lymph The fluid that circulates through the LY M P H
VESSELS. Lymph is clear and colorless or white with
fat, depending on its location. It contains about 90
percent water and carries proteins, globulins, GLU-
COSE, electrolytes, and other chemicals dissolved
within it. Leukocytes, primarily lymphocytes and
monocytes, circulate in the lymph, suspended in
the fluid. Lymph originates from and returns to the
BLOOD. Fluid from the blood (PLASMA) seeps from
the capillaries into the spaces between the cells.
This interstitial fluid carries the NUTRIENTSfrom the
blood, surrounding the cells in a bath from which
they withdraw the nutrients they need. Leukocytes
in the blood move freely between the lymph and
the blood. Lymph capillaries draw the interstitial
fluid back into the lymph vessels, which carry the
lymph they collect through a network of lymph
vessels. Ultimately the lymph vessels return the
lymph to the blood via its portals into the right and
left subclavian veins.
Compared to the blood the HEART pumps
through the circulation, the lymph moves
leisurely through its network of vessels, achieving
a top rate of about 100 milliliters an hour in the
major trunk vessels (the lymphatic ducts). It flows
primarily as a function of gravity, with some help
from the massaging actions of contracting skeletal
muscles during movement. Because most of the
body’s INFECTION-fighting action takes place in the
lymph nodes and other lymph tissues, the lymph
is the primary pathway for transporting pathogens
for destruction by macrophages and other leuko-
cytes in the lymph nodes. The lymph also is the
primary channel for the body to carry the residue
of infection to other structures and systems that
eliminate it from the body (through phagocytosis
as well as other means). CANCERcells can overload
the lymph, hijacking it to become the pathway for
their spread (METASTASIS) to other organs and parts
of the body.
For further discussion of the lymph within the
context of blood and lymph structure and func-
tion please see the overview section “The Blood
and Lymph.”
See also CISTERNA CHYLI; LYMPH NODE; RIGHT LYM-
PHATIC DUCT; THORACIC DUCT.
lymphadenitis INFLAMMATION or INFECTION of
LY M P Hnodes. Lymphadenitis characterizes systemic
infections such as infectious mononucleosis and
regional infections such as SEXUALLY TRANSMITTED
DISEASES(STDS). It may affect any lymph nodes in
the body though is most noticeable when it affects
LYMPH NODEclusters near the surface of the SKIN,
such as in the neck, axillae (underarms), and
groin (inguinal). The typical symptoms of lym-
phadenitis are palpable lymph nodes that may
range in size from that of a small pea to that of a
large marble. The swellings are often painful, and
the skin above the area may be reddened (erythe-
matous) and warm to the touch when infection of
the lymph nodes themselves is the cause. Diagno-
sis may require lymph node biopsy when there
are no clear signs of infection or when lym-
phadenitis continues beyond six weeks.
Lymphadenitis without signs of infection may
indicate cancer, either affecting the lymph struc-
tures (LYMPHOMA) or in METASTASISfrom any loca-
tion in the body. Pathogens or cancer cells
traveling through the lymph can initiate such a
massive activation of phagocytic response that the
resulting action of macrophages and lymphocytes
overwhelms the lymph nodes with cellular debris
faster than the lymph can carry it away.
See also LYMPH VESSELS; MONONUCLEAR PHAGOCYTE
SYSTEM; MONONUCLEOSIS, INFECTIOUS; PHAGOCYTOSIS.lymphadenopathy Swelling and enlargement of
the LY M P Hnodes. Lymphadenopathy indicates that
the affected lymph nodes are fighting an INFECTION
in nearby tissues, and the enlargement is most
often benign and normal. A common manifesta-
tion of lymphadenopathy is swollen lymph nodes
in the neck when a person has a sore THROAT, or
under the arm when there is a cut or bruise on
the hand or arm. The swollen lymph nodes typi-
cally feel firm to the touch and may hurt. As the
underlying infection improves, the swelling
retreats, and the lymph nodes return to normal
size. When lymph nodes throughout the body are
swollen, the underlying cause is likely a systemic
infection such as a VIRUS. Occasionally persistent
lymphadenopathy suggests LYMPHOMAor LEUKEMIA,
cancers of the lymph tissues or BONE MARROW.
See also LYMPHADENITIS; LYMPH NODE.lymphangioma A noncancerous LESIONmade up
of LYMPH VESSELS. Pathologically, doctors classify alymphangioma 149