2 blood coagulaltion

Platelets (thrombocytes)

Disk shaped cells 1X3 microns in size

Lack nuclei but contain mitochondria, other cytoplasmic organelles and dense bodies

Erythrocyte: platelet ratio: 20:1Platelets are descendants of Megakaryocytes

Platelet factor IV and -thromboglobulin are substances normally present within intact platelets.

Beta thromboglobulinPro-platelet basic protein

A protein stored in alpha granules of platelets and released in large amounts after platelet activation

It is a chemokine

Platelet granules

Dense granules contain:

ADP, ATP, Ca2+, and serotonin

-Granules contain:

Platelet factor IV, -thromboglobulin, PDGF, thrombospondin, fibrinogen and von Willebrand factor

Fibrinogen (Factor 1)

Length 460 Å

Mass: 340 kdal

Consists of six polypeptide chains: 2(A, B, )

Thrombin cleaves 4 Arg-Gly peptide bonds in fibrinogen

Fibrinopeptides…..1

2 A peptides (18 aa residues each) and 2 B peptides (20 aa residues each)

Fibrin monomer: ()2 representing 97% of the amino acid residues of fibrinogen

Fibrinopeptides….2

Have large net negative charges

Aspartate and glutamate residues in abundance

Fibrinopeptides…..3

In addition tyrosine-O-sulphate which is negatively charged is found in fibrinopeptide B

These surface negative charges repel each other and keep fibrinogen molecules apart

in vivo activators of the intrinsic pathway

Collagen and other sub-endothelial vessel wall constituents

Gram-negative bacterial endotoxins

Cell-wall products from gram-positive organisms

Some fatty acids

Antigen-antibody complexes

In vitro activators of the intrinsic pathway

Activators

Glass

Kaolin

Some acids

Non-activators

Silicon

Some plastic surfaces