Video Transcript
Which of the following is a major
function of the lymphatic system? (A) Transporting oxygen and glucose
to respiring cells. (B) Returning excess fluids that
collect in tissue back to the blood. (C) Initiating the diffusion of
gases across cell membranes in the lungs. Or (D) filtering blood and
regulating the excretion of waste products.
The lymphatic system is closely
linked to the human circulatory system. So let’s take a look at how these
two systems interact at a section of body tissue so we can work out the correct
answer to this question.
You may remember that within the
circulatory system, blood is carried away from the heart through blood vessels
called arteries, which transports the blood into smaller and smaller vessels as they
approach body tissues. The smallest of these vessels are
called capillaries. And they are the site of the
exchange of materials between the blood and the body tissues.
The cells of the body tissues,
which have been shown here in orange, are surrounded by a space called the
interstitial space, which is filled with interstitial fluid. Useful substances, like oxygen and
glucose, are transported from the blood in the capillaries and into the interstitial
fluid, where the substances can be taken up by the body cells as required.
Waste products will move in the
opposite direction from the body cells, into the interstitial fluid, and then into
the capillaries to enter the bloodstream. The blood containing these waste
products is then transported through larger and larger blood vessels, eventually
emptying into veins that carry blood back to the heart.
Not all of the interstitial fluid
is reabsorbed back into the bloodstream however. Some of the fluid that remains in
the interstitial spaces is absorbed by structures called lymphatic capillaries, one
of which has been shown here in green. Once the fluid has been taken up by
the lymphatic capillaries, it is referred to as lymph. This lymph is carried into larger
lymphatic vessels, passed through various lymphatic organs, and eventually empties
back into the circulatory system.
If we take a look back at our
answer options, we can see that the correct answer is option (B). A major function of the lymphatic
system is returning excess fluids that collect in tissue back to the blood.
