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
Describe the cortex & medulla of the lymph node.
Cortex:
-lymphoid follicles
-paracortex
-high endothelial blood vessels
Medulla:
-medullary cords
-lymphocytes
-macrophages
-plasma cells
>medullary sinus
—macrophages
—reticular cells
Describe primary VS secondary lymphoid follicles.
Primary -> ANTIGEN -> secondary
Describe high endothelial venules (diapedesis).
-in paracortex
-cuboidal
-allow extravasation of lymphocytes
Medulla with sinus & cords (picture).
S = sinus
C = cords
Close up of sinus with macrophages.
Labeled lymph node picture.
Describe porcine lymph nodes.
-backwards = central lymphoid follicles
-afferent lymphatics (V) enter though hilus (H) & follow trabeculae (t) to the central lymphatic nodules (n)
-peripheral sinus/cord (L)
Describe hemal nodes.
-alongside bloodstream
-in ruminants = dark colored
-erthryocytes in sinus
-no lymphatic supply
-near spleen, kidney, lg blood vessels (ventral side of vertebrae)
-function like the spleen
Describe hemolymph nodes.
-in pigs
-RBCs in sinus due to hemorrhage
What are the functions of the spleen?
- Filter blood
-old RBCs & WBCs
-recover & store iron
-macrophage of red pulp = contain RBCs & hemosiderin - Sample/remove antigen from blood via phagocytosis
- Immune response against blood borne antigens (B & T)
- Hematopoiesis in fetus
- Store RBCs in horse, cat, dog
-more smooth muscle & elastic in capsule = contraction & release of RBCs into blood
-defense spleen = less smooth muscle in capsule (human & rabbit)
-ruminants & pigs = intermediate
Describe the splenic structure.
-outer capsule = dense CT with smooth muscle & elastic fiber
>gives rise to trabeculae = collagen, elastic fibers, smooth muscle
>each trabecular contain central artery or vein
Describe white pulp VS red pulp.
WHITE
-central arterioles
-periarterial lymphoid sheath - PALS (T)
-follicles (B)
RED
-venous sinus (RBCs)
-reticular fiber & cells
-macrophage, lymphocyte, plasma cells
-PAMS
Describe splenic blood flow.
-via central artery & branches w periarterial lymphatic sheath (PALS) = white pulp
-branches = penicillary arteries
-end in blind ending capillaries w periarteriolar macrophage (PAMS) in red pulp
-capillaries drain into red pulp parenchyma & then venous sinuses in an open circulation
-capillaries drain into venous sinus = closed circulation
-sinus well developed in dogs (cats, horse, ruminant = non sinusal spleen)
Describe MALT.
-GALT
-BALT
-tonsil
-ocular
-urogenital
-mammary
BALT picture.
(Lymphoid tissue)
GALT picture.
Light purple areas
-peyers patch
-aggregated lymphatic nodules
EX. Anti mesenteric side of ileum
Peyers patch picture.
Describe micro fold cells.
-peyers patch are covered by a columnar layer of micro fold cells (M cells)
-specialized epithelial cells
-pinocytose GI contents & secrete content on the lymphocytes & macrophages of peyers patch
Describe lacteals.
-blind ended lymph capillaries in small intestine villi
Describe lymphatic vessels.
-blind ended tubes
-endothelial lining
-absorb fluid from interstitum & pass it back to blood
-inflammatory cell & antigen movement from peripheral tissue
-lymph flow in one direction = from periphery to heart
-surrounding tissue compress/expand vessel
-one way valve = prevent backflow
-anchoring fibrils = pull endothelial cells apart & fluid enters vessel
Picture of lymphatic vessel, arteriole, venule.
- Left = lymphatic vessel with a valve
-no erythrocytes - Middle = arteriole
-1-3 layers of circular sm muscle - Right = venule
-no sm muscle in wall
Describe function of lymphatics.
-deliver lymph to lymph nodes
-drain tissue fluid through fenestrated capillaries
Describe palatine tonsil.
-collection of lymphatic nodules present in tunica muscle of pharynx
-may/may not have crypts
-no afferent lymphatics, samples lumen
-efferent lymphatics drain tonsils
-local antibody production
