Bone marrow produces millions of new blood cells every second, but the total number remains almost constant. So where do the old red blood cells, white blood cells, and platelets go?
According to scientists, every blood cell has a lifespan. Red blood cells (erythrocytes) are the longest-lived blood cells, lasting about 120 days.
The lifespan of white blood cells (leukocytes) varies depending on their type. Granulocytes and monocytes have a lifespan of 4-5 days, while lymphocytes can live up to 100-200 days. Platelets (thrombocytes) have a shorter lifespan, ranging from 3-5 days.
Most blood cells are destroyed in the spleen and liver. When they die in the tissues, they are engulfed and digested by specialized cells in the immune system called macrophages.
Normal red blood cells have a flexible membrane that allows them to easily pass through the narrow pores of the splenic capillaries by changing shape. However, towards the end of their life cycle, the red blood cell membrane loses its elasticity and becomes unable to penetrate the capillaries. Therefore, these cells are filtered in the spleen and engulfed by phagocytic cells of the reticuloendothelial system. For this reason, the spleen is often called the "red blood cell graveyard." According to some data, more than 70% of red blood cells that have completed their life cycle end up in the spleen.
When red blood cells are broken down in the liver, bilirubin pigment is formed. This pigment enters the intestines with bile, where it undergoes further chemical transformations, resulting in the formation of stercobilin, which gives stool its brown color, and urobilin, which is excreted in the urine.
The iron released during the breakdown of red blood cells is later reused in building new blood cells, while some of it is stored as a reserve in the liver and spleen.
Platelets play a crucial role in blood clotting (stopping bleeding). When the wall of a blood vessel is damaged, platelets adhere to its surface, expand, and take on a star-like shape, then stick together, forming a blood clot that seals the damaged area. Platelets that survive this process are destroyed within a few days in the spleen and liver.
White blood cells, the body's first line of immune defense, are either destroyed in the liver or, more often, die at the site of inflammation. This can sometimes be observed through the formation of pus at the site of inflammation. Pus is an inflammatory secretion resulting from the body's response to infection, and it contains large amounts of proteins, lysed white blood cells, dead cells from infected tissues, and microorganisms.
