Periarteriolar lymphoid sheaths

Periarteriolar lymphoid sheaths (or periarterial lymphatic sheaths, or PALS) are a portion of the white pulp of the spleen. They are populated largely by T cells and surround central arteries within the spleen; the PALS T-cells are presented with blood borne antigens via myeloid dendritic cells.

(This is in contrast to the lymphoid portions of the white pulp, where B cells predominate.)

External links

Histology image: 07703loa – Histology Learning System at Boston University
Histology image: 62_06 at the University of Oklahoma Health Sciences Center
Diagram at okstate.edu
Diagram

Organs of the lymphatic system

Primary organs

Bone marrow	Hematopoietic stem cell

Thymus	Cortex Medulla Hassall's corpuscles

Secondary organs

Spleen	structural: Hilum Trabeculae Diaphragmatic surface of spleen Visceral surface of spleen Red pulp Cords of Billroth Marginal zone White pulp Periarteriolar lymphoid sheaths Germinal center blood flow: Trabecular arteries Trabecular veins

Tonsils	Palatine Lingual Pharyngeal Tubal Tonsillar crypts Waldeyer's tonsillar ring

Lymph nodes	lymph flow: Afferent lymph vessels Cortical sinuses Medullary sinuses Efferent lymph vessels T cells: High endothelial venules B cells: Primary follicle/Germinal center Mantle zone Marginal zone layers: Capsule/Trabeculae Subcapsular sinus Cortex Paracortex Medulla (Medullary cord) Hilum

MALT	GALT Peyer's patch Germinal center

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