Lymphoid Tissue Forms the basis of the immune system of the body Forms the basis of the immune...
-
Upload
josephine-hood -
Category
Documents
-
view
227 -
download
0
Transcript of Lymphoid Tissue Forms the basis of the immune system of the body Forms the basis of the immune...
Lymphoid Tissue
Forms the basis of the immune system of the bodyForms the basis of the immune system of the body LymphocyteLymphocyte, the principal cell of lymphoid tissue, , the principal cell of lymphoid tissue,
is responsible for the proper functioning of the is responsible for the proper functioning of the immune systemimmune system
Classified as Classified as primaryprimary & & secondarysecondary lymphoid lymphoid tissuetissue
Organized into Organized into diffusediffuse and and nodularnodular lymphoid lymphoid tissuetissue
Types of Lymphoid Organs Primary lymphoid organsPrimary lymphoid organs are responsible for are responsible for
the development and maturation of the development and maturation of lymphocytes into mature cells e.g. fetal liver, lymphocytes into mature cells e.g. fetal liver, bone marrow and thymusbone marrow and thymus
Secondary lymphoid organsSecondary lymphoid organs are responsible are responsible for the proper environment in which the for the proper environment in which the immunocompetent cells can react with each immunocompetent cells can react with each other and with the antigens e.g. lymph nodes, other and with the antigens e.g. lymph nodes, spleen, and mucosa associated lymphoid spleen, and mucosa associated lymphoid tissue tissue
Organization of Lymphoid Tissue1. Diffuse Lymphoid Tissue
Occurs throughout the body, especially Occurs throughout the body, especially under wet epithelial membranes where the under wet epithelial membranes where the connective tissue is infiltrated by lymphoid connective tissue is infiltrated by lymphoid cells e.g. cells e.g. lymphocytes, plasma cells, lymphocytes, plasma cells, macrophages and reticular cellsmacrophages and reticular cells
Particularly evident in the Particularly evident in the lamina proprialamina propria of of GIT & subepithelial connective tissue of the GIT & subepithelial connective tissue of the respiratory tractrespiratory tract
2. Nodular Lymphoid Tissue
Includes:Includes: Lymph nodesLymph nodes ThymusThymus SpleenSpleen TonsilsTonsils
Cells of Immune System
Lymphocytes are generally classified into:Lymphocytes are generally classified into: B lymphocytesB lymphocytes (B cells) (B cells) T lymphocytesT lymphocytes (T cells) (T cells) Null cellsNull cells: composed of two types: composed of two types
Stem cellsStem cellsNatural killer cellsNatural killer cells
B Lymphocytes
Small lymphocytes that are formed, and Small lymphocytes that are formed, and become immunocompetent in the become immunocompetent in the bone bone marrow.marrow.
The activated cells The activated cells enter the general enter the general circulationcirculation, , undergo mitosisundergo mitosis, and , and transform into antibody-producing transform into antibody-producing plasma cells plasma cells andand B-memory cells B-memory cells
T Lymphocytes
Histologically identical to B lymphocytesHistologically identical to B lymphocytes Formed in Formed in bone marrowbone marrow, migrate to the cortex , migrate to the cortex
of the of the thymusthymus to become immunocompetent to become immunocompetent There are several subtypes e.g. There are several subtypes e.g. T helper cells, T helper cells,
T cytotoxic cells, T suppressor cells and T T cytotoxic cells, T suppressor cells and T memory cellsmemory cells
Assist B lymphocytes in the performance of Assist B lymphocytes in the performance of their functions their functions
Antigen Presenting Cells
Derived from Derived from monocytesmonocytes They phagocytose, catabolize and process They phagocytose, catabolize and process
antigen and present to T lymphocytesantigen and present to T lymphocytes Include macrophages, dendritic cells Include macrophages, dendritic cells
(Langerhans cells of the epithelium & (Langerhans cells of the epithelium & mucosa), B cells and epithelial reticular mucosa), B cells and epithelial reticular cells of thymuscells of thymus
Stem Cells
Undifferentiated cellsUndifferentiated cells Give rise to the various cellular Give rise to the various cellular
elements of the blood elements of the blood
Natural Killer Cells
Cytotoxic cellsCytotoxic cells Formed in the bone marrowFormed in the bone marrow Become immunocompetent as soon as Become immunocompetent as soon as
they are formedthey are formed They kill some virally altered cells and They kill some virally altered cells and
tumor cellstumor cells
Lymph Nodes Ovoid, kidney shaped Ovoid, kidney shaped
organs organs Each node has:Each node has:
A A convex surfaceconvex surface which receives which receives afferent lymph vesselsafferent lymph vessels
AA hilumhilum where where efferent lymph vesselsefferent lymph vessels leave and drain lymph leave and drain lymph from the organsfrom the organs
Histological Structure of Lymph Node Each lymph node has a dense Each lymph node has a dense
irregular collagenous irregular collagenous connective tissue connective tissue capsule capsule
Derived from the capsule, Derived from the capsule, connective tissue connective tissue septaeseptae (trabeculae)(trabeculae) extend into the extend into the outer part (cortex) of the node outer part (cortex) of the node and divide it into incomplete and divide it into incomplete compartmentscompartments
The framework of the node is The framework of the node is formed by formed by reticular reticular connective tissueconnective tissue
Each lymph node is Each lymph node is divided into three divided into three regions: regions: CortexCortex ParacortexParacortex MedullaMedulla M
PC
C
Lymph Nodes: CORTEX contains the:contains the:
Subcapsular sinus, Subcapsular sinus, which is continuous which is continuous and drains into the and drains into the
Cortical sinusesCortical sinuses Lymphoid nodulesLymphoid nodules
(primary & secondary) (primary & secondary) composed mainly of composed mainly of B B lymphocyteslymphocytes and and reticular cellsreticular cells
CPC
M
n
c scs
csn
Lymph Nodes: PARACORTEX It is the region between cortex and It is the region between cortex and
medullamedulla Contains thymus dependent zone mainly Contains thymus dependent zone mainly
T lymphocytesT lymphocytes High endothelial venules ( HEV) lined by High endothelial venules ( HEV) lined by
simple cuboidal epithelium instead of simple cuboidal epithelium instead of simple squmaus epithelium to facilitate simple squmaus epithelium to facilitate passage of mature T lymphocyte coming passage of mature T lymphocyte coming from thymus to paracortex of lymph from thymus to paracortex of lymph node. node.
Has NO nodulesHas NO nodules
PCC
M
Lymph Nodes: MEDULLA consists of:consists of:
Medullary cordsMedullary cords Medullary sinusoidesMedullary sinusoides..
TheThe medullary cords medullary cords are are composed of composed of T lymphocytes, T lymphocytes, plasma cells plasma cells andand macrophages macrophages
The The medullary sinusoidesmedullary sinusoides are are continuous with the continuous with the subcapsularsubcapsular and and corticalcortical sinuses.sinuses.
There in no lymphatic There in no lymphatic Nodules.Nodules.
MS
pc
Lymph Nodules Lymph nodules are Lymph nodules are
small masses of lymph small masses of lymph tissue in which tissue in which B B lymphocyteslymphocytes are are produced. produced.
Lymph nodulesLymph nodules may be: may be: Primary nodulesPrimary nodules Secondary nodulesSecondary nodules
PNSN
Primary nodules
which are formed which are formed of virgin (not of virgin (not activated) and activated) and memory memory B B lymphocyteslymphocytes
Secondary NoduleContains:Contains: Germinal centresGerminal centres, central , central
light areas filled with light areas filled with immature lymphocytes. Here immature lymphocytes. Here new lymphocytes proliferate new lymphocytes proliferate from stem cells that originate from stem cells that originate in the bone marrow. Germinal in the bone marrow. Germinal centerscenters contains large contains large lymphocytes, mitotic figures, lymphocytes, mitotic figures, macrophages and plasma macrophages and plasma cellscells
The germinal centre is The germinal centre is surrounded by a darker-surrounded by a darker-staining region called the staining region called the corona corona that contains small that contains small B B lymphocytes ( not activated).lymphocytes ( not activated).
c
Lymph Flow Through The Lymph Node
Afferent lymph vesselsAfferent lymph vessels
Subcapsular sinusesSubcapsular sinuses Cortical sinusesCortical sinuses
Medullary sinusesMedullary sinuses
Efferent lymphatic Efferent lymphatic vesselsvessels
Lymph Node: Function
Maintenance and production of Maintenance and production of immunocompetent cells immunocompetent cells
Proliferation of lymphocytes. Activated T- and Proliferation of lymphocytes. Activated T- and B- lymphocytes multiply in the lymph nodesB- lymphocytes multiply in the lymph nodes
Filtration of lymph Filtration of lymph ( not blood)( not blood) Phagocytosis Phagocytosis
Thymus Bilobed lymphoid organ Bilobed lymphoid organ
located in located in thoraxthorax Derived from Derived from endodermendoderm Enclosed in a thin Enclosed in a thin
connective tissue connective tissue capsulecapsule SeptaeSeptae extend from the extend from the
capsule into the organ, capsule into the organ, incompletely subdividing incompletely subdividing it into it into lobuleslobules
Possesses Possesses no lymph no lymph nodules nodules
L
L
S
C
Thymus cont’d Each Each lobulelobule is divided into an is divided into an outer outer
cortexcortex and and inner medullainner medulla CORTEXCORTEX: Composed of : Composed of epithelial reticular epithelial reticular
cellscells, , macrophagesmacrophages, and , and thymocytesthymocytes (small T (small T lymphocytes). Here the immature T cells lymphocytes). Here the immature T cells undergo proliferation, reticular cells release undergo proliferation, reticular cells release hormone and factor to activate T lymphocyte hormone and factor to activate T lymphocyte and transform into immunocompetent cells and transform into immunocompetent cells and then migrate to medullaand then migrate to medulla
MEDULLAMEDULLA: consists of : consists of epithelial reticular epithelial reticular cellscells, , large T lymphocyteslarge T lymphocytes and and thymic thymic (Hassall’s) corpuscles(Hassall’s) corpuscles
Microphage will engulf not activated T Microphage will engulf not activated T lymphocyte. lymphocyte.
1 - cortex 1 - cortex 2 - medulla 2 - medulla 3 - Hassal's 3 - Hassal's corpuscle corpuscle 4 - interlobular 4 - interlobular connective tissue connective tissue (septa)(septa)
Hassall’s Corpuscle
Are composed of Are composed of groupsgroupsof of keratinized keratinized epithelial cellsepithelial cells
Increase in number Increase in number with agewith age
Probably represent a Probably represent a degenerative degenerative phenomenonphenomenon
CM
HC
Epithelial Reticular Cells Separate the cortex from the Separate the cortex from the
capsule and the trabeculaecapsule and the trabeculae Surround the cortical capillariesSurround the cortical capillaries
thus forming a thus forming a blood-thymus blood-thymus barrierbarrier
Form a Form a specialized barrier between specialized barrier between cortex & medullacortex & medulla, preventing , preventing medullary material from gaining medullary material from gaining access to the cortexaccess to the cortex
Thus provide an antigen free Thus provide an antigen free environment for the potentiation of environment for the potentiation of the immunocompetent T the immunocompetent T lymphocyteslymphocytes
They also They also form Hassall’s (thymic) form Hassall’s (thymic) corpusclescorpuscles
Thymus
Thymus
Lymph Node
Lymph Node