Name: ______________________________________________________ Period: _______ Date: _________
Introduction to Lymphatic System
LT: I can explain the purpose and the parts of the lymphatic system.
Directions: Read and annotate the paragraph below. When finished, read the questions, locate the answer in
the paragraph, underline the answer and tag (write the number) of the question for that answer.
The lymphatic system is a vital system in the human body. Often considered as a subsystem of the
circulatory system, the lymphatic system works to maintain fluid balance within our tissues. It also plays a very
important role within the immune system by removing microorganisms and other pathogens from body
tissues.
The circulatory system is responsible for transporting nutrients and oxygen to cells through the blood vessels.
The smallest of these vessels are the capillaries. In the capillaries the blood pressure forces plasma out into
the tissue fluid that surrounds the cells in a given area.
Not all the fluid that leaves the capillaries is able to return to the heart via the circulatory system. Fluid
leaves the vascular system across capillary walls at a greater rate than it returns. It is estimated that over a 24hour period the difference in volume between plasma leaving the capillaries and that which returns to the
veins is about three liters. If not for the lymphatic system this fluid would accumulate and cause large-scale
swelling of the tissues. Fortunately, a system of lymph capillaries drains away this fluid so that it does not
accumulate in the tissues of our body. The lymph fluid also contains substances such as fats, proteins, ions,
clotting factors, lymphocytes, and cellular waste products that cannot return via the circulatory system. Once
inside the lymph vessels, this fluid is collectively known as lymph.
Unlike blood vessels, which are a closed circuit, lymph capillaries are blind-ended tubes that start in the tissues
of our body. They are found everywhere in our body except the brain and spinal cord. In the small intestine
there are special lymph capillaries called lacteals, which are involved in the absorption of fats. All lymph
capillaries join to form larger lymphatic vessels. These lymphatic vessels ultimately merge into large vessels
that join into two major ducts: the thoracic duct and the right lymphatic duct. These ducts empty their
contents back into the main veins, which bring blood back to the heart.
The lymphatic system does not have a heart to create pressure and cause fluid to move. Contractions
of skeletal muscle squeezes lymphatic vessels and pushes lymph fluid along. Like veins, larger lymphatic
vessels have valves that prevent lymph from flowing in the reverse direction.
At intervals along the lymphatic vessels are lymph nodes, which are primary lymphoid structures. They range
in size from being nearly invisible to the naked eye to the size of a marble. The lymph capillaries, lymphatic
vessels, and lymph nodes together make up the lymphatic system. Also included in the lymphatic system are
three structures known as the lymphoid organs and include the tonsils, thymus, and spleen.
Cells within the lymph nodes, including white blood cells or lymphocytes, play a very important role within
the immune system of our body by removing bacteria and other foreign matter from the lymph as it passes
through the nodes. Some lymphocytes also produce antibodies, which play an important role in fighting
infection. The organs and tissues of the lymphatic system are the major production sites of two main types of
lymphocytes: T cells and B cells, which respond and proliferate in response to an infection. Also found within
the lymph nodes are white blood cells called phagocytes, which engulf and destroy particles such as bacteria
and dead cells by a process known as phagocytosis.
The lymphatic system is thus a vital system in not only maintaining fluid balance within our body but
also as a crucial wall of defense against the many foreign bodies such as bacteria that enter our body every
day.
READING RESPONSE
After you have read and annotated the article, complete the questions and fill in the blanks below:
A. What are capillaries and what do they do?
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B. __________________________ are found everywhere in our body except the ____________________and
_________ ____________.
C. Cells within the ________________ nodes, including ____________ ____________ ______________ or
lymphocytes, play a very important role within the ________________ system of our body by removing
__________________and other foreign matter from the lymph as it passes through the _______________.
D. Some ____________________________ also produce ______________________, which play an important
role in fighting ______________________.
E. Also found within the lymph nodes are ______________ ______________ ______________ called
phagocytes, which engulf and destroy particles such as _______________________ and dead cells by a
process known as phagocytosis.
F. Make an inference about the purpose of the lymphatic system. Use the “I think… because… and I know”
based upon the information in the article.
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