Leukopoiesis in animals
The process of formation of leukocytes is known as Leukopoiesis. Leukocytes are produced from the pleuripotent stem cells.
Fate of WBCs
It is very difficult to assess the life span of leukocytes because the WBCs move between blood and tissue. The life span of granulocytes is normally 9 days but once they are released into circulation from bone marrow their life span is 4 to 8 hours.
During infection, the life span in shortened. “B” lymphocytes live for 3-4 days only but “T” lymphocytes may live for 1-3 years in tissues and return to circulation many times.
The monocytes also have short transit time in the blood (24 hours) before migrating to the tissues where they become tissue macrophages and can live for months or even years.
Abnormalities of leukocytes
Leukocytosis – It is an increase in the number of leukocytes which is an indication of presence of some infection. Leukocytosis may be physiological (related to time of day, meal, exercise, epinephrine, stress) or pathological. Bacterial infection shows leukocytosis with neutrophilia, whereas viral infections result in neutropenia.
Leukemia – Pathologically, cancer of leukocyte producing tissues results in abnormally high white cell count which is known as leukemia.
