Blood Clotting and Platelet Formation

Blood Clotting

• Blood clotting (hemostasis) is a series of reactions using clotting factors (procoagulants), mostly plasma proteins, numbered I to XIII in order of discovery.
• Platelet plug is reinforced with fibrin threads.
• Blood clots seal larger vessel breaks.
• Clotting involves changing blood from liquid to a gel.
• Vitamin K is needed to synthesize certain clotting factors.

Platelet Formation

• Platelet formation is regulated by thrombopoietin.
• Platelets are formed in the myeloid line from megakaryocytes.
• Stage IV megakaryocytes send cytoplasmic projections into the lumen of capillaries.
• Projections break off, forming platelet fragments.
• Platelets degenerate in about 10 days.

White Blood Cell (Leukocyte) Count

• Procedure used to count white blood cells (WBCs) per cubic millimeter of blood.
• Normal range is 5,000-10,000 per cubic millimeter.
• A differential WBC count identifies different types of leukocytes and their percentages.
• These percentages can change depending on disease conditions.

Blood Types and Transfusion

• ABO blood groups are typed because they cause the most vigorous transfusion reactions.
• Blood types arise from antigens.
• Antigens are substances perceived as foreign that trigger an immune response.
• Mismatched blood leads to agglutination and could possibly lead to a fatal reaction.
• Transfusion reactions occur when blood types mismatched.

Hemostasis Definition

• Hemostasis is a process that stops bleeding.
• Chemical inside blood triggers blood clotting.
• Blood clotting is triggered by Hageman factor and when blood contacts a foreign surface..

Platelet Plug Formation

• Platelets stick to collagen fibers in damaged blood vessels.
• Von Willebrand factors stabilize platelet-collagen adhesion.
• When activated, platelets swell, become spiked and sticky, releasing chemical messengers (positive feedback).
• ADP causes more platelets to stick and release their contents.
• Serotonin and thromboxane A2 enhance vascular spasms and platelet aggregation.

White Blood Cell (Leukocyte) Disorders

• Abnormal proliferation of specific WBCs can be fatal.
• Leukemia is named according to the abnormal WBC clone involved.
• Acute leukemia quickly affects children, while chronic is more common in older adults.
  • Treatments include irradiation, antileukemic drugs and stem cell transplants.

Definition: Chemical Inside Blood Triggers Blood Coagulation

• Chemical inside blood triggers blood coagulation.
• Triggered by Hageman factor (inside blood)
• Triggered when blood comes into contact with a foreign substance.

Hemostasis Disorders

• Petechiae indicate spontaneous, widespread hemorrhage due to suppression/destruction of red bone marrow.
• Platelet count below 50,000/µL is a diagnostic indicator.
• Treatment includes transfusion of concentrated platelets.

Blood Vessel Response to Injury

• Blood vessels respond to injury with vasoconstriction (narrowing).
• Vascular spasms are triggered by direct injury to vascular smooth muscle and chemicals released by endothelial cells and platelets.
• Pain reflexes are also involved.

Clot Development and Persistence

• A thrombus (or blood clot) is a clot formed in an unbroken blood vessel.
• Thrombi may block blood circulation leading to tissue death.
• Anticoagulants like heparin and warfarin are used to clinically prevent venous thrombosis.

Blood Cell Types

• Blood cells include erythrocytes, leukocytes, and platelets (thrombocytes).
• Neutrophils (polymorphonuclear leukocytes), are the first to arrive at infection sites, phagocytic, and 54-62% of leukocytes.
• Elevated in bacterial infection.