Download Lymphoid Tissue

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 & macrophages
Consists of…….
• Lymphatic vessels
• Specific lymphoid organs (lymph node,
spleen, thymus)
• Lymphatic tissue found within the tissues of
other organs (in bone marrow, 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
– Capillaries unite to form larger lymph
vessels
• Resemble veins in structure
• Connect to lymph nodes at various
intervals
Lymphatic Capillaries
Lymphatic capillary & 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 Lymphatic Vessel 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 germinal center 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) Macrophage; (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:
 White pulp (basophilic)
 Red pulp (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: Cords of Billroth)
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 T cell production &
maturation.
• Thymosin supports T cell activities.
Tonsils
– Multiple groups of large
lymphatic nodules
– Location – mucous
membrane of the oral
and pharyngeal cavities.
– Palatine tonsils
• Posterior-lateral wall
of the oropharynx
– Pharyngeal tonsil
• Posterior wall of
nasopharynx
– Lingual tonsils
• Base of tongue
Palatine Tonsil
• Aggregation of lymphatic
nodules within diffuse
lymphoid tissue.
• Covered by stratified
squamous epithelium.
• Tonsillar crypts (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