lymphoid system

LYMPHATIC SYSTEM

Primary (central organs)Secondary (peripheral organs)

PRIMARY LYMPHOID ORGANS(BONE MARROW & THYMUS)

SECONDARY LYMPHOID TISSUE(SPLEEN, LYMPH NODE & MALT)

LYMPHOID TISSUE(RETICULAR FIBRES & CELLS)

Lymph Node Groups

Regions of lymph node

LYMPH FLOW

FILTER OF LYMPH

Regions of lymph node

High Endothelial Venules (HEV)

Lymph node medullaMedullary cordsMedullary sinuses

Thymus (thyme leaf)

CORTEX & MEDULLA

Thymic cortex contains

Extensive population of T lymphoblasts ( Thymocytes)
Macrophages
Thymic epithelial cells (TECs) that have certain features of both epithelial and reticular cells.

THYMUS – EPITHELIAL RETICULAR CELLS

Joined by desmosomes
Form stroma (cytoreticulum)
Produce factors for T cell differentiation (thymopoietin, thymosin)
Blood-thymus barrier – prevents most circulating antigens to enter into cortex




TEC

Thymic Medulla

More lightly stained
contains fewer & larger, more mature lymphocytes

Medullary TECs form the following:

A second layer of the boundary between cortex and medulla.
A cytoreticulum
Large aggregates of TECs, sometimes concentrically arranged, called Hassall corpuscles or (thymic corpuscles) are unique to the medulla.

Hassall Corpuscles

MALT (70% OF LYMPHOID TISSUE) BALT GALT

TONSILS
• Palatine
• Lingual
• pharyngeal

PEYER’S PATCHES

MALT of Appendix

SPLEEN (FILTER OF BLOOD)

Spleen

CAPSULE

TRABECULAE
WHITE PULP
RED PULP
Spleen(Stroma)

Parenchyma (White & Red pulp)

WHITE PULP1-PALS 2-LYMPHOID FOLLICLE

RED PULP OF SPLEEN1- SINUSOID2- CORDS OF BILROTH

Blood flow in spleen

BLOOD FLOW IN SPLEEN1- CLOSED CIRCULATION2- OPEN CIRCULATION

Closed

Open

Splenic sinusoid

Erythrocyte Removed by Splenic Macrophage

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