10.03.2015 Lymphoid Tissue

Dr. Archana Rani Associate Professor Department of Anatomy KGMU UP, Lucknow

What is lymphoid tissue?

• Specialized form of connective tissue

• Supporting framework: reticular cells & reticular fibres

• Large number of lymphocytes

• Other cells: Plasma cells & Consists of…….

• Lymphatic vessels

• Specific lymphoid organs (, , )

• Lymphatic tissue found within the tissues of other organs (in , GI tract, urinary tract, respiratory tract) Functions

• Defense of body

• Phagocytosis of foreign cells

• Involved in production of lymphocytes and plasma cells Lymphatic Vessels

– Originate as lymph

– Capillaries unite to form larger lymph vessels • Resemble veins in structure • Connect to lymph nodes at various intervals Lymphatic Capillaries Lymphatic & Vessel Lymphatic Vessels Channels of Lymphatics – Lymphatics ultimately deliver lymph into 2 main channels • Right lymphatic duct –Drains right side of head & neck, right arm, right thorax –Empties into the right subclavian vein • Thoracic duct –Drains the rest of the body –Empties into the left subclavian vein Channels of Lymphatics

Major of the Trunk

Lymphatic Tissue

– 3 types • Diffuse lymphatic tissue – No capsule present – Found in connective tissue of almost all organs • Lymphatic nodules – No capsule present – Oval-shaped masses – Found singly or in clusters • Lymphatic organs – Capsule present – Lymph nodes, spleen, thymus Diffuse lymphatic tissue

• Called as mucosa associated lymphatic tissue (MALT).

• Accumulation of lymphatic tissue in the mucous membrane of gastrointestinal, respiratory, urinary and reproductive tracts.

• Located where they come in direct contact with antigens. Lymphatic Nodule

• Circumscribed concentration of lymphatic tissue (lymphocytes and related cells).

• Not surrounded by capsule.

Lymphatic Nodule Lymphatic Organs Lymph Node

– Consists of connective tissue framework & numerous lymphocytes.

– Bean shaped structures placed in pathway of lymphatic vessels.

– Enclosed by a fibrous capsule.

– Cortex = outer portion • Germinal centers produce lymphocytes – Medulla = inner portion • Medullary cords

Lymph Node

• Lymph enters nodes through afferent lymph vessels, flows through sinuses, exits through efferent lymph vessel.

Lymph Node 1.Capsule 2. lymphoid nodule with 3. subcapsular sinus 4. intermediate sinus 5. medullary cords 6. medullary sinuses 7. trabecula Cortex of Lymph Node Medulla of Lymph Node

Medullary sinuses Medullary cords Medullary sinus of a lymph node containing reticular cells with long processes and elongated nuclei, macrophages, and many lymphocytes. (1) ; (2) reticular cell; (3) trabecula. H&E stain. High magnification. (Courtesy of PA Abrahamsohn.)

Cells of Lymph Node

• Lymphocytes • Plasma cells • Reticular cells • Macrophages and other phagocytic antigen processing cells • Lymphatic and vascular endothelial cells Functions of Lymph Node

• 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. Spleen

• Largest lymphoid organ • Encapsulated • Structure is similar to a node • Capsule present • But no afferent vessels or sinuses Spleen

• Substance is arranged in form of:  (basophilic)  (reddish) • Supporting Elements:  Capsule  Trabeculae  Trabecular network  Lymphocytes, macrophages, blood cells  Red pulp: splenic cords Spleen White pulp: Lymphoid Nodule (Malpighian corpuscle)

1. Germinal center 2. Central artery Red Pulp of Spleen (Splenic cords: ) Functions of Spleen

• Filtration of blood. • Immune response against antigens circulating in blood. • Site for production of B & T lymphocytes. • Formation of blood cells during fetal life. • Storage of blood. • Site of destruction of aged erythrocytes.

Thymus

– Location – behind the sternum in the mediastinum – Development: • Infant – conspicuous • Puberty – maximum size • Maturity – decreases in size – Function • Differentiation and maturation of T cells Thymus

• Consists of 2 lobes (rt. & lt.) covered by connective tissue capsule. • Septa passing inwards from the capsule subdivide the lobe into a large number of lobules. • Lobule: outer cortex, inner medulla • Supporting stroma: epithelioreticular cells Thymic Lobule

• Cortex: densely packed small lymphocytes. • Medulla: Lymphocytes are less densely packed. Presence of Hassall’s corpuscles. Functions of thymus

• Provides the environment for stem cells where they can divide and mature into T lymphocytes.

• Thymopoietin induces production & maturation.

• Thymosin supports T cell activities.

– Multiple groups of large lymphatic nodules – Location – mucous membrane of the oral and pharyngeal cavities. – Palatine tonsils • Posterior-lateral wall of the oropharynx – Pharyngeal • Posterior wall of nasopharynx – • Base of tongue

• Aggregation of lymphatic nodules within diffuse lymphoid tissue.

• Covered by stratified squamous .

• (opening of numerous mucous glands) Functions of tonsil

• Production of lymphocytes.

• Immunological response against antigens & organisms coming in contact with epithelium. References

1. diFiore’s Atlas of Histology with functional Correlations, 12th Edition.

2. Textbook of Human Histology. Inderbir Singh, 1st Edition.

3. Textbook of Histology. GP Pal, 3rd Edition.

MCQ

• The supporting framework of lymphatic tissue is formed by all except: 1. Reticular cells 2. Plasma cells 3. Macrophages 4. Fibrocyte

MCQ

• Afferent lymphatics in lymph node pour their lymph into: 1. Trabeculae 2. Subcapsular sinus 3. Medullary sinus 4. Lymph nodule

MCQ

• Cords of Billroth is a feature of: 1. White pulp of spleen 2. Red pulp of spleen 3. Thymus 4. Tonsil

MCQ

• The tonsil is covered by: 1. Simple squamous epithelium 2. Stratified squamous epithelium 3. Stratified cuboidal epithelium 4. Stratified columnar epithelium MCQ

• Hassall’s corpuscles is a feature of: 1. Lymph node 2. Spleen 3. Thymus 4. Tonsil