Primary Haemostasis, Platelets, and Von Willebrand Factor

Comprehensive review flashcards covering thrombopoiesis, primary haemostasis, platelet function, platelet disorders, and von Willebrand disease.

Platelets are produced in the bone marrow from large precursor cells known as __________.

megakaryocytes

The normal platelet count in peripheral blood ranges from __________ per microliter.

$$150\text{-}400 \times 10^3/\mu\text{L}$$

Circulating platelets have a discoid shape and measure __________ in diameter.

$$1\text{-}4\,\mu\text{m}$$

The average volume of a single platelet is __________.

$$7\text{-}10\,\text{fL}$$

Red blood cells have a normal mean corpuscular volume (MCV) of __________.

$$80\text{-}100\,\text{fL}$$

Megakaryocytes mature through a nuclear process called __________ synchronous replication.

endomitotic

Endomitosis is a modified form of mitosis that lacks __________ and daughter cell division.

telophase

During megakaryocyte endomitosis, nuclear lobes increase in multiples of __________.

$$2$$

Platelets enter the circulation as fragmentations of the __________ of megakaryocytes.

cytoplasm

Platelet production is regulated primarily by TPO, a hormone produced by the __________.

liver

As platelets age, they lose surface __________ acid, exposing underlying galactose residues.

sialic

Desialylated aging platelets bind to the hepatic __________ receptor to trigger TPO synthesis.

Ashwell-Morell

Thrombopoietin (TPO) stimulates megakaryocyte growth and differentiation by binding to the __________ receptor.

MPL

Under normal physiological conditions, __________ of total platelets circulate in the peripheral blood.

$$70\%$$

Circulating platelets have an average lifespan of __________ days before removal.

$$7\text{-}10$$

In severe splenomegaly, the proportion of platelets sequestered in the spleen can increase up to __________.

$$90\%$$

Primary haemostasis results in the formation of an initial weak platelet plug through interactions with the __________.

vessel wall

Secondary haemostasis stabilizes the primary platelet plug via the action of __________.

coagulation factors

Transient vasoconstriction following blood vessel injury is initiated by a __________ mechanism.

neural

Prostacyclin ($\text{PGI}_2$) is synthesized by endothelial cells from __________ acid.

arachidonic

Prostacyclin ($\text{PGI}_2$) serves an inhibitory function by preventing platelet activation and __________.

aggregation

Endothelial cells secrete tissue plasminogen activator (tPA), which converts plasminogen to plasmin to stimulate __________.

fibrinolysis

Direct platelet adhesion to subendothelial collagen occurs via receptors GPVI and __________.

GPIa/IIa

Indirect platelet adhesion occurs when collagen-bound vWF connects to the platelet receptor complex __________.

GPIb-IX-V

Alpha granules inside platelets contain haemostatic proteins including vWF, Fibrinogen, and __________.

coagulation factors

Delta granules inside platelets contain non-protein molecules including ADP, Serotonin, and __________.

calcium

Activated platelets synthesize __________, which promotes further platelet recruitment and local vasoconstriction.

thromboxane ($\text{TXA}_2$)

Platelet aggregation occurs when activated __________ surface receptors bind circulating fibrinogen.

GPIIb/IIIa

Fibrinogen bridges neighboring platelets together by cross-linking their __________ receptor complexes.

GPIIb/IIIa

Thrombocytopenia caused by aplastic anaemia or leukaemia is classified under the mechanism of __________ production.

decreased

Immune thrombocytopenic purpura (ITP) causes low platelet counts through the mechanism of increased __________.

destruction

Massive transfusion with platelet-poor fluids causes thrombocytopenia via __________.

dilution

Splenomegaly resulting from portal hypertension causes thrombocytopenia through platelet __________.

sequestration

Disseminated Intravascular Coagulation (DIC) leads to thrombocytopenia through widespread microthrombi formation and platelet __________.

consumption

A platelet count of $50\text{-}100 \times 10^9/\text{L}$ is usually associated with abnormal bleeding during __________.

major surgery or trauma

Spontaneous petechiae and easy bruising typically appear when platelet counts fall between __________.

$$10\text{-}20 \times 10^9/\text{L}$$

A platelet count below __________ creates a severe risk of life-threatening spontaneous mucosal or intracranial bleeding.

$$10 \times 10^9/\text{L}$$

Small, non-palpable, non-blanching skin spots measuring less than 3 mm are termed __________.

petechiae

Mucocutaneous haemorrhages measuring between 3 mm and 10 mm are categorized as __________.

purpura

Skin haemorrhages larger than 1 cm are defined as __________.

ecchymoses

Chédiak-Higashi syndrome involves a defect in platelet storage known as __________ granule deficiency.

delta

Gray platelet syndrome is an inherited disorder characterized by a lack of __________ granules.

alpha

Bernard-Soulier syndrome is an inherited defect of platelet adhesion caused by a deficiency of receptor __________.

GPIb

Glanzmann's thrombasthenia is an inherited defect of platelet aggregation caused by a deficiency of receptor __________.

GPIIb/IIIa

Antiplatelet drugs such as Clopidogrel and Ticlopidine inhibit platelet aggregation by blocking the __________ receptor.

ADP

Aspirin impairs platelet activation by inhibiting the synthesis of __________.

thromboxane ($\text{TXA}_2$)

The Platelet Function Analyzer (PFA-100) measures __________ time as blood occludes the test aperture.

closure

In endothelial cells, von Willebrand factor is synthesized and stored in specialized organelles called __________ bodies.

Weibel-Palade

Von Willebrand factor has a circulating half-life of approximately __________ hours.

$$16$$

Type 1 von Willebrand disease, accounting for 75% of cases, is inherited in an autosomal dominant pattern as a __________ deficiency.

quantitative partial