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Related Concept Videos

Extrinsic and Intrinsic Pathways of Hemostasis01:20

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Blood clotting or coagulation involves extrinsic and intrinsic pathways, which ultimately merge into the common pathway, forming a fibrin clot.
The Extrinsic Pathway
The extrinsic pathway of coagulation is typically initiated by tissue damage that exposes blood to tissue factor (TF), a protein released by the damaged tissue cells outside the blood vessels—this interaction with TF triggers biochemical reactions involving specific clotting factors. The key player here is Factor VII, which...
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Coagulation01:09

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The coagulation phase is a critical part of the body's process to prevent blood loss following injury to blood vessels. It involves chemical reactions that form a clot to seal the injured area. The clotting process begins shortly after injury, within 15-20 seconds for severe damage and 1-2 minutes for minor injuries.
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Colloidal solids are solid particles suspended in solution. They are usually negatively charged, attracting a compact primary layer of positively charged ions, which attract more counterions to form an electrical double layer. Electrostatic repulsion between the charged double layers prevents the particles from colliding, stabilizing the colloids. These solids are often undesirable because they can contain toxins that are difficult to remove. Coagulation is a technique that helps aggregate and...
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The platelet phase, the second stage of hemostasis, commences around 15-20 seconds after an injury. It follows and overlaps with the vascular phase, during which blood vessels constrict to minimize blood loss.
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Introduction to Hemostasis01:05

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Hemostasis is a complex physiological process that prevents excessive bleeding when a blood vessel is injured. It's crucial for maintaining the integrity of the circulatory system, as it ensures that our blood remains fluid while still within the vascular network and yet clots to prevent blood loss upon vessel injury.
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Rapidly dividing tumors, embryos, and wounded tissues require more oxygen than usual, lowering the oxygen concentration in the blood. At low oxygen or hypoxic conditions, an oxygen-sensitive transcription factor called the hypoxia-inducible factor 1 or HIF1 is activated. HIF1 is a dimeric protein of alpha (ɑ) and beta (β) subunits.  Under optimal oxygen conditions, HIF1β is present in the nucleus while HIF1ɑ remains in the cytosol. HIF1ɑ is hydroxylated by prolyl...
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Related Experiment Video

Updated: Jan 19, 2026

Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
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Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay

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A candidate activation pathway for coagulation factor VII.

Tina M Misenheimer1, Kraig T Kumfer1, Barbara E Bates1

  • 1Morgridge Institute for Research, Madison, WI, U.S.A.

The Biochemical Journal
|September 21, 2019
PubMed
Summary
This summary is machine-generated.

The initiation of blood coagulation is unclear. This study shows that activated factor IX (IXa) and a variant (IXaα) can activate factor VII (VII) to VIIa, suggesting a reciprocal activation pathway independent of cofactors.

Keywords:
bloodcoagulationenzyme activationfactor IXfactor VIIserine proteases

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Related Experiment Videos

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Area of Science:

  • Biochemistry
  • Hematology
  • Molecular Biology

Background:

  • The initiating protease of the extrinsic blood coagulation pathway (factor VIIa) is not fully understood.
  • Congenital factor IX deficiency is linked to decreased plasma factor VIIa, suggesting factor IX activation is involved in factor VIIa generation.
  • Factor VIIa activates factor IX through two cleavage sites (R191 and R226), producing factor IXa. A variant, factor IXaα, is cleaved only at R226.

Purpose of the Study:

  • To investigate the hypothesis that factor IXaα activates factor VII.
  • To explore a potential reciprocal activation pathway between factor IX and factor VII in blood coagulation.

Main Methods:

  • Utilized a mutant factor IX that generates only factor IXaα upon activation.
  • Assayed the coagulant activity of factor IXaα compared to factor IXa.
  • Measured the efficiency of factor IXaα and factor IXa in activating factor X.
  • Determined the amidolytic activity and kinetic parameters of factor IXaα and factor IXa in converting factor VII to factor VIIa, with and without phospholipids, factor VIIIa, or tissue factor.

Main Results:

  • Factor IXaα exhibited 1.6% of the coagulant activity of factor IXa and was less efficient in activating factor X.
  • Factor IXaα and factor IXa displayed indistinguishable amidolytic activity.
  • Both factor IXaα and factor IXa catalyzed the conversion of factor VII to factor VIIa with similar kinetics, enhanced by phospholipids but not by factor VIIIa or tissue factor.

Conclusions:

  • Factor IXa and factor IXaα appear to participate in a reciprocal activation pathway of factor VII and factor IX.
  • This proposed pathway does not require a protein cofactor.
  • The precise initiating protease for the extrinsic coagulation pathway remains uncertain, potentially involving either factor VIIa or activated factor IX.