How blood cells are made

1. Hematopoiesis
EHS Unit 7 Day 2

2. Learning Targets
• Describe the process, locations and control
mechanisms that are involved in
hematopoiesis.

3. Hematopoiesis
• Simply, how blood is made.
– Here we are talking about the cellular components
of blood:
• Platelets
• RBCs
• WBCs
– Plasma is made up of water and solutes absorbed
from the digestive tract and proteins made mostly
in the liver.

4. Locations of Hematopoiesis
• In Fetal development:
– Yolk sac, and then liver as body matures.
• In adults:
– RBCs and platelets are made in the bone marrow.
– WBCs are made in lymph tissues (more on that later)
– In case of disease, the spleen and liver may help make
blood cells, but this causes organ enlargement and is
not normal functioning.

5. How RBC’s are born
• In the Red Bone Marrow:
– Stem Cells called hemacytoblasts (can become any
type of blood cell) are stimulated by erythropoietin
(hormone released from the kidneys).
– They then develop hemoglobin, and when they are
ready, eliminate their nucleus and go out to do their
job.
– In normal cases, the rate of RBC recycling and
production match each other.
– If it occurs too slowly, we call it anemia.
– If it occurs too quickly, we call it plycythemia.

6. How WBCs are born…
• White blood cells, like RBCs are made from
hemocytoblasts in the bone marrow. Some are mad in
the lymph tissues.
• 2 hormones (interlukin and colony stimulating factor)
make the stem cells turn into WBCs. These hormones
come from immune tissues and active immune cells.
• Exposure to antigens and disease will create the
specialized WBCs our immune system needs to fight
disease.
• If this occurs too quickly, it may be leukemia.
• If this occurs too slowly, the body may be at risk for
infection.

7. How Platelets are born…
• Again, in the red bone marrow from the same
blood stem cell (hemocytoblast).
• A hormone called thrombopoietin made in the
liver makes the stem cells turn into
megakaryocytes.
• Megakaryocytes then break into little cell
pieces that function as platelets.

8. Regulation
• In general, the organs that produce the
hormones that stimulate production are the
ones monitoring levels of blood cells.
– RBC production is regulated by kidneys and liver.
– WBC production is regulated by immune tissues
and cells.
– Platelet production is regulated by the liver.