FUNCTIONS OF THE LYMPHATIC SYSTEM
One of the basic tenets of life is that many organisms consume or
use other organisms in order to survive. Some microorganisms, such as certain
bacteria or viruses, use humans as a source of nutrients and as an environment
where they can survive and reproduce. As a result, some of these microorganisms
can damage the body, caus-ing disease or even death. Any substance or
microorganism that causes disease or damage to the tissues of the body is
considered a pathogen. Not
surprisingly, the body has ways to resist or destroypathogens.
The lymphatic (lim-fat′
ik) system functions are
1.
Fluid balance. About 30 liters (L) of fluid pass from theblood
capillaries into the interstitial spaces each day, whereas only 27 L pass from
the interstitial spaces back into the blood capillaries . If the extra 3 L of interstitial
fluid remained in the interstitial spaces, edema would result, causing tissue
damage and eventually death. Instead, the 3 L of fluid enters the lymphatic
capillaries,where it is called lymph
(limf), and it passes through the lymphatic vessels to return to the blood. In
addition to water, lymph contains solutes derived from two sources:(a)
Substances in plasma, such as ions, nutrients, gases, and some proteins, pass
from blood capillaries into the interstitial spaces and become part of the lymph;
(b) substances such as hormones, enzymes, and waste products, derived from
cells within the tissues, are also part of the lymph.
2. Lipid absorption. The lymphatic system absorbs lipids andother substances from the
digestive tract (see figure 16.14) through lymphatic vessels called lacteals (lak′ t̄e -̆a lz) located in
the lining of the small intestine. Lipids enter the lacteals and pass through
the lymphatic vessels to the venous circulation.The lymph passing through these
lymphatic vessels appears white because of its lipid content and is called chyle (k̄ı l).
3.
Defense.
Pathogens, such as microorganisms and otherforeign substances, are
filtered from lymph by lymph nodes and from blood by the spleen. In addition,
lymphocytes and other cells are capable of destroying pathogens. Because the lymphatic
system is involved with fighting infections, as well as filtering blood and
lymph to remove pathogens, many infectious diseases produce symptoms associated
with the lymphatic system (see the Diseases and Disorders table).
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