Video Transcript
The diagram below shows a
simplified drawing of the interactions of a lymphatic capillary with the surrounding
tissue. Which of the following correctly
identifies the processes represented by the black and white arrows? (A) The black arrows represent the
movement of the blood, and the white arrows represent the movement of the lymph. (B) The black arrows represent the
movement of the lymph, and the white arrows represent the movement of the blood. (C) The black arrows represent the
movement of urea, and the white arrows represent the diffusion of ions. Or (D) the black arrows represent
the diffusion of ions, and the white arrows represent the movement of urea.
Let’s remove the answer options to
make space to work the question through. The question asks us about the
lymphatic capillaries, which are shown here in green between the capillary blood
vessels. While the lymphatic capillaries and
capillary blood vessels carry different substances, they are both incredibly small
vessels that are important for circulation and even immune function. Let’s look at the diagram we are
given more closely in order to try and answer our question correctly.
You might’ve learned that all of
the cells in the body require oxygen and nutrients in order to survive, and these
are delivered by the bloodstream. Specific blood vessels called the
arteries are responsible for carrying blood away from the heart to the body
cells. Most arteries, except the pulmonary
artery, which leads to the lungs, carry oxygenated blood.
As these vessels move away from the
heart, they divide into smaller and smaller vessels called arterioles, like the one
in our diagram. These further divide into the
smallest type of blood vessel called capillaries, which have walls one cell
thick. They are leaky vessels that will
allow some of the fluid to move out and bathe the body cells. This is called interstitial fluid,
and it provides the cells with the nutrients and oxygen they require and allows
waste to be removed.
The majority of this interstitial
fluid will reenter the blood by being reabsorbed by the capillaries. Then, the blood moves to the
venules, which combine to form veins. Veins are the blood vessels that
carry blood back to the heart so it can then be pumped to the lungs to be
reoxygenated, starting the process all over again.
Any interstitial fluid that is left
over will be absorbed by the lymphatic capillaries that transport excess fluid away
from the tissues. Once the interstitial fluid enters
the lymphatic capillaries, it is called lymph. This fluid then travels throughout
the lymphatic system and through specific organs called lymph nodes, which you
might’ve heard of before since they often swell when you get sick.
The lymph nodes filter the blood of
damaged or cancerous cells. They also produce and store the
white blood cells called B and T lymphocytes. These attack any pathogens entering
the lymph nodes and are also released into the blood to fight infections. Eventually, the lymph rejoins the
blood so that it can continue to circulate the body.
After reviewing each vessel in our
diagram and their function in the body, we should be able to answer our question
correctly. We just learned that the arterioles
and venules, which contain white arrows in this diagram, will carry blood and the
lymphatic capillaries, which have black arrows, will carry lymph. Therefore, the correct answer to
our question, “Which of the following correctly identifies the processes represented
by the black and white arrows?,” is answer choice (B). The black arrows represent the
movement of the lymph, and the white arrows represent the movement of the blood.
