

What is the effect of secretin on bile secretion?

It increases the secretion of bile rich in water and HCO3- Signup and view all the answers

What is the primary stimulant of bile secretion by liver cells?

Bile salts Signup and view all the answers

What is the effect of CCK on the gall bladder?

It causes the gall bladder to contract and the sphincter of Oddi to relax Signup and view all the answers

What is the characteristic of prehepatic or hemolytic jaundice?

It is caused by an excessive breakdown of red blood cells Signup and view all the answers

What is the effect of prehepatic or hemolytic jaundice on the excretion of urobilinogen?

It increases the excretion of urobilinogen in stool and urine Signup and view all the answers

What is the characteristic of post-hepatic or obstructive jaundice?

It is caused by an obstruction of the bile ducts Signup and view all the answers

What is the effect of cholagogues on the bile secretion?

They decrease the secretion of bile Signup and view all the answers

What is the reason for urine contents not being significantly increased in acholuric jaundice?

Hemobilirubin cannot be filtered by the renal glomeruli Signup and view all the answers

What is the characteristic of urine in hepatic jaundice?

Yellowish foams are produced when shaken Signup and view all the answers

What is the cause of anemia in the context of hemolytic jaundice?

Excessive hemolysis Signup and view all the answers

What is the characteristic of stool in post-hepatic jaundice?

Very pale color Signup and view all the answers

What is the result of regurgitation of conjugated bilirubin into the bloodstream?

Marked rise in plasma cholesterol and alkaline phosphatase Signup and view all the answers

What is the result of deficient absorption of vitamins in post-hepatic jaundice?

Signs of deficiency of vitamins A, D, E, and K Signup and view all the answers

What is the cause of pruritis in post-hepatic jaundice?

Bile salts Signup and view all the answers

What is the characteristic of urine in post-hepatic jaundice?

Very dark color with intense foams when shaken Signup and view all the answers

Study Notes

Heme Catabolism and Bilirubin Metabolism

Heme catabolism is the process of breaking down heme into bilirubin
Bilirubin is then conjugated with glucuronic acid to form bilirubin glucuronide
UDP-glucuronyltransferase is the enzyme responsible for this conjugation reaction

Bile Secretion and Functions

Bile is secreted by hepatocytes at a rate of 500 ml/day
Bile is stored in the gallbladder and concentrated between meals
Bile salts play a crucial role in fat digestion and absorption, and also help excrete waste products like bilirubin
Bicarbonate in bile neutralizes acid in the duodenum

Regulation of Bile Secretion and Gallbladder Emptying

Bile salts are the most important stimulant of bile secretion by liver cells
Secretin and CCK are hormones that regulate bile secretion and gallbladder emptying
Secretin stimulates the secretion of bile rich in water and HCO3-
CCK stimulates the gallbladder to contract and the sphincter of Oddi to relax

Cholagogues and Choleretics

Cholagogues are medicinal agents that promote the discharge of bile from the system
Choleretics are substances that increase the volume of secretion of bile from the liver and the amount of solids secreted
Examples of cholagogues and choleretics include bile salts, CCK, secretin, and acetylcholine

Jaundice

Jaundice is a condition characterized by elevated levels of bilirubin in the blood
There are three types of jaundice: prehepatic, hepatic, and post-hepatic
Prehepatic jaundice is caused by excessive breakdown of red blood cells
Hepatic jaundice is caused by liver disease and the inability to process bilirubin
Post-hepatic jaundice is caused by obstruction of the bile ducts, preventing bilirubin from being eliminated in the feces

Causes and Types of Jaundice

Prehepatic jaundice is characterized by unconjugated hyperbilirubinemia, increased urobilinogen, and normal fat digestion and absorption
Hepatic jaundice is characterized by impaired liver function, decreased conjugation and excretion of bilirubin, and disturbed fat digestion and absorption
Post-hepatic jaundice is characterized by conjugated hyperbilirubinemia, pale stool, and dark urine

Blood Changes in Jaundice

Anemia and increased reticulocytes are common in prehepatic jaundice
Causes of prehepatic jaundice include spherocytosis, sickle cell anemia, G6PD deficiency, pyruvate kinase deficiency, and thalassemias

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Description

This quiz covers the mechanisms of bile secretion, heme catabolism, and bilirubin metabolism in the liver. It explains the roles of cholagogues and choleretics, and the steps involved in converting heme to bilirubin.