Review:  Red Blood Cell (RBC) Lifecycle

• RBCs last about 120 days.
• Macrophages phagocytose (engulf and destroy) old RBCs.
• The process of recycling approximately 1 to 3 million RBCs per second.

Review:  Hemoglobin Structure

• RBCs contain hemoglobin, which lacks organelles and a nucleus.
• Hemoglobin is composed of:
  • Four polypeptides:
    • 2 alpha chains.
    • 2 beta chains.
  • Four heme groups:
    • Each heme contains an iron atom.
    • Iron gives blood its characteristic reddish hue.

1.  Recycling of Hemoglobin

Breakdown

• Globins (the protein part) are degraded into amino acids.
• Heme:
  • Iron:
    • Removed from heme.
    • Stored or reused to make new hemoglobin.
  • Remaining heme:
    • Converted to bilirubin.

2.  Bilirubin Formation

• Bilirubin initially appears as unconjugated bilirubin:
  • Not water-soluble.
  • Toxic if accumulated in blood.
• Liver cells conjugate bilirubin:
  • Make it water-soluble.
  • Facilitate excretion into the bile.

3.  Excretion

• Bilirubin is secreted into bile, enters the intestine, and aids fat emulsification.
• In the intestine, bilirubin is processed and eventually excreted via feces.

Impaired Bilirubin Processing and Jaundice

• Excessive hemolysis (destruction of RBCs) produces more bilirubin than the liver can handle.
• Elevated bilirubin builds up in blood, leading to jaundice:
  • Yellowish discoloration of skin and sclera (white part of eyes).
• This condition indicates liver dysfunction or excessive RBC breakdown.

Summary

• Normal RBC breakdown involves hemoglobin recycling and bilirubin excretion.
• Disruptions lead to jaundice, signaling potential liver or hematologic issues.
• The liver plays a crucial role in processing waste products from blood.