The lymphatic system has two main functions.
Its network of vessels, valves, ducts, nodes,
and organs helps balance the
body's fluid by draining excess fluid,
known as lymph, from the body's tissue
and returning it to the blood after filtering it.
Some types of blood cells
are also made in the lymph nodes.
The lymphatic system also plays an important
role in the body's immune system.
Infection, even a trivial infection is,
the most common cause
of swollen lymph nodes.
Let's look at a cut section of a lymph node
to see what happens.
Afferent means towards.
Afferent lymph vessels bring unfiltered fluids
from the body into the lymph node
where they are filtered.
Efferent vessels, meaning away from,
carry the clean fluid away and back to the
bloodstream where it helps form plasma.
When the body is invaded by foreign organisms,
the swelling sometimes felt in the neck,
armpits, groin, or tonsils
comes from the microorganisms trapped inside the lymph nodes.
Eventually, these organisms are destroyed and eliminated by cells that line the node walls.
Then the swelling and pain subside.