1. Lymphatic
System Organs
DR KIRTI SOLANKE 1

2. INTRODUCTION
• Not a primary tissue type but a variety of
connective tissue.
• Components-1.lymphatic vessels
2.lymphatic organs
3.cells
4.lymph
2

3. Primary Lymphatic Organs and Tissues
• The primary (central) lymphatic organs and
tissues include the thymus, bone marrow and gut
associated lymphatic tissue (GALT).
• They are sites of
– antigen-independent proliferation, and
– differentiation into cells pre-programmed to
recognise specific antigens.
• These immunocompetent cells then enter the
blood and lymph:
– get dispersed in the connective tissue and
– penetrate into epithelia that line mucosal surfaces.
3

4. Secondary Lymphatic Organs and Tissues
• These are the effector lymphatic tissues.
• They include the lymphatic nodules, lymph
nodes, tonsils and the spleen.
• Here lymphocytes undergo antigen-
dependent proliferation and differentiation
into effector lymphocytes and memory cells.
4

5. 5

6. Lymphatic capillaries are not ubiquitous-absent in
cornea, cartilage, thymus, central and peripheral
nervous sys & bone marrow.
Lymphatic circulation Vascular circulation
• Deep • Superficial
• Valves closely placed • Less closely placed
• Blind ends • Both ends open
• No pericytes • Pericyte
• Irregular shape in cut sec. • Cylindrical form
• Basal lamina incomplete • Continuous
• Greater caliber • Less caliber
6

7. LYMPH
• Lighter specific gravity
than blood
• Contains no
RBCs,platelets,fibrinogen
but it contains numerous
Lymphocytes.
• Lymphocytes are added
when it passes through
LN.
• Coagulate at much
slower rate than blood
• Does not carry O2 but
may contain CO2.
• Chyle-fat globules,
lacteal
7

8. 8

9. • Lymph vessels of- thyroid gland
-oesophagus
-coronary and triangular
ligaments of liver
may drain directly into thoracic duct.
9

10. Functions of lymphoid system
1) To maintain – pressure &
-volume of extracellular fluid by
returning excess water to the circulation.
2) The site of clonal production of
immunocompetent lymphocytes and
macrophages in the specific immune
response.
10

11. CELLS OF LYMPHATIC SYSTEM
Chief cells are lymphocytes-type of WBC’S.
• B lymphocytes
• T lymphocytes
• Natural killer cells
• epithelioreticular cells - MESENCHYMAL
• Supporting cells-
– interact with lymphocyte
– Present antigens to Lymphocytes
• OTHER TYPE OF WBC’S
-monocyte
-macrophages
-neutruphils
-eosinophils
-basophils
11

12. • ANTIGEN PRESENTING CELLS
– dendriti cells-Bone marrow derived
– follicular cells
– langerhan’s cells
12

13. Derivation and Distribution of Lymphocytes
13

14. T Lymphocytes
• These evolve in the thymus
• part of the cell-mediated or thymus-
dependent response to antigens.
• Upon interaction with an antigen, they will
differentiate and proliferate into - 3 types
of effector T lymphocytes:
14

15. 1.Cytotoxic lymphocytes (killer T cells) (primary effector
cells in cell-mediated immunity.)
scan the surface of other cells for signs of viral
infection or abnormality, killing them if necessary by
causing them to lyse.
2.Helper T lymphocytes,
recognise foreign antigens presented by macrophages.
release interleukin hormones to stimulate ‘processed’ B
cells to produce antibodies.
3.Suppresser T lymphocytes, suppress the activity of B
cells.
15

16. HELPER T CELL SUBTYPES(CYTOKINES)
• Th1 cell • Th2 cells
• interact with cytotoxic • interact with B
CD8,NK ,macrophages. lymphocyte
• CMI • HIR
• For controling • Exracellular pathogens
intracellular pathogens
• Viruses &
microorganisms.
• IL 2,Interferon gamma • IL4, 5 ,10,13.
16

17. B Lymphocytes
• These evolve in bone marrow and GALT, and
are part of the humoral response.
• They will only react with the antigen they
have been genetically programmed for.
• Once activated by this antigen, they may
differentiate and proliferate into either:
• Plasma cells, that produce antibodies.
17

18. • The antibody binds, forming an antibody-antigen
complex, that may be phagocytosed by
macrophages.
• Memory cells, which, after exposure to the
specific antigen, will be able to participate in a
rapid, secondary response with the same
antigen.
• They do not participate in an initial or primary
response.
18

19. 19

20. B – Lymphocytes
T-Lymphocyte
– Prog In Thymus – Prog In B M
– Long life span – Variable lifespan
– For CMI – For H.I.
– Graft Rejection – Plasma Cells – Ab
– 60% to 8o% – 20 to 30%
– CD 2,CD3,CD7 – CD9,CD19,CD20 & CD24
– T cell receptors(TCRs) – Bcell receptors
– CD4,CD8 – MHC II
20

21. NK LYMPHOCYTE/NULL CELLS
• Neither T nor B cells
• Specialised to kill certain types of target cells
• 5 to 10%
• Do not mature in thymus
• Kill in the same way as that of CTLS
• After recognition of tranformed cell,secrete
perforins & fragmentins
• CD 56, CD94.
21

22. Macrophages
• These are involved in both types of immune
response.
• They can process and present the antigen to
the B cells or helper T cells.
• Or they can destroy the antigen by digestion
after it has been processed by other cells of
the immune system.
22

23. CLASSIFICATION
I. FUNCTIONAL
LYMPHOID ORGANS
CENTRAL PERIPHERAL
THYMUS LYMPH NODE
BONE MARROW SPLEEN
MALT, GALT
23

24. II. MORPHOLOGICAL
LYMPHOID ORGANS
DISCRETE DIFFUSE
LN, SPLEEN
BM, PEYER’S PATCHES
THYMUS, TONSIL
24

25. LYMPH NODE
• Oval/Kidney Shape, 0.1 – 0.5cm Long
• Normal young body contains up to 450,of which 60
to 70 in head and neck,100 in thorax,250 in abd&
pelvis
• Greatest no. lie close to the viscera mainly
mesenteries.
25

26. Lymph Node: Gross Appearance
26

27. 27

28. 28

29. 29

30. 30

31. • Capsule – Trabeculae, hilus-
collagenous framework
• Lymph flow
– Retculin Meshwork-sinuses
– Subcapsular Sinus
– Cortical Sinuses
– Medullary Sinuses
– Eff Lymph Ch
• Cortex medulla-diff in
arrangement
31

32. 3
2
1
32

33. • Role of germinal
centre-affinity
maturation
• Two zones in GC-dark
zone-centroblast-
undergoing rapid
proliferation-
hypermaturation of
their antibody mol.
• light zone-centrocytes-
ineract with the FDC-
carrying unprocessed
antigen on their
surface.
33

34. Lymph Node
34

35. 35

36. Lymph Node
A - Afferent lymphatic channels
B - Subcapsular sinus
C - Follicle
D - Sinuses
E - Paracortical region
F - Medullary cords
G - Efferent lymphatic channel
36

37. Variations in nodes
• In large nodes –trabeculae are prominent
• In small nodes-thin and frequently interrupted
• Hemal nodes
• lymphadenitis
37

38. • Diffusely distributed lymphatic nodules
represent local immune response to antigen
that are present in tissue fluid.
• LN-lymph.
• Spleen-circulating blood-mainly HIR.
38

39. The Spleen
• The spleen is the largest
lymphatic organ, located
in the upper left quadrant
of the abdominal cavity.
• The spleen functions to
filter the blood, and react
immunologically to
blood-borne antigens
mainly HIR,to dispose of
defective blood
cells,store blood cells
&platelets,hematopoiesis
39

40. Structure of the Spleen
• There is an external capsule of dense connective
tissue.
• trabeculae extend into the substance of the organ.
• myofibroblasts, and is thus contractile.
• medial surface of the spleen, the hilum allows
passage of the splenic vessels, nerves and lymphatic
vessels.
• The substance of the spleen is known as the splenic
pulp.
• white pulp areas,
• surrounded by red pulp.
40

41. Spleen
41

42. The White Pulp
• This mainly consists of lymphocytes.
• Branches of the splenic artery course through
the trabeculae and then enter the white pulp,
known as the central artery
• The lymphocytes aggregated around the
central artery in a cylindrical fashion
-periarterial lymphatic sheath (PALS) of the
artery.
• Lymph nodules in the PALS may displace the
central artery from its central position in the
white pulp.
42

43. The Red Pulp
• This has large numbers of red blood cells
(RBCs).
• It consists of splenic sinuses, separated by
splenic cords (of Billroth).
43

44. 44

45. 45

46. 46

47. 47

48. 48

49. 49

50. 50

51. Spleen
51

52. SPLENIC A
SEGMENTAL A
TRABECULAR A
CENTRAL A
FOLLICULAR A
PENICILLAR A
ELLIPSOIDS
PRE CAPILLARY A
SINUSOIDS
TRABECULAR VEINS
SPLENIC VEIN

53. 53

54. Splenic Circulation
• The splenic artery branches into the
trabecular, the central arteries.
• The central arteries of the white pulp then
branch into penicillar arterioles in the red
pulp.
• These are actually capillaries, and may be
sheathed by aggregations of macrophages.
• Blood from these penicilli leaves the vascular
system to populate the splenic pulp, before
re-entering the red pulp.
54

55. Two theories
• Closed Circulation Model
• In this model, the splenic arterioles are a "continuous vascular
channel".
• They only empty into the splenic sinuses of the red pulp.
• The blood then leaves the sinuses before re-entering them.
•
• Open Circulation Model
• In this model, the arterioles empty directly into the splenic cords.
• Thus, blood percolates through the reticular meshwork of the
pulp.
• It then only enters the splenic sinuses from the extravascular side.
• This model has more supporting evidence than the former.
• FUNCTIONS
55

56. THYMUS
• Introduction
• Gross anatomy
• development
• Histology
-Circulation
-Relation with
immunology
• Functions
• Age changes
• Recent advances 56

57. The Thymus (neuroendocrine organ)
• The thymus -4-6 cm long
2.5-5 cm wide
1cm thick,20 gm bi-lobed
organ
• left lobe higher
superior mediastinum,
anterior
to the heart and great vessels
• Thyrothymic ligament
• b/d supply-inf thyroid A,Internal
thorasic A.
• Lymphatics-
parasternal,brachiocephalic,trache
obronchial
57

58. Structural components
• Stroma-capsule
-trabeculae
• Parenchyma –epithelioreticular cells
-lymphocytes
-macrophages
-mast cells
58

59. Development
• 3rd &4th endodermal pouch-epithelial reticular
cells
• Local cardiac neural crest mesenchyme
control dev of gland.
59

60. Development
• .
60

61. 61

62. Histology
• Important environment-acquiring immune
tolerance
• Dev of T lymphocyte-interaction between
-thymocyte &
-epithelioreticular
cells,APC,chemical factors
• Capsule-incomplete trabeculae-irregular
lobule-0.5-2mm in dia.
62

63. Thymus
63

64. CIRCULATION
• Thymic cortex and medulla functionally independent.
lymphoid stem cells from BM outer
cortex progeny proliferate & differentiat
inner cortex medullary venules at CM
junction.
64

65. cortex medulla
• Dark staining-small L • Paler staining-large L
• Less in no • Macropgages,dendritic cells
are more
• Plasma cells absent • Plasma cells present
• b/d supply mainly by • Mainly thymic A,arteriole
capillaries
65

66. Epithelioreticular cells
• Parenchyma: epithelioreticular cells.
– are epithelial cells having stellate shape
– form cytoplasmic reticulum: a framework for the
thymic lymphocytes.
– correspond to the other reticular cells in
lymphatic tissues,
– but no reticular fibres in the thymus.
– Feature of both epithelial (intercellular junctions,
intermediate filament)and reticular
cells(framework)
--thymic nurse cells
– crosstalk 66

67. Epithelioreticular cells
• 6 types
• Type l-boundary of capsule & cortex
• Type ll-within cortex, compartmentalize the
cortex
• Type lll-between cortex and medulla
• Type lV –b/w cortex & medulla,barrier at CM
junction
• Type V-like type ll in cortex
• Type lV – corpuscles, keratohyaline granules,
produce lL-4&7.
67

68. OTHER CELLS
• Myeloid lineage-monocyte
• Macrophages-PAS cells
• Fibroblast
• Myoid cells
• Hassall’s corpuscles-distinguishing feature of
thymic medulla.30-100μm in dia.
IL-4,IL-7;named after Arthur Hill
Hassall British physician
• Plasma cells are rare in cortex.
• adipocytes 68

69. HASSALL’S CORPUSCLES

70. 70

71. 71

72. THYMIC HORMONES
• epithelial reticular cells -
1.thymopoietin
2.thymosin alpha
Induce expression of T lymphocyte surface
markers
72

73. THYMIC BARRIER
• No afferent lymphatics
• Physical barrier-Capillary endothelium
-Endothelial basal lamina
- pericyte
-thin perivascular connective tissue sheath
with macrophages
- Basal lamina of the
epithelioreticular cells
- Epithelioreticular cell sheath
73

74. 74

75. Changes of Thymic Structure with Age
(involution)
• Largest at birth
• fully functional at 20 weeks of foetal life.
• progressive involution of adipose tissue.
– Accelerated by adrenal corticosteroids and sex hormones
• In juveniles:
– isolation of cortical compartments,
– reduction of cortical and medullary volume, and
– appearance of more, larger blood vessels,
• until the adult thymus is mainly dominated by fat.
75

76. 76

77. Thymus
77

78. 78

79. Applied
• Myasthenia gravis
• Yellow fever vaccine
• DiGeorge syndrome-absent-thymus &
parathyroid ,defect in cardiac outflow tract
79

80. QUANTIFICATION OF THYMIC
FUNCTION
• RTE (Recent thymic emigrant)-
– newly produced peripheral naive T cells
– retain some phenotypic signature of recent thymic
maturation
– distinguishes them from long lived
80

81. 81

82. THANK
YOU
82

83. APPLIED
-should ask about a history of thymus disorder or dysfunction,
irrespective of age, including myasthenia gravis, thymoma,
thymectomy, or DiGeorge syndrome, before administering
yellow fever vaccine.
(Barwick RS, Marfin AA, Cetron MS. Yellow fever vaccine-associated disease.
In: . Washington: ASM Press, 2004: 25-34 vaccine was not one of the live
vaccines assessed in the study.)
83

84. Involution of the thymus
After puberty much of the parenchyma of the thymus, in particular cortical
lymphoid tissue, is replaced by adipose tissue. The process, which is called
involution, initially proceeds rapidly but slows down in adulthood. Involution
is under the control of steroid hormones (both sexual hormones and stress
hormones). Although most pronounced in the thymus, involution is a
common feature of all lymphoid tissues.
Another age-related phenomenon is the increase in size of the thymic (or
Hassall's) corpuscles. Thymic corpuscles are rounded eosinophilic structures,
which consist of concentrically arranged, flattened cells. Thymic corpuscles
are likely to be formed by reticular cells. Similar structures occur also in the
tonsils. The size of these structures varies from 20 µm to more than 100 µm
in diameter. Thymic corpuscles may calcify, and their core may "dissolve"
leading to the formation of a cyst.
84

85. DIFFUSE LYMPHATIC ORGANS
• Lymphatic nodules-solitary lymphatic nodules
-temporary structers
-in the lamina propria
• Permanent aggregates
85

86. PALATINE TONSIL
• Shape,location,bed of palatine
• Waldeyer’s ring
86

87. 87

88. LYMPHATIC NODULES/FOLLICLES
• In the lamina propria aggregations of small
lymphocytes-a form of uncapulated lymphatic
tissue
• Follicular associated epithelium-covering
mucosa-associated L T.
• In small & large intestine these specialised
cell have characterised short microvilli on
their luminal surface called micrifold (M) cells
• In palatine tonsils-modified stratified
squamous reticulated epithelial cells.
88

89. 89

90. Gut Associated Lymphoid Tissue
• In the lamina propria and submucosal of the gastrointestinal
tract from the tongue to the colon are collections of lymphoid
tissue. In some areas, the lymphoid tissue is more prominent:
– Lingual Tonsil:
at the posterior tongue are larger
collections of lymphoid tissue.
– Pharyngeal Tonsil:
these are the structures commonly
called "tonsils" and comprise tissues
functionally equivalent to lymph nodes.
90

91. 91

92. 92

93. Gut Associated Lymphoid
Tissue
93

94. 94