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CHAPTER
20
The Lymphatic System and
Lymphoid Organs and Tissues
Objectives
Lymphatic System
1. List the functions of the lymphatic vessels.
Lymphoid Cells and Tissues
4. Describe the basic structure and cellular population of lymphoid tissue. Differentiate
between diffuse and follicular lymphoid tissues.
Lymph Nodes
5. Describe the general location, histological structure, and functions of lymph nodes.
Other Lymphoid Organs
Developmental Aspects of the Lymphatic System and Lymphoid Organs and
Tissues
7. Outline the development of the lymphatic system and the lymphoid organs and tissues.
Suggested Lecture Outline
I. Lymphatic System (pp. 752–754; Figs. 20.1–20.2)
A. The fluid that does not circulate back into the blood from the interstitial fluid is collected
by the lymphatic vessels (p. 752).
B. The lymphatic vessels form a one-way system in which lymph flows only toward the
heart (p. 752).
2. The lymph capillaries flow into the collecting lymphatic vessels and carry the lymph
to the lymphatic trunks.
II. Lymphoid Cells and Tissues (pp. 754–755; Fig. 20.3)
A. Lymphoid Cells (p. 754; Fig. 20.3)
1. Lymphocytes arise in the red bone marrow and mature into one of two lymphocytes:
T cells, or B cells.
B. Lymphoid tissues house and provide a proliferation site for lymphocytes and furnish an
ideal surveillance site for lymphocytes and macrophages (pp. 754–755; Fig. 20.3).
1. Lymphoid tissues may be diffuse lymphoid tissues, found in nearly every body organ,
or lymphoid follicles, which may form part of larger lymphoid organs or be found as
aggregations, such as the Peyer’s patches in the intestinal wall.
III. Lymph Nodes (pp. 755–757; Fig. 20.4)
A. The principal lymphoid organs in the body are the lymph nodes, which act as filters to
remove and destroy microorganisms and other debris for the lymph before it is trans-
ported back to the bloodstream (p. 755).
IV. Other Lymphoid Organs (pp. 757–759; Figs. 20.5–20.9)
A. The spleen is the largest lymphoid organ, located in the left side of the abdominal cavity
directly below the diaphragm (pp. 757–758; Figs. 20.5–20.6).
1. The spleen’s main function is to remove old and defective RBCs and platelets as well
B. Thymus (pp. 758–759; Figs. 20.5, 20.7)
1. The thymus secretes hormones that cause T lymphocytes to become immuno-
competent.
C. Mucosa-associated lymphoid tissues, MALT, are a set of lymphoid tissues located in
mucous membranes throughout the body (p. 759; Figs. 20.8–20.9).
1. Tonsils are the simplest lymphoid organs—forming a ring of lymphoid tissue around
the opening to the pharynx—which serve to gather and remove many of the pathogens
entering the pharynx in food or inhaled air.
V. Developmental Aspects of the Lymphatic System and Lymphoid Organs and
Tissues (pp. 759–760)
A. By the fifth week of embryonic development, the beginnings of the lymphatic vessels
and the main clusters of lymph nodes are apparent and develop from the budding of
Cross References
Additional information on topics covered in Chapter 20 can be found in the chapters listed below.
1. Chapter 3: Interstitial fluid
2. Chapter 4: Reticular connective tissue
Lecture Hints
1. Emphasize the difference between lymphatic capillaries and blood capillaries.
2. Note the differences between lymph nodes and lymphatic nodules.
3. Point out that the same factors that help venous return also aid lymph movement.
Because blood and vessels are structurally similar, and follow the same general path-
ways, logic dictates that factors affecting their fluid movements should also be similar.
Activities/Demonstrations
1. Audiovisual materials are listed in the Multimedia in the Classroom and Lab section of
this Instructor Guide (p. 387).
2. Use a torso model and/or dissected animal model to exhibit lymph organs.
Critical Thinking/Discussion Topics
1. Explain why and how lymphedema occurs after a modified radical mastectomy or other
such surgery.
2. Indicate the reason why a physician checks for swollen lymph nodes in the neck when
examining a patient who shows respiratory symptoms.
Library Research Topics
1. Research the causes, effects, and treatment of lymphedema.
List of Figures and Tables
All of the figures in the main text are available in JPEG format, PPT, and labeled & unlabeled
format on the Instructor Resource DVD. All of the figures and tables will also be available in
Transparency Acetate format. For more information, go to www.pearsonhighered.com/educator.
Figure 20.1 Distribution and special features of lymphatic capillaries.
Figure 20.2 The lymphatic system.
Figure 20.8 Histology of the palatine tonsil.
Figure 20.9 Peyer’s patch (aggregated lymphoid nodules).
System Connections Homeostatic Interrelationships Between the Lymphatic
System/Immunity and Other Body Systems
Answers to End-of-Chapter Questions
Multiple-Choice and Matching Question answers appear in Appendix H of the main text.
Short Answer Essay Questions
10. Blood, the carrier of nutrients, wastes, and gases, circulates within blood vessels through
the body, exchanging materials with the interstitial fluid. Interstitial fluid, formed by
11. Lymph nodes are very small bean-shaped structures consisting of both a medulla and a
cortex, which act as filters to cleanse lymph before it is allowed to reenter the blood.
Each node is surrounded by a dense fibrous capsule from which connective tissue strands
called trabeculae extend inward to divide the node into a number of compartments. The
12. a. The anatomical characteristic that ensures slow passage of lymph through a lymph
node is the fact that there are fewer efferent vessels draining the node than afferent
vessels feeding it. (p. 755)
Critical Thinking and Clinical Application Questions
1. a. With removal of the lymphatic vessels, fluid has built up in the tissues and drains very
slowly back to the bloodstream.
b. Yes, she can expect to have relief; lymphatic drainage is eventually reestablished by
regrowth of the lymphatic vessels. This is likely to be a recurrent problem, however,
Suggested Readings
Alitalo K. “The Lymphatic Vasculature in Disease.” Nature Medicine 17 (11) (Nov. 2011):
1371–1380.
Hecht, Jeff. “Cream Slows Snake Venom’s Invasion.” New Scientist 211 (2819) (July 2011):
16.
Keen, D. C. “Non-Cancer-Related Lymphoedema of the Lower Limb.” Nursing Standard 22
(24) (Feb. 2008): 53–61.
Loukas, M., et al. “The Lymphatic System: A Historical Perspective.” Clinical Anatomy 24
(7) (Oct. 2011): 807–816.
