1. The Lymphatic System

2. The lymphatic system is a subsystem of the circulatory system.
Only developed in higher vertebrates with extensive vascular
system.
the lymphatic system originally evolved to combat fluid leakage
from capillaries.
They do not form a closed ring or circuit like the circulatory
system.
Instead, begin blindly in the intercellular spaces of the soft tissues
of the body.

3. Lymphatic tissue is a type of connective
tissue characterised by large numbers of
lymphocytes.
The stroma (framework) of lymphatic
tissue is a network of reticular fibres.
Connective tissue cells including fibroblasts
and macrophages are present.

4. The Functions
1. Body defence mechanism
– Produce, maintain & distribute lymphocytes
1. Regulation of body fluid
– Return fluid & solutes from tissues to blood ~ 3 L/day
– maintain normal blood volume
1. Distribution of hormones, nutrients & waste products
from their tissues of origin to general circulation
– E.g. Absorb Lipid from GIT (Lacteal) & transport them into
the blood
4. Regulate concentrations of plasma proteins
– return plasma proteins to the blood.

5. Importance of the lymphatic system in
maintaining fluid balance.

6. Plasma filters into the interstitial spaces from blood flowing
through the capillaries.
Much of this interstitial fluid is absorbed by tissue cells or
reabsorbed by the blood.
small amount of interstitial fluid is left behind.
 increased interstitial fluid would cause massive edema.
Edema would cause tissue destruction or death
Lymphatic vessels "drains" excess fluid and return it to the
venous blood just before it reaches the heart.

7. Role of the lymphatic system in fat
absorption and transport

8. Some small fatty acids can directly enter intestinal capillaries
of the villi of the small intestine
However, majority of fatty acids are long chained and are
absorbed differently.
Within the intestinal lumen, bile salts form aggregates called
micelles that are water soluble. Fatty acids and monoglycerides
are aggregated into the centres of the micelles.

9. Micelles transport the fatty acids and monoglycerides to the
brush borders of the villi.
fatty acids and monoglycerides diffuse into the epithelial cells of the villi.
Within epithelial cells, fatty acids and monoglycerides are
resynthesised into triglycerides.
The triglycerides combine with cholesterol, lipoprotein, and
phospholipids to form globules called chylomicrons.
The chylomicrons leave epithelial cells and enter the lacteal of the villus.
Lymphatic vessels carry chylomicrons to the venous blood of the left
subclavian vein via the thoracic duct.

11. Components of LS
Lymph
Lymphatic vessels
Lymphoid organs/tissues
(Primary & Secondary)

12. Organization
Lymphatic capillaries
Lymphatic vessels
Lymph Nodes
Collecting vessels
Lymphatic trunks
Collecting ducts
Subclavian veins

13. Lymphatic Vessels

14. Collection & drainage of lymph
Thoracic duct
Lymph from ¾ of the body
(lower half & left side of
upper half) drains into it
Empties into left subclavian
vein.
Right lymphatic duct
Lymph from right side of
upper half
Empties into right subclavian
vein.

15. Lymph
Clear, watery fluid found in the lymphatic vessels
Composed of fluid (plasma) and lymphocytes
Lymphocytes are stored in lymph nodes found in larger
lymphatic vessels
It contains clotting factors and clots on standing in vitro.
Contains protein (lower than that of plasma) & water-
insoluble fats

16. Probable approximate protein content of
lymph in humans.
Source of Lymph Protein Content
(g/dL)
Choroid plexus 0
Ciliary body 0
Skeletal muscle 2
Skin 2
Lung 4
Gastrointestinal tract 4.1
Heart 4.4
Liver 6.21
Average 3-5 g/dL
Ganong (2001)

17. Lymph flow
Lymph flow is sluggish (2-3 L/day)
Through thoracic duct 100ml/hour, other channels 20 ml/hr =
Total 120 ml/hr
Any factor that increases interstitial fluid pressure will increase
lymph flow, e.g.
Elevated capillary pressure
Decreased Plasma colloid osmotic pressure
Increased interstitial fluid protein
Increased permeability of capillaries

18. Lymph flow
Contraction of lymphatic vessels’ wall
Backflow prevented by lymphatic valves
Muscle & respiratory pumps also promote lymph flow
During exercise, lymph flow may increase as much as 10-
15x.

19. Respiratory & Muscle pumps
Respiratory pumps
X-rays show that lymph drains into central veins most
rapidly at the peak of inspiration.
The descent of diaphragm during inspiration, causes
intraabdominal pressure to increase as intrathoracic pressure
decreases.
This simultaneously causes pressure to increase in the
abdominal portion of the thoracic duct and to decrease in
the thoracic portion.

20. Research has shown that thoracic duct lymph is literally
"pumped" into the venous system during inspiration.
The rate of flow of lymph into venous circulation is proportional to
the depth of inspiration.
The total volume of lymph that enters the central veins
during a given time period depends on both the depth of
inspiration and the overall breathing rate.
Muscle pumps
Contracting skeletal muscles also exert pressure on the
lymphatics to push the lymph forward.

21. Muscle Pump

22. Lymphatic Organs & Tissues
Primary
Bone marrow
Thymus gland
Secondary
Lymph nodes
Spleen
Lymphatic Tissues

23. Thymus Gland
Located in the upper part
of the mediastinum behind
the sternum and extends
upwards into the root of
the neck.
Functions as a production
& maturation place for T
cells (lymphocytes)

24. Functions of Thymus Gland
Lymphocytes that enter the thymus mature and develop
into activated T-lymphocytes i.e. able to respond to
antigens encountered elsewhere in the body.
They then divide into two groups :
those that enter the blood, some of which remain in circulation
and some lodge in other lymphoid tissue
those that remain in the thymus gland and are the source of
future generations of T-lymphocytes.

26. Lymph Nodes
Bean-shaped organ, capsular & located along lymphatic
vessels.
Contains T and B cells (lymphocytes) and macrophages.
Lymph nodes filter lymph. Foreign substances & dead cells
are trapped in the reticular fibres of lymph nodes. (99% of
these substances are removed here)
Macrophages destroy some foreign substances by
phagocytosis (engulfing) while lymphocytes destroy others
through immune reactions.
Proliferation of T & Plasma cells occurs here
 Antibodies produced by the B- lymphocytes enter the lymph and the
blood draining the node.

27. Lymph Node

30. Location of
Lymph Nodes

31. An enlargement of these nodes is common in
inflammation and malignant disease.
As a result, palpation (feeling) of the neck, armpits and
the groin area is an important part of clinical
investigation

32. Spleen
The largest lymphatic tissue.
Consists of white pulp & red pulp.
white pulp is lymphatic tissue (contains lymphocytes &
macrophages)
Immune cells:
T cells destroy and attack antigen directly
B cells or plasma cells react via antigen-antibody binding.
Macrophages destroy some foreign substances by phagocytosis.

34. As blood flows through spleen, any disease organisms within
it will come into contact with lymphocytes.
Contact activates lymphocytes, which then attack the
foreign invaders.
As blood flows through spleen, macrophages remove worn-
out red and white blood cells and platelets and produce the
pigment bilirubin from the breakdown of haemoglobin.
Because a lot of blood circulates through the spleen, this
organ serves as reservoir for blood.

35. Lymphatic Nodules
Concentrations of lymphatic tissues (not surrounded by a
capsule) in the mucous membranes of GI, urinary &
reproductive tracts, and respiratory airways
small & solitary, or large masses e.g.:
Tonsils (2 palatine, 2 lingual & 1 pharyngeal)
Peyer’s patches (in intestinal mucosa)
 Vermiform appendix--an outgrowth from the caecum (first
part of the large intestine).

36. A lymph nodule consists mainly of large numbers of
lymphocytes enmeshed within reticular fibres
Lymph nodules do not have vessels bringing lymph to them.

37. Location of Palatine Tonsil