Lymph node, spleen, thymus, tonsil- discussion, viva

Lymphatic system:

1. What is the function of lymphatic system?
• The function of lymphatic system is immunity / to protect the organism from invading pathogens or antigens
2. What are the components of lymphatic system?
• Cells- distributed throughout the body as single cells or aggregations of cells or non-encapsulated lymphatic nodules
• Lymphatic organs- lymph node, spleen, thymus, tonsil
3. Name the lymphatic organs surrounded by connective tissue capsule
• Lymph node, spleen, thymus
4. Name the lymphatic organ covered by epithelium
• Tonsil

Lymph node:

1. What are the parts of lymph node?
• Outer cortex- network of reticular fibers, non-encapsulated aggregations of lymphocytes called lymphatic nodules with pale germinal center
• Inner medulla- medullary cords (irregularly arranged lymphocytes, macrophages, plasma cells in network of reticular fibers) and medullary sinuses
2. What is direction of flow of lymph?
• Afferent lymphatic vessel--subcapsular sinus--trabecular sinus--medullary sinus--efferent lymphatic vessel
3. What is the function of lymph node?
• The function of lymph node is to filter the lymph as it enters the lymph node
4. What are lymph sinuses?
• Lymph sinuses are the spaces with fine network of reticular fibers filled with lymph
• Subcapsular sinus- sinus present beneath the connective tissue capsule
• Trabecular sinus- sinus present around the connective tissue septa (trabeculae) entering the lymph node
• Medullary sinus- sinus present in the medulla
5. What are germinal centers?
• The germinal centers are the pale regions in the center of lymphatic nodule which represent the active sites of lymphocyte proliferation

Spleen:

1. What are the parts of spleen and their components?
• Red pulp- splenic cords of Billroth (network of reticular fibers with macrophages, lymphocytes, plasma cells, blood cells) and splenic/blood sinuses
• White pulp- dark staining lymphoid aggregations/nodules surrounding a central artery. Along with lymphocytes, antigen-presenting cells and macrophages are also seen
2. What is the function of red pulp?
• The function of red pulp is to filter the blood. It removes the antigens, microorganisms, platelets and aged or abnormal erythrocytes from the blood.
3. Is there a germinal center in the lymphatic nodule present in spleen?
• Yes
4. What are the types of lymphatic cells seen in white pulp?
• T cells- surround the central arteries
• B cells- present in rest of lymphatic nodule
5. What are the functions of spleen?
• Fetal life- produces granulocytes and erythrocytes
• Important reservoir for blood
• Filters blood
• Takes part in immunity
6. Is spleen essential for life?
• No, it is not

Thymus:

1. Where is thymus located?
• Thymus is located in the root of neck and upper anterior mediastinum
2. What are the stages of thymus?
• Childhood- most active upto puberty
• After puberty- undergoes involution
• Adults- replaced with adipose tissue
3. What are the parts of thymus?
• Connective tissue capsule divides the thymus into incomplete thymic lobules. Each thymic lobule has peripheral cortex and inner medulla which is continuous with adjacent lobules
• Cortex- densely packed lymphocytes
• Medulla- few lymphocytes, more epithelial reticular cells, thymic/Hassall's corpuscles
4. What are Hassall's corpuscles?
• They are oval structures consisting of round or spherical aggregations of flattened epithelial cells around the calcified or degenerating mass of epithelial cells
5. What are the functions of epithelial reticular cells?
• The epithelial reticular cells forms the blood-thymus barrier and secretes hormones necessary for proliferation, differentiation and maturation of T-cells
6. What happens to the child if thymus is removed?
• The child may not be able to fight pathogens and death may occur as a result of infection and lack of functional immune system
7. What are the hormones secreted by epithelial reticular cells?
• Thymulin, thymopoietin, thymosin, thymic humoral factor, interleukins, interferon
8. Name the layers forming blood-thymic barrier?
• Endothelial cells
• Epithelial reticular cell
• Macrophages

Tonsil:

1. Where is tonsil located?
• Tonsil is located at the oro-pharyngeal isthmus on either side of oral cavity
2. What are the parts of tonsil?
• Attached surface- covered by connective tissue capsule
• Free surface- covered by stratified squamous non-keratinized epithelium which invaginates into the tonsil as tonsillar crypts
• Tonsillar crypts are surrounded by numerous lymphatic nodules