Lymph nodes & spleen, nonlymphoid
Lymph nodes-general
Anatomy-lymph nodes

Topic Completed: 1 November 2013

Minor changes: 29 September 2020

Copyright: 2003-2020,, Inc.

PubMed Search: Lymph nodes [title] anatomy [title]

Nat Pernick, M.D.
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Cite this page: Pernick N. Anatomy-lymph nodes. website. Accessed October 20th, 2020.
Definition / general
  • A secondary lymphoid organ, where B and T cells proliferate in response to exogenous antigen; primary lymphoid organs are bone marrow and thymus
  • Other secondary lymphoid organs are spleen and Peyer patches
  • Tertiary lymphoid organs are tissues with few lymphocytes that recruit more when inflammation is present
  • Lymph nodes are organized to detect and inactivate foreign antigens present in lymph fluid that drains skin, GI tract and respiratory tract, the major organs in contact with the environment
  • Afferent lymph vessels:
    • Penetrate capsule, enter marginal sinus, communicate with intranodal sinuses, then become efferent vessels, which lack an endothelial lining
    • Intranodal vessels contain littoral cells or histiocytes with phagocytic properties
  • Capsule:
    • Thin fibrous connective tissue covering of lymph node
    • May be thicker at hilus
    • Connected to fibrous trabeculae which penetrate the node
    • Capsule may contain smooth muscle cells (Anat Rec 1975;183:517)
  • Cortex:
    • Subcapsular portion of node with largest number of follicles (primary or secondary)
  • Primary follicle:
    • Round aggregates of small, dark staining inactive (naïve) B lymphocytes, usually near the capsule, within a network of follicular dendritic cell processes
    • No germinal center present
  • Secondary follicle:
    • Arises from primary follicle that develops germinal centers (see below) due to antigenic stimulation of B cells and production of antibodies
    • Contains pale staining germinal center which may be polarized towards site of antigen entry
    • Surrounded by mantle zone and marginal zone lymphocytes
    • Germinal center:
      • Contains predominantly B lymphocytes (including centroblasts and centrocytes) and scattered follicular T helper cells and T regs
      • Also tingible body macrophages and follicular dendritic cells
    • Mantle zone:
      • Tightly packed small B lymphocytes of the primary follicles, pushed aside by the germinal centers
    • Marginal zone:
      • Less packed small B lymphocytes with more cytoplasm
      • Light zone on outer rim of mantle zone
      • Contains a mix of post-follicular memory B cells derived after stimulation of recirculating cells from T cell dependent antigen and naïve B cells
      • Often not well developed in lymph nodes
  • Paracortex:
    • Tissue between cortical follicles and medulla (see below)
    • Contains predominantly dark staining mature T cells, B immunoblasts, interdigitating dendritic cells, plasmacytoid dendritic cells, histiocytes, and high endothelial venules (postcapillary venules lined by plump endothelial cells that express leukocyte adhesion molecules and contain intraluminal lymphocytes)
    • Expands during cell mediated immunological reactions
    • Has coarse network of reticulin fibers
  • Medulla:
    • Portion of node closest to hilum
    • Contains the medullary cords, sinuses and vessels but minimal number of follicles
  • Medullary cords:
    • Found in hilar region between the sinuses, composed mostly of small B and T lymphocytes, plasmacytoid lymphocytes, plasmablasts and plasma cells
  • Sinuses:
    • Carry lymph from afferent to efferent lymphatics
    • Subcapsular sinus is below capsule and partially lined by endothelium
    • Becomes "medullary" as it approaches the hilum and is lined by macrophages
    • Also contains mast cells and plasma cells
  • Vessels:
    • Blood enters and leaves lymph node at hilus

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Lymph node structures

Gross description
  • Ovoid with gray-tan cut surface
Microscopic (histologic) description
  • At low power, lymph node structures are capsule, cortex and medulla, follicles, paracortex, sinuses
Microscopic (histologic) images

AFIP images

Normal lymph node

Primary follicle

Lymph node

Secondary follicle

Secondary follicle

Paracortical T zone

Interdigitating dendritic cells

Smooth muscle proliferation in lymph node hilum

Positive stains
Negative stains
  • bcl2 (not expressed in germinal center B lymphocytes)
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