CHAPTER 6 - LYMPHOID ORGANS Flashcards
LYMPHOID ORGANS
- Divided into two:
Primary and Secondary lymphoid organs
- Main producers of lymphocytes (B cells and T cells)
Primary
o Followed by release to the circulation
then to the secondary lymphoid organ (SLO)
Primary
- Provide appropriate microenvironments or the development and maturation of lymphocytes
Primary
- Thymus
Primary
- Bone marrow
Primary
- Site of maturation and site where lymphocytes can perform their main functions.
Secondary
- Trap antigen from defined tissues or vascular spaces and are sites where mature lymphocytes can interact effectively with the antigen
Secondary
o Tonsils, spleen (lymph nodes (Lymphatics and skin), Peyer’s patches, appendix, and mucosa- associated lymphoid tissue (MALT)
Secondary
function as potential sites for contact with foreign antigen, and they increase the probability of an immune response.
Secondary
- Adenoids
Secondary
- Tonsils
Secondary
- Lymph nodes
Secondary
- Spleen
Secondary
- Peyer’s Patches
Secondary
- Appendix
Secondary
- MALT
Secondary
– lymphatics and skin
Lymph nodes
– entry through circulation
Spleen
– a specialized type of MALT and are located at the lower ileum of the intestinal tract
Peyer’s Patches
- Largest tissue of the body (adult: 1300 to 1500g)
Bone Marrow
Bone Marrow
- Two parts:
- Red marrow
- Yellow Marrow
– produces blood cells
Red marrow
– higher percentage; cannot produce HSC
but adipose/fat cells instead
Yellow Marrow
- Primary function: Primary source of pluripotent stem cells that give rise to all hematopoietic stem cells (HSC) that fives rise to other blood cells
Bone Marrow
- Major organ for B cell maturation (“B” cells = “B”one marrow) gives rise to the precursor cells of the thymic lymphocytes.
Bone Marrow
- common lymphoid progenitor
HSC
- common myeloid progenitor
HSC
– produced in the BM then undergo further maturation to a B cell (either released to the circulation or proceeds to SLO)
B cell progenitor
– produced in the BM then proceeds to the thymus for further maturation
T cell progenitor
- Center for antigen-independent lymphopoiesis (production of lymphocytes)
Bone Marrow
o Without the stimulus of an antigen
Bone Marrow
o Maturation does not end as B cells and T cells
Bone Marrow
= Plasma cell (can produce
Abs)
B cell + Ag
= memory B cell (remembers Ag encounter)
T cell + Ag
o Produce large numbers of B cells, each with unique
antigen receptors (antibodies) such that, overall, there is sufficient B cells diversity to recognize millions of microbial antigens in the environment.
Bone Marrow
- Same to the concept of Ab-diversity by Paul Ehrlich (Side Chain Theory)
Bone Marrow
- An Ag looks for a particular cell with a specific receptor to become an Ab
Bone Marrow
- To avoid autoimmunity (attacking of own cells due to overreactivity of B cells)
Eliminate B cells with antigen receptors having high affinity for self-molecules.
61-89% = (?)
T cells (Most abundant)
10-20% = (?)
B cells
- Primarily involved in adaptive/specific
immunity
T cells & B cells
22% =(?)
NK cells
- Neither B or T cells
NK cells
- Large Granular: Lymphocytes
NK cells
- Primarily involved in innate/natural
immunity
NK cells
– produced in the BM (+ T cell progenitor: thymus)
Thymocytes
– produced, matures and develops in the BM
B cells
– matures and develops in the thymus
T cells
- Site of T-cell development and maturation
Thymus
- Rearrangement of gene segments that encode T cell receptor
Thymus
- Flat bilobed organ above the heart
Thymus
- Each Lobe surrounded by a capsule and divided into lobules.
Thymus
Thymus
- Each lobule:
o Outer cortex
o Inner medulla
(?) : densely packed with immature T cells: thymocytes
Outer cortex
(?) : sparsely populated with thymocytes
Inner medulla
Function example:
o Ag enters the wound → trapped in the axillary lymph
nodes (kulani); filters the lymph
Lymph Nodes
- lined with macrophages, creating an ideal location for phagocytosis
Subcapsular sinus
Blast transformation – B cells become plasma cells that are capable of producing Ab
Germinal center
– B cells become plasma cells that are capable of producing Ab
Blast transformation
Cells: Macrophages, most of B cells, follicular dendritic cells
Cortex (outermost layer)
- Contains Naïve B cells (resting B cells)
Primary Follicles
o Has not encountered an Ag
Primary Follicles
- Consist of antigen-stimulated B cells
Secondary Follicles
- Has encountered an Ag
Secondary Follicles
The interior of a secondary follicle is known as the (?)
germinal center
Cells: Most T cells
Paracortex
- Space between cortex/follicles and medulla
Paracortex
- T lymphocytes are mainly localized in the (?).
paracortex
T lymphocytes are in close proximity to antigen-presenting cells called (?).
interdigitating cells
Cells: mostly macrophages, numerous plasma cells
Inner Medulla
The (?) is less densely populated but contains some T cells (in addition to B cells), macrophages, and numerous plasma cells.
medulla
Particulate antigens are removed as the fluid travels across the node from cortex to medulla.
Inner Medulla
The transit time through a lymph node is approximately 18 hours.
Inner Medulla
- If contact with antigen takes place, lymphocyte traffic shuts down due to the proliferation of activated cells.
Inner Medulla
- Accumulation of lymphocytes and other cells causes the lymph nodes to become enlarged, a condition known as (?) .
lymphadenopathy
- Recirculation of expanded numbers of lymphocytes then occurs
Inner Medulla
- Largest secondary lymphoid organ
Spleen
- It is located in the upper-left quadrant of the abdomen
Spleen
(?) : removal of the spleen
Splenectomy
o Increases risk of infection with encapsulated bacteria and severe malaria
Splenectomy
(?) :intraerythrocyticparasite
Plasmodium
Cells: Platelets, RBCs, WBCs
Red Pulp
- Responsible for apoptosis or programmed cell death
Red Pulp
Cells: WBCs
White Pulp
- Also known as the lymphoid tissue
White Pulp
- contains T cells
Periarteriolar Lymphoid Sheath (PALS)
- contains Naïve B cells (resting B cells)
Primary Follicles
- contains dendritic cells (best Ag presenting cells; traps antigen)
Marginal Zone
- Nasal
NALT
– lines the throat and nasal passages
Nasal
- Tonsils
NALT
- Gut
GALT
- Contains the Peyer’s patches
GALT
Liver
GALT
– specialized
epithelium and contains antigen presenting cells and
intraepithelial lymphocytes.
Peyer’s patches
- Bronchus
BALT
- Contains lymphoid aggregates and follicles along
main bronchi
BALT
Secondary lymphoid organs
Appendix
o Concentrate of lymphoid tissue
Appendix
o Produces IgA
Appendix
(?) : important in trapping Ags that enters the GIT
lymphoid tissue
(?) : helps in regulating the density and quality of the normal flora
IgA
- Almost the same as BALT
Cutaneous Associated Lymphoid Tissue (CALT)
- Found in the skin or epidermis
Cutaneous Associated Lymphoid Tissue (CALT)
- Most of these are T cells, which are uniquely positioned to
combat any antigens that enter through the skin.
Cutaneous Associated Lymphoid Tissue (CALT)
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