Lymphoid Levels Course Materials

‭Lymphoid levels‬ ‭ t the lymphoid tissue level there‬‭is a contingent‬‭of fixed cells and a contingent of circulating‬ A ‭cells; for the cells to circulate, particular structures are needed: they are high endothelial veinlets,‬ ‭therefore non-squamous cells (like capillaries) but cubic cells and these cells will express certain‬ ‭integrins which will be recognized by different types of lymphocytes. Remember that depending on‬ ‭the organ, the high endothelial veinlets do not have the same integrin expression, also depending on‬ ‭the local inflammatory reaction and this is what will allow the recruitment at the tissue level of‬ ‭leukocytes and certain lymphocytes.‬ ‭At the level of the lymphoid organs‬‭, 90% of lymphocytes‬‭enter these organs through these high‬ ‭endothelial veinlets and 10% will enter via the lymphatic vessels. This will allow naive‬ ‭lymphocytes to carry out a circulation between the different lymphoid organs, for fighters:‬ ‭lymphocytes effectors to go from the secondary lymphoid organs where they were prepared towards‬ ‭the peripheral fabrics where they will have to carry out their combat mission. These high‬ ‭endothelial veinlets for memory lymphocytes allow permanent circulation of these lymphocytes at‬ ‭the peripheral level in the secondary lymphoid organs and this is important for the case where there‬ ‭is a second antigenic contact, to have a reaction which is much more rapid .‬ ‭ xample for the migration of cells in a tissue and the importance of cytokines:In the case of the‬ E ‭thymus, the pre T cells come into the thymus at the level of the corticomedullary junction, in fact in‬ ‭this organ we distinguish a cortical and a medullary. The elements will then migrate into the most‬ ‭external subcapsular part and then function of maturation, of differentiation we will have a reverse‬ ‭migration which will take place periphery towards the corticomedullary junction. In fact each time‬ ‭there is a step of maturation, the T lymphocyte will acquire new receptors for cytokines:‬ ‭chemokines and it is the acquisition of these receptors which allows the lymphocyte to be able to‬ ‭move to another tissue area and again progress in its differentiation and education. In the thymus‬ ‭we will therefore distinguish several areas from one functional point of view and these areas‬ ‭correspond to different chemokine concentrations. Each stage of maturation corresponds to the‬ ‭expression of different receptors for chemokines. In the hematopoietic bone marrow we will find‬ ‭the same process with local concentrations of variable chemokines, different chemokines which‬ ‭will ensure that the area has cell migration. This MOH is a specialized fabric.‬ -‭ Hematopoietic bone marrow‬ ‭It is a specialized tissue whose main function is hematopoiesis. It is all of the phenomena that will‬ ‭allow the continuous replacement of blood cells. It's a complex process subject to regulation which‬ ‭will result in the genesis of mature cells adapted to our needs (physiological or physiopathological‬ ‭such as infection).‬ ‭ ‬ ➔ ‭Anatomy:‬‭MOH is contained in bone cavities which are‬‭determined by spans which will‬ ‭make it possible to determine, to identify cubicles which will communicate with each other and in‬ ‭these cubicles there is the MOH. This MOH is richly vascularized. It contains fatty tissue in‬ ‭variable quantities and the further we advance in life, the greater the quantity of fatty tissue will be.‬ ‭ rom birth untilAt 4 years old, all bone cavities are filled with active MOH called “red”.‬ F ‭From the age of 4 we have adipose involution which occurs first at the level of the medulla and‬ ‭therefore the red bone marrow is replaced by inactive bone marrow called “yellow”.‬ ‭In‬ ‭adulthood,‬ ‭MOH‬ ‭is‬ ‭found‬ ‭mainly‬ ‭in‬ ‭flat‬ ‭bones‬ ‭or‬ ‭the‬ ‭ends‬ ‭of‬ ‭bones.‬ ‭long.‬ ‭For‬ ‭flat‬ ‭bones‬ ‭the‬ s‭ ternal‬‭manubrium‬‭where‬‭spinal‬‭punctures‬‭and‬‭therefore‬‭the‬‭myelogram‬‭are‬‭carried‬‭out.‬‭We‬‭find‬‭the‬ ‭MOH‬‭at‬‭the‬‭level‬‭of‬‭the‬‭ribs,‬‭the‬‭bones‬‭of‬‭the‬‭vault‬‭of‬‭the‬‭skull,‬‭the‬‭iliac‬‭bones‬‭and‬‭the‬‭iliac‬‭bones‬ ‭are‬‭one‬‭of‬‭the‬‭preferred‬‭sites‬‭for‬‭doing‬‭the‬‭myelogram‬‭and‬‭osteomedular‬‭biopsies,‬‭and‬‭the‬‭ends‬‭of‬ ‭the long bones.‬ ‭This tissue has a total weight between 1.6 and 3kg in adults.‬