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The human spleen stores red blood cells and platelets, releasing them during exercise or stress.
The spleen's venous sinuses hold a reserve of red blood cells and platelets. During exercise or stress, signals trigger contraction that releases these cells into circulation.
The spleen is often described as a blood filter, but it also acts as a storage organ. Its venous sinuses can hold a reserve of red blood cells and platelets, which are released into circulation when the body needs them most. [1]
How the spleen stores blood cells
The spleen's red pulp contains a network of venous sinuses. Red blood cells can temporarily pool in these sinuses, and platelets are also sequestered there. This reserve is not static; it can be mobilised quickly. [1][2]
During exercise or stress, the sympathetic nervous system triggers the spleen to contract. This contraction squeezes the stored cells into the bloodstream, boosting the oxygen-carrying capacity and clotting potential when demand rises. [1][3]
Why this matters
- Athletes can experience a temporary increase in red blood cell count during intense exercise due to splenic contraction. [3]
- The spleen's platelet reserve may help respond to injury or stress by rapidly increasing circulating platelets. [2]
- People without a spleen (splenectomy) may have altered blood cell counts and a higher risk of certain infections. [1]
A dynamic reservoir
The spleen's role as a blood reservoir is well established in physiology. It highlights how the body maintains reserves for sudden demands, beyond its better-known immune functions. [1][3]
Sources
- Spleen: Anatomy, Function, and Treatment Healthline
- The spleen: anatomy, physiology, and clinical significance StatPearls
- Splenic contraction and red blood cell release during exercise Journal of Applied Physiology
