Health Information

Introduction

Platelets or thrombocytes are small colourless, nonnucleated and moderately refractive bodies. Theses formed elements of blood are considered to be the fragments of cytoplasm. Their diameter is 2.5 microns and the volume is 7.5 cubic microns. Normally the platelets are spherical or rod shaped and become oval or disc shaped when inactivated. Sometimes, the platelets are of dumb bell, comma, cigar or any other unusual shape.

Structure and composition

Platelets have a cell membrane or surface membrane, microtubules below the cell membrane and the cytoplasm.

Cell membrane

It is 6nm thick and contains lipids (phospholipids, cholesterol and glycolipids), carbohydrates, proteins and glycoproteins. Of these substances, glycoproteins and phospholipids are functionally important.

Glycoproteins

Glycoproteins prevent adherence of blood platelets to normal endothelium but, accelerate the adherence of platelets to collagen and damaged endothelium in ruptured blood vessels. Glycoproteins also form the receptors for ADP and thrombin.

Phospholipids

Phospholipids accelerate the clotting reactions. The phospholipids from the precursors of thromboxane A2 and other prostaglandin related substances.

Microtubules

Microtubules form a ring around the cytoplasm below the cell membrane. Microtubules are made up of polymerized proteins called tubulin. The tubules provide a structural support for the inactivated platelets to maintain the disc like shape.

Cytoplasm

The cytoplasm of the platelets includes Golgi apparatus, endoplasmic reticulum, mitochondria, microtubule, micro vessels, filaments and different types of granules. Cytoplasm also contains some chemical substances like proteins, enzymes, hormonal substances, etc.