Video Transcript
The figure shows a cross section of
a lymph node. What cells can be found inside the
structure? (A) Stem cells that develop into
all types of blood cells. (B) Lymphocytes, macrophages, and
other white blood cells. (C) Aging red blood cells and their
breakdown products. Or (D) only T lymphocytes in their
final stages of maturation.
The immune system is a collection
of organs, special cells, and chemicals that work to prevent and fight off illness
and infection. One part of the immune system is
the lymphatic system. It contains a network of lymph
vessels which transport a fluid called lymph between the body tissues and the
capillaries of the circulatory system. Located at the junctures of several
lymph vessels are small organs called lymph nodes. As our blood circulates, fluid
moves out of the capillaries and into body tissues, as represented by the black
arrows. Some of this fluid is then
reabsorbed by the lymph vessels. It is now referred to as lymph and
will be transported to the lymph nodes, as shown by the pink arrows.
The lymph nodes have the important
role of monitoring the lymph and blood to detect any signs of an infection. If a pathogen is detected, the
immune cells in the node will quickly initiate a response. You may have experienced swollen
nodes around your neck or throat during a cold, flu, or other illness. These enlarged nodes are a result
of accelerated division of the white blood cells inside as they prepare to destroy
the pathogens.
There are several types of white
blood cells, also referred to as leukocytes, found inside of lymph nodes. B lymphocytes, like all white blood
cells, are made in the bone marrow. They also complete their maturation
there before moving to the lymph nodes. B lymphocytes produce antibodies,
which are proteins that bind to specific antigens, triggering an immune
response. T lymphocytes are white blood cells
that travel from the bone marrow to complete maturation in the thymus gland.
There are a few different types of
T cells, which are responsible for a variety of immune processes, including killing
infected or abnormal cells and regulating the immune response. Macrophages are white blood cells
that engulf pathogens by phagocytosis, break them apart, and then display parts of
the pathogen on their cell surface. This allows the pathogen to be
easily identified by other immune cells.
Now that we’ve reviewed the form
and function of lymph nodes, let’s return to our answer choices. We can eliminate choice (A),
because the stem cells that develop into blood cells are found in the bone marrow,
not the lymph nodes. We can also eliminate choice (C),
which describes the spleen. T lymphocytes can be found in the
lymph nodes, but they complete maturation in the thymus and are not the only cell
type in the nodes. So, choice (D) can be ruled out as
well.
Therefore, the correct answer is
(B). The lymph node contains
lymphocytes, macrophages, and other white blood cells.
