Metabolisme Bilirubin (Prehepatik, Hepatik, Posthepatik) dan Penyakit Kuning (ikterik)

Summary

This video explains the complex process of bilirubin metabolism in the body. Bilirubin is a byproduct of iron metabolism, primarily derived from the breakdown of red blood cells (erythrocytes). The process involves the conversion of heme into biliverdin, which is then transformed into indirect bilirubin. This indirect bilirubin travels through the bloodstream, bound to albumin, to the liver. In the liver, it is conjugated with glucuronic acid to form direct bilirubin, which is excreted into the intestines. A portion is reabsorbed back into the bloodstream, while the rest is excreted via urine. This cyclical process is vital for maintaining proper bilirubin levels in the body.

Takeaways

• 😀 Bilirubin is a waste product from the metabolism of iron in the body, with 70% derived from red blood cells (erythrocytes).
• 😀 The remaining bilirubin is produced from other iron-containing proteins, such as myoglobin and iron-containing enzymes.
• 😀 As erythrocytes age, they are broken down primarily in the spleen, releasing hemoglobin.
• 😀 Hemoglobin is then split into heme and globin. The heme structure contains carbon monoxide, iron, and a protoporphyrin ring.
• 😀 The iron is recycled, while the protoporphyrin ring is converted into biliverdin, which is then transformed into indirect bilirubin.
• 😀 The conversion of biliverdin into bilirubin is catalyzed by the enzyme heme oxygenase.
• 😀 Indirect bilirubin is water-insoluble and needs to bind to albumin to be transported through the bloodstream to the liver.
• 😀 In the liver, indirect bilirubin is made water-soluble by binding with glucuronic acid, forming direct (conjugated) bilirubin.
• 😀 Direct bilirubin is excreted into the duodenum, where it undergoes further transformation by gut bacteria into urobilinogen.
• 😀 Some urobilinogen is reabsorbed and returned to the liver, while the rest is excreted via urine or further processed in the intestines.
• 😀 The cycle of urobilinogen moving between the intestines and liver is called the enterohepatic circulation, and it is important for bilirubin metabolism.

Q & A

What is bilirubin and how is it formed?

Bilirubin is a waste product resulting from the breakdown of iron-containing molecules in the body. 70% of bilirubin originates from the breakdown of erythrocytes (red blood cells), while the rest comes from other iron-containing proteins such as myoglobin and enzymes.

How are erythrocytes broken down to produce bilirubin?

When erythrocytes age, they are broken down primarily in the spleen, releasing hemoglobin. Hemoglobin is further broken down into heme and globin. The heme is then metabolized into biliverdin, which is a precursor to bilirubin.

What happens to the heme during metabolism?

The heme is metabolized by the enzyme heme oxygenase, which produces biliverdin. Biliverdin is then converted into indirect bilirubin by the enzyme biliverdin reductase.

What is the role of albumin in bilirubin transport?

Indirect bilirubin is not water-soluble, so it binds to albumin in the bloodstream for transport. Albumin helps carry the bilirubin to the liver for further processing.

How does bilirubin become water-soluble?

In the liver, the enzyme glucuronyl transferase adds glucuronic acid to the indirect bilirubin, transforming it into direct bilirubin (also called conjugated bilirubin), which is water-soluble and ready for excretion.

What is the significance of glucuronyl transferase in bilirubin metabolism?

Glucuronyl transferase plays a crucial role in converting indirect bilirubin into its direct, water-soluble form by adding glucuronic acid to it. This step is essential for bilirubin to be excreted from the body.

How is direct bilirubin excreted from the liver?

Once bilirubin is converted to its direct form (conjugated bilirubin), it is excreted from the liver into the duodenum through the bile ducts.

What happens to bilirubin in the intestines?

In the intestines, bacteria produce an enzyme called beta-glucuronidase, which converts direct bilirubin into urobilinogen. Some of the urobilinogen is reabsorbed and returns to the liver, while a small portion is excreted in urine.

What is the urobilinogen cycle?

The urobilinogen cycle refers to the recycling of urobilinogen in the body, where it moves between the intestines and liver. Urobilinogen can be reabsorbed back into the bloodstream or excreted through urine or feces.

What happens if there is too much bilirubin in the body?

Excess bilirubin can lead to jaundice, a condition where the skin and eyes turn yellow. If too much bilirubin is present in the urine, it can also cause a dark discoloration.