Platelets and red blood cells

Platelets play a central role in the blood clotting process. They are often administered prophylactically or therapeutically in order to prevent/minimize blood loss due to haemorrhage in persons suffering from thrombocytopenia (low blood platelet levels see Chapter 6). 

Platelet concentrate consists of platelets obtained from whole blood. The platelets obtained from a unit of blood are usually resuspended in 20-50 ml of the original plasma and contain not less than 5.5x10 platelets/unit (for blood preparations, a unit refers to the amount of that product purified from a single Unit of whole blood). Like whole blood, platelets have a short shelf-life and must be used within 72 h of blood collection. 

Concentrated red blood cells are prepared from the whole blood of a single donor, from which the anticoagulant and some of the plasma have been removed. According to the British Pharmacopoeia (Chapter 3), the preparation must have a packed cell volume greater than 70% (plasma-reduced blood is similar, except that its packed cell volume must be between 60-65%). 

Red blood cell preparations are usually stored at 2-8°C (although the United States Pharmacopeia includes frozen storage below —65°C). If stored unfrozen, its useful shelf-life must not exceed the shelf-life of the whole blood from which it was derived. If stored frozen, the shelf-life is extended to 3 years (although the product must subsequently be used within 24 h after thawing). 

Red blood cell fractions are administered to patients suflfering from severe anaemia, including patients with sickle cell anaemia and new born babies suflfering from haemolytic disease. 

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Figure 12.4 Terminal steps of a blood clot (haemostatic plug) cross-linked fibrin molecules bind together platelets and red blood cells congregated at the site of damage, thus preventing loss of any more blood...

Large doses of glucocorticoids have been associated with the development of peptic ulcer, possibly by suppressing the local immune response against Helicobacter pylori. They also promote fat redistribution in the body, with increase of visceral, facial, nuchal, and supraclavicular fat, and they appear to antagonize the effect of vitamin D on calcium absorption. The glucocorticoids also have important effects on the hematopoietic system. In addition to their effects on leukocytes, they increase the number of platelets and red blood cells. 

A variety of chemical agents has been used to induce thrombosis in animals. Topical FeCU was described by Reimann-Hunziger (1944) as thrombogenic stimulus in veins. Kurz et al. (1990) showed that the thrombus produced with this method in the carotid arteries of rats is composed of platelets and red blood cells enmeshed in a fibrin network. This model is used as a simple and reproducible test for evalua-... 

Peripheral hlood progenitor cells—Immature blood cells, which are capable of producing white blood cells, platelets, and red blood cells. 

Troup, S. B., C. F. Reed, G. V. Marinetti, and S. N. Swisher Thromboplastic factors in platelets and red blood cells Observations on their chemical nature and function in in vitro coagulation. J. din. Invest. 39, 342 (1960). 

Fig. 2. Histograms representing (a), the frequency of occurrence of platelets (PLT) and red blood cells (RBC) and illustrating coincidence where SL is low angle scatter, 2°C—3° and SH is high angle scatter, 5°C—15° (b), the volume of RBC, from 0 to 200 fL (c), the hemoglobin (HGB) concentration from 0 to...

There are undifferentiated stem cells of the blood elements in the bone marrow that differentiate and mature into erythrocytes, (red blood cells), thrombocytes (platelets), and white blood cells (leukocytes and lymphocytes). The production of erythrocytes is regulated by a hormone, erythropoietin (see the section on kidney toxicity), that is synthetized and excreted by the kidney. An increase in the number of premature erythrocytes is an indication of stimulation of erythropoiesis, i.e., increased production of erythrocytes in anemia due to continuous bleeding. 

In general, arterial thrombi are platelet-rich ( white clots ) and form at ruptured atherosclerotic plaques, leading to intraluminal occlusion of arteries that can result in end-organ injury (e.g., myocardial infarction, stroke). In contrast, venous thrombi consist mainly of fibrin and red blood cells ( red clots ), and usually form in low-flow veins of the limbs, producing deep vein thrombosis (DVT) the major threat to life results when lower extremity (and, occasionally, upper extremity) venous thrombi embolize via the right heart chambers into the pulmonary arteries, i.e., pulmonary embolism (PE). 

The blood is generally warmed to 37 °C immediately prior to transfusion. Whole blood is often used to replace blood lost due to injury or surgery. The number of units (one unit equals approximately 510 ml) administered depends upon the health and age of the recipient, along with the therapeutic indication. Administration of whole blood may also be undertaken to supply a recipient with a particular blood constituent (e.g. a clotting factor, immunoglobulin, platelets or red blood cells). However, this practice is minimized, in favour of direct administration of the specific blood constituent needed. 

While confirming the general normality of the mutant mice and problems with lymphocyte homeostasis, these studies focused on identifying defects in peripheral leukocytes. The Lsc- - mice had a twofold increase in circulating neutrophils and lymphocytes but normal platelet counts and red blood cells. In functional studies, the Lsc-/ neutrophils showed a reduced ability to stimulate formation of Rho-GTP and abnormal pseudopod development in response to fMLP. An increased motility and lower adherence of the neutrophils when stimulated with fMLP (Francis et ah, 2006) are similar to the behavior of B cells from Lsc / mice when stimulated with serum (Girkontaite et ah, 2001). While these studies imply a role for a G12/i3 Lsc-RhoA pathway in the phenotypes of these cells, the molecular details are not yet known. 

For example, one of the most prominent features of blood cell deposition is that platelets are always the first to adhere to the surface and red blood cells (RBC) are deposited later (Dutton, Webber, Johnson Baier, 1969). This is especially intriguing since the concentration of RBC in the blood is about ten times higher than that of the platelets. However, a simple explanation is offered by equations (16) and (19) which show that the rate of cellular deposition is most sensitive to the term — 4> in)- Inspection... 

We observed that the incubation of platelets or red blood cells in the presence of AlFx evoked changes in the phosphoinositide signaling system and a significant decrease of platelet [Ca2+]i [68, 64]. This response was not different in platelets isolated from the blood of AD patients as compared with healthy age-matched subjects or young healthy subjects. 

Whole blood selenium levels can vary between 10 and 3000 ng Se/ml. These levels reflect dietary Intake. With an Se intake of about 50 pg/day, plasma Se levels in humans are about 70 ng/ml, and red blood cell Se is about 90 ng/ml (Levander et a ., 1983). Maximal activity of GSH peroxidase, as determined by assays of the platelet enzyme, is supported where the plasma selenium level is about 100 ng/ml. 

SCANNING FORCE MICROSCOPY STUDY OF ACTIVATED HUMAN PLATELETS INTERACTION WITH LEUCOCYTES AND RED BLOOD CELLS... 

Platelets are the smallest cellular elements of blood of 2.5 pm in average normal diameter. They fulfill an essential role in hemostasis and thrombosis. Thrombosis is a complex phenomenon, involving interaction of endothelial cells and blood cellular elements like platelets, leukocytes and red blood cells. Moreover, platelets influence both thrombosis formation and fibrinolysis. 

In the present paper, changes of platelet surface morphology, platelet aggregation and interaction with leukocytes and red blood cells in thrombus... 

This study indicates that SFM images not only provide detailed insight into changes of the activated human platelets shape after adhesion event and after physiological agonist addition in cell suspension, but also they render a comprehensive perspective regarding the platelet interaction with leukocytes and red blood cells in thrombus formation. 

The SFM study demonstrated that activated human platelets play a significant role in leukocytes and red blood cells recruitment in a thrombus formation. In turn, they can also promote formation of larger and more stable platelet aggregates in an evolving thrombus. 

Any disorder or agent that injures the stem cells or prevents their proliferation can drastically affect the absolute platelet count. The minimal platelet count necessary for initial hemostasis is 50 000 mm If the platelet count falls below 20 000 mm a condition known as thrombocytopenia exists and the affected organism is extremely vulnerable to spontaneous bleeding episodes. Usually, thrombocytopenia due to marrow failure is also associated with reduced leukocyte and red blood cell production since chemicals or disorders that affect the megakaryocytes also impact other stem cells. This is typically determined by examining a peripheral smear of the blood or by a hematologist s bone marrow aspiration. 

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