Definition
Definition
Platelets are components of the blood also called thrombocytes, they are not strictly speaking cells, but small sacs of larger dimensions than usual cells, containing active chemical substances allowing the process of coagulation, and more precisely of primary hemostasis (formation of the blood clot).
Generalities
These substances are:
- La serotonin.
- Le calcium.
- The e.
- L'adenosine triphosphate.
- Le growth factor (PDGF).
Symptoms
physiology
The number of platelets is normally between:
- 150 and 000 per micro L of blood in adults.
- 150 to 000 per micro L of blood in the newborn.
- 200 to 000 per micro L of blood in children.
Thanks to the intervention of a hormone ( thrombopoietin ), megakaryocytes are produced from the bone marrow and then transformed into platelets.
More specifically, the formation of platelets, also called thrombocytes , is known as thrombocytopoiesis . Some stem cells differentiate into megakaryoblasts, one of the precursors of platelets. The next step is the transformation of megakaryoblasts into promegakaryocytes , which themselves become megakaryocytes , also called giant cells of the bone marrow.
Platelets, with an average diameter of 3 µm and an average volume of 7 microcubes, are the largest cells in the bone marrow. Next, through cytoplasmic fragmentation, megakaryocytes give rise to thrombocytes , which are the platelets themselves. Finally, small fragments of megakaryocytes lead to the formation of platelets. These are anucleate formations, shaped like small, more or less spherical plaques.
Platelets live for about 8 to 10 days before being destroyed in the spleen . They play an essential role in coagulation , acting within the plasma (the liquid part of the blood), following the rupture of a blood vessel , or damage to its endothelium (the inner lining of the artery or vein).
The adhesion and agglutination (aggregation) of platelets at the wound site allow them to form a temporary plug that helps to seal the breach after their contents are released. This results in the formation of a " platelet plug " (a type of stopper).
During the inflammatory reaction, platelets can ingest particles , leading to the release of their contents in the presence of viruses or bacteria , thus increasing the number of white blood cells that intervene at the site of inflammation, through the vascular wall.
Pathophysiology
Acquired thrombopathy results from an abnormality in their function.
We find it in:
- La cirrhosis.
- The renal failure (deficiency of blood filtration by the kidneys).
- An attack on the bone marrow.
- A intoxication (Phenylbutazone, phenacetin, acetylsalicylic acid: aspirin, etc.).
Congenital thrombopathies.
Among these, we must mention Glanzmann's disease , which causes purpura . This is an abnormal flow of blood on the skin or mucous membranes (the layer of cells covering the inside of hollow organs in contact with the air) which are dotted with small bright red or bluish spots which, with age, become brownish or yellowish.
Thrombocytopenia is defined as a decrease in the number of platelets below 150,000 per microliter.
. It occurs during:
- The autoimmune diseases (the patient produces antibodies against his own organism). This occurs for example during the lupus erythematosus, from the use of the methyldopa, idiopathic thrombocytopenic purpura and post-transfusion purpura.
- From an attack of the bone marrow (neoplasia, myeloid metaplasia, granuloma from the TB, sarcoidosis etc.).
- In leukemia (entering a process of alteration of the maturation of the megakaryocytes such as myelodysplastic syndrome for example).
- From increased consumption (disseminated intravascular coagulation, Gram-negative septicemia, Moshcowitz disease).
- The ionizing radiation.
- Congenital diseases (May-Hegglin, Aldrich syndrome).
- On the cancer.
- From a viral infection (mumps, infectious mononucleosis, hepatitis, rubella).
- In bacterial infection (sepsis).
- From a deficit in vitamin B12.
- From the taking of some medications : quinine, gold salts, sulfonamides, heparin.
- From Gaucher disease.
- Du Felty syndrome.
- Du Aldrich syndrome.
- Of the'May-Hegglin anomaly.
- Of the'congenital amegakaryocytosis.
- Of the'Fanconi anemia.
- From Moschowitz disease.
- The burns.
- From extracorporeal circulation.
- From the taking of medications (quinine, diuretics, quinidine, thiazide, estrogen, sulfonamide, gold salt)
Thrombocytosis, or thrombocytosis , is an increase in the number of platelets due to:
- The infections.
- A hemorrhage acute.
- A inflammation.
- Un cancer.
- A deficiency in fer.
- The removal of the rates.
Medical exam
Labo
The examination of platelets is called a smear test : it consists of spreading a liquid or secretion of the body, whatever it may be, onto a glass slide, allowing its examination using an optical microscope.
Thanks to the microscope, it is possible to see the morphology of certain platelets, which, as we know, play a very important role in hemostasis . For specialists, once fixed and stained, thrombocytes in a blood smear show no nuclei. On the contrary, a central reticular mass (resembling the mesh of a net) is visible : a substance called the chromomere . This is dotted with reddish-purple granules surrounded by a peripheral zone of paler, pinkish coloration called the hyalomere.
Their aggregation and the measurement of bleeding time (time taken by the blood to coagulate after an incision made in the earlobe) allow us to get an idea of their competence in the process of blood clot formation (primary hemostasis).
Platelet count , that is, the number of platelets, is not easy to obtain. This is because platelets tend to clump together rather than fragment. This is why there are sometimes considerable variations depending on the laboratory and especially the method used.
This is how we obtain different numbers depending on whether it is an electronic count or not.
- In a healthy adult the number of platelets is between 150 and 000 per microliter of blood, that is to say 350 to 000X150 to the power of 350 per liter of blood.
- In a child aged between one and four years, the platelet count is between 160 and 000 per microlitre, or 500 to 000×160 to the power of 500 per litre of blood.
- Platelet counts decrease by about a quarter towards the end of pregnancy and increase by more than half at high altitudes.