Lymphoid System Flashcards
What are the functions of the lymphoid system?
- Phagocytosis
-macrophages - Production of immunological cells
-APCs (dendritic, macrophage, B cells)
-B & T lymphocytes
Describe primary lymphoid organs.
produce lymphocytes
1. Bone marrow = B cells mature
2. Cloacal bursa/bursa of fabricius (birds only) = B cells mature
3. Thymus = T cells mature
lymphocytes made in bone marrow mature in bone marrow, bursa, or thymus
Describe secondary lymphoid organs.
lymphocytes migrate to secondary lymphoid organs for activation & presentation of antigen
1. Lymph nodes (not in birds)
-filter antigens before returning it to blood
2. Spleen
-filters antigens from blood
3. MALT
-local immune response
4. Tonsils
What are the functions of primary lymphatic organs?
- Where T & B cells originate
- Access by antigen is controlled by barriers
- Apoptotic elimination of self reactive cells
- Released to circulation to sites where antigens are encountered (secondary lymphoid)
Describe bone marrow.
-source of pluripotent stem cells (B & T)
-stromal cells
>release factors that aid in cell differentiation
>macrophages
Describe the cloacal bursa.
‘Bursa of fabricus’
1. Dorsal wall of cloaca
2. Function is equivalent to bone marrow in mammals (B cell differentiation)
Describe the thymus.
- Located in mediastinum (cranial to heart)
- Epithelial reticulum & lymphocytes
- Lymphocytic stem cells migrate from bone marrow
- Fill spaces between reticular epithelial cells
- Develop into T cells which migrate to secondary lymphoid organs & MALT
Describe the thymus cortex.
- Stains darker = high # of lymphocytes
- Positive selection
-good developing lymphocytes (thymocytes) - Tingible body macrophages near medulla
-phagocytose dead bad T cells
Describe the thymus medulla.
- Epithelial reticular cells
- Negative selection
-bad lymphocytes (auto reactive)
-phagocytosed by tingible body macrophages - Medullary reticular epithelial cells form thymic/hassalls corpuscles
-lg central calcified/degen cells surrounded by concentric circles of keratinized cells
Canine thymus picture.
Cortex = darker
Medulla = lighter with Hassalls corpuscles (pink circles)
Canine thymus medulla picture.
Describe blood vessels in thymus.
- Arteries enter via corticomedullary junction within CT septa
- Divide into arterioles within septa
- Branch into capillary network in cortex ‘cortical capillaries’
- Cortical capillaries = blood thymus barrier
-continuous endothelium
-perivascular CT
-sheath of epithelial reticular cell processes
Describe thymic involution.
- Thymus active in young animals & involutes after sexual maturity
- Gradual depletion of lymphocytes
- Replacement by adipocytes
Describe the lymph node.
- Capsule
-dense, irregular CT
-trabeculae - Cortex
-subcapsular sinus
-lymphoid follicles (B cell rich)
-paracortex (T cell rich)
-high endothelial blood vessels - Medulla
-medullary cords
-medullary sinus - Stroma
-reticular cells & fibers
Describe the flow of the lymph node.
Afferent lymphatic vessel -> subcapsular sinus -> cortical (trabecular) sinus -> medullary sinus -> efferent lymphatic vessel
CORTEX:
-lymphoid follicles & lymphocytes
MEDULLA:
-macrophages, lymphocytes, plasma cells