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Histology

ofthe

LymphaticSystem

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Lymphatic System

Consists of lymphatic organs,

tissues, cells and lymph vessels

It is a part of immune system

Organs include:Tonsils

Lymph nodes

ThymusSpleen

Tissues in the form of MALT

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Tonsils

They belong to MALT but considered organsbecause they are partially encapsulated

Tonsils are covered by epithelium

They include:1. Palatine tonsils

2. Pharyngeal tonsils

3. Lingual tonsils

4. Tubal tonsils

Waldrys ring

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Palatine Tonsils

A pair of them located in the oropahrynx

Covered by stratified squamous epthelium

10-20 crypts in each one

A Sheet of lymphatic nodules and freelymphocytes below the mucosa

A dense capsule separates it from the

subjacent tissues

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Pharyngeal Tonsil

One in the oropharynx covered bypseudostratified columnar epithelium

Form a thin sheet of lymphoid nodules and

diffuse lymphocytes No crypts

Very thin capsule

Adenoid

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Lingual Tonsils

They are multiple small ones at the base ofthe tongue

Covered by stratified squamous epithelium

One crypt for each tonsil

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Lymph Node

Shape

Structure

Cells

Cortex

Medulla

Lymph circulation

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Thymus Gland

Location

Development and Growth

Structure

1. Capsule and lobules

2. Cortex (T-Cell precursor, Reticuoepithelialcells, Macrophages)

3. Medulla ( T-Cells, Hassall corpuscles Vascularization

Lymphatic

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T-Cells Differentiation

It is the site of terminal differentiation andselection of T-lymphocytes

No receptors on the cell surface of precursor

cells They divide by mitosis and presented to self

antigens bound to class I and II MHC on thesurface of epithelial cells, macrophages anddendritic cells

Positive and negative selections

Mature T-Cells with receptors leave the thymus

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The Spleen

Largest lymphoid organ

Contains large number macrophages

It is a blood filter

Structure: capsule, trabeculae, splenic pulp

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Splenic pulp

Spleen composed of a network of reticulartissue with reticular cells, lymphocytes, otherblood cells, macrophages and APCs

White pulp Red pulp

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White Pulp

Blood supply

Periarterial lymphatic sheath (PALS)

Lymphoid nodule

Marginal zine

Penicillar arteries

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Red Pulp

Splenic cords supported by reticular fibersand contain T-Cells , B-Cells, macrophages,plasma cells, and many blood cells.

Splenic sinusoids Closed circulation

Open circulation

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