The continuous process of blood cell formation hematopoiesis takes place in hematopoietic tissue. In the developing embryo, the first site of blood formation is the yolk sac.
Thymus Bone Marrow The major cell types of lymphoid tissues include T cells and B cells, both derived from an uncommitted lymphoid stem cell. The designation "T" derives from the origin of many T cells in the thymus.
The "B" cells are the "bursa equivalent" cells so named because in birds, B cells are concentrated in a bursa of Fabricius next to the gut, and early studies were done in birds.
The B cells are responsible for production of globular proteins known as immunoglobulins that are directed against antigens. B cell markers include the CD19 and CD20 antigens. The immunoglobulins are, therefore, antibodies. The cells specialized to produce immunoglobulins are plasma cells.
The plasma cells have an eccentrically placed nucleus with radially-arranged chromatin, a prominent Golgi apparatus next to the nucleus the perinuclear "hof"and abundant cytoplasmic endoplasmic reticulum for synthesizing immunoglobulin. Plasma cells specialize in terms of antibody production.
When the immune system responds to an infection, there are typically antibody responses to a variety of antigens, so that there are different types of immunoglobulin produced with specificities for the antigens.
Such a response is called "polyclonal" because several clones of plasma cells, each producing a specific antibody, are stimulated to produce different immunoglobulins mostly IgG, but the earliest production of antibody is of the IgM type. A neoplastic transformation of B cells that results in a proliferation of plasma cells causes a "monoclonal" production of immunoglobulin, because the neoplasm called a myeloma is a proliferation derived from a single clone.
The use of immunizations e. An encounter with the real infectious agent at a later date will result in quick production of antibodies against the infectious agent, because there are circulating antibodies as well as plasma cells in "storage" waiting to respond to the challenge.
The T cells are primarily involved in cell-mediated immune responses. They are identified by the presence of the CD3 antigen. In fetal life and childhood, the T cells arose in the thymus and then populated other lymphoid tissues.
The major T cells are the "helper" cells that mark with the CD4 antigen and the "suppressor" cells that mark with the CD8 antigen. The recognition and stimulation of T cells is largely dependent upon recognition of major histocompatibility complex MHC antigens, also known as HLA antigens.
Many cells of the human body express these antigens. The T cells are often aided by macrophageswhich phagocytize infectious agents, process the antigens, and present them to the T cells and to B cells.
Antibodies coating an invading micro-organism can lead to lysis by specialized lymphocytes called "natural killer" or NK cells.
The granules contain mediators of the inflammatory process such as histamine. Dendritic reticulum cells serve to assist in storing and transferring antigens to lymphoid cells which will respond to the antigens.
The dendritic cells located in skin and mucous membranes are known as Langerhans cells. Within lymph nodes, they are known as follicular dendritic cells. These dendritic cells are named because of the long cell processes which catch antigens and "warehouse" them.
Lymph Nodes The lymphatic channels of the body drain into groups of lymph nodes that are strategically placed to filter the lymph draining body regions and to provide immune surveillance based upon the antigen content of the lymph.
The afferent lymphatic channels drain into the periphery of a lymph node in a region under the connective tissue capsule known as the subcapsular sinus. In the periphery of a lymph node is the paracortical region where lymphoid follicles are located. A follicle is a loosely arranged structure with an outer mantle of small T lymphocytes and a germinal center composed of B lymphocytes, follicular dendritic cells, and macrophages.
The interfollicular zones between the follicles are populated mainly by T cells. From the periphery of the node, connective tissue trabeculae extend toward the hilum of the node.
Sinuses drain toward the hilum and contain mainly macrophages. The medullary cords located near the hilum of the node contain mainly plasma cells and small lymphocytes.
From the hilum, the efferent lymphatic channels egress. The structure of a lymph node is diagrammed above: A - Afferent lymphatic channels.Aug 08, · Hematopoiesis is the synthesis of blood cells.
Pluripotent hematopoietic stem cells in the bone marrow divide and differentiate into erythrocytes, leukocytes, or megakaryocytes.
Replication and differentiation are regulated by hormones, cytokines, and growth factors/5(51). Dec 19, · Bone marrow is the major site of hematopoiesis. As the RBCs and platelets have a limited life span they need to be replaced continuously.
Pluripotent stem cell, called the hematopoietic stem cell is the main type of cell which differentiates into all the blood cell lines/5(2). Aug 08, · Hematopoiesis is the synthesis of blood cells. Pluripotent hematopoietic stem cells in the bone marrow divide and differentiate into erythrocytes, leukocytes, or megakaryocytes.
Replication and differentiation are regulated by hormones, cytokines, and growth factors.
The aggregate weight of adult /5(51). The glycoprotein erythropoietin (Epo) regulates the red blood cell (RBC) mass in response to changes in tissue oxygenation.
Epo stimulates erythropoiesis by promoting erythroid precursor cell viability, proliferation, and differentiation, thus enhancing the oxygen-carrying capacity of blood.
Feb 22, · Multiple Waves of Hematopoiesis during Development. The initial wave of blood production in the mammalian yolk sac is termed ‘‘primitive.’’ The primary function for primitive hematopoiesis is production of red blood cells that facilitate tissue oxygenation as the embryo undergoes rapid growth.
The myeloid cell line forms erythrocytes (or red blood cells) and megakaryocytes that form platelets and leukocytes, except for lymphocytes which are produced by the lymphoid cell line. 7. Which cells are produced by the lymphoid cell line? Lymphocytes. 8. Erythropoiesis produces red blood cells.
9. List the steps for red blood cell (erythrocyte) production.