LYMPHOID ORGANS. Dr. Iram Tassaduq

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2 LYMPHOID ORGANS Dr. Iram Tassaduq

3 COMPONENTS OF IMMUNE SYSTEM Lymphocytes Diffuse Lymphatic Tissue Lymphatic Nodules Lymph node Spleen Bone marrow Thymus

4 Functions of Immune System Has the ability to distinguish self from non-self Inactivates/destroys foreign substances Foreign molecule Molecules present in viruses, bacteria, parasites. Microorganisms and other cells (virusinfected cells, cancer cells, cells of transplanted organs)

5 ANTIGEN Any substance that can induce immune response Examples are foreign protein, foreign tissue, toxin, infectious organism or transformed tissue Antigens must be processed by cells of immune system before they can initiate a response

6 CELLS OF IMMUNE SYSTEM Lymphocytes 1. B Lymphocytes 2. T Lymphocytes Helper Cytotoxic Gamma/delta Natural killer cells

7 CELLS OF IMMUNE SYSTEM Monocytes Macrophages Neutrophils Basophils Eosinophils Reticular Dendritic Langerhans Epithelioreticular

8 DIFFERENTIATION OF LYMPHOCYTES Antigen independent differentiation occurs in thymus, GALT and bone marrow Antigen dependent differentiation occurs in Lymphatic Nodules,spleen,tonsil and lymph node. Formation of effector lymphocytes and memory cells

9 LYMPHOID ORGANS Widely distributed in body Lymphatic vessels collect lymph from various parts of body and deliver it to blood circulation mainly through thoracic duct

10 Lymphoid Tissue Lymphoid tissue is CT with rich supply of lymphocytes Exists free within regular CT or is surrounded by capsules. Very little cytoplasm so stain dark blue with H&E. Rich network of reticular fibrils produced by fibroblast whose many processes rest on fibrils.

11 LYMPH NODE Small Bean shaped I mm to I-2 cm. Although widely distributed may be concentrated in certain areas. Lymphatic vessels are either afferent or efferent.

12 Lymph Nodes Functions include: Filtration of particles and microorganisms to keep them out of general circulation. Interaction of circulating antigens in lymph with lymphocytes to initiate immune response. Activation, proliferation of B lymphocytes and antibody production. Activation, proliferation of T lymphocytes.

13 Structure of Lymph Node

14 HISTOLOGICAL STRUCTURE

15 HISTOLOGICAL STRUCTURE

16 HISTOLOGICAL STRUCTURE Two zones Cortex Medulla

17 CORTEX Superficial or Nodular Deep or Para cortex

18 PARACORTEX Also called thymus dependent cortex due to abundance of T cells

19 HISTOLOGICAL STRUCTURE Important site of B cells proliferation and their transformation into plasma cells

20 High endothelial Venules. (HEVs.) Located in Deep Cortex Absorb fluid and electroytes Cause migration of lymphocytes into lymph nodes

21 MEDULLA Formed by cords of lymphatic tissues surrounded by lymphatic sinuses Cords contain B lymphocytes

22 MEDULLA

23 Medulla of Lymph Node Lymphocytes predominate Medullary sinuses Medullary cords

24 CELLS OF LYMPH NODE Lymphocytes Macrophages Plasma cells Reticular cells Follicular Dendritic cells APC

25 FILTRATION OF LYMPH

26 FILTRATION OF LYMPH

27 SUBCAPSULAR SINUS

28 Cells of Subcapsular sinus

29 Flow of blood and Lymph In Lymph Node

30 SUPPORTING ELEMENTS OF LYMPH NODE Capsule Trabeculae Reticular tissue.

31 Cells of reticular meshwork Derived from Mesenchyme Stellate or elongated Oval euchromatic nucleus Small acidophilic Cytoplasm. Four types; Reticular cells Dendritic cells Macrophages Follicular Dendritic cells.

32 RETICULAR CELLS OF LYMPH NODE

33 DENDRITIC CELLS

34 Tonsils Multiple groups of large lymphatic nodules Location mucous membrane of the oral and pharyngeal cavities Palatine tonsils Lateral walls of the oropharynx Pharyngeal tonsil Posterior wall of nasopharynx Lingual tonsils Base of tongue

35 PALATINE TONSIL

36 PALATINE TONSIL

37 HISTOLOGICAL STRUCTURE Stratified squamous epithelium Crypts Diffuse and Nodular lymphoid tissue Capsule infiltrated with lymphocytes

38 Pharyngeal tonsil Pseudo stratified epithelium No crypts Capsule present

39 Lingual Tonsils Stratified squamous epithelium Lymphatic nodules Wider crypts

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41 GUT ASSOCIATED LYMPHOID TISSUE

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