Platelets, also called thrombocytes and they are also lack of hemoglobin .
  • What is platelets in blood ?

Platelets are membrane- bound cell fragments . It have no nucleus and absent hemoglobin ,they are between one or two micrometres in diameter and about 1/10th to 1/20th as abundant as white blood cells. Less than 1% of whole blood consists of platelets .

Platelets structure

Important Facts

Platelets are produced at a rate of  200 billion per day. Their production is regulated by the hormone called thrombopoietin . The circulating life of a platelets is 8-10 days . The sticky surface of the platelets allow them to accumulate at the site of broken blood vessels to form a clot . This aids in the process of hemostasis ( blood stopping). It secret factors that increase local platelets aggregation (e.g., thromoboxane A ) , enhance vasoconstriction (e.g., serotonin ) and promote blood coagulation (e.g., thromboplastin ).
Hemostasis – Hemostasis is the natural process of stopping blood flow or loss of blood following an injury ( hemo – blood ; stasis – standing).


  • What are the shape of platelets ?

The shape of platelets are rounded or oval disc- like bodies but quickly become stellate in extracted blood .



  • What are the size of platelets ?
The size of  platelets are the smallest formed elements of the blood. They are only 2-5 micrometre wide .


The platelets  are fewer than the red blood cells and more than the white blood cells in number . There are about 250,000 platelets in a cubic millimetre of blood.                                                       Increase and decrease in the number of platelets is known as thrombocytosis and thrombocytopenia respectively. 
  • What is normal range of platelets ? 

The normal range of  platelets from 150,000 to 450,000 platelets per microliter of blood .

  • What happens when platelets are low ?

When your platelets are low your body , your blood are not clots . A low platelet count from mild to severe, depending on its underlying cause . The symptoms are if injury in your body your blood  are not clot and are  possible to fatal for your body . A low  platelet count are called as thrombocytopenia .

  • What happens when platelets are high?

When platelets are high is usually the existing conditions such as cancer,lung cancer , gastrointestinal cancer , ovarian cancer, breast cancer , or lymphoma . A high  platelets count are known as thrombocytosis .


  • What color of platelets in blood ?
The platelets are colourless like the leucocytes.  


  • How does structure of platelets ?
 The platelets are flat , non- nucleated fragments of  large cells in the bone marrow, rather than true cells.  They are bounded by a membrane  and contain a few organelles and secretory granules in the cytoplasm.  They have at the center a group of basophilic granules, which give the appearance of a nucleus.  At the site of injury, the platelets release platelets factor or thromboplastin that helps in blood clotting .
Diagram of platelets structure
Structure of platelets



The platelets are formed in the red bone marrow.  Their formation is known as thrombopoiesis .  
How to formation of platelets ?
Formation of platelets


Lifespan and disposal

The platelets survive for 3-7 days only.  They are disposed of by phagocytosis in the blood itself. 

Spindle cells or Thrombocytes 

These are biconvex, nucleated cells with granular cytoplasm.  They are found in vertebrates other than mammals. The spindle cells aid in clotting of blood like the platelets of mammals. 




The process of formation of blood cellular components is called haematopoiesis . The tissues in which blood is formed are termed haemopoietic tissue . These include red bone marrow and lymphoid tissues ( spleen , thymus and lymphatic nodes ).
            Erythrocytes , leucocytes and platelets all arise from a common source , the pluripotent stem cells in the red bone marrow . 

Diagram of Hematopoiesis
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