Ciclo da Bilirrubina

Summary

In this video, Gabriel Sandrin explains why poop is brown, connecting it to the process of bilirubin metabolism. He outlines how red blood cells break down in the spleen, releasing hemoglobin, which is transformed into bilirubin. The bilirubin travels through the bloodstream, attaches to albumin for transport to the liver, where it's processed into bile. In the intestines, bacteria convert bilirubin into stercobilin, the compound responsible for the brown color of stool. This fascinating biological cycle explains the color of our poop, making it both educational and intriguing for viewers.

Takeaways

• 😀 Stool is always brown due to the bilirubin cycle, regardless of what we eat.
• 😀 Red blood cells have a lifespan of about 120 days before being destroyed in the spleen.
• 😀 Old red blood cells are less flexible and are destroyed in the spleen through hemolysis.
• 😀 The hemoglobin from broken red blood cells is split into heme and globin.
• 😀 The heme part undergoes a transformation, eventually becoming biliverdin (green).
• 😀 Biliverdin is quickly converted into bilirubin, which is released into the bloodstream as indirect bilirubin.
• 😀 Indirect bilirubin is not water-soluble and needs albumin to travel through the blood.
• 😀 Albumin acts as a transport carrier for indirect bilirubin to the liver.
• 😀 In the liver, indirect bilirubin is conjugated with glucuronic acid, making it water-soluble (direct bilirubin).
• 😀 Direct bilirubin is excreted into the bile and reaches the intestines, where it’s metabolized by bacteria.
• 😀 The bacterial metabolism of direct bilirubin produces stercobilin, which gives stool its brown color.

Q & A

Why are feces always brown, regardless of what we eat?

Feces are brown because of the cycle of bilirubin, which is a byproduct of the breakdown of hemoglobin from old red blood cells. This process is linked to the production and transformation of bilirubin in the liver and intestines.

What happens to red blood cells when they get old?

When red blood cells age (after about 120 days), they are destroyed in the spleen. This breakdown releases hemoglobin, which undergoes further processing to produce bilirubin.

How are old red blood cells destroyed in the spleen?

Old red blood cells are destroyed in the spleen because the cells lose their flexibility and can no longer pass through the small capillaries. The spleen filters and eliminates these cells.

What are the main components of hemoglobin after it breaks down?

Hemoglobin breaks down into heme and globin. The heme portion is then further broken down into biliverdin (green) and eventually into bilirubin (yellow).

What is the role of albumin in the process of bilirubin transport?

Albumin binds to bilirubin to make it soluble, allowing it to travel through the bloodstream to the liver. Bilirubin is not soluble on its own, so it requires albumin to be transported.

What happens to bilirubin in the liver?

In the liver, bilirubin undergoes a process called conjugation, where it is made water-soluble. This form of bilirubin is known as direct bilirubin.

What is the difference between indirect and direct bilirubin?

Indirect bilirubin is the form of bilirubin that is bound to albumin and is not water-soluble, whereas direct bilirubin is conjugated in the liver and becomes water-soluble, allowing it to be excreted in bile.

What role does bile play in the digestion process related to bilirubin?

Bile, which is produced by the liver, contains direct bilirubin. This bile is secreted into the intestines, where bilirubin plays a role in digestion and is later transformed by intestinal bacteria.

How does bilirubin contribute to the color of feces?

In the intestines, bilirubin is metabolized by bacteria into compounds such as stercobilin. Stercobilin is responsible for the brown color of feces.

Can bilirubin be found in the urine?

Yes, some bilirubin can return to circulation and be excreted in the urine. When it appears in the urine, it is known as urobilinogen.