Platelets and Hemostasis Quiz

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Questions and Answers

What role does Factor III play in the stabilization process?

It activates Factor II directly.

It creates loose fibrin strands.

It interacts with thrombin to facilitate clot formation.

It converts loose fibrin strands into a stable form. (correct)

Under what condition is Factor II activated?

After it interacts with Factor III.

Upon interaction with activated thromboplastin.

When it comes in contact with positively charged strands.

When it is exposed to negatively charged surfaces. (correct)

What is the relationship between thrombin and Factor II?

Thrombin is responsible for the activation of Factor II. (correct)

Thrombin inhibits the activity of Factor II.

Thrombin converts Factor II into fibrin.

Thrombin binds to Factor II without activation.

Which component is necessary for the activation of thrombin?

Prothrombin. Signup and view all the answers

What is the function of the interaction between prekallikrein and kinetic agents?

It helps activate the intrinsic pathway. Signup and view all the answers

Which statement regarding Factor III is incorrect?

It interacts with Factor II for activation. Signup and view all the answers

What triggers the activation of factor XII in the coagulation cascade?

Contact with negatively charged surfaces. Signup and view all the answers

What initiates the activation process of platelets?

Thrombin and ADP Signup and view all the answers

Which of the following statements about platelet aggregation is true?

It is a loose and recessible process. Signup and view all the answers

What is the role of fibrinogen in platelet aggregation?

To bridge between platelets via receptors. Signup and view all the answers

Which of the following best describes the process of platelet fusion?

It is reinforced by high concentrations of thrombin and ADP. Signup and view all the answers

What happens to platelets during activation?

They swell and develop pseudopodia. Signup and view all the answers

Which component is NOT directly involved in platelet aggregation?

Vitamin K Signup and view all the answers

What is the nature of the release reaction in platelets?

Calcium dependent and triggers aggregation. Signup and view all the answers

What stimulates platelet aggregation?

Release of ADP and TXA2. Signup and view all the answers

Which process occurs after platelet activation and leads to the formation of a platelet plug?

Pseudopodia formation. Signup and view all the answers

What initiates the extrinsic pathway of clot activation?

Exposure of tissue factor due to external trauma Signup and view all the answers

What role does thrombin play in the clotting process according to the activation sequence?

It creates a circular process enhancing clot formation Signup and view all the answers

How does tissue factor interact with factor II in this activation process?

It binds to factor II to facilitate clot formation Signup and view all the answers

Which of the following statements about the 'vicious circle' in clot formation is correct?

It enhances the formation of clot until a limiting reaction occurs Signup and view all the answers

What is the primary consequence of exposing tissue factor in the extrinsic pathway?

Initiation of the clotting cascade Signup and view all the answers

What is the effect of vasoconstriction on calcium levels in platelets?

It increases free Ca++ in the cytoplasm. Signup and view all the answers

Which statement accurately describes platelet aggregation?

It is a loose and reversible process. Signup and view all the answers

What role does cyclooxygenase play in the function of aspirin regarding myocardial infarction?

It decreases TxA2 and prostacyclin production. Signup and view all the answers

Which factors are included in the fibrinogen group of coagulation factors?

I, II, V Signup and view all the answers

What is the effect of high concentrations of ADP in platelet fusion?

It leads to a tight and irreversible process. Signup and view all the answers

Which process is responsible for the exposure of PF3 during blood coagulation?

Platelet procoagulant activity. Signup and view all the answers

What is the primary role of the fibrinogen in the coagulation process?

To act as a bridge between platelets. Signup and view all the answers

Which coagulation factor is classified under the prothrombin group?

II (Prothrombin) Signup and view all the answers

What is the primary outcome of the self-propagating process in platelet aggregation?

Release of more ADP and thromboxane A2. Signup and view all the answers

Which type of factor is identified by the designation XIII?

Fibrin-stabilizing factor Signup and view all the answers

What is the primary purpose of coagulation factors in hemostasis?

To form a stable clot by converting soluble fibrinogen into insoluble fibrin Signup and view all the answers

Which coagulation factor is activated by thrombin?

Factor I Signup and view all the answers

What role does vitamin K play in the coagulation process?

It is required for the synthesis of certain coagulation factors Signup and view all the answers

Which factor is considered essential for clotting reactions?

Calcium (Factor IV) Signup and view all the answers

How is the hemostatic plug initially formed during bleeding?

By adhering platelets to the site of vascular injury Signup and view all the answers

What type of surface activates specific coagulation factors?

An electro-negatively charged surface Signup and view all the answers

Which factor is primarily responsible for converting prothrombin into thrombin?

Factor II Signup and view all the answers

What is the end product of the coagulation cascade?

Insoluble fibrin Signup and view all the answers

What is the role of thrombin in the coagulation process?

It activates platelets and converts fibrinogen to fibrin Signup and view all the answers

Which statement accurately describes coagulation factors?

They act as a cascade activating the next factor Signup and view all the answers

Study Notes

Platelets

Small, granulated, non-nucleated bodies
Count: 300,000/mm³ (150,000-450,000)
Lifespan: 8 days
Thrombopoietin (from liver and kidneys) facilitates megakaryocyte maturation
30% stored in spleen; splenectomy increases platelet count (thrombocytosis)
Lack nuclei and cannot reproduce
Plasma membrane: specialized for adhering to injury sites
- Glycoprotein coat: negatively charged to prevent platelet adhesion to endothelium
- Receptors for collagen, von Willebrand factor, fibrinogen, and ADP
- Phospholipids crucial for platelet adhesion
- Open canalicular system for calcium uptake and release of substances
Cytoplasm contains:
- Contractile proteins (actin and myosin) for shape changes
- Microtubules for maintaining disc shape
- Granules

Hemostasis

Stop bleeding
Steps:
1. Vasoconstriction
2. Temporary hemostatic plug (platelet function)
3. Definitive hemostatic plug (clotting factors)

Vessel Constriction

Mechanism:
- Nervous (pain from damaged vessel)
- Local myogenic contraction (direct trauma)
- Chemical substances (from platelets, like serotonin and thromboxane A2)
- Endothelin from injured endothelium.
- Immediate effect = obliterates lumen of blood vessel.

II. formation of temporary hemostatic plug (platelets):

Platelet adhesion : platelets adhere to exposed collagen in damaged blood vessels.
- Glycoprotein receptors & von Willebrand factor aiding adhesion to collagen
Platelet activation:
- Release granules
- Become activated by ADP, thrombin →swell & pseudopodia (extending arms). -Calcium release important
- ADP, serotonin: activate and aggregate platelets
- Platelet-derived growth factor (PDGF) promotes wound healing
- Platelet activation factor (PAF) promotes platelet aggregation
Platelet aggregation: platelets stick together (loose & reversible).
- Requires fibrinogen receptors (GpIIb/IIIa receptors) acting as bridges for platelets
- Stimulated by ADP, thromboxane A2, PAF
Platelet fusion: irreversible process for a stronger plug -High concentrations of ADP and thrombin cause this fusion
Platelet procoagulant activity: exposes phospholipid surfaces (PF3) -activates coagulation factors

III. Formation of Definitive Hemostatic Plug

Purpose: Converting soluble fibrinogen to insoluble fibrin to form a stable clot.
Factors involved:

Intrinsic Pathway: activated by contact with a foreign surface
Extrinsic Pathway: activated by tissue factor exposure

Both pathways converge to the common pathway
Prothrombin group, Fibrinogen group, Contact group factors
Example: Conversion of prothrombin to thrombin, thrombin to fibrin, factor XIII stabilizes fibrin. Common pathway includes fibrinogen, prothrombin, fators III, VII, IX, and X.

IV. Fibrinolytic System

Dissolves clots (fibrinolysis).
Plasmin (fibrinolysin) is the active component that degrades fibrin and fibrinogen
Thrombomodulin produced by endothelial cells inhibits clotting.
Important anticoagulants such as heparin and antithrombin III.
t-PA (tissue plasminogen activator): important fibrinolytic component

Hemostatic Function Tests:

Bleeding time: necessary time for bleeding to stop on damaged area (without clotting).
Coagulation time: necessary time needed for the blood to clot (intrinsic and extrinsic system).
Tests for blood coagulation: Prothrombin time (extrinsic system) and partial thromboplastin time (intrinsic system), used to identify problems with activating factors (X, XI, VIII).

Abnormalities of Hemostasis

Decreased Clotting: thromocytopenia, deficiency factors
Increased Clotting: thrombosis (excessive clotting), DIC (disseminated intravascular coagulation)

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Description

Test your knowledge on the functions and characteristics of platelets, including their role in hemostasis. This quiz covers platelet count, lifespan, and mechanisms involved in stopping bleeding. Perfect for students studying biology or medical sciences.