Download The lymphatic system consists of lymphatic vessels and

The lymphatic system consists of lymphatic vessels and associated
lymphoid organs.
LEARNING OBJECTIVE [ edit ]
Describe how the lymphatic system consists of lymphatic vessels and associated lymphoid organs
KEY POINTS [ edit ]
Lymphatic vessels are thin-walled, permeable vessels with valves to prevent backflow of lymph.
Lymphatic vessels function in picking up excess tissue fluid and returning it to the bloodstream,
a process essential to preventedema.
A lymph node is an organized collection of lymphoid tissue, through which the lymph passes on
its way to returning to theblood. Lymph nodes are located at intervals along the lymphatic
system.
TERMS [ edit ]
lymph node
small oval bodies of the lymphatic system, distributed along the lymphatic vessels, that are
clustered in the armpits, groin, neck, chest, and abdomen. They act as filters, with an internal
honeycomb of connective tissue filled with lymphocytes and macrophages that collect and destroy
bacteria, viruses, and foreign matter from lymph. When the body is fighting an infection, these
lymphocytes multiply rapidly and produce a characteristic swelling of the lymph nodes.
edema
an excessive accumulation of serum in tissue spaces or a body cavity
lymph
A colorless, watery, bodily fluid carried by the lymphatic system, that consists mainly of white
blood cells.
lymphocyte
A type of white blood cell or leukocyte that is divided into two principal groups and a null group:
B-lymphocytes, which produce antibodies in the humoral immune response, T-lymphocytes,
which participate in the cell-mediated immune response, and the null group, which contains
natural killer cells, cytotoxic cells that participate in the innate immune response.
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Lymphatic Vessels
The lymphatic system is a collection
system which starts in the tissue space as
initial lymph collectors that have
fenestrated openings to allow fluid and
particles to enter. These initial lymph
collectors are valveless vessels and go on
to form the precollector vessels which
have rudimentary valves (which are not
considered to be fully functional). These
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structures go on to form increasingly larger lymphatic vessels which form co-laterals and
have lymph-angions (lymph hearts). The lymphatic system, once thought to be passive, is
now known to be an active pumping system with active pumping segments with a function
similar to that of peristalsis. Lymph hearts have stretchreceptors and smooth muscle tissue
embedded in their walls. The lymphatic vessels make their way to the lymph nodes and from
the lymph nodes the vessels form into trunks which connect to the internal jugular group
of veins in the neck, as shown in .
The lymphatic system
This diagram shows the network of lymph nodes and connecting lymphatic vessels in the human
body.
Lymphatic Tissues and Organs
Lymphatic organs play an important part in the immune system, having a considerable
overlap with the lymphoid system. Lymphoid tissue is found in many organs, particularly the
lymph nodes, as well as in the lymphoid follicles associated with the digestive system such as
the tonsils. Lymphoid tissues contain lymphocytes, but they also contain other types of cells
for support. The system also includes all the structures dedicated to the circulation and
production of lymphocytes (the primary cellular component of lymph), which includes
thespleen, thymus, bone marrow, and the lymphoid tissue associated with the digestive
system.