Lymphatic Tissues Flashcards
Week 7
Diffuse Lymphoid
- Strategically located tissue beneath the surface of most organs
- Most prominent in the gut and respiratory system
F: Site of initial immune response - travel to region lymph nodes - proliferation and differentiation
- most specialized beneath the intestine: lamina appropria
Diffuse lymphoid tissue (lamina Popria)
- Beneath mucous membrane of the following tracts:
- alimentary, respiratory, genitourinary
- Loose connective tisue
- fibroblasts, scattered smooth muscle
- Lymphocytes, eosinophils, plasma cells
Lymph Nodules; Mucosa-associated lymphoid tissue (MALT)
GALT: gut
BALT: bronchus (respiratory)
- Germinal center: located in the central region of the nodule
- lymphocytes + dendritic cells – becomes enlarged during immune response
- Mantle zone: small lymphocytes – not proliferating
GALT lymph nodules
- Germinal center paler
- immature cells, euchromatic nuclei, mitotic figures present
- Mantle Zone
- heterochromatic nuclei
Tonsils
Lymph nodules
- Whole pharynx is lined by stratified squamous
Palantine tonsils; Tonsillar crypts
- Aggregation of lymph nodules found in specific locations
- Tonsils: covered by a stratified squamous epi on top of a basement membrane
- Multiple nodules
- Drain through efferent lymphatic vessels to the circulation
Peyer’s patch – ileum (end of SI that connects to LI) of small intestine
- Aggregation of lymph nodules found in the distal end of the small intestine
- multiple nodules with T and B lymphocytes
- shaped like a C, distinguishable from appendix
- appendix goes all the way around
Appendicitis
- Occurs when the appendix becomes blocked and bacteria infect the wall and lumen of the appendix
- Inflammatory cells infiltrate - primarily neutrophils
- marginalization - leaving blood stream (neutrophils line up around veins and arteries)
- Edema: fluid build up between smooth muscle cells
- enlarged appendix
Lymphatic and Blood Systems
Run near each other because of dynamic interplay
Lymph Nodes
- Immature dendritic cells reside in peripheral tissues
- Dendritic cells migrate via lymphatic vessels to regional lymph nodes
- Mature dendritic cells activate naive T cells in lymphoid organs such as lymph nodes
Lymph vessels
- Pick up and return excess filtered fluid
- Defense against disease
- Lymph nodes have phagocytes which destroy bacteria-filtered from interstitial fluid
- Defense against disease
- Transport of absorbed fat
- Return on filtered protein
Lymphatic vessels and lymph nodes
Lymphocytes circulate the body
- enter from the tissue through afferent lymphatic
- enter from blood through high endothelial venules
- Leave through efferent vessel
Lymphatic histology
- simple squamous with basement membrane
- vales prevent backflow
- smooth muscle for propulsion
- peristalsis
Lymph Node Structure
- Capsule: DCT
- Trabeculae: extends into node (DCT framework)
- Reticular tissue: skeleton of the organ
- reticular cells and fibers containing many cell types
- hilium: opening
- capsule: outside
- medulla: inside
- cortex:
Reticular cell
- Fibroblast-like cell: secrete collagen and reticular fibers
- secrete factors that attract T+B lymphocytes and dendritic cells
- chemokines
Dendritic cells and macrophages
- Antigen presenting cells
- Phagocytose foreign antigens and display on either MHC I/II to T cells
- Dendritic cell: large SA and higher expression of MHC II
Parenchyma of the lymph node
Cortex:
- superficial: contains lymph nodules
- germinal centers: proliferating B cells
- Deep: free of nodules and contains mostly T cells
- AKA thymus dependent cortex
Medulla: contains T+B cells and macrophages
- draings into medullary sinus -> efferent lymphatic
Follicular Dendritic cells
- Interact with B cells in the germinal center
- not antigen-presenting cells
- bind to antibody-antigen complexes using specialized receptors
Deep Cortex
- Mostly T cells and contains high endothelial venules (HEVs)
- HEV: site of entrance of 90% of circulating lymphocytes
- 10% enter through afferent lymphatics
- HEV: site of entrance of 90% of circulating lymphocytes
- lined by simple cuboidal to columnar epithelium
- macrophages extend processes into the lumen
- antigen sampling
- lymphocytes exit via diapedysis
Medulla and Hilum
- Contains medullary sinuses, draining lymph
- converge onto the efferent lymphatics at the hilum
- vessels lined by simple squamous epi with valves are present
Arthracosis of the lymph node
- Carbon build-up in lymph nodes of the pulmonary region
- No major affect on nodes but the lungs are severely damages
Thymus
- located anterior to the heart
- fully formed and functional at birth and persists until puberty
- degenerates and filled with CT in adults
- site of T-cell education
- Looks similar to lymph nodes at low mag
- all T-cells
- Capsule: DCT
- Trabeculae: sep the thymus into lobules
- Cortex: basophilic because of tightly packed heterochromatic T cells
- Medulla: lightly stained because of larger T cells with euchromatic nuclei
Thymus vs Lymph nodes
Distinguishing features:
- epithelioreticular cells (6 types): 1-3 found in cortex and 4-6 found in medulla
- thymic corpuscles: type 6 epithelioreticular cells
Thymus epithelioreticular cell of the cortex
Type 1: form boundary between cortex and capsule - anchored to one another through a series of adhesion molecules
Type 2: form the extracellular meshwork of the cortex
- stellate in shape - express MHC I/II - T cell education
Type 3: Form the boundary between cortex and medulla
- form a sheet: also express MHC I/II
Type 4: together with type III they form the barrier between cortex and medulla
Type 5: Form Form meshwork of the medulla
Type 6: make up the thymic corpuscles - T cell education
