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


Topic Completed: 1 November 2013

Minor changes: 29 September 2020

Copyright: 2003-2020, PathologyOutlines.com, Inc.

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

Nat Pernick, M.D.
Page views in 2019: 7,173
Page views in 2020 to date: 5,546
Cite this page: Pernick N. Anatomy-lymph nodes. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/lymphnodesnormalanatomy.html. 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
Terminology
  • 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
Drawings

Images hosted on other servers:
Missing Image

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)
Back to top
Image 01 Image 02