Hematology | Erythropoiesis: Lifespan & Destruction: Part 2

Summary

This video explains the life cycle of red blood cells (RBCs), focusing on their breakdown after 100-120 days. Key proteins like spectrin and ankyrin allow RBCs to be flexible, enabling them to pass through capillaries. As RBCs age, they lose flexibility and are removed by macrophages in the spleen. Hemoglobin is broken down into globin (recycled into amino acids) and heme (converted into iron and bilirubin). Bilirubin is processed in the liver, becomes part of bile, and is excreted. Disruptions in this process, such as blockages in bile secretion, can lead to conditions like jaundice.

Takeaways

• 😀 Red blood cells (RBCs) typically have a lifespan of 100 to 120 days, after which they undergo destruction.
• 😀 The structural integrity of RBCs is maintained by key proteins: spectrin (a web-like protein) and ankyrin (which binds spectrin to the cell membrane).
• 😀 As RBCs age, their cytoskeletal proteins degrade, causing the membrane to become rigid and less flexible, making the RBC more likely to be destroyed.
• 😀 The spleen plays a major role in RBC destruction, with sinusoidal capillaries and macrophages involved in capturing and phagocytosing damaged RBCs.
• 😀 Hemoglobin is broken down into globin (which is converted into amino acids) and heme (which is processed further into iron and biliverdin).
• 😀 Iron from heme is either stored in the liver as ferritin or can be recycled for new processes, contributing to the body's iron supply.
• 😀 The breakdown of heme produces biliverdin, which is converted to bilrubin. This unconjugated bilirubin is toxic and must bind to albumin for safe circulation.
• 😀 The liver conjugates bilirubin with glucuronic acid, making it water-soluble (conjugated bilirubin), which is excreted as bile.
• 😀 Bile aids in fat digestion and contains conjugated bilirubin, which is eventually released into the duodenum and small intestine, before being excreted or further processed.
• 😀 Bacterial flora in the intestines break down bilirubin into urobilinogen, which can be reabsorbed into the bloodstream or excreted through urine as urobilin, contributing to the yellow color of urine.
• 😀 Some urobilinogen is further broken down in the intestines to stercobilin, which gives feces their characteristic brown color. This process is vital for diagnosing issues in the biliary or pancreatic systems, such as gallstones.

Q & A

What is the typical lifespan of a red blood cell (RBC)?

The typical lifespan of a red blood cell is 100 to 120 days.

What key proteins are responsible for the flexibility of red blood cells?

The key proteins responsible for the flexibility of red blood cells are **spectrin** and **ankyrin**. These proteins form a cytoskeletal network that allows the cell to be pliable and flexible.

How do older red blood cells lose their flexibility?

As red blood cells age, the proteins in their cytoskeleton, particularly spectrin and ankyrin, begin to degrade. This causes the cell membrane to become rigid, reducing its flexibility and leading to its eventual destruction.

Why do red blood cells need to be flexible?

Red blood cells need to be flexible to squeeze through capillaries that are smaller in diameter than the cells themselves. This flexibility allows the cells to deform as they pass through narrow blood vessels.

Where does the destruction of aged red blood cells primarily occur?

The destruction of aged red blood cells primarily occurs in the **spleen**, where they get trapped in sinusoidal capillaries and are engulfed by macrophages.

What happens to the components of hemoglobin during RBC breakdown?

During red blood cell breakdown, **hemoglobin** is split into two parts: **globin**, which is broken down into amino acids and recycled, and **heme**, which is further broken down into iron and biliverdin.

What happens to iron after the breakdown of heme?

After the breakdown of heme, **iron** binds to a protein called **apoferritin**, forming **ferritin**, which stores the iron. Some iron is also released into the bloodstream through **ferroportin** to be used in other processes.

What is the significance of conjugated bilirubin in the liver?

Conjugated bilirubin is formed in the liver when **bilirubin** binds with **glucuronic acid**, making it water-soluble. This form of bilirubin is excreted into the bile and plays a key role in fat digestion.

What role do bacteria in the gut play in the processing of bilirubin?

Bacteria in the gut break down **conjugated bilirubin** into **urobilinogen**. Some of this urobilinogen is reabsorbed into the bloodstream, while some is excreted as **urobilin** in the urine, contributing to its yellow color.

What clinical signs indicate a problem with the biliary or pancreatic system?

A lack of **urobilinogen** in the feces, or a lack of bilirubin in the urine (which would cause pale urine), can indicate an obstruction in the biliary or pancreatic system. **Jaundice** (yellowing of the skin or eyes) is another clinical sign, often caused by a buildup of **bilirubin** in the tissues.