The lymphatic system consists of lymph, lymphatic vessels, lymph nodes, and lymphatic organs that work together to drain excess interstitial fluid, transport lipids and lymphocytes. The lymphatic system includes primary organs like the red bone marrow and thymus that produce lymphocytes and secondary organs like lymph nodes, spleen and lymphatic nodules that filter lymph and initiate immune responses. Lymph flows through lymphatic vessels and is returned to blood circulation through the thoracic duct and right lymphatic duct. Diseases that can affect the lymphatic system include lymphangitis, filariasis, lymphedema, lymphomas and lymphadenopathy.

1. The Lymphatic
System
1

2. 2
•WHAT IS LYMPH ?
TISSUE FLUID (INTERSTITIAL FLUID)
THAT ENTERS THE LYMPHATIC
VESSELS

3.  CONSISTS OF:
1. LYMPH
2. LYMPHATIC VESSELS
3. STRUCTURES AND ORGANS
CONTAINING LYMPHATIC
TISSUE
4. RED BONE MARROW
3
Lymphatic System Structure and Function
Fig.1: Components of
the lymphatic
system.
600 lymph nodes in
body
 Functions of the lymphatic
system
1. Drains excess interstitial
fluid.
2. Transports dietary lipid
from gastrointestinal tract
to blood. The lipid-
containing lymph is called

4. 4

5. 5
Components of lymphatics
 Lymph
 Lymphatic Vessels
 Lymphatic Organs
 Lymphatic cells

6. Lymph
 Most components of
blood plasma filter
freely through the
capillary walls to form
interstitial fluid.
 More fluid filters out
of blood capillaries
than returns to them
by reabsorption.
 The excess filtered
fluid drains into
lymphatic vessels and
becomes lymph,
6
Fig.2: Capillaries and
lymphatics.

7. Lymphatic Vessels
7
 Vessels begin as lymphatic
capillaries. These are
closed at one end.
 Lymphatic capillaries unite
to form large lymphatic
vessels. These resemble
veins in structure but
thinner walls and more
valves.
 A series of swellings are
present along the
lymphatic vessels. These
are the lymph nodes.
Fig.3: The distribution of
lymphatic vessels in the body
showing the lymph nodes. Also
shown is the closed end of a
lymphatic capillary.

8. 8
Lymphatic Vessels
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

9. • ULTIMATELY, THE LYMPH DRAINS
INTO 2 MAIN CHANNELS:
1. THORACIC DUCT: A LONG DUCT
THAT DRAINS LYMPH FROM THE
ENTIRE LEFT HALF OF THE BODY
AND THE RIGHT HALF BELOW THE
RIBS INCLUDING THE RIGHT LOWER
LIMB.
2. RIGHT LYMPHATIC DUCT: A SHORT
DUCT THAT DRAINS LYMPH FROM
THE RIGHT SIDE OF THE BODY
ABOVE THE RIBS INCLUDING THE
RIGHT UPPER LIMB.
9
Fig.4: Areas of
lymph drainage to
the two main
lymphatic ducts.

10.  Each of these ducts open into the junction of
the subclavian and internal jugular veins as
they form the brachiocephalic vein.
 In this way, the lymph will return to the blood.
10
Fig.5: Opening of the
lymphatic ducts into the
venous circulation.

11. 11
Lymphatic Cells
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
Lymphocytes

12. 12
Lymphatic Organs
Primary organs
Red bone marrow
Thymus gland
Secondary organs
Lymph nodes
Lymph nodules
Spleen

13. • 2 GROUPS BASED ON FUNCTION
1. PRIMARY LYMPHATIC ORGANS:
• SITES WHERE B AND T LYMPHOCYTES ARE FORMED
AND MATURE.
• RED BONE MARROW AND THYMUS.
2. SECONDARY LYMPHATIC ORGANS
• SITES WHERE MOST IMMUNE RESPONSE OCCURS,
MEANING THAT THEY ARE THE SITES WHERE THE
MATURE LYMPHOCYTES PERFORM THEIR FUNCTION.
• LYMPH NODES, SPLEEN, LYMPHATIC NODULES.
13
Lymphatic Organs and Tissues

14. The Thymus
 The thymus is an asymmetric bilobed organ where
mature T-cells are formed.
 It’s located in the superior mediastinum just behind
the manubrium. It may descend into the anterior
mediastinum to lie between the sternum and the
pericardial sac. Sometimes it may ascend into the
neck reaching as high as the thyroid gland.
 The fibrous capsule that surrounds the gland sends
connective tissue trabeculae into the gland dividing
it into lobules. Each lobule is formed of a dark outer
region with immature T-cells (the cortex) and an
inner lighter region with mature T-cells (the
medulla).
14

15.  The thymic tissue is most
numerous in younger age.
As the person grows, this
tissue is gradually replaced
by fatty tissue.
15
Fig.6: To the left,
histology of the thymus.
Below, position of the
thymus.

16. Red Bone Marrow
 Red bone marrow is the site of formation of the
blood elements: red blood cells, white blood cells
and platelets.
 Inside the red bone marrow B lymphocyte form
and mature; T lymphocytes are formed in the red
bone marrow but they’re immature. T-cells
become mature in the thymus.
 Red bone marrow in adults is present in the flat
bones and the epiphyses of some long bones.
16

17. Lymph Nodes
 Lymph nodes are capsulated bean shaped structures that
are found along the course of the lymphatic vessels.
They’re usually present in groups and they’re scattered
all over the body.
 The capsule sends trabeculae into the node dividing it
into compartments. Beneath the capsule there’s a space
called the Subcapsular Sinus.
 The node has an outer cortex with lymphatic nodules
formed of B-cells and plasma cells. Deep to it is the
inner cortex formed of T-cells with no nodules. Deep to
the cortex is the medulla which contains B-cells, plasma
cells and macrophages embedded in reticular fibers.
 Between the lymphatic tissue in the cortex and medulla
are spaces called cortical and medullary sinuses.
17

18. 18
Lymph nodes
Capsular shell
Fibroblasts and reticulin
fibers
Macrophages
Dendritic cells
T cells
B cells

19. 19
Head & Neck Nodes

20. 20
Axillary Nodes

21. 21
Inguinal Lymph nodes

22. Important Note:
• In any organ in the body, the tissues forming the
organ can be divided into two types:
1. The Parenchyma: any tissue in the organ
responsible for performing the function of the
organ. Example: in the lymph nodes, the lymphoid
tissue is the parenchyma.
2. The Stroma: tissues in the organ that are not
related to the function of the organ but play a
supporting role. Example: in the lymph nodes, the
capsule, the trabeculae, the reticular fibers and
fibroblasts are the stroma.
22

23. Subcapsula
r Sinus
Afferent
s
Cortica
l
Sinuse
s
Medullar
y Sinuses
Efferent
s
 From the convex side of the lymph node several
incoming lymphatic vessels enter the node. These are
called afferent lymphatic vessels.
 The concave side of the node is called the hilum.
From it, one or two outgoing lymphatic vessels leave
the node. These are called efferent lymphatic vessels.
Also through the hilum arteries and nerves enter and
veins exit the node.
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The flow of lymph in a lymph node

24. 24
Fig.7: Structure of a lymph
node.

25. Functions of lymph nodes:  Filter of lymph
1. Antigens in the lymph are trapped and the
lymphocytes in the nodes react to it and initiate
the immune response.
2. Macrophages in the node may directly destroy
the antigen.
 It’s important to know what lymphatic vessels
drain a certain organ and what are the lymph
nodes in its course, because this represent a
pathway by which infections and cancer cells
can spread. 25

26. • LARGEST SINGLE MASS OF LYMPHATIC TISSUE IN THE BODY.
• IT’S AN OVAL, SOFT ORGAN LOCATED IN THE LEFT
HYPOCHONDRIAC REGION.
• ITS SUPERIOR SURFACE IS SMOOTH AND RELATED TO THE
DIAPHRAGM AND RIBS 9,10 AND 11. ITS VISCERAL SURFACE IS
IRREGULAR AND RELATED TO THE STOMACH, PANCREAS,
KIDNEY AND COLON.
• STROMA – CAPSULE, TRABECULAE, RETICULAR FIBERS, AND
FIBROBLASTS.
• PARENCHYMA:
• WHITE PULP – LYMPHATIC TISSUE (LYMPHOCYTES AND
MACROPHAGES) SURROUNDS BRANCHES OF SPLENIC ARTERY
(THE ARTERY THAT SUPPLIES THE SPLEEN AND ENTERS
THROUGH THE HILUM).
26
The Spleen

27. • RED PULP – BLOOD-FILLED VENOUS SINUSES
SURROUNDED BY SPLENIC CORDS WHICH
CONTAIN RED BLOOD CELLS, MACROPHAGES,
LYMPHOCYTES AND PLASMA CELLS.
• MACROPHAGES REMOVE RUPTURED, WORN
OUT OR DEFECTIVE BLOOD CELLS.
• STORAGE OF UP TO 1/3 OF BODY’S PLATELET
SUPPLY.
• PRODUCTION OF BLOOD CELLS DURING FETAL
LIFE.
• FUNCTION: FILTER OF BLOOD
27

28. 28
Fig.8: The spleen and its
histology.

29. • COLLECTION OF LYMPHATIC TISSUE NOT
SURROUNDED BY A CAPSULE.
• SCATTERED THROUGHOUT LINING OF
GASTROINTESTINAL, URINARY,
REPRODUCTIVE AND RESPIRATORY
TRACTS.
• MOST OF THEM ARE SMALL AND SOLITARY.
• SOME ARE LARGE – TONSILS, PEYER’S
PATCHES, APPENDIX.
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Lymphatic Nodules

30. 30

31. LYMPHAGITIS
31
Inflammation of the
lymph vessels
Commonest cause
bacteria called
streptococcus
pyogenes(most
common).
Lymph vessels appear
as red streaks through
the skin

32. 32
Filariasis
is a parasitic disease
caused by
microscopic, thread-
like worms. The adult
worms only live in the
human lymph system.
The lymph system
maintains the body's
fluid balance and fights
infections.

33. 33
Lymphedema
Occurs due to
accumulation of
lymphatic fluid in the
interstitial tissue.
Sometimes can be
appreciated after
wearing tight clothing
or jewelry on affected
limb.

34. 34
Lymphomas
Cancers originating
either from the
lymphocytes in the
lymph nodes or the
lymphatic tissue in
organs

35. 35
Lymphadenopathy
Means a disease of
the lymph nodes
Lymph nodes
become swollen/
enlarged and may be
painful to touch

36. 36
Tonsillitis
Infection of the
pharyngeal tonsils
Tonsils are swollen,
Fever and pain
during swallowing
usually present