Hematopoiesis is blood cell production. Your body continually makes new blood cells to replace old ones. Hematopoiesis ensures you have a healthy supply of blood cells to supply oxygen to your tissue (red blood cells), fight infection (white blood cells) and clot your blood when you’re injured (platelets). Most blood cells get made in your bone marrow.
Hematopoiesis (pronounced “heh-ma-tuh-poy-EE-sus”) is blood cell production. Your body continually makes new blood cells to replace old blood cells so you have a steady blood supply. Hematopoiesis starts before birth and continues as a cycle throughout life.
It’s easier to remember what hematopoiesis is when you consider its roots. Hematopoiesis is derived from two Greek words:
Put these words together, and you get hematopoiesis, the process of making blood. Hematopoiesis is also called hemopoiesis, hematogenesis and hemogenesis.
Your blood cells are the building blocks of your blood. Hematopoiesis includes the production of all blood cell types, including:
Red blood cells, or erythrocytes, carry oxygen from your lungs to organs throughout your body. They also carry carbon dioxide to your lungs so you can get rid of it by exhaling it. Your blood has more red blood cells than any other type of blood cell. The production of red blood cells is called erythropoiesis.
White blood cells, or leukocytes, fight infection and protect your body from harmful invaders, or germs. They also destroy abnormal cells. The production of white blood cells is called leukopoiesis.
Broadly, the types of white blood cells are:
Neutrophils, basophils and eosinophils have similar functions and can be grouped together and called granulocytes. The other types of white blood cells are monocytes and lymphocytes.
Platelets, or thrombocytes, are sticky cell fragments that clump together to form a clot if you’re injured. They create a seal in damaged tissue that prevents you from losing too much blood. The production of platelets is called thrombopoiesis.
The most common site of blood cell production is the spongy tissue inside of your bones called bone marrow. Hematopoiesis that occurs in your bone marrow is called medullary hematopoiesis. Blood cells get made in your bone marrow and released into your bloodstream.
Hematopoiesis takes place in different locations before birth than it does after you’re born.
Blood cell production starts when you’re still in the uterus. It begins in the yolk sac, a structure that surrounds an embryo at the beginning of pregnancy. Toward the end of pregnancy, most blood cell production happens in your bone marrow. Key milestones in hematopoiesis during pregnancy are:
Most blood cell production happens in your bone marrow from infancy and into adulthood. Certain types of white blood cells called lymphocytes develop in your thymus, too.
Disease creates the exception. If you have a condition that prevents your bone marrow from making enough blood cells, hematopoiesis may shift to your blood cell production sites before birth. Blood cell production may shift to your liver, spleen or lymph nodes.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
Hematopoiesis begins with an originator cell common to all blood cell types. It’s called a hematopoietic stem cell (HSC). An HSC develops into a precursor cell, or “blast” cell. A precursor cell is on track to become a specific type of blood cell, but it’s still in the early stages. A precursor cell goes through several cell divisions and changes before it becomes a fully mature blood cell.
The specific types of hematopoiesis include:
With each change, an originator cell becomes more specialized — less like a stem cell and more like a red blood cell, white blood cell or platelet.
Red blood cell production occurs in your bone marrow. An HSC matures into a precursor cell called an erythroblast. An erythroblast becomes an immature red blood cell called a reticulocyte. Finally, a reticulocyte develops into a mature red blood cell.
Although they’re all white blood cells, granulocytes (basophils, eosinophils and neutrophils) have slightly different origins from monocytes and lymphocytes. In addition, monocytes and lymphocytes follow different development paths.
Granulocytes (basophils, eosinophils and neutrophils) get made in your bone marrow. An HSC follows a development path called the myeloid cell line for granulocyte production. The word “myeloid” means “relating to the bone marrow” — where granulocytes get made.
For granulocytes to form, an HSC becomes a precursor cell called a myeloblast. A myeloblast forms a myelocyte, which later becomes a basophil, eosinophil or neutrophil.
Monocytes get made in your bone marrow, while lymphocytes (B-cells, T-cells and natural killer cells) get made in your bone marrow and other lymph tissue. For instance, very young forms of lymphocytes develop in the bone marrow and then travel to the thymus, where they will mature and develop into T-cell lymphocytes.
Platelet production occurs in your bone marrow, where an HSC matures into a precursor cell called a megakaryoblast. The megakaryoblast becomes a megakaryocyte. Fragments of the megakaryocyte break off, becoming platelets.
The rate of blood cell production depends on your needs. For example, your body may increase white blood cell production to fight germs if you’re sick. In general, hematopoiesis lasts as long as the life cycle of a blood cell. Once it’s time for a blood cell to die, a healthy body has made a new one to replace it.
Your body regulates blood cell production so that you have just the right amount of blood cells. Certain conditions can interfere with hematopoiesis, causing you to have too few or too many blood cells. Having abnormal amounts of blood cells can cause a range of symptoms and conditions.
Multiple factors and conditions can disrupt hematopoiesis, with effects ranging from mild to severe. For instance, as you age, fat deposits can collect in your bone marrow so there’s less room for hematopoiesis.
Also, some medications can interfere with hematopoiesis, leading to low blood cell counts. For instance, chemotherapy kills cancer cells, but it also may lower your white blood cells (neutropenia). Low blood cell counts may be a side effect of taking certain medications.
A note from Cleveland Clinic
Hematopoiesis is a common, ongoing process essential for your health and survival. Many factors that compromise your health can also influence your body’s ability to make blood cells. A process that takes place (for the most part) in your bone marrow maintains the steady blood supply that keeps your tissues oxygenated and your body infection-free.
Last reviewed by a Cleveland Clinic medical professional on 10/12/2022.
Learn more about our editorial process.