Anatomy and Physiology



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 veins O lymphatic vessels

O arteries O blood capillaries O lymph nodes

Lymph capillaries lymphatic collecting vessels lymph node

Lymph duct lymph trunks 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.

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