What are platelets?

The article was written by a doctor of Hematology - Blood Transfusion - Laboratory Department - Vinmec Ha Long International General Hospital.

Platelets (Platelets or Thrombocytes) are one of three types of blood cells. Platelets are a fragment of cells without a nucleus, arising from a sample of mature platelets in the bone marrow and first described in the 1800s by Bizzzero.

Platelets are disc-shaped, about 2 - 3 μm in diameter, about 0.5 μm thick. The membrane of platelets is a double phospholipid membrane containing numerous surface receptors. Inside the cytoplasm there are granules containing substances involved in platelet aggregation and hemostasis (Figure 2). Platelets are found only in mammals, whereas in other animals platelets circulate as monocytes.

Note: E.C: outerwear. CM: cell membrane. SMF: submembrane skeletal fibers. M.T: ring of microtubules around platelets. C.S and OCS: indentation of the cytoplasmic membrane from the walls of the canals to the platelet surface and open system. M: mitochondria. D.T.S: system of solid tubes containing calcium. Gly: glycogen granules. B.D: solid body. G: alpha particle.
The life of platelets is 7-10 days. In the body, the organ responsible for destroying old platelets is the spleen. The spleen is the site of capture and destruction of platelets and other blood cells in the body. Abnormal development of the spleen such as splenomegaly can increase platelet retention and destruction, causing a decrease in the number of platelets in the peripheral blood. Therefore, in many cases of severe thrombocytopenia, the patient may be indicated for splenectomy to reduce platelet destruction.

Platelets play important roles in many processes including hemostasis, clot formation, clot contraction, vasoconstriction and repair, immunity, inflammation, atherosclerosis.
The main function of platelets is hemostasis, that is, the process of stopping bleeding where the vascular endothelium (inner wall of a blood vessel or lymph vessel) is injured. The platelets then gather at the wound to seal this hole (unless the hole is too large). At this time, the platelets must undergo an activation phase to release the substance in the functional granules and change shape to stick together to form platelet plugs and blood clots. If the damage to the blood vessel is small, the plug itself can stop the bleeding. But if the damage is larger, then additional clot formation is required.
The process has 3 stages
Platelet adhesion: When the vessel wall is damaged, the collagen layer underneath the endothelial cells is revealed. Platelets will come and stick to this collagen layer. Platelets release active factors: After platelets bind to collagen, it is activated. This cell enlarges, sticks out the prosthetic legs, and releases a lot of substance. Including a large amount of ADP, Thromboxane A2. Platelet Aggregation: ADP and thromboxane A2 activate proximal Platelets. Activation that enables them to adhere to the primary layer of platelets is called platelet aggregation. Then the platelet layer comes later to release active substances that activate and stick to another layer of Platelets. In this way, more and more layers of Platelet cells come to stick to the lesion to form a Platelet Node.

The formation of these "platelet plugs" (primary hemostasis) is often combined with secondary hemostasis by synthetic fibrin. This effect is due to the function of "rejuvenating" the endothelial cells of these cells.

Normal platelet count is 150 - 450 G/L whole blood. A platelet count above this range is called thrombocytosis; less than 150 G/L is called thrombocytopenia. The normal platelet count of each person will be different and will vary depending on the psychological state of each person, gender, age, race and especially the test equipment.
Too low a platelet count (severe thrombocytopenia) can cause bleeding. And the number of platelets is too high (thrombocytosis) will form blood clots, blocking blood vessels that can cause stroke, heart attack, pulmonary embolism, blood vessel blockage...
Increased urination Demand is seen in: Bone marrow proliferative disorders, idiopathic thrombocytopenic purpura, bone marrow fibrosis, after bleeding, after splenectomy, inflammatory diseases... Thrombocytopenia is seen in: Suppression or replacement bone marrow replacement, chemotherapeutic agents, splenic hypertrophy, disseminated intravascular coagulation, platelet antibodies, post-transfusion purpura, allogeneic thrombocytopenia in neonates...

Primary thrombocythemia
Primary thrombocythemia is a chronic myeloproliferative disorder characterized by elevated platelet counts, proliferative platelets, and a tendency to hemorrhage or thrombosis, with signs and symptoms such as: Weakness, headache, paresthesia of extremities, bleeding, splenomegaly, and erythema with ischemia. Diagnosis is based on persistent platelet count >450 G/L, absence of myelofibrosis or Philadelphia chromosome (or BCR-ABL), or any other disorder that causes thrombocytosis.
Secondary Thrombocytosis
Secondary Thrombocytosis is more common, not due to the bone marrow, but to another disease or condition that stimulates the bone marrow to make more Platelets. It can be caused by infection, inflammation, some types of cancer, and a reaction to medication... Symptoms are usually not serious. Platelet count returns to normal as the other condition gets better.
Platelet dysfunction
Platelet dysfunction is a condition in which platelets do not work as they should, causing bleeding or bruising on the skin, while the number is normal. Platelets have many roles in blood clotting, platelet dysfunction can lead to coagulation disorders to varying degrees.
Dysfunction can be hereditary or acquired. Inherited platelet dysfunctions include von Willebrand disease which is the most common hereditary hemorrhagic disease and the less common inherited platelet intrinsic disorder. Acquired platelet dysfunction is often caused by diseases (eg, kidney failure) as well as the use of aspirin and other medications...
Thrombocytopenia: Thrombocytopenia can be caused by
Platelet production decreased, Increased platelet retention in the spleen, with normal platelet life, Increased destruction or consumption of platelets (immune or non-immune causes), platelet dilution. Thrombocytopenia in pregnancy Drug-induced thrombocytopenia due to immune-mediated platelet destruction (usually, heparin, trimethoprim/sulfamethoxazole, more rarely quinine) Drug-induced thrombocytopenia caused by myelosuppressive drugs dose dependent (eg chemotherapy) Thrombocytopenia associated with infection, Immune thrombocytopenia (ITP, formerly known as immune thrombocytopenic purpura)...

The basic function of platelets is to participate in the process of hemostasis, blood clotting to protect the body from blood loss. Therefore, severe thrombocytopenia can be life-threatening. When the platelet count is too low, the patient's body will be able to spontaneously bleed or bleed on a very slight collision. Cases of severe bleeding include: Gastrointestinal bleeding (vomiting blood), urinary tract bleeding (hematuria), meningitis (stroke)...
Signs of thrombocytopenia
When platelets drop, the main sign is bleeding. Depending on the level of decreased platelets, the manifestations of bleeding are different:
Subcutaneous hemorrhage: Manifestations are dots, small bruises or bruises... Hemorrhages of the mucous membranes of eyes, nose, bleeding teeth mouth; Visceral bleeding: Manifestations are blood in the urine, blood in the stool, vomiting blood.... In women, menstruation may be heavy, prolonged, and menstruating. The most severe symptom of hemorrhage is cerebral hemorrhage (patients have headache, nausea or focal neurological symptoms).

Platelets are small but important cells in the blood that help the body control bleeding. If there are symptoms such as easy bruising on the body, uncontrollable bleeding wounds or nosebleeds, frequent bleeding gums, menorrhagia ... need to see a doctor soon for advice and testing. A routine blood test is a simple and common test that checks for normal platelet counts.
If you have a need for consultation and examination at Vinmec Hospitals under the national health system, please book an appointment on the website (vinmec.com) for service.

References
2/ Nguyen Cong Khanh (2004). Pediatric Clinical Hematology. Medical Publisher.
3/ Do Trung Phan (2003) . Hematopoietic stem cell disease. Medical Publisher.
4/ Department of Hematology-Blood Transfusion, Hanoi Medical University (2014). Lecture on Hematology-Blood Transfusion (Graduate). Medical Publisher.
5/ https://login.medlatec.vn//ImagePath/images/20200915/20200915_tieu-cau-1.jpg
6/ http://www.vienhuyethoc.vn,
7/ http://bthh.org .VN.