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Home , Myeloid tissue

LYMPHOIDSYSTEM LYMPHOIDSYSTEM

The consists of Immune cells that continuously circulate between the and Lymphoid organs. The consistsof Lymphatic organs and the circulating clear fluid called Lymph. The Lymphatic system was first described in the seventeenth century independently by Olaus Rudbeck and Thomas Bartholin. Lymphoid organs are classified into 2 types.They are: (1) Primary Lymphoid Organs (2) SecondaryLymphoid Organs. PRIMARY & SECONDARY LYMPHOID ORGANS PRIMARY LYMPHOID SECONDARY LYMPHOID ORGANS ORGANS Central lymphoid organs. Peripheral lymphoid organs. Primary lymphoid organs are the Secondary lymphoid organs are the sites where Leukocytes (WBCs) sites where Adaptive immune are generated. It includes: (i) responses (Acquired immunity) marrow and (ii) . are initiated. It includes: (i) , (ii) and (iii) MALT. The Lymphoid stem cells The Lymphoid stem cells becomes proliferate (rapid increase), functional. differentiate and mature. Contains either B – cell or T – cell. Contains both B – cell or T – cell. cannot enter in. Antigens enter in and stimulates the Lymphoid cells. PRIMARY & SECONDARY LYMPHOID ORGANS PRIMARY LYMPHOID SECONDARY LYMPHOID ORGANS ORGANS Site of Maturation for T & Bcells. Site of Cell function for T & Bcells. Develop before Secondary Develop after Primarylymphoid lymphoid organs during Ontogeny organs during Ontogeny. (Organization and development of organs). Differentiation of Interaction of immune cells (Type of WBCs, with each other andantigen E.g., T cells, B cells & NK cells) processing are taken place in is taken place in Primary lymphoid Secondary lymphoid organs. organs. Decrease in size and strength with Increase in size with age. age.

THYMUS

Growth and maturation of T - lymphocytes takes place in Thymusonly. It is large at the time of birth (70 g) but with age, the size keep on reducing and becomes very small by attaining puberty (3 g). It is aflat, bilobed situated above the . Each Lobe is surrounded by a Capsule and is divided into Lobules, which are separated from each other by strands of Connective called Trabeculae. Each lobule is organized into 2 compartments: the outer compartment, or cortex, is densely packed with immature T cells, called Thymocytes, whereas the inner compartment, or medulla, is sparsely populated with Thymocytes. Both the cortex and medulla of the thymus are crisscrossed (moved or travel around) by a three -dimensional stromal - cell network composed of Epithelial cells, Dendritic cells and , which make up the framework of the organ and contribute to the growth and maturation ofThymocytes. Some thymic epithelial cells in the outer cortex, called Nurse cells, have long membrane extensions that surround as many as 50 Thymocytes, forming large multicellular complexes. Hassall corpuscles are a characteristic morphologic feature located within the medullary region of the thymus. FUNCTIONS OF THYMUS The main function of the Thymus is to release Thymosin hormone that will stimulate the maturation of T - cells. Failure of Thymus development shows dramatic decrease in circulating Lymphocytes of the T-cell lineage and absence of Cell - mediatedimmunity. Aging is accompanied by a decline in Thymic function. BONEMARROW is the soft, flexible present within the bone cavities. In humans and Mice, bone marrow is the site of B - cell origin and development. Bone marrow forms around 4 % of total body weight. There are two categories of bone marrow tissue: Red marrow and Yellow marrow. From birth to early adolescence, the majority of our bone marrow is red marrow. As we grow and mature, increasing amounts of red marrow is replaced by yellow marrow. Bone marrow can generate 200 billions of new blood cells everyday. RED AND YELLOW BONEMARROW RED BONE MARROW YELLOW BONEMARROW Also known as . Also known as Fatty tissue. Hematopoietic (formation of Multipotent Stromal components) in nature (connective tissue cell of any organ) and produces RBC, WBC & in nature and produces Fat, . and Bone. Gets its red color from the Gets its yellow color from the hemoglobin in the erythroid carotenoids in the fat droplets in cells. the highnumber of fat cells. High Vascular supply. Poor Vascular supply. Function - Helps to remove old Function - When blood supplyis cells from circulation. extremely low, yellow marrow can be converted to red marrow in order to produce more blood cells. FUNCTIONS OF BONEMARROW Bone marrow is the site of B - cell origin and development. A bone marrow transplant can save the lives of people battling , lymphoma and other blood cancers. Bone marrow generates RBCs which carry oxygen to the tissues. Bone marrow generates Platelets or Thrombocytes help prevent bleeding and aid in clotting of blood. (, & ) and Macrophages fight against microbial infections. They also remove dead cells and remodel tissue and . LYMPHNODE Lymph nodes are a group of small, bean-shaped organs (2.6 cm in length) found mainly in the neck and trunk of the . They play vital roles in the filtration of antigens and debris from Lymph (circulating colourless watery fluid) and in the generation of immune responses to pathogens. Lymph nodes are often removed from cancer patients as their filtration function catches tumor cells metastasized (spread to other sites in the body) from primary tumors.

STRUCTURE OF LYMPHNODE The Capsule is made of Collagen and has asub-capsular Sinus. The Lymph flows into the Sinus carrying Lymphocytes, processing macrophages and Dendritic cells to the node Cortex, Paracortex andMedulla. Morphologically, Lymph node can be divided into 3 roughly concentric regions: (1) Cortex, (2) Paracortex and (3) Medulla. The outermost layer, Cortex contains Lymphocytes (mostly B - cells), Macrophages and Follicular dendritic cells arranged in Primary follicles. The Primary follicles enlarge into Secondary follicles, each containing aGerminal center. STRUCTURE OF LYMPHNODE Beneath the cortex is the Paracortex, which is populated largely by T - lymphocytes and also contains Interdigitating dendritic cells thought to have migrated from tissues to the node. The innermost layer of a lymph node, the Medulla is more sparsely populated with Lymphoid-lineage cells of those present, many are Plasma cells actively secreting antibody molecules. The Medullain the core of the lymph node mainly processes T- lymphocytes. FUNCTIONS OF LYMPHNODE Drainage of fluid from blood stream into the tissues. Filtration of the lymph at the lymph nodes. Filtering blood. Raise an immune reaction and fight against microbial infections. SPLEEN The Spleenis an organ found in virtually all Vertebrates. The spleen is an organ located in the left side of the Abdominal cavity under the Diaphragm, the muscular partition between the Abdomen and the Chest. Similar to a Lymph node, it acts primarily as a blood filter. Old RBCs are recycled in the Spleen. Platelets and WBCs are storedin Spleen. The spleen also helps to fight against certain kinds of bacteria that cause Pneumonia and Meningitis.

STRUCTURE OF SPLEEN The spleen varies in size and shape between people, but it’s commonly Ovoid shaped and Reddish brown in colour. The spleen, in healthy adult humans, is approximately 7 cm (2.8 in) to 14 cm (5.5 in) in length. It usually weighs between 150 g and 200 g. The spleen is surrounded by a Capsule that extends a number of projections (Trabeculae) into the interior to form acompartmentalized structure. The compartments are of two types, the (i) Red pulp & (ii) White pulp, which are separated by a diffuse . STRUCTURE OF SPLEEN The splenic Red pulp consists of a network of sinusoids populated by Macrophages and numerous RBCs and few Lymphocytes. It is the site where old and defective red blood cells are destroyed and removed. The splenic White pulp surrounds the branches of the Splenic , forming a Periarteriolar lymphoid sheath (PALS) populated mainly by T - lymphocytes. Primary lymphoid follicles - Rich in B - cells and some of them contain Germinal centers. STRUCTURE OF SPLEEN The Marginal zone, located peripheral to the PALS, is populated by Lymphocytes and Macrophages. In the marginal zone, antigen is trapped by Interdigitating dendritic cells, which carry it to the PALS. The initial activation of B and T - cells takes place in the T-cell - rich PALS. Like Lymph node, the Primary follicles enlarge into Secondary follicles, each containing a Germinal center. FUNCTIONS OF SPLEEN Similar to a Lymph node, Spleen acts primarily as a blood filter. Old RBCs are recycled in the Spleen. Platelets and WBCs are storedin Spleen. The spleen also helps to fight against certain kinds of bacteria that cause Pneumonia and Meningitis. SPLENOMEGALY Splenomegaly – Enlargement of Spleen. Aspleen weight of 400 - 500 g indicates Splenomegaly, while a weight of more than 1000 g is Labelled Massive Splenomegaly. Causes - Viral infections, Bacterial infections (Syphilis), Parasitic infections (Malaria), Cirrhosis (Chronic damage), Hemolytic anaemia, Blood cancers, Metabolic disorders, Inflammatory disease (Rheumatoid arthritis) and Pressure on . Symptoms – Enlarged abdomen, Painful abdomen and shoulder, Weakness, Feeling full without eating, Anaemia, Fatigue, Frequent infections and Easy bleeding. MALT The mucous membranes lining the digestive, respiratory, and urogenital systems have a combined surface area of about 400 m2 and are the major sites of entry for most pathogens. These vulnerable membrane surfaces are defended by a group of organized lymphoid tissues mentioned earlier and known collectively as Mucosal-associatedlymphoidtissue (MALT). MALT can be further classified as Gut-associated lymphoid tissue (GALT) or -associated lymphoid tissue (BALT). The Tonsils, and Peyer’s patches are representative of lymphoidtissue found in and around mucosal epithelia. Tonsils Tonsils are collections of Lymphoid tissue facing into the Aerodigestive tract. The Tonsils play a role in protecting the body against Respiratory and Gastrointestinal infections. Each tonsil consists of a network of crypts (pits) that store cells used to fight infection. The tonsils contain B & T-cells, that fights againstinfections. Tonsils also produce Antibodies against Polio, Streptococcal pneumonia, Influenza, and numerous infections. Tonsillitis occurs when bacterial or viral organisms cause inflammation of the Tonsillar tissue. This results in fever, difficulty swallowing, sore throat, pain, loss of voice and throat tenderness.

Appendix Appendix - Blind- ended tube connected to the Cecum. The Cecum is a pouch like structure of the Colon, located at the junction of the Smalland the Large intestines. The human appendix averages 9 cm in length but can range from 2 to 20 cm. The diameter of the appendix is usually between 7 and 8 mm. Appendicitis – Inflammation ofAppendix. Functions of Appendix - 1) Maintaining Gut flora, 2) Important component of Mucosal immune function and 3) Storehouse for good bacteria, “rebooting” the digestive system after diarrheal illnesses. Surgical removal of the appendix causes no observable health problems.

Peyer’s Patches

Peyer’s patches are small masses of lymphatic tissue found throughout the Ileum region of the . Peyer’s patches are roughly egg-shaped lymphatic tissue nodules that are similar to lymph nodes in structure, except that they are not surrounded by aconnective tissue capsule. Important part of the immune system by monitoring intestinal bacteria populations and preventing the growth of pathogenic bacteria in the intestines. Peyer’s patches also playing an important role in traping antigens from pathogens and destroying them.