Lymphatic system It was studied for the first time by Thomas Bartholin in 1703. It is a sub-system of circulatory system in vertebrate body that consists of a complex network of lymph vessels or lymphatic’s lymph tissues (nodes) and organs such as tonsils, thymus and spleen which carries a milky fluid Called lymph. LYMPH Colorless clearly watery fluid contains lymphocytes similar in composition to with the exception of some proteins. The Main functions of lymph are as under:  Carries plasma proteins which seep out of the capillary beds from the blood stream.  It also carries larger particles such as bacteria and other waste product, cell debris from the damaged tissues which is then filtered out and destroyed by the lymph node. In lacteals fats absorbed into blood plasma called (chyle) which has a milky appearance.

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Lymphatic system
It was studied for the first time by Thomas Bartholin in 1703.
It is a sub-system of circulatory system in vertebrate body that consists of a complex network of
lymph vessels or lymphatic’s lymph tissues (nodes) and organs such as tonsils, thymus and
spleen which carries a milky fluid Called lymph.
LYMPH
Colorless clearly watery fluid contains lymphocytes similar in composition to with the
exception of some proteins. The Main functions of lymph are as under:
 Carries plasma proteins which seep out of the capillary beds from the
blood stream.
 It also carries larger particles such as bacteria and other waste product,
cell debris from the damaged tissues which is then filtered out and
destroyed by the lymph node.
 In lacteals fats absorbed into blood plasma called (chyle) which has a
milky appearance.
LYMPH CAPILLARIES
They are blind end tubes in the interstitial spaces and have same structure as blood
capillaries. All tissues have lymph vessels except CNS, cornea of eye, and bones.

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LYMPH VESSELS
Lymph capillaries join up to form larger lymph vessels. Lymph vessels are found running
alongside the arteries and veins. Wall of lymph vessels are consists of three layers as in the
blood vessels.
LYMPHATIC DUCTS
Lymph vessels are joined together to form a larger vessels called lymphatic ducts. They are of
two types which are:
 THORACIC DUCT
It drains lymph from both legs, pelvic and abdominal cavity, left half of
the thorax, head, neck and left arm and open into the left subclavian vein in the root of
neck.
 RIGHT LYMPHATIC DUCT
It drains lymph from the right half of the thorax, head, neck,
and right arm and open into the right subclavian vein.

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LYMPH NODE
Nodes are oval or bean shaped organs covered by capsule. Invagination of the capsule forms
many cavities called trabeculae which consist of lymphocytes and macrophages. They also
consist of two types of tissues called the lymphatic and reticular tissues. Lymph enters into the
nodes through three or four vessels called afferent vessels while their exit occurs through
another vessel called efferent vessel. Nodes help in phagocytosis of pathogens and thus help in
filtration. There are more than hundred nodes present in human body some of them are:
 Cervical node located in neck region.
 Axillary node located in armpits.
 Inguinal node located in groin.
 Thoracic region.
 Abdominal region.
 Pelvic region.

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TONSILS
Pair of soft masses located in the pharynx composed of tissues similar to lymph nodes
covered by pink mucosa. Tonsils trap pathogens present in the inhaled air and hence help in the
filtration of air. Sometimes tonsils are itself infected by pathogens (TONSILITIS) and
inflammation occurs due to whichtonsils become swell up and are called HYPERTROPHIC due to
which breathlessness and sleep apnea (choking and snoring sound during sleeping) occur.
SPLEEN
Spleen is the largest organ of lymphatic system 12 cm long and 7cm wide, purplish in color,
weight 200 g consists of lymphocytes and macrophages.
FUNCTIONS OF SPLEEN
 Phagocytosis: spleen helps in the destruction of old and abnormal
RBC’s and their breakdown products (bilirubin and iron) are
transported to liver.
 Storage of blood: spleen store about 350 ml of blood every time it
releases it in hemorrhagic condition and during the stimulation of
sympathetic nervous system.
 Erythropoiesis: spleen is the best site for the production of blood
cells in fetal life.
THYMUS GLAND
Thymus gland is located in the chest cavity. At the time of birth its size is about from 10 to 15g
and grows until puberty to about 30 to 40g then it is returned to approximately its weigh at
birth.
T lymphocytes are produced in this gland. Thymus gland also provides each lymphocyte with the
ability to react to only one specific antigen. T lymphocytes are then transported to the blood
stream.

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EXCHANGE ACROSS CAPILLARY WALLS
There are two types of pressure involved in this process which are:
Blood pressure /capillary hydrostatic pressure:
Pressure that is exerted by blood on the walls of the blood vessels is called blood
pressure. Due to this pressure water, some proteins and small solutes squeezed out of
the capillary into the interstitial spaces.
Osmotic pressure:
Pressure exerted by proteins (mainly Albumin) in blood vessels plasma that usually
tends to pull water into the capillary from interstitial spaces.
CREATED BY: AZIZ KHAN
BS ZOOLOGY: 3RD
SEMESTER
UNIVERSITY OF SWAT