blood cells

How blood cells form

• blood cells form by the process of hematopoiesis, which occurs in red bone marrow

• all formed elements are derived from a common stem cell (hemocytoblast)

  • hemocytoblasts differentiate into lymphoid stem cells which create lymphocytes, and myeloid stem cells which create all other types of blood cells.

• hormones are the stimulation factor for producing blood cells

  • red blood cell production is stimulated by erythropoietin

  • white blood cell production is stimulated by colony-stimulating factors (CSFs) and interleukins

  • Platelet production is stimulated by thrombopoietin

How does blood clot?

• when a blood vessel is injured, platelets begin the process of forming a blood clot (aka hemostasis)

• the process is important in restrictions blood loss after cut or bruise

Hemostasis steps

1. the blood vessel contracts, causing reduced blood loss at the wound

2. platelets are chemically attracted to the wounded epithelium and stick together

3. injured tissues release tissue factor which interacts with the platelets causing the production of the enzyme thrombin. Thrombin + fibrinogen proteins = fibrin filaments that form a mesh (scab)

If blood does not clot properly?

• abnormal clot formed within the blood vessel is a thrombus

• when a thrombus dislodges and floats through the blood, that is called embolus