Lymph node and spleen under the microscope !
- Organ
The lymph node filters lymph and the spleen filters blood. Under the microscope the node has a cortex and medulla; the spleen has white and red pulp.
Updated 2026-11-01
See it in 3D: Spleen · Neck lymph nodes
What it is
The lymph node and the spleen are secondary lymphoid organs built on a mesh of reticular fibres, but they filter different fluids and so look different. The node receives lymph through afferent vessels and passes it along sinuses between a cortex with follicles and a medulla with cords; the spleen receives no lymph and organizes its tissue around arteries. This page covers the microscopic structure; immune function is covered in the Immunology section.
Structure
- Node: a connective tissue capsule with trabeculae; afferent vessels enter on the convex side and the efferent leaves at the hilum, with the artery and vein.
- Node, path of lymph: subcapsular sinus → trabecular (cortical) sinuses → medullary sinuses → efferent vessel.
- Node, outer cortex: B-cell follicles; primary follicles have no germinal centre, secondary follicles have a pale germinal centre ringed by a dark mantle zone.
- Node, paracortex: a T-cell zone with high endothelial venules, where lymphocytes leave the blood to enter the node.
- Node, medulla: medullary cords with plasma cells and macrophages, separated by medullary sinuses.
- Spleen: capsule and trabeculae, no cortex or medulla and no afferent lymphatics.
- Spleen, white pulp: the periarteriolar lymphoid sheath (T cells) around the central artery and B-cell follicles; the marginal zone surrounds it.
- Spleen, red pulp: splenic cords (of Billroth) and venous sinusoids lined by elongated «barrel-stave» endothelium on a discontinuous basal lamina, which red cells must squeeze through.
How to tell the lymphoid organs apart under the microscope
| Organ | Layout | Giveaway feature | Epithelium and lymphatics |
|---|---|---|---|
| Lymph node | Complete capsule; cortex with follicles, paracortex and medulla with cords | Subcapsular sinus under the capsule and high endothelial venules in the paracortex | No epithelium; afferent lymphatics on the convex side, efferent at the hilum |
| Spleen | Capsule with trabeculae; scattered white pulp in abundant red pulp | Follicles with an off-centre central artery and lots of blood around them | No epithelium; no afferent lymphatics, efferent only |
| Thymus | Lobules with a dark cortex and a pale medulla | Hassall's corpuscles in the medulla; no follicles or germinal centres | Mesh of thymic epithelial cells; no afferent lymphatics |
| Palatine tonsil | No complete capsule; follicles with germinal centres under an epithelium | Deep crypts lined by non-keratinized stratified squamous epithelium | Surface epithelium; no afferent lymphatics, efferent only |
Markers
- Silver stain: reticular fibres (type III collagen)
- CD20: B follicles
- CD3: paracortex and periarteriolar sheath
- CD138: medullary plasma cells
Clinical notes
- Viral infections tend to expand the paracortex; antibody responses expand the follicles and their germinal centres.
- In sickle cell disease, repeated infarcts leave a small, scarred spleen (autosplenectomy).
- Traumatic rupture of the spleen bleeds heavily because the red pulp is a large blood reservoir.
Test yourself
Think of the answer, then tap the question to see it.
Which zone of the lymph node is rich in T cells?
The paracortex, between the cortical follicles and the medulla.
Why does the spleen have no subcapsular sinus?
It receives no lymph through afferent vessels: it filters blood, not lymph.
What surrounds the central artery in the splenic white pulp?
The periarteriolar lymphoid sheath, made mostly of T cells.
What feature of splenic sinusoids forces red cells to deform?
Elongated endothelial cells with slits between them and a discontinuous, ring-like basal lamina.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Thymus and tonsils under the microscope
- Lymphatic vessels
- Blood cells on a smear: erythrocytes, leukocytes, platelets
- Hematopoiesis and bone marrow
- Connective tissue proper: cells and fibres
Related conditions
Microorganisms
Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.
Sources: 21.1 Anatomy of the Lymphatic and Immune Systems (OpenStax, Anatomy and Physiology 2e, 2022); Lymph Nodes (NCI SEER Training Modules, 2026); Spleen (NCI SEER Training Modules, 2026).
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Representative model, for educational purposes only.