دانلود کتاب هماتولوژی – اصل و عمل پایه

Normal blood cells have limited life spans; they must be replenished in precise numbers by a continuously renewing population of progenitor cells. Homeostasis of the blood requires that proliferation of these cells be efficient yet strictly constrained. Many distinctive types of mature blood cells must arise from these progenitors by a controlled process of commitment to, and execution of, complex programs of differentiation. Thus developing red blood cells must produce large quantities of hemoglobin but not the myeloperoxidase characteristic of granulocytes, the immunoglobulins characteristic of lymphocytes, or the fibrinogen receptors characteristic of platelets. Similarly, the maintenance of normal amounts of procoagulant and anticoagulant proteins in the circulation requires an exquisitely regulated production, destruction, and interaction of the components. Understanding the basic biologic principles underlying cell growth, differentiation, death, and the homeostasis of critical proteins requires a thorough knowledge of the structure and regulated expression of genes because the gene is now known to be the fundamental unit by which biologic information is stored, transmitted, and expressed in this regulated fashion. Genes were originally characterized as mathematic units of inheritance. They are now known to consist of molecules of deoxyribonucleic acid (DNA). By virtue of their ability to store information in the form of nucleotide sequences, to transmit it by means of semiconservative replication to daughter cells during mitosis and meiosis, and to express it by directing the incorporation of amino acids into proteins, DNA molecules are the chemical transducers of genetic information flow. Efforts to understand the biochemical means by which this transduction is accomplished have given rise to the disciplines of molecular biology and molecular genetics.