Blood Physiology

Hematopoiesis Blood cell formation Occurs in red marrow – Flat bones – Skull – Pelvis – Ribs – Sternum Lymphocytes that form T cells and B cells are also formed in lymph nodes

Hematopoiesis In bone marrow, all blood cells originate from a single type of stem cell. Stem cell divides it becomes either – An immature red blood cell – A white blood cell – A platelet-producing cell The immature cell then divides, matures further, and ultimately becomes a mature red blood cell, white blood cell, or platelet.

Hematopoiesis

Red Blood Cell Formation Reticulocyte – Young RBC, still contains ER – Matures within 2 days of release in circulation Erythropoietin – Controls the rate of erythropoiesis – Hormone released by kidneys

Red Blood Cell Formation Mature red cells cannot divide to reproduce – No nucleus – No organelles Life span ~120 days – Old/damaged cells removed by spleen and liver – Hemoglobin is recycled

WBC & Platelet formation Both hormone controlled – WBC’s – Interleukins & colony stimulating factors – Platelets – thrombopoietin Hemostasis – “Stoppage of bleeding” – Stimulated by damage to blood vessels – 3 events, rapid sequence

Hemostasis 1.Vascular Spasms – Vasoconstriction Narrow blood vessel Limit blood loss 2.Platelet Plug Formation – Platelets “stick” to damaged tissue – Attract more platelets to area – Also called “white thrombus” 3.Coagulation

Coagulation 1.TF is released by injured tissue – Stimulates clotting 2.PF3 – Coats platelets – Interacts with TF, vitamin K, clotting factors, Ca – Activates the “clotting cascade” 3.Prothrombin is converted to thrombin 4.Thrombin mixes with fibrinogen to form fibrin – Forms the “clot”

Coagulation Entire sequence of clot formation usually occurs in 3-6 minutes Within 1 hour of clot formation – The clot begins to retract – Pulls the damaged edges together Once the endothelium is regenerated, the clot is broken down