Flashcards in Lymph Nodes_BTED Deck (78):
What are lymph nodes?
Encapsulated, bean-shaped organs located along lymphatic vessels
What are the two types of lymphatic vessels that serve the lymph node?
1) Afferent lymphatic vessel
2) Efferent lymphatic vessel
What does the afferent lymphatic vessels do?
Convey lymph toward the node and enter it at various points on the convex surface of the capsule
What does the efferent lymphatic vessels do?
Convey lymph away from node and leave at the hilum
What is the hilum?
Depression on the concave surface of the node that also serves as the entrance and exist for blood vessels and nerves.
How big is the lymph node?
Rang from a few mm to several cm in size
Where are the lymph node found?
Often in clusters - axilla, groin, neck
What are the functions of the lymph node?
1) Filter lymph
2) play vital role in immune response - bacteria and other toxic substances are destroyed by macrophage of lymph node
What are the supporting elements of the lymph node?
3) Reticular tissue
What are the capsules composed of?
Composed of Dense CT that surrounds the node
What are the Trabecular composed of?
Dense CT which extends from the capsule into the substance of the node forming a gross framework
What are the Reticular tissue composed of?
Reticular cells and reticular fibres that form a fine supporting meshwork throughout the remainder of the organ.
Name the cells of the reticular framework
1) Reticular cell
2) Dendritic cell
4) Follicular dendritic cells
What do reticular cells do?
1) Supporting role
2) Express surfaace molecules
3) Produce substances that attract T cells, B cells and dendritic cells
What are Dendritic cells?
Unique bone marrow derived APC
What does Dendritic cell do?
Monitor the local environment for foreign substances that they then process and present to antigen specific T cells.
What does macrophages do?
Both phagocytic and antigen presenting cells that express MHC I, MHC II, and costimulatory molecules.
What is follicular dendritic cells?
Have multiple, thin, hairlike branching cytoplasm processes that interdigitate between B lymphocytes int he germinal centers
What is the parenchyma of the lymph node is divided into?
What is the cortex?
Forms the outer portion of the node except at the hilum
What does the cortex contain?
- Dense mass of lymphatic tissue (reticular framework, dendritic cells, follicular dendritic cells, lymphocytes, macrophages and plasma cells) and lymphatic sinuses, the lymph channels.
- B cell rich
What is the medulla?
Inner part of the lymph node
Where is the lymphatic nodules found?
Outer part of the cortex called the superficial (nodular) cortex.
What is the deep cortex (paracortex)?
Portion of the cortex between the medulla and superficial cortex is free of nodules
What does the deep cortex contain?
Most of to the T cells in the lymph node.
What are the boundaries of the paracrotex?
Not precise - expands in viral infection
Where do the lymphocytes from the blood?
Into the nodes through High Endothelial Venues in paracortex
What does the medulla of the lymph node consist of?
Medullary cords and medullary sinuses.
Where is the subcapular (cortical) sinus found?
Just beneath the capsule of the lymph node is a sinus interposed between the capsule and the cortical lymphocytes
What are the cords of the lymph node medulla?
Extensions of lymphoid tissue that extend from the paracortex
What does the cords of the lymph node medulla contain?
1) B lymph
2) Plasma cell
What are the sinuses of the lymph node medulla?
Spaces that contain lymph, lymphocytes, macrophages, etc.
Continuous with cortical sinuses and join at hilum to form efferent lymphatic.
Name secondary follicles
2) Antigen presenting ells
3) Follicular dendritic cells
Are BCL2 found in large proliferating B cells?
Are BCL2 found in smaller mature B cells
Yes and the cell is surrounded by mantle zone
What are paracortical high endothelial venues for?
Paracortex rich in T cells
What is the lymph flow?
Afferent lymphatic vessels to Subcapular sinus to cortical sinus to medullary sinus to efferent lymphatic vessels
What is the thymus?
Bilobed organ locate din the superior mediastinum, anterior to the heart and great vessels.
Dual embryonic organ - lymphocytes and epithelium from pharyngeal pouches (3rd pair)
What happens to the thymus at puberty?
Birth: Thymus fully formed and functional. It persists as a large organ until about the time of puberty when T cell differentiation and proliferation are reduced and most of the lymphatic tissue is replaced by adipose tissue. The organ be restimulated under conditions that demand T - Cell proliferation.
What is the general architecture of the thymus?
Possess a thin connective tissue capsule from which trabecular extend into the parenchyma of the organ.
What do the capsule and trabecular contain?
Efferent lymphatic vessels
What do the connective tissue of the thymus contain?
1) Collagen fibres
3) Plasma cell
6) Mast cells
7) Adipose cells
What does the thymus parenchyma contains?
Developing T cells in an extensive meshwork from by epithelioreticular cells
What is the outer portion of the thymus parenchyma called?
Name the cells of the cortex of thymus
1) T lymphocytes - thymocytes
3) Epithelium - epitheliocytes
Where are the thymocytes found in the cortex of the thymus?
Occupy spaces within an extensive meshwork of epithelioreticular cells
What are the difference between cortex and medulla?
Cortex has dense lymphocytes and Medulla has looser lymphocytes.
What are the parts of the thymus
Cortex and Medulla
Lymphocytes and epithelium
Where are the thymus epithelial cells found?
1) Squamous blood thymus barrier
3) Corticomedullary barrier
4) Hassal's Corpuscles
What is the function of the thymus?
1) T lymphocye maturation and education
2) Regulation of T cell function in the peripheral tissues
3) If absent at birth, child dies in infancy due to infections
What is the size of the thymus at birth then at puberty and at adulthood?
Birth: 15 Gm
Puberty: 30 - 40 Gm
What is one difference between thymus and lymph nodes?
No afferent lymphatics - does not filter lymph ( in contrast with lymph nodes)
Describe the properties of the medulla of the thymus
1) Looser, less cellular than cortex (loosely packed T cells)
2) Differentiated T lymphocytes
3) Hassal's Corpuscles present
4) Function: not clear
What are Hassal's Corpuscles?
isolated masses of closely packed, concentrically arranged type VI epithelioreticular cells that exhibit flattened nuclei.
TEM studies of these cells reveal keratohyalin granules,
What are in the center of Hassal's Corpuscles?
May display evidence of keratinisation.
What is thymic cell education?
Stem cell maturation and differentiation into immunocompetent T cells. Characterised by expression and deletion of specific surface CD antigen
What indicates an early stage of T cell differentiation (double-negative stage)?
Expression of CD2 and CD7 molecules on the T - cell surface
Lack of CD4 and CD8
What indicates middle stage of T cell differentiation?
Expression of CD 1 molecule
What is the double positive stage of T cell differentiation?
As maturation progress, the T cells express TCR, CD3, and both CD4 and CD8 molecules
What is positive selection?
When the lymphocyte recognises self MHC molecules (MHC I and MHC II from cytoreticulum) and self or foreign antigen, it will survive
What happens to cells that pass the positive selection test?
Leave the cortex and enter the medulla
What happens after cells leave the cortex and enter medulla?
Undergo negative selection, where cells that recognise self antigen from cytoreticulum displayed by self-MHC are eliminated (apoptosis) - prevents immune attack on self
What happens in the cortex in relation to central tolerance?
Where does early stage of T cell differentiation (double-negative stage) occur?
Multiopotential lymphatic stem cell enter the medulla of the thymus via a post capillary venue and then migrate to the periphery of the thymus lobule.
What happens after negative selection?
Cells become either cytotoxic CD8+ T lymphocytes of helper CD4+ T lymphocytes. Ready for immune response, leave thymus from medulla and enter blood circulation.
What promote the process of thymic cell education?
Hormonal substances secreted by Type VI epithelioreticular cells within the Hassall's corpuscle
What are the layer of Thymic epithelium?
(out to in)
Blood thymus barrier
What are the lymphocytes - thymocytes in the cortex of the medulla?
Progenitor cells come from Bone marrow
Most are T cells versus other lymphoid organs
What happens to the T lymphocytes in the thymus when it undergoes differentiation?
- Undergo maturation in cortex, pushed deep into medulla, where maturing lymphocytes enter the high endothelial venules and depart to peripheral locations.
- Subsequently populate peripheral lymphoid tissues and undergo final maturation
What is the function of thymocytes?
Homing to peripheral lymphoid tissues
What is the homing mechanism of the thymocyte of the thymus?
Homing mechanism is through receptor ligand binding between 'homing molecules' on the circulating lymphocytes which stick to their counterparts on endothelial cells in different location.
What molecules is involved in homing mechanism of the thymocyte of the thymus?
Multiple homing molecules appear to be involved including lectin like molecule (selections), CD44 and integrins
What is the function of the epitheliocytes (Thymic epithelial cells) of thymus
1) Form stream support meshwork throughout thymus
2) T cell education, maturation
3) Secret hormone
What does T cell education do?
Promote T cell differentiation, proliferation, subset maturation and the development of an effective T cell arm to the immune system
What hormones does the Thymic epithelial cells secrete?
What does paracrine hormone do?
That regulate T cell maturation and proliferation in thymus
What proteins support the paracrine hormone secretion of the Thymus?