Erythropoiesis

What is erythropoiesis?

Erythropoiesis (pronounced “ur-i-throw-poy-EE-sus”) is your body’s process of making red blood cells (erythrocytes). Erythropoiesis ensures you have the right number of blood cells — not too few or too many. Red blood cells are important because they:

• Transport oxygen you breathe in through your lungs to tissues throughout your body.
• Transport carbon dioxide from tissues throughout your body to your lungs so you can breathe it out.

Erythropoiesis is one type of hematopoiesis. Hematopoiesis is your body’s process of making all three types of blood cells: red blood cells (erythropoiesis), white blood cells (leukopoiesis) and platelets (thrombopoiesis).

Where does erythropoiesis occur?

Erythropoiesis starts before people are born. This is fetal erythropoiesis. By the time people are born, erythropoiesis takes place in people’s bone marrow. Bone marrow is the spongy tissue inside of your bones.

Fetal erythropoiesis

The location of erythropoiesis changes as a fetus develops during pregnancy.

• Week three: Erythropoiesis begins in the yolk sac. A yolk sac is a structure that nourishes a developing embryo.
• Months two and three: Erythropoiesis occurs in a fetus’s liver and spleen.
• Month five: Erythropoiesis occurs in a fetus’s bone marrow.

Erythropoiesis in children and adults

By the time you’re born, erythropoiesis happens primarily in your bone marrow.

• Children: Erythropoiesis occurs in the bone marrow of many different types of bones.
• Adults: Erythropoiesis occurs in certain bones, including your pelvis, vertebrae, ribs and breastbone.

What is the difference between medullary and extramedullary erythropoiesis?

“Medullary” refers to your bone marrow. Medullary erythropoiesis happens in your bone marrow, while extramedullary erythropoiesis happens outside your bone marrow.

Extramedullary erythropoiesis is normal at some stages of fetal development. During adulthood, extramedullary erythropoiesis is often a sign of a disease or condition affecting your bone marrow.

What are the stages of erythropoiesis?

With erythropoiesis, an originator cell called a hematopoietic stem cell (HSC) matures into a fully mature red blood cell, or erythrocyte. A cell advances through many stages for this to happen.

Each type of blood cell (red blood cells, white blood cells and platelets) begin as an HSC. For a red blood cell to eventually form, an HSC becomes a common myeloid progenitor (CMP) cell. A CMP may mature into a red blood cell, platelet or some types of white blood cells. A CMP that eventually becomes a red blood cell develops into a megakaryocyte-erythroid progenitor cell (MEP).

Once it’s developed into a MEP, the cell is on track to become a red blood cell. It progresses through the following stages as it develops:

• Proerythroblast.
• Erythroblast.
• Normoblast.
• Reticulocyte.
• Erythrocyte (fully mature red blood cell).

Your bone marrow releases mature blood cells into your bloodstream. Once they’re in your bloodstream, your red blood cells can move oxygen from your lungs to your tissue. They can move carbon dioxide from your tissues to your lungs (to be exhaled).

How long does erythropoiesis take?

It takes about a week for a red blood cell to fully mature.

What is a red blood cell's (erythrocyte's) lifespan?

Red blood cells live for approximately 120 days.

What causes erythropoiesis?

Your body’s sensitivity to oxygen levels regulates erythropoiesis. If your tissues don’t have enough oxygen (hypoxia), your body will ramp up red blood cell production. More red blood cells mean there’s more oxygen flowing to your tissues and cells.

A hormone called erythropoietin triggers erythropoiesis.

What is erythropoietin?

A hormone called erythropoietin (EPO) spurs red blood cell production. Hormones are chemical messengers that coordinate essential body functions. Your kidneys secrete most of your body’s EPO.

The process goes like this:

1. Your tissues lack oxygen because your red blood cells are low.
2. Your kidneys secrete more EPO in response.
3. The EPO stimulates your bone marrow to make more red blood cells.
4. Your kidneys detect an increase in hemoglobin, a key protein in red blood cells, and secrete less EPO in response.
5. Your body achieves a balance (homeostasis) where you have the right amount of red blood cells.

Your kidneys constantly secrete low levels of EPO to keep red blood cell production going. You lose about 1% of your red blood cells each day. Erythropoiesis replaces the red blood cells that have reached the end of their lifespan.

Your kidneys may secrete more or less EPO in response to conditions or injuries affecting your red blood cell levels.

What happens when there’s a problem with erythropoiesis?

Problems with erythropoiesis may cause you to have too few red blood cells (anemia) or too many red blood cells (erythrocytosis).

• Anemia: You don’t have enough red blood cells to carry oxygen to your body’s tissues. As a result, you may feel weak, tired or cold. There are different types of anemia.
• Erythrocytosis: You have too many red blood cells. Depending on what’s causing erythrocytosis, you may experience mild symptoms, like a headache or fatigue. You may be at risk of more severe complications like blood clots.

What conditions can impact erythropoiesis?

Many conditions can impact your body’s ability to make and regulate red blood cells.

Lung diseases

• Asthma.
• Chronic obstructive pulmonary disease (COPD).

Cancers affecting your blood or bone marrow

• Leukemia.
• Lymphoma.
• Myeloma.
• Myeloproliferative disorders.

Other factors

• Nutritional deficiencies (Iron, B12, folate).
• High altitudes (Your body secretes more EPO in response to the decreased oxygen at high altitudes.).

A note from Cleveland Clinic

Your body continually makes new red blood cells throughout your lifetime. As red blood cells die, your body senses the changes and boosts the production of EPO and (as a result) red blood cells. Having the right amount of red blood cells is essential to maintaining a healthy supply of oxygen to your tissues. Fortunately, your body automatically regulates this process closely without any effort on your part. Your healthcare provider can recommend treatments to cure or manage many conditions that interfere with erythropoiesis.