University:
Mt. San Antonio College
Course:
MEDI 90 | Medical Terminology
Academic year:

2024
Views:

398

Pages:

1
Author:

Larbi M.

Lymphocytes (Ly) Coming from the bone marrow, the lymphoid cells mature in the central lymphoid organs: bone marrow for the B lymphocytes, thymus for the T lymphocytes then migrate to the peripheral lymphoid organs, where they meet the antigens. From the lymph nodes, the lymphocytes will recirculate in the peripheral circulation, via the lymphatic vessels, to return to the lymph nodes. This circulation of lymphocytes between the blood and lymphatic systems ensures a permanent redistribution of their different populations. Circulating lymphocytes are not the term for a cell line but only an aspect of resting cells, capable of transforming to play their role (immunoblasts, plasma cells). The quantitative determination of lymphocytes in the hemogram includes the count of T lymphocytes and B lymphocytes. Only specialized studies focusing on membrane markers make it possible to differentiate between B and T lymphocytes as well as their different subpopulations. Platelets (Pa) Platelets (or thrombocytes) come from the fragmentation of the cytoplasm of a very large bone marrow cell, the megakaryocyte. These themselves come from the differentiation of a stem cell, then from specific progenitors, according to a unique mode of division and maturation, marked by endomitosis: the nucleus multiplies without the cell dividing: 2N being the number of chromosomes of the precursor cell, the megakaryocytes of successive generations will contain 4N, 8N, 16N, 32N, 64N. At the same time, the cytoplasm enlarges and platelets are formed. Megakaryocytes that release platelets are usually at the 32N stage, but 16N and 64N forms also release platelets. These represent small territories of the megakaryocyte cytoplasm demarcated by demarcation membranes. The younger the nucleus, the larger the defined territory (large platelets). They therefore do not have a nucleus. Each megakaryocyte produces several thousand platelets. Thrombopoiesis Thrombopoiesis is regulated by a hematopoietic growth factor with homologies to erythropoietin, thrombopoietin produced mainly by the liver and kidney. Thrombopoietin binds to a receptor present on megakaryocytes (Mpi). The membrane which surrounds platelets has a lipid composition like that of other blood cells but differs in the distribution of phospholipids and especially in the presence of a certain number of glycoproteins with a fundamental role in herostasis phenomena. Its interior organization with a cytoskeleton, granulations of different types, a communication system with the outside world, is very complex and justifies the fact that it can be considered as a real cell.