Video Transcript
In this video, we will learn about
the lymphatic system and the different roles it plays in the body. We will also learn about the
different components of the lymphatic system and why they are important.
Our bodies have several different
systems that carry out all of our life processes: our digestive system that breaks
down our food, our respiratory system that provides us with energy, our circulatory
system that supplies our organs with oxygen and nutrients, our nervous system that
controls our responses to stimuli, and our immune system that keeps us healthy and
free from infection. But all of these systems don’t work
alone. They’re all interconnected and
dependent on one another, working together to make sure that all of our life
processes are running smoothly.
In this video, we are going to
learn about the lymphatic system, which plays an important role in both the
circulatory system and the immune system. Let’s start by looking at how the
lymphatic system and circulatory system work together in the body.
As you may know, the circulatory
system consists of the heart, which acts as a central pump, and a network of blood
vessels. The heart pumps blood into vessels
called arteries, which carry blood away from the heart and towards the other organs
of the body. At the tissues of these organs, the
arteries branch into smaller and smaller vessels. The tiniest of these vessels are
called capillaries, and these branch out, surrounding the cells of the organs. This forms a capillary bed, as you
can see here.
Let’s zoom in to one section of the
capillary bed to see what happens here. In the capillary bed, some of the
fluid from the capillaries leaks out, filling the spaces between the cells of the
organs. These spaces are called
interstitial spaces. The fluid that fills the
interstitial spaces, which is now called the interstitial fluid, is rich in oxygen
and nutrients that the cells of the body need. The cells take up these essential
molecules from the interstitial fluid and release their waste products back into
it. Most of the interstitial fluid is
then reabsorbed into the capillaries. The capillaries then merge into
larger vessels, eventually pouring into veins, which carry blood away from the
organs and back toward the heart.
However, not all of the
interstitial fluid is reabsorbed. A small volume of this fluid
remains in the interstitial spaces of the body tissues. So what happens to this remaining
fluid? Well, this is where the lymphatic
system comes into play. Like the circulatory system, the
lymphatic system has tiny lymphatic vessels called lymphatic capillaries. These lymphatic capillaries have a
similar structure to veins. And they absorb the fluid from the
interstitial spaces, eventually returning it to the circulatory system. Once the fluid has been taken up by
the lymphatic capillaries, it is referred to as lymph.
The fluid that makes up
interstitial fluid is originally supplied by small blood vessels called arterioles
that branch into smaller blood vessels called capillaries. Some blood plasma flows out of the
capillaries and into the interstitial spaces to make up interstitial fluid. The nutrients can then be absorbed
from the interstitial fluid into the cells of the body tissues to be used as
required. The cell’s waste products can then
move into the interstitial fluid and then into the capillaries, into small blood
vessels called venules, and eventually to the heart.
As lymph is derived from
interstitial fluid, it’s also derived from blood plasma, which is 90 percent
water. It also carries proteins, fats,
salts, and white blood cells, which are also called leukocytes.
Let’s take a look at where the
lymph goes once it’s been collected by the lymphatic capillaries. Once the extra fluids have been
collected by the lymphatic capillaries, these tiny vessels merge into larger and
larger lymphatic vessels. These lymphatic vessels have
flap-like structures called valves, which make sure that the fluid only flows in one
direction, away from the capillary beds. The lymphatic vessels pass the
lymph through other lymphatic organs, such as lymph nodes, which we will discuss in
more detail later on in the video.
Eventually, the larger lymphatic
vessels lead into two main lymphatic ducts, which are known as collecting ducts. One of these two ducts, the
thoracic duct, has been labeled on this diagram. These ducts empty the lymph into
veins called the subclavian veins, which make up part of the venous system. Remember, veins generally carry
blood away from body tissues and organs toward the heart. They’ve been labeled in this
diagram in blue. The subclavian veins can return the
blood and the lymph to the vena cava, which then drains into the heart.
There’s an important difference
between the lymphatic system and the circulatory system that we can spot in this
diagram. The circulatory system forms a
closed loop, carrying blood from the heart to the organs via the arterial system and
then back to the heart through the venous system. The lymphatic system, on the other
hand, only carries lymph in one direction, from the interstitial spaces to the veins
surrounding the heart. This is why we call the lymphatic
system an open system.
Another interesting function of the
lymphatic system is the absorption of fats into the bloodstream. This occurs across the surface of
the small intestine. If we were to cut a cross section
through a part of the small intestine, it might look something like this. The inner surface of the small
intestine is covered with small fingerlike projections called villi. A singular villi is called a
villus. Villi serve to increase the surface
area of the small intestine for the absorption of nutrients from food that passes
through it.
Let’s take a closer look at just
one villus. Each villus has a network of blood
vessels, as you can see here. These blood capillaries connect the
villi to the circulatory system. Most of the nutrients from food
that we digest are absorbed directly into the bloodstream, but fat molecules are too
large to enter these capillaries. Because of this, each villus in the
small intestine also has a single lymphatic capillary. These special lymphatic capillaries
in the digestive system are called lacteals.
Lacteals are larger than blood
capillaries, which is another key difference between the lymphatic system and the
circulatory system. This allows the fat molecules to
enter these vessels instead and make their way into the larger vessels of the
lymphatic system. Through the network of lymphatic
vessels, these fat molecules are eventually transported into the bloodstream.
We mentioned earlier that the
lymphatic vessels pass the lymph through the lymphatic organs before returning it to
the bloodstream. These lymphatic organs have
important functions in the immune system. The first lymphatic organs that
we’ll learn about are the lymph nodes. These are small bean-shaped
structures about one centimeter in size. If you’ve ever had a cold or sore
throat, you might have felt swollen lymph nodes just below your jaw on either side
of your neck. The diagram here shows several
lymph nodes around the neck, but we actually have hundreds of them in groups all
over the body.
Let’s take a closer look at just
one of these lymph nodes. When the lymphatic vessels collect
fluid from the interstitial spaces, they might take up pathogens, which are
biological agents that can cause disease. If pathogens are allowed to enter
the bloodstream, they can reach the other organs of the body and cause harmful
infections. The role of the lymph nodes is to
act like a filter for these pathogens. Lymph nodes contain immune cells
called lymphocytes, which are a type of white blood cell. If the lymph that’s delivered to
the lymph nodes contains pathogens, they are trapped by the lymphocytes.
This is why the lymph nodes
sometimes become swollen. The lymphocytes are activated and
generate an immune response against these pathogens. This immune response attempts to
destroy or inactivate the pathogens, hopefully preventing them from causing
infections. The activated lymphocytes multiply
to form large numbers and exit the lymph nodes along with the lymph. They can then circulate around the
body, attacking any other similar pathogens.
The second lymphatic organ that
we’ll learn about in this video is the spleen. It’s located in the upper-left part
of the abdomen, just behind the stomach. Usually, it’s between seven and 14
centimeters long. An enlarged spleen can be a sign of
certain infections or other health conditions. Like the lymph nodes, the spleen
also behaves as a filter, destroying the pathogens that might be present in
lymph. The spleen also filters out old or
damaged red blood cells from the bloodstream. It also stores the iron that’s
obtained from these damaged red blood cells. The iron is eventually returned to
the bone marrow. Hemoglobin is produced in the bone
marrow using this iron. Hemoglobin is a protein that
contains iron and is responsible for carrying oxygen in red blood cells.
Let’s apply what we’ve learned
about the lymphatic system to a practice question.
Which of the following is a primary
function of lymph nodes? (A) Lymph nodes circulate the lymph
back to the tissue it came from. (B) Lymph nodes are responsible for
the transport of lymph from tissue to the circulatory system. (C) Lymph nodes are responsible for
initiating an immune response to an infection by a pathogen. Or (D) lymph nodes initiate the
conversion of waste material in the lymph into useful substances.
This question asks us about the
primary function of lymph nodes. Let’s take a look at the lymphatic
system and the role of lymph nodes to figure out the answer. The lymphatic system plays
important roles in the circulatory system and the immune system. In the circulatory system, blood is
pumped from the heart to the different tissues of the body through blood
vessels. When the blood vessels reach the
body tissues, they branch into finer vessels, which are called capillaries. The capillaries form a network
around the cells of the tissues, forming a capillary bed.
Fluid containing oxygen and other
nutrients is released from the capillaries and into the spaces between the
cells. The spaces between the cells are
called the interstitial spaces. The cells take up the oxygen and
nutrients they need and release their waste products back into the interstitial
fluid in these spaces. Most of the interstitial fluid
remaining is then taken up by the capillaries and fed back into the bloodstream to
be returned to the heart. However, a small volume of fluid
remains in the interstitial spaces. The lymphatic system is responsible
for collecting this remaining fluid. This occurs in lymphatic
capillaries, which then drain back into the circulatory system. Once the fluid is taken up by the
lymphatic vessels, it is called lymph.
Lymph contains a lot of water and
carries proteins, fats, and other materials. It might also carry pathogens, for
example, disease-causing microorganisms or viruses, from the tissues. As the lymph travels through the
lymphatic vessels on its way back to the bloodstream, it passes through lymphatic
organs called lymph nodes.
Lymph nodes are small bean-shaped
structures found in groups all over the body. They contain immune cells called
lymphocytes. If the lymph passing through the
lymph nodes contains pathogens, the lymphocytes become activated. They generate an immune response to
the pathogen, destroying or inactivating it. The lymphocytes then exit the lymph
nodes along with the lymph to travel through the bloodstream and attack all other
similar pathogens throughout the body.
If we take a look at the options in
the question, we can see that option (C) correctly outlines the primary function of
lymph nodes in the body. The correct answer is therefore
option (C). The lymph nodes are responsible for
initiating an immune response to an infection by a pathogen.
Let’s review the key points that
we’ve learned about the lymphatic system in this video. The lymphatic system collects lymph
from the interstitial spaces between the cells in body tissues. The lymphatic system then carries
lymph through lymphatic vessels to empty it into the circulatory system. The lymphatic system consists of an
open loop of vessels that are wider than blood vessels. Lymph nodes are small lymphatic
organs that contain immune cells responsible for initiating an immune response
against pathogens. The spleen is another lymphatic
organ and possibly the most important in the body. Among its other roles, it contains
immune cells called lymphocytes that filter pathogens out of the bloodstream. There are special lymphatic
capillaries in the digestive system called lacteals, which help in the absorption of
fat molecules.
