lymphatic system

1. Lymphoid Tissue
Dr. Archana Rani
Associate Professor
Department of Anatomy
KGMU UP, Lucknow
10.03.2015

2. What is lymphoid tissue?
• Specialized form of connective tissue
• Supporting framework: reticular cells & reticular
fibres
• Large number of lymphocytes
• Other cells: Plasma cells & macrophages

3. 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)

4. Functions
• Defense of body
• Phagocytosis of foreign cells
• Involved in production of lymphocytes and
plasma cells

5. Lymphatic Vessels
–Originate as lymph capillaries
–Capillaries unite to form larger lymph
vessels
• Resemble veins in structure
• Connect to lymph nodes at various
intervals

6. Lymphatic Capillaries

7. Lymphatic capillary & Vessel

8. Lymphatic Vessels

9. 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

10. Channels of Lymphatics

11. Major Lymphatic Vessel of the Trunk

12. 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

13. 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.

14. Lymphatic Nodule
• Circumscribed concentration of lymphatic
tissue (lymphocytes and related cells).
• Not surrounded by capsule.

15. Lymphatic Nodule

16. Lymphatic Organs

17. 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

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

19. Lymph Node

20. 1.Capsule 2. lymphoid nodule with germinal center 3. subcapsular sinus 4.
intermediate sinus 5. medullary cords 6. medullary sinuses 7. trabecula

21. Cortex of Lymph Node

22. Medulla of Lymph Node
Medullary sinuses
Medullary cords

23. 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.)

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

25. 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.

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

27. 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

28. Spleen

29. White pulp: Lymphoid Nodule
(Malpighian corpuscle)
1. Germinal center
2. Central artery

30. Red Pulp of Spleen
(Splenic cords: Cords of Billroth)

31. 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.

32. 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

33. 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

34. Thymic Lobule
• Cortex: densely
packed small
lymphocytes.
• Medulla:
Lymphocytes are less
densely packed.
Presence of
Hassall’s
corpuscles.

35. 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.

36. 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

37. Palatine Tonsil
• Aggregation of lymphatic
nodules within diffuse
lymphoid tissue.
• Covered by stratified
squamous epithelium.
• Tonsillar crypts (opening
of numerous mucous
glands)

38. Functions of tonsil
• Production of lymphocytes.
• Immunological response against antigens
& organisms coming in contact with
epithelium.

39. 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.

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

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

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

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

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