function: keeping the own antigen environment, eliminating theforeign substances/antigenslymphoid tissue lymphoid organs:

primary (red bone marrow, thymus): development oflymphocytessecondrary(lymph node, spleen, tonsils, Peyer s patches, appendix): mature lymphocytes can be found here

basic tissue: lymphoreticular- reticular connective tissue, reticular fibers, reticular cells; thymus: epithelial reticular cellsmain cell types: lymphocytes, macrophages, dendritic cells, endothelial cells

unit of the lymphoid tissueround, oval structure, many lymphocytesprimary: dark, ruond, little lymphocytes, intrauterinesecondary: bigger (200-400 m), originating from the primary, in the middle: light area- germinal center (centroblasts, centrocytes, FDC), peripheral: cap zone

structure of a lymphoid follicle

germinal center

cap zone

along the course of lymphatic vesselsbean-shaped, encapsulated organsafferent lymphatic vessels efferent lymphatic vesselsconnective tissue capsule trabeculae hilusamong trabeculae: reticular connective tissuecortex: lymphoid follicles (B dep. zone)paracortex: no lymphoid nodules (T dep. zone)medulla: medullary lymphoid sinuses, medullary cordsmarginal sinus intermediate sinus medullarysinus efferent lymphatic vessels (hilus)

24. lymph node (HE)

cortex

medulla

lymphoid follicle

paracortex

trabecula

epithelial, lymphatic, adipose form during life2 lobes+ capsule lobulescortex: peripheral, darker, thymocytes, macrophages, epithelial reticulum cellsmedulla: central, lighter, more epithelial reticulumcells, Hassal-corpuscules (eosinophil,concentricallyarranged,flattened epithelial cells with keratohyalingranules), neuroendocrine cells, myoid (Hammar) cellsno lymph folliclesfunction: mature and differentiation of T lymphocytesblood-thymus barrier: pericytes, capillary basal lamina, basal lamina of the epithelial reticular cell, cells of theendothelium, epithelial reticular cells

25. Thymus,HE

cortex

medulla

interlobular connective tissue

25. Thymus,HE

medulla

Hassal scorpuscles

intraperitoneal organconnective tissue capsule trabeculae parenchyma (pulp)red pulp (80%), white pulp (20%)reticular connective tissue, reticulum cells, reticular fibersred pulp: Billroth s cords, sinuseswhite pulp: PALS (A. centralis- T dep. zone), lymhoid folliclesMalpighi (B dependent), marginal zoneopen and closed circulation

26. Spleen, HE

capsules

trabecules

red pulp

white pulp

26. Spleen, HE

PALS

lymhoid tissue in the mucosaWaldeyer s lymphatic ring:

pharyngeal tonsilspalatine tonsilstubal tonsilslingual tonsils

tonsillary epithelium+ lymhoid tissue (lymphoreticular connective tissue)tubal and pharyngeal t.: ciliated pseudostratified epithelium with goblet cellslingual and palatine t.: stratified squamos nonkeratinized epithelium

epithelium crypts: lingual t.- shallow, wide// palatine t.: narrow, deeplingual t.: seromucous glands crypts, strited muscle fibersfollicles (B dep.), interfollicular area (T dep.)epithelium is often infiltrated with lymphocytes

27. Palatine tonsil, HE

crypttonsillaryepithelium

lymphoid follicles

lymphoid follicle

crypt

27. Palatine tonsil, HE

stratified squamousnonkeratinizedepithelium

28. Lingual tonsil, HE

tonsillaryepithelium

lymphoid tissue

seromucousglands

crypt

28. Lingual tonsil, HE

seromucous glandsstratified muscle fibers