Platelets origin

Transfusion-induced autoimmune disease has been a significant complication in the treatment of patients who require multiple platelet transfusions. Platelets and lymphocytes carry their own blood group system, ie, the human leukocyte antigen (HLA) system, and it can be difficult to find an HLA matched donor. A mismatched platelet transfusion does not induce immediate adverse reactions, but may cause the patient to become refractory to the HLA type of the transfused platelets. The next time platelets with an HLA type similar to that of the transfused platelets are transfused, they are rejected by the patient and thus have no clinical efficacy. Exposure to platelets originating from different donors is minimized by the use of apheresis platelets. One transfusable dose (unit) of apheresis platelets contains 3-5 x 10 platelets. An equal dose of platelets from whole blood donation requires platelets from six to eight units of whole blood. Furthermore, platelets can be donated every 10 days, versus 10 weeks for whole blood donations. 

Platelets originate by budding off from multinucleate precursor cells, the megakaryocytes. As the smallest formed element of blood (dia. 1 -4 pm), they can be activated by various stimuli. Activation entails an alteration in shape and secretion of a series of highly active substances, including serotonin, platelet activating factor (PAF), ADP, and thromboxane A2. In turn, all of these can activate other platelets, which explains the explosive nature of the process. 

Fig. 16.9 Electron micrographs of soil lepidocro-cite. a) Large multidomainic lath-like crystal viewed perpendicularto [001] with laminar pores from a re-doximorphic soil, Natal, South Africa, b) Poorly crystalline grassy lepidocrocite crystals mixed with tiny ferrihydrite particles and pseudo-hexagonal kaolinite platelets. Origin as before (a. b courtesy P. Self), c) Small lepidocrocite crystal from a hydromorphic soil (with ferrihydrite) viewed perpendicularto [001] and showing (020) lattice fringes (see also Schwert-mann. Taylor, 1989,with permission).

On the other hand, evidence is accumulating which seems to indicate that fibrin plays a passive role in clot retraction and is simply carried along by actively contracting elements of platelet origin (Discombe, 1950 Bloom, 1955 Sokal, 1960 Castaldi et al., 1962 Rodman et al., 1963). 

DAT is predominantly expressed by dopaminergic brain neurons, NET by noradrenergic neurons in the central and peripheral nervous system, and SERT is restricted to the axons of serotonergic neurons, which originate in the raphe nuclei and innervate numerous higher brain regions therefore SERT is widely distributed in the brain. Outside the brain, 5HT transport can be measured on non-neuronal cells (e.g. platelets, lympho-blastoid cells and smooth muscle cells) most of the 5HT appearing in the circulation is taken up by platelets. 

For a bed of catalyst particles in the form of flat platelets it is found that the mass transfer rate is increased by a factor of 1.2 if the velocity of the external fluid is doubled. The mass transfer coefficient ho is proportional to the velocity raised to the power of 0.6. What is the value of ho at the original velocity ... 

The substrate phenyl phosphate, which is hydrolyzed by the serum acid phosphatases originating from many tissues, has been used in most of the published studies. Total serum acid phenylphos-phatase is elevated in diseases of the liver, disease of bone such as Paget s disease, and several blood dyscrasias, especially those involving platelets (99>100). 

Optimized microfabrication and advanced assembly led to the use of thin platelets, in an original version 100 pm thick with a 80 pm micro channel depth, so that very thin walls (20 pm in the case sketched) remain for separating the fluids. Therefore, also the total inner reaction volume with respect to the total construction volume or the active internal surface area is very large. The latter surface amounts to 300 cm (for both the heat transfer and reaction sides) at a cubic volume of 1 cm. Indeed, the micro heat exchangers exhibited high heat transfer coefficients for gas [46] and liquid (Figure 3.10) [47, 48] flows. 

PLATELETS. Platelets are nonnucleated discoid or elliptical cells that originate from the fragmentation of giant polyploid megakaryocytes located in the bone marrow. The average diameter of the platelet is 1.5 pm. Each platelet is surrounded by a trilaminar membrane, and its cytoplasm contains a dense body (delta granule), a surface-connected canalicular system,... 

The best results of this treatment came in the first reported series of patients. As is often the case, this highly selected group of patients responded better than subsequently studied series. In the original report, 21 patients with idiopathic and 22 with secondary thrombocytopenic purpura were given 2 mg doses of intravenous vincristine (1 mg in children) every 7-10 days. Improvement in platelet count was seen in 16 patients (76%). 

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