19 Questions
What are the mechanisms involved in achieving hemostasis?
Vascular constriction, formation of a platelet plug, formation of a blood clot, eventual growth of fibrous tissue into the blood clot
What are the characteristics of platelets?
Minute discs formed in the bone marrow from megakaryocytes, no nucleus, life span of 8 to 12 days
What is the normal concentration of platelets in the blood?
Between 150,000 and 300,000 per microliter
What happens when platelets come in contact with a damaged vascular surface?
They swell, pseudopods form on their surfaces, and they become sticky, adhering to collagen in the vessel wall and to each other
What is the first step in achieving hemostasis?
Vascular constriction
What factors contribute to vascular constriction?
Local myogenic spasm, factors released from damaged tissue & platelets, nerve reflex
What initiates the clotting process in the blood?
Factors from damaged tissue, platelets, and blood proteins
What is the purpose of fibrinolysis in the body?
To clean up extra and old clots
What is the function of tissue plasminogen activator (t-PA) in the body?
To convert plasminogen to plasmin and remove unnecessary blood clots
What test is used to assess capillary resistance?
Hess test (capillary resistance test)
What is the normal range for the Hess test in terms of petichial hemorrhages?
0 – 8
What does the bleeding time test measure?
The time required to arrest bleeding from a ruptured capillary
What are the two methods for conducting the bleeding time test?
Duke’s method and Ivy’s method
What is the normal range for bleeding time using Ivy’s method?
2 – 8 minutes
What does the clotting time test measure?
The time taken for the blood to clot outside the vascular system
What is the normal range for clotting time using the capillary tube method?
4 – 9 minutes
Name four conditions that cause excessive bleeding in humans.
- Vitamin K deficiency
- Hemophilia
- Thrombocytopenia (platelet deficiency)
- Side effect of certain drugs (anticoagulants)
What is an abnormal clot that develops in a blood vessel called?
Thrombus
What is a clot that freely circulates through the bloodstream called?
Emboli
Study Notes
Hemostasis Mechanisms
- Hemostasis is achieved through a series of mechanisms, including vascular constriction, platelet activation, and blood clotting.
- Vascular constriction is contributed to by factors such as endothelin, thromboxane A2, and epinephrine.
Platelet Characteristics
- Platelets are small, anucleate cells with a lifespan of 7-10 days.
- The normal concentration of platelets in the blood is 150,000-450,000/μL.
- When platelets come in contact with a damaged vascular surface, they undergo activation, releasing chemical signals that attract more platelets and start the clotting process.
Hemostasis Process
- The first step in achieving hemostasis is platelet activation, which leads to the formation of a platelet plug.
- The clotting process is initiated by the exposure of subendothelial tissues, such as collagen and tissue factor.
- Fibrinolysis is the process of clot dissolution, and its purpose is to remove clots after tissue repair.
- Tissue plasminogen activator (t-PA) is an enzyme that initiates fibrinolysis by converting plasminogen to plasmin.
Hemostasis Tests
- The Hess test is used to assess capillary resistance, with a normal range of 20-100 petechial hemorrhages.
- The bleeding time test measures the time it takes for a standardized wound to stop bleeding.
- There are two methods for conducting the bleeding time test: Ivy's method and Duke's method.
- The normal range for bleeding time using Ivy's method is 3-9 minutes.
- The clotting time test measures the time it takes for blood to clot.
- The normal range for clotting time using the capillary tube method is 4-10 minutes.
Bleeding Disorders
- Four conditions that cause excessive bleeding in humans are hemophilia, thrombocytopenia, von Willebrand disease, and liver disease.
- An abnormal clot that develops in a blood vessel is called a thrombus.
- A clot that freely circulates through the bloodstream is called an embolus.
Test your knowledge of the mechanisms involved in hemostasis, including vascular constriction, platelet plug formation, blood clotting, and fibrous tissue growth. Explore the processes that prevent blood loss when a vessel is severed or ruptured.
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