The document outlines the structure and function of lymph nodes as part of the immune system. It describes the gross and microscopic features of lymph nodes, detailing the organization into regions such as the cortex, paracortex, and medulla, as well as the types of cells present. Key functional aspects include the roles of B-cells, T-cells, and the process of lymph filtration and immune response in the lymph nodes.

1. GROSS AND MICROSCOPIC
FEATURES OF LYMPH NODE
DR SURAJ PD SAH

2. IMMUNE SYSTEM
 Protects the organism against invading pathogens or
antigens ( bacteria , parasites and viruses).
 The lymphoid system includes all cells, tissues ,and organs
that contain aggregates of immune cells called
lymphocytes.
 Lymphoid organs are divided into two major categories –
 1. Primary lymphoid organs – Bone marrow and thymus.
 2. Secondary lymphoid organs - Lymph node, spleen,
tonsils, MALT and Peyer patches.

3. LYMPH NODE
GROSS FEATURES:
• Lymph nodes are bean-shaped structures about 0.1 – 2.5
cm in length.
• The node is enclosed in a capsule and has an indentation
on one surface known as the hilum.
• The hilum is the point at which arteries carrying nutrients
and lymphocytes enter the lymph node and veins leave it.

4. • Afferent lymphatic vessels enter the lymph
node through the capsule peripherally
and efferent lymphatic vessels leave the
node via the hilum.
• The Afferent takes lymph from peripheral
sites to the node, while the efferent takes
processed lymph from the nodes back to
the circulation.

6. MICROSCOPIC FEATURES
A horizontal section through the lymph node reveals that
the dense connective tissue capsule (composed of elastin,
collagen and fibroblasts)
Additionally, there is a pericapsular adipose tissue layer that
surrounds the connective tissue capsule. This layer contains
arterioles and venules that supply the lymph node.
Capsule projects into lymph node interiorly is called
trabeculae; giving the lymph node a lobular appearance,
 The lymph node is divided into an outer cortex and an inner
medulla.

8.  Histological staining of the node reveals that the
cortex stains darker than the medulla with
hematoxylin and eosin (H&E) due to its higher cell
content.
 Beneath the fibrous capsule is the subcapsular sinus.
subcapsular sinus communicates with the cortical
sinuses that travel parallel to the capsular
trabeculation. They carry lymph to the medullary sinus
 The medullary sinuses drain the lymph coming from the
cortical sinuses to the efferent lymphatic vessel via the
hilum.

9. Cortex
 The cortex contains spherical collections of lymphocytes is
called lymphoid nodules or lymphoid follicles. It primarily
contain B-cells,specialized follicular dendritic cells and some
supporting T-cells.
 These can either be primary or secondary follicles
depending on their cellular population.
 Primary lymphoid follicles contain small, dormant
lymphocytes.
 while secondary lymphoid follicles contain a lighter/pale
staining area of active lymphocyte proliferation known as
a germinal centre.

11. Paracortex
Deep to the cortical layer and superficial to the medulla is
the Paracortex. This region contains mostly T-cells of the CD4
(cluster of differentiation) and CD8 subsets.
 Migrating dendritic cell lines (such as Langerhans cells)
found in this area present processed antigen to the T-cells.
Medulla
The cords also contain plasma cells, small lymphocytes and
macrophages.
 The lymphocytes of the medulla are less organized and
form irregular medullary cords.

12. • The germinal centre supports affinity maturation (high affinity
antibody production) of B-cells.
• It is subdivided into a dark zone, light zone and a mantle zone. The
B-cells of the dark zone are known as centroblasts. They rapidly
replicate, resulting in hypermutation of their antibody molecules.
• Centroblasts migrate to the light zone, where they are referred to
as centrocytes.
• Here they compete for binding with the unprocessed antigens
presented on the surface of follicular dendritic cells.
• Those centrocytes that successfully bind to the follicular dendritic
cells will survive, while the others will die.
• Small, quiescent cells are peripherally marginalized due to the rapid
proliferation of the central cells. These cells form the mantle
zone of the germinal centre.

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