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Related Concept Videos

Extrinsic and Intrinsic Pathways of Hemostasis01:20

Extrinsic and Intrinsic Pathways of Hemostasis

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 forms a...
Clot Retraction and Fibrinolysis01:16

Clot Retraction and Fibrinolysis

After a fibrin clot is formed, the next step is clot retraction, a vital process facilitated by platelet contractile proteins, such as actin and myosin. These proteins pull the fibrin strands closer together and condense the clot. This action reduces the size of the clot, creating a smaller, denser structure that effectively seals off the damaged vessel. Clot retraction consolidates the clot and helps with wound healing by bringing the edges of the damaged blood vessel closer together.
Coagulation01:09

Coagulation

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.
During the coagulation phase, clotting factors, or procoagulants, play a vital role in initiating and progressing the coagulation cascade. This cascade is a series of reactions...
Anticoagulant Drugs: Low-Molecular-Weight Heparins01:30

Anticoagulant Drugs: Low-Molecular-Weight Heparins

Hemostasis is a crucial process that prevents excessive blood loss from damaged blood vessels. It involves various mechanisms such as vasoconstriction, platelet adhesion and activation, and fibrin formation. The importance of each mechanism depends on the type of vessel injury. In contrast, thrombosis is the abnormal formation of a blood clot within the blood vessels, leading to potential complications if the clot obstructs blood flow. Thrombosis can be caused by increased coagulability of the...
Formation of the Platelet Plug01:22

Formation of the Platelet Plug

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.
As the injured blood vessel contracts, endothelial cells undergo contraction, revealing collagen fibers in the basement membrane and underlying connective tissue. Furthermore, the plasma membrane of endothelial cells becomes adhesive, preparing the site for platelet adhesion. Platelets...
Introduction to Hemostasis01:05

Introduction to Hemostasis

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.
The three phases of hemostasis involve many clotting factors present in plasma and several substances released by platelets and injured tissue cells. It is a fast, localized, and...

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Related Experiment Video

Updated: Jul 8, 2026

Characterizing Modulators of Protease-Activated Receptors with a Calcium Mobilization Assay Using a Plate Reader
07:13

Characterizing Modulators of Protease-Activated Receptors with a Calcium Mobilization Assay Using a Plate Reader

Published on: May 24, 2024

Kallikrein activates prothrombin.

Thomas W Stief1

  • 1Department of Clinical Chemistry, University Hospital Marburg, Germany. thstief@med.uni-marburg.de

Clinical and Applied Thrombosis/Hemostasis : Official Journal of the International Academy of Clinical and Applied Thrombosis/Hemostasis
|December 28, 2007
PubMed
Summary
This summary is machine-generated.

Human plasma kallikrein directly activates prothrombin, generating thrombin. This bypasses the traditional intrinsic hemostasis pathway, offering a novel insight into blood clotting mechanisms.

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Last Updated: Jul 8, 2026

Characterizing Modulators of Protease-Activated Receptors with a Calcium Mobilization Assay Using a Plate Reader
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Characterizing Modulators of Protease-Activated Receptors with a Calcium Mobilization Assay Using a Plate Reader

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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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04:37

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Published on: May 23, 2025

Area of Science:

  • Biochemistry
  • Hematology
  • Enzymology

Background:

  • Kallikrein is a key enzyme involved in hemostasis and inflammation.
  • Normally, kallikrein is generated during intrinsic hemostasis and activates factor XII.

Purpose of the Study:

  • To investigate the direct activation of prothrombin by human plasma kallikrein.
  • To explore a potential shortcut in the intrinsic hemostasis system.

Main Methods:

  • Incubation of human plasma kallikrein with prothrombin in the presence and absence of calcium ions.
  • Measurement of generated thrombin activity using a chromogenic substrate assay.
  • Kinetic analysis of prothrombin activation by kallikrein.

Main Results:

  • Kallikrein directly activates prothrombin to generate thrombin.
  • Calcium ions significantly enhance the rate of thrombin generation.
  • Low concentrations of kallikrein can produce significant thrombin levels, indicating a potent catalytic activity.

Conclusions:

  • Human plasma kallikrein can directly activate prothrombin, independent of the classical intrinsic clotting pathway.
  • This direct activation represents a potential shortcut in hemostasis, leading to rapid thrombin generation.
  • The findings suggest a novel mechanism contributing to hemostasis and potentially thrombosis.