organ and tissues of immune system
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Immunology Lecture 4th
Organs & Tissues of
Dr. Humera Kausar
23rd Sep 2014
Organ of Immune System
Leucocytes and erythrocytes are derived from bone
marrow stem cells. Lymphocytes, the dominant cells
of immune system mature in the bone marrow (B-
lymphocytes) and Thymus (T-lymphocytes),Hence
these are called primary lymphoid organ or
generative lymphoid organ.
1) Bone Marrow
Primary lymphoid organ
BM is the Largest tissue of a mammalian body.
An adult contain 3kg of bone marrow.
BM has two distinct kind red and yellow marrow
Primary lymphoid organ
Flat, bilobed organ situated above the heart.
function of thymus is to generate & select a repertoire of T-Cells.
Each lobe is surrounded by a capsule and divided in to lobules, which is separated by strands of connective tissues called trabeculae.
THYMUS Cortical Epithelial
Medullary Epithelial Cells
Cortex and medulla is crisscrossed by 3-dimensional network of stromal cells composed of epithelial cells, dendritic cells and macrophages.
Many of these stromal cells interact physically with developing thymocytes.
Thymic epithelial cells secrete several hormonal factors necessary for the differentiation & maturation of T-Cells.
As thymocyte develop, an enormous diversity of T cell receptor is generated by a series of gene rearrangement.
Thymus induces apoptosis of those T-cells that fails to recognize MHC complexes or react with MHC complexes.
More than 95% of thymocytes die by apoptosis in the thymus.
n is known
Secondary lymphoid organ
are the sites where mature
lymphocytes respond or interact
to foreign antigens that Includes
LYMPH & LYMPHATICS
•Lymph is a clear body fluid which clots like blood.
•Lymph forms when dissolved proteins and solutes filter out of venules and capillaries. (due to hydrostatic & osmotic
Overview of blood and lymph system and how leukocytes travel from one system to another
Site of exchange between theblood and lymph systems
Lymph carrying antibodiesand immune cells collect in thoracic duct where the lymph empties back into the blood circulatory system
•Lymph flows uni directionally towards lymph nodes.
• Efferent lymph from regional lymph nodes may drain into one or more additional nodes before flowing into major efferent lymphatic.
• Thoracic duct carries lymph draining from the gut and lower half of the body.
•Lymphatic system is "garbage collector”
LYMPH & LYMPHATICS
1) Lymph nodes
are small nodular
throughout the body
Lymphnodes are bean shaped connective tissue bags, filled with mobile cell (lymphocyte, macrophages, dendritic cells) organized in functional compartments.
Trap Ag & Cells containing Ag.
Provide a site for clonal expansion.
Cortex (B-cells, macrophages, follicular DC)
Paracortex (T-cells, DC)
Medulla (sparsely populated lymphoid cells, many plasma cells)
Posses distinct regions of T-cell and B-cell activity and are surrounded by a fibrous capsule.
Follicular dendritic cells, of the germinal center, trap Ag-Ab complexes on membrane for long time.
Antigenic stimulation in node can increase the no. of lymphocytes 10-50 fold, resulting in visible swelling of the node.
Primary follicles (comprises a net work of follicular dendritic cells & resting B-cells)
Secondary follicles (a ring of concentrically packed B lymphocytes surrounding a germinal center).
The spleen is an organ found in virtually all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter.
Functions of spleen
The site of immunocytes residence. The site of immune response. Produce some active
substances,such as complement,et al.
Function of filtration.
SPLEEN PLAYS A MAJOR ROLE IN
MOUNTING IMMUNE RESPONSES TO
ANTIGENS IN BLOOD
LYMPHNODES ARE SPECIALIZED FOR
TRAPPING ANTIGENS FROM LOCAL TISSUES
Spleen is surrounded by a capsule from which a number of projections extend in to the interior to form a compartmentalization.
Red zone & White zone are separated by marginal zones.
Red pulp populated by macrophages, numerous RBC,s and few lymphocytes.
Red pulp is the site where old & defective red cells are destroyed & removed.
Splenic white pulp surrounds the branches of splenic artery, forming a Periarteriolar lymphoid sheath (PALS).
PALS rich in T cells.
Marginal zones rich in B cells & Dendritic cells.
PALS rich in T cells.
Primary lymphoid follicles are attached to the PALS.
These follicles are rich in B cells & some contains germinal centers.
Marginal zones, peripheral to the PALS are populate by lymphocytes and macrophages.
Blood born Ag. & lymphocytes enter the spleen through splenic artery, empty in to marginal zone.
Ag trapped by DC, carry it to the PALS.
Blood lymphocytes also migrate from marginal zone to the PALS.
Initial activation of T & B cells takes place in the T-cell rich PALS.
Activation of DC T helper B-cell
Activated B cells with Th Cells migrate to primary follicles in marginal zone.
On antigenic challenge, primary follicles develop into characteristic secondary follicles containing germinal centers.
Where rapidly dividing B cells & plasma cells are surrounded by dense cluster of lymphocytes.
Lymphoid tissues Besides the secondary lymphoid organ, there
are some structures which consist of aggregates of lymphocytes, macrophages, and other accessory cells. All such anatomically well defined structures are collectively called mucosa -associated lymphoid tissues.(MALT).
They contain aggregates of immune cells
BALT Surface area 400 m2
Having lose clusters of lymphoid cells (B-cells, T cells, macrophages)
Population of Plasma cells in MALT is far exceeds that of in spleen, lymph nodes & bone marrow combined.
Peyer's patches (or aggregated lymphoid nodules) are organized lymphoid tissues, named after the Swiss anatomist Johann Peyer. They are aggregations of lymphoid tissue that are usually found in the lowest portion of the small intestine, the ileum, in humans.
Payer,s patches found within the intestinal lining, contains well organized follicles from which germinal centers developed upon antigenic stimulation.
Tonsils play a role in defense against antigens entering through the nasal and oral epithelial routes.
Nodular structure consisting of a meshwork of reticular cells and fibers interspersed with lymphocytes, macrophages, granulocytes and mast cells.
B-cell are organized in to follicles and germinal centers.
Germinal centers are surrounded by regions showing T-cell activity.