Histology of lymphoid system

1. Lymphoid SystemLymphoid System

2. ObjectivesObjectives
• Understand the location of lymphatic organs.
• Discuss the microscopic features of Lymph Node.
• Discuss the microscopic features of Spleen.
• Discuss the microscopic features of Thymus.
• Discuss the microscopic features of Tonsil.

3. Functions of the LymphaticFunctions of the Lymphatic
SystemSystem
24-
3
• Reabsorbs excess interstitial fluid:
–returns it to the venous circulation
–maintain blood volume levels
–prevent interstitial fluid levels from rising out
of control.

4. Functions of the LymphaticFunctions of the Lymphatic
SystemSystem
• Transport dietary lipids:
– transported through lacteals
– drain into larger lymphatic vessels
– eventually into the bloodstream.
• lymphocyte development, and the
immune response.

5. Components of the LymphaticComponents of the Lymphatic
SystemSystem
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• Lymph
• Lymphatic Vessels
– Lymphatic Capillaries
– Lymphatic Vessels
– Lymphatic Trunks
– Lymphatic Ducts

6. Components of the LymphaticComponents of the Lymphatic
SystemSystem
• Lymphatic Organs
– Thymus
– Lymph Nodes
– Spleen
– Tonsils
• Lymphatic cells

8. LymphLymph
What is lymphWhat is lymph??
Tissue fluid (interstitial fluid) that enters
the lymphatic vessels

9. Lymph VesselsLymph Vessels
• Lymphatic capillaries –
• Lymphatic collecting vessels
• Lymphatic trunks –
• Lymphatic ducts –

10. Lymphatic CapillariesLymphatic Capillaries
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Features of structure:
• Blind end
• Single layer of overlapping
endothelial cells
• More permeable than that of
blood capillary
• Absent from avascular
structures, brain, spinal cord
splenic pulp and bone marrow

11. Lymphatic VesselsLymphatic Vessels
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Features of
structure
•Three layered wall but
thinner than vein,
•More numerous valves
than in vein
•Interposed by lymph
nodes at intervals
•Arranged in superficial
and deep sets

12. LYMPH TRUNKSLYMPH TRUNKS
??

13. Lymphatic ductsLymphatic ducts
Right lymphatic duct
•Formed by union of right jugular, subclavian,
and bronchomediastinal trunks
•Ends by entering the right venous angle
Thoracic duct
•formed by left and right lumbar trunks and
intestinal trunk
•Enter thoracic cavity & ascends

14. DRAINAGE PATTERN
THORACIC DUCT –
Drains lymph from lower
limbs, pelvic cavity,
abdominal cavity, left side of
thorax, and left side of the
head, neck and left upper
RIGHT LYMPHATIC DUCT
-Receives lymph from right
half of head, neck, thorax
and right upper limb, right
lung, right side of heart,
right surface of liver

15. Lymphatic CellsLymphatic Cells
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• Also called lymphoid cells.
• Located in both the lymphatic system and
the cardiovascular system.
• Work together to elicit an immune
response.
Types of lymphatic cells are:
– macrophages
– epithelial cells
– dendritic cells
–

16. Lymphatic organsLymphatic organs
Primary organs
–Red bone marrow
–Thymus gland
Secondary organs
–Lymph nodes
–Lymph nodules
–Spleen

17. Lymph NodeLymph Node
• Covered by a capsule which extends to form
Trabeculae.
• Divided into outer cortex and inner medulla.
• OUTER CORTEX contains:
Lymphatic nodules with germinal center
• INNER MEDULA contains:
Medullary Cords and Medullary Sinus

18. Lymph nodeLymph node
SC --- Subcapsular Sinus
C --- Cortex
M --- Medulla
H --- Hilum
LN --- Lymphatic Nodules
T --- Trabeculae
MS --- Medullary Sinus
MC --- Medullary Cords
LN
Capsule
SC
C
M
H
T
MC
MS

19. Lymph nodeLymph node
CT --- Connective tissue
C --- Cortex
M --- Medulla
P --- Paracortex
LN --- Lymph Node
T ---Trabeculae
MS --- Medullary Sinus
MC --- Medullary Cords

20. Lymph nodeLymph node
C -- Capsule, S -- Subcapsular Sinus, N -- Lymph Node

21. Lymph nodeLymph node

22. SpleenSpleen
• Covered by a capsule which extends to form
Trabeculae.
• Trabeculae contains trabecular arteries & Veins.
• Lymphatic nodules with germinal centers
constitutes the white Pulp.
• Central artery passes through lymphatic nodules.
• Red or Splenic pulp contains pulp arteries,
Venous sinuses and Splenic cords (Cords of
Billroth).

23. SpleenSpleen

24. SpleenSpleen

26. Splenic Cords and SplenicSplenic Cords and Splenic
SinusoidsSinusoids

27. ThymusThymus
• Covered by a capsule which extends to form
Trabeculae.
• Trabeculae extends inwards to forms numerous
incomplete lobules (lobulated appearance).
• Each lobule consists of dark staining outer cortex
and a light staining inner medulla.

28. ThymusThymus
• Cortex contains densely packed lymphocytes (No
lymphatic nodules).
• Medulla contains fewer lymphocytes but more epithelial
reticular cells.
• Medulla also contains Thymic (Hassall’s) Corpuscles.
• Thymic (Hassall’s) Corpuscles are oval structures
consisting of round whorls of flattened epithelial cells.

29. ThymusThymus

30. ThymusThymus

32. Lymphatic Nodules
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• Oval clusters of lymphatic cells with some extracellular
matrix that are not surrounded by a connective tissue
capsule.
• Filter and attack antigens.
• In some areas of the body, many lymphatic nodules group
together to form larger structures.
– mucosa-associated lymphatic tissue (MALT) or tonsils
– very prominent in the mucosa of the small intestine,
primarily in the ileum
• Peyer patches
– also present in the appendix

33. Palatine TonsilPalatine Tonsil
• Surface of the Tonsil is covered by Stratified
Squamous nonkeratinized epithelium.
• Tonsil is invaginated by deep grooves called
Tonsillar Crypts.
• Below epithelium lymphatic nodules are present in
the connective tissue.
• Dense connective tissue underlies the palatine
tonsil and forms capsule.

34. Palatine TonsilPalatine Tonsil

35. TonsilTonsil

36. Appendix MALTAppendix MALT

37. MALT (Mucosa Associated
Lymphoid Tissue(
37

38. Let’s reviseLet’s revise
some importantsome important
factsfacts

39. Name the structures labelled A-E.
QUESTION. 1QUESTION. 1

40. Which of these is a primary lymphoidWhich of these is a primary lymphoid
organ ?organ ?
A. Lymph Node
B. Spleen
C. Tonsil
D. Bone Marrow
QUESTION. 2QUESTION. 2

41. Which is the correct statement about the
Lymphatic system?
A. It Reabsorbs excess interstitial fluid and
returns it to the venous circulation.
B. Transports dietary lipids through lacteals.
C. Helps in lymphocyte development, and the
immune response.
QUESTION. 3QUESTION. 3

42. QUESTION. 4QUESTION. 4
Any
Question ?

43. RefrenceRefrence
• Atlas of histology and
function correlations
• www.cabrillo.edu
• www.wikispaces.com

44. Thank YouThank You
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the true test.the true test.