Lymphoid System Flashcards
The Immune system
Provides protection for the body against invading pathogens
- initial protection of body provided by epithelium that covers all surfaces
- Immune system takes over protection once epithelial barrier is breached
Types of immune system
Innate( natural) immune system
Adaptive (acquired) immune system
Innate(natural) immune system
nonspecific, performed by complements, macrophages, neutrophils, and natural killer cells
Adaptive (acquired) immune system
Reacts against specific antigenic component, performed by lymphoid system
Two types: Humoral immunity
Cellular (cell mediated) immunity
Lymphoid tissue
Specialized form of connective tissue that involved in adaptive immune defense of body
Lymphocyte
Principal functional cell
Mature and immature forms
( lymphoblasts, medium and small lymphocytes)
Humoral Immunity
Antigen stimulates production of an antibody ) from B-lymphocytes: plasma cell) which neutralizes antigen
Cellular (cell mediated) Immunity
Cell(t-lymphocytes) directly attacks foreign cell or altered host cell through binding to the specific antigen or “epitope”
Types of Lymphocytes
B lymphocyte
T lymphocyte
Null cell
Indistinguishable when viewed under the light microscope
B Lymphocytes
Surface antibodies (IgD & IgE) act as receptors
Effector cell
- Plasma cell –> production of antibodies
Memory cell
- Programmed to react to specific antigen
Antigen
Molecule(s) that is (are) foreign to the body
Antibody (immunoglobulin)
Protein secrete to neutralize an antigen
Key component of a humoral immune response to an antigen
T Lymphocytes
Surface receptors bind with antigens
Effector cell
- Destroy foreign cells and altered cells by enzymes and cytokines
Memory cell
- Programmed to react to specific antigen
Null Cells
Small portion of lymphocytes
NK cells (natural killer cells)
- Destroy foreign, viral, altered, or cancer cells without help of t lymphocytes or passage through thymus
Stem Cells
Cell of origin for cells of blood
Dendritic cells
Antigen presenting cell
Other cell types
Macrophages
Granulocytes
Reticular Connective tissue
Framework of lymphoid tissue
Reticular cells
Reticular Cells
A “fibroblast”with specialized function to produce and maintain reticular connective tissue
Arrangements of lymphoid tissue
Diffuse lymphoid tissue (T-cell zone)
Dense solitary lymph nodules (B-cell zone)
Mucosa-Associated Lymphoid Tissue (MALT)
Non-encapsulated lymphoid tissue located in the mucosa
Examples: Gut and bronchus associated ( GALT and BALT)
Lymphoid organs
Highly organized lymphoid tissue Capsule with trabeculae or septa (connective tissue)
Have both diffused lymphoid tissue and nodules (except in thymus)
Primary Lymphoid organs
Sites where lymphocytes produced &/ or become immunocompetent
Organs include bone marrow and thymus
Secondary Lymphoid organs
Site where “immunocompetent” lymphocytes contact antigens and proliferate
Organs include lymph nodes, Spleen, Tonsils, Peyer’s patches, Hemal Nodes
Lymph Node
Secondary Lymphoid organ
Is palpable
Function: Regional filtration of tissue fluid (lymph)
- Antigen recognition
- Antibody production
- Lymphopoiesis
Tissue Fluid of Lymph node
Fluid component of blood that leaves circulatory system to enter extracellular matrix of connective tissue
- Leaves extracellular matrix & re enters blood capillaries & venues
Lymph
Is excess tissue fluid.
Enters lymphatic capillaries for returned to the general circulatory system
Lymph Channels (pathway for tissue fluid through lymph node)
Afferent lymphatic vessels
Intranodal channels
- Subcapsular sinus
- Intermediate sinus
- Medullary sinus
Efferent lymphatic vessel
Stroma
Capsule
- Dense irregular connective tissue
Trabeculae
- Internal struts
Reticular Connective Tissue
- Form intranodal sinuses
- Stellate reticular cells and squamous cells
Parenchyma: Lymph node
Cortex
- Outer layer housing lymphoid nodules; B-lymphocytes
Parecortex
- Area between cortex and medulla, housing T-lymphocytes “thymus-dependent zone”
Medulla
- Center area composed of medullary cords and sinuses
Primary nodule
Resting stage
congregation of B lymphocytes
Naive B-lymphocytes
Immunocompetent but never interacted with an antigen
Coming from bone marrow, enter node from high endothelial venules (HEVs) of paracortical (thymic dependent) region
Memory B lymphocytes
May enter through HEVs or afferent lymphatic vessels
Secondary Nodule
Site of proliferation(mitosis) of B-lymphocytes following antigen binding
Forms a germinal center by activated lymphocytes
Outlined with corona
Germinal center is formed in a pre-existing primary nodule
- primary nodule activation to form germinal center, then become secondary nodule
Germinal Center
Activated B-lymphocytes come to primary nodule & proliferate
Lymphoblast formed, and further divided to plasma cells and memory cells
Follicular dendritic cell assists with proliferation of lymphocyte, and present antigen to lymphocyte
Corona (mantle)
Dense accumulation of lymphocytes surrounding germinal center
Composed of:
- Displaced naive & memory B-lymphocytes & T-lymphocytes from original primary nodule
- transient newly formed memory B-lymphocytes & plasma cell
Paracortex
- “Thymus dependent zone”
- Diffuse lymphoid tissue
- Localization of T-lymphocytes & interdigitating dendritic cells
(antigen presenting cells) - Site of proliferation of T-lymphocytes
- “high endothelial venules” vascular sites where lymphocytes leave the vascular beds and enter
lymph node
Medulla
Medullary cord
Lymph Sinuses
Medullary Cord
Diffuse lymphoid tissue
* Congregation of plasmacells, lymphocytes &
macrophages
Lymph Sinuses
Open channels formed by reticular tissue, filled with lymphocytes and lymph fluid
Blood circulation in Lymph Nodes
- Nodal artery enters node at hilus
– Branches traverse medulla in trabeculae
– Branches leave trabeculae to enter paracortex & cortex
– Capillary bed formed in cortex
– Capillaries merge to form High Endothelial Venules
– Venules drains into larger veins, which exit at the hilus
High Endothelial Venules
Located in PARACORTEX
Endothelial cells are cuboidal in shape
Receptors for recognition by lymphocytes (traveling in blood)
Lymphocytes leave blood & enter the paracortex and nodules
Peyer’s Patch
Secondary lymphoid organ
Most abundant in wall of ileum
Aggregated Lymphoid Nodules
Diffuse lymphoid tissue between & around nodules
Lymphoid nodules located in submucosa
Diffuse lymphoid tissue extends into lamina propria
Classified as component of “Gut Associated Lymphoid Tissue”
(GALT)
no capsule
only efferent lymphatic vessels
Peyer’s Patch: Aggregated lymphoid nodules
*Primary nodules
*Secondary nodules
*Germinal center
*Corona
Peyer’s Patch: diffused lymphoid tissue
*Between & around nodules
*“High endothelial venules”
Site where B-lymphocytes & Tlymphocytes leave circulating
blood & enter Peyer’s patch
Peyer’s Patch: B-lymphocytes
Proliferate in germinal center of secondary nodules
Peyer’s Patch: T-lymphocytes
localized in satellite region adjacent to proximal portion of nodules
Peyer’s Patch: M- cells (microfold cells)
*Specialized cells in simple columnar epithelium that lines luminal surface of ileum ABOVE PEYER’S PATCH
*Apical surface of M cell contacts lumen of ileum
*Sample (capture) antigens in lumen of ileum
*Antigen presenting cells embedded in basal surface of M cell
Tonsil
*Incompletely encapsulated
*Multiple sites around nasal and oral body openings
*Secondary lymphoid organ
*Intercept antigens entering body orifices
Tonsil : Stroma
Capsule
