PROPERTIES OF PLATELETS

PROPERTIES OF PLATELETS

Platelets have three important properties (three ‘A’s):

1. Adhesiveness

2. Aggregation

3. Agglutination.

ADHESIVENESS

Adhesiveness is the property of sticking to a rough surface. During injury of blood vessel, endothelium is

damaged and the subendothelial collagen is exposed. While coming in contact with collagen, platelets are

activated and adhere to collagen. Adhesion of platelets involves interaction between von Willebrand factor secreted by damaged endothelium and a receptor protein called glycoprotein situated on the surface of platelet membrane. Other factors which accelerate adhesiveness are collagen, thrombin, ADP, Thromboxane A2, calcium ions, P-selectin and vitronectin.

AGGREGATION (GROUPING OF PLATELETS)

Aggregation is the grouping of platelets. Adhesion is followed by activation of more number of platelets by

substances released from dense granules of platelets. During activation, the platelets change their shape

with elongation of long filamentous pseudopodia which are called processes or filopodia . Filopodia help the platelets aggregate together. Activation and aggregation of platelets is accelerated by ADP, thromboxane A2 and platelet-activating factor.

AGGLUTINATION

Agglutination is the clumping together of platelets. Aggregated platelets are agglutinated by the actions of

some platelet agglutinins and platelet-activating factor.

FUNCTIONS OF PLATELETS

Normally, platelets are inactive and execute their actions only when activated. Activated platelets immediately release many substances. This process is known as platelet release reaction. Functions of platelets are carried out by these substances.

Functions of platelets are:

1. ROLE IN BLOOD CLOTTING

Platelets are responsible for the formation of intrinsic prothrombin activator. This substance is responsible for the onset of blood clotting .

2. ROLE IN CLOT RETRACTION

In the blood clot, blood cells including platelets are entrapped in between the fibrin threads. Cytoplasm of

platelets contains the contractile proteins, namely actin, myosin and thrombosthenin, which are responsible for clot retraction.

3. ROLE IN PREVENTION OF BLOOD LOSS (HEMOSTASIS)

Platelets accelerate the hemostasis by three ways:

i. Platelets secrete 5-HT, which causes the constrict tion of blood vessels.

ii. Due to the adhesive property, the platelets seal the damage in blood vessels like capillaries.

iii. By formation of temporary plug, the platelets seal the damage in blood vessels .

4. ROLE IN REPAIR OF RUPTURED BLOOD VESSEL

Platelet-derived growth factor (PDGF) formed in cytoplasm of platelets is useful for the repair of the endothelium and other structures of the ruptured blood vessels.

ROLE IN DEFENSE MECHANISM

By the property of agglutination, platelets encircle the foreign bodies and destroy them.

Post a Comment

0 Comments