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BY SUDIR VIGNESHWAR K.N
1ST YEAR M.B.B.S
Lymph Node

Lymph Nodes in 5 main topics
▪ General Features
▪ Microscopic Features
▪ Lymph and Blood Circulation
▪ Functions
▪ Clinical aspects

General Features
 Secondary lymphoid organs
 Check-posts of Lymphatic vessels
 Composed of Lymphatic Tissue
 Oval shaped-organ or bean-shaped organ
 1 cm in normal dimensions
 Less than 100 mg in weight
 Concentrated in the Cervical, Axillary, Abdominal and
Inguinal regions
 Each with a specific area of drainage

Lymph Node - A Histologcal Overview

Generalized graphical structure

Microscopic Features {Histology}
Histologically, a lymph node can be broadly classified into 2 main regions:
CORTEX
MEDULLA

CORTEX
The outer zone that consists of densely packed by T- lymphocytes
Highly darkly stained region
Several rounded areas called as Lymphatic nodules or follicles are seen
-each nodule has a paler staining Germinal Centre surrounded by a zone
of densely packed B-lymhocytes.
Enclosed by the Capsule with mainly composed of collagen fibres, some elastic fibres
and some smooth muscles. Below it is the Subcapsular Sinus.
Trabeculae or septa extend into the node from the capsule, dividing it into lobules.
Remaining spaces occupied by the reticular fibres forming a reticular framework in the
cortex. Reticular cells are associated called as fibroblasts.
Hilum is the part of the capsule where blood vessels enter and exit the node

MEDULLA
 Surrounded by the Cortex.
 Lighter staining zone.
 Lymphocytes are fewer than the Cortex.
 The lymphocytes present are arranged in the form of anastomosing cords
called Medullary Cords.
 Several blood vessels can be seen.

Lymph and Blood Circulation
Lymphatic Circulation
 Apart from the lymphocytes, the reticular fibres and the reticular cells, the
spaces present are modified to form lymph channels through which Lymph
circulates.
 The sinuses are lined by endothelium that permit lymphocyte and
macrophage movement.
1. Lymph enters via the Afferent Lymphatic channels through the convex
surface piercing the capsule entering the subscapular sinus.
2. From this sinus, a number of radial cortical sinuses or trabeculae sinuses
runs to the medulla.
3. When these sinuses reach the medulla, they join to form larger Medullary
Sinuses.
4. These medullary sinuses in turn join to form one or more Efferent Lymph

Blood circulation
1. Afferent arteries enter the lymph node at the hilum.
2. They pass through the medulla to reach the cortex where they end in
arterioles and capillaries.
3. These capillaries are arranged in loops that drain into venules.
4. Post -capillary venules in lymph nodes are unusually lined by Cuboidal
epithelium in the place of simple squamous epithelium. These are
therefore called as High Endothelial Venules. This special modification is to
enable the passage of lymphocytes between the bloodstream and the
surrounding tissue due to specialised Tissue Receptors.

FUNCTIONS
1. Centres of Lymphocyte production, where both the B–
Lymphocytes and T – Lymphocytes are produced here
from pre-existing lymphocytes. These pass into the
lymph and into the blood stream.
2. Bacteria and particulate matter are filtered from the
lymph by the Macrophages via phagocytosis. These are
then categorised as Antigens which are presented to
the Lymphocytes stimulating their proliferation. THUS,
they act as secondary lymphoid organs.
Thus , they play a very crucial role in Immunity.

CLINICAL ASPECTS
1. As they play a key role in immunity, they also tend to get infected
and inflamed. This condition is called as Lymphadenitis.
2. Metastasis {Cancerous cells} spread from the localised regions to
areas which they connect. Pathological examination of the lymph
nodes that are inflamed, can give info about the origin of the
cancer.
3. When the source of cancer is in the lymph node, then it is called
as Lymphoma as it is a cancer of the Lymphoid Tissue
In the above three severe cases, lymph removal or
Lymphadenectomy is performed.

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Lymph Node - A Histologcal Overview

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