Activation of Yellow marrow into Red marrow

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 When the body senses a shortage of blood cells, it sends signals to reactivate the yellow bone marrow.

1. Detection of Blood Cell Shortage

  • In conditions like anemia, injury, or infection, there are not enough red blood cells (RBCs) or other blood cells.

  • The body detects low oxygen levels or low cell counts in the blood.

 2. Signal Release

  • The kidneys release a hormone called erythropoietin (EPO).

  • Cytokines (immune signaling proteins) are also released.

  • These signals reach the bone marrow through the blood.

 3. Stem Cell Activation in Yellow Marrow

  • The yellow marrow contains mesenchymal stem cells (fat-storing stem cells).

  • Under normal conditions, these produce fat.

  • But in response to signals (like EPO and cytokines), they start converting into hematopoietic cells (blood-producing cells).

4. Fat Cells Decrease

  • Fat cells in yellow marrow shrink or die off.

  • More space opens up for blood-forming cells to grow.

5. Red Marrow is Re-Established

  • The yellow marrow now behaves like red marrow.

  • It starts producing RBCs, WBCs, and platelets again.

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