Anatomy and Physiology
Lab Week 4
The Lymphatic System
The lymphatic system is similar to the circulatory system. Lymph, like
blood flows through a system of vessels. In addition to lymphatic vessels,
the lymphatic system also consists of the thymus, lymph nodes, lymph and
the spleen. Unlike the circulatory system, the lymphatic vessels do not form
a closed circuit. Lymph flows once through the vessels and then drains into
the circulating blood.
The lymphatic system functions in the maintenance of fluid balance in
tissues and plays a role in the body’s immune system. The lymphatic vessels
keep the cardiovascular system functional by maintaining blood volume.
The lymphoid organs help defend the body from pathogens by providing
operating sites for phagocytes and cells of the immune system. The system
acts as a filtering mechanism for contaminants and micro organisms and
serves as a protective device against foreign invaders, such as cancer.
Toxins are filtered out of the lymph and the fluid returns to the blood
cleansed.
Station 1 Function and Flow
The lymphatic system is a specialized subdivision of the circulatory
system. Although the cardiovascular system has pump (the heart) and
arteries, veins and capillaries, the lymphatic system lacks two of these
structures: the ___arteries____and ___pump____. Like the
___veins__ of the cardiovascular system, the vessels of the lymphatic
system are equipped with _____valves__________________ to
prevent backflow. The lymphatic vessels act primarily to pick up__
__fluid__ which has leaked into the ___interstitial___ ______
and return it to the ___bloodstream__. Approximately ___20L_____
of fluid is forced out the cardiovascular system into the interstitial
space in a day. ___17L_________ is returned to the cardiovascular
system at the venous end. The remaining 3L of fluid enters the
lymphatic system where it is __filtered__ and returned to the
bloodstream.
B. Answer the following questions.
1. What are the 3 primary functions of the lymphatic system?
a. ____draining excess interstitial fluid___
b. _____transporting dietary lipids___
c. _____carrying out immune responses____
Station 2 – Flow and Structure
O
heart
O arteries
Lymph capillaries
Lymph duct
O
O
veins
blood capillaries
O
O
lymphatic vessels
lymph nodes
lymphatic collecting vessels
lymph trunks
lymph node
valves
C. Answer the following questions regarding lymphatic return.
1. Describe 3 mechanisms that aid in the assistance of lymphatic
return.
1. skeletal muscle pump
The ‘milking action’ of skeletal muscle contractions compresses
lymphatic vessels and force lymph toward the subclavian veins.
2. respiratory pump
Lymph flows from the abdominal region, where pressure is higher,
toward the thoracic region, where it is lower. When the pressures
reverse during exhalation, the valves prevent backflow of lymph.
3. When a lymphatic vessel distends, the smooth muscle in its walls
contracts, which helps move lymph from one segment of the vessel
to the next.
2. If lymphatic return is blocked, what will occur?
Tissue edema.
Blood protein concentration will fall.
Blood osmotic pressure will fall.
Station 3 Structure
Match the terms found on the cue cards with the appropriate description
____spleen____1. the largest lymphatic organ
___lymph nodes_2. filter lymph
___thymus___ 3. produces hormones that help to program immune
system
__lymph nodes_4. scattered throughout body superficially and deeply
along lymph vessels
___thymus ___5. located in mediastinum
___spleen ____6. located below stomach and diaphragm
____tonsils____7. aggregations of lymph nodules found in mucus
membranes
____tonsils___8. participate in responses against inhaled or ingested
foreign substances
____spleen____9. removes aged and defective red blood cells
Station 4 - General Questions.
Answer the following questions.
1. How do lymphatic capillaries differ from blood capillaries?
Lymphatic capillaries are slightly larger in diameter than blood
capillaries and have one-way openings that drain interstitial fluid
into them. In addition, they are attached to surrounding tissues by
anchoring filaments and they are closed at one end.
2. Why are the walls of lymphatic vessels thin, like veins?
The pressure in lymphatic vessels is low.
3. What would be missing in lymph leaving a lymph node, compared
with lymph entering the node?
Bacteria, viruses, worn out cells, and other debris engulfed by
macrophages.
4. Would you describe the flow of lymph through lymph nodes as being
fast or slow, compared with blood capillaries? Explain.
Slower than blood capillaries due to the lymph node structure. Each
lymph node has more afferent vessels entering it than efferent
vessels leaving it. This slows lymph flow through the node allowing
time for foreign substances to be trapped and destroyed by
phagocytosis or immune responses.
Station 5 Application Questions
1. If you look into a child’s mouth, there are ‘golf balls’ puffing from
each side of the oral cavity. What are these structures?
Palatine tonsils
2. Bacteria and viruses in infected tissues easily enter lymph vessels.
Explain why.
Bacteria and viruses can be picked up by lymphatic capillaries that
have large openings to drain interstitial fluid. From here, microbes
enter the lymphatic vessels.
3. If a woman had a radical mastectomy (removal of a cancerous breast,
surrounding tissues with axillary lymph nodes, and anterior thoracic
muscles), would you expect the arm on that side to be enematous
(have edema)? Explain.
Yes. Lymph nodes have lymphatic vessels leading into them that
would drain the axillary area around the lymph nodes of excess
interstitial fluid. When these structures are removed, excess
interstitial fluid may build up.
4. A patient has enlarged right inguinal nodes that are very tender to the
touch. Examination of the feet reveals a small cut between the right
3rd and 4th toes that are warm and red. What would your initial
impression be and why the nodal enlargement?
Bacteria entered the body through the small cut between the toes and
travelled up the lymphatic vessels of the leg into the inguinal lymph
nodes. Lymph travels through the lymph nodes slowly, allowing
phagocytosis to occur by macrophages. The increased number of
bacteria in the lymph nodes causes swelling.