In this video, we will learn to
describe the structure and function of the major components of the blood, those
components being red blood cells, white blood cells, platelets, and plasma. Then we’ll try some practice
questions and at the end we’ll summarize what we’ve learned.
We tend to simply think of blood as
a red liquid that oozes from our body when we accidentally cut a finger or scrape a
knee. But your blood is actually a type
of connective tissue, which means that it is composed of many cells suspended in a
nonliving matrix or a substance. The two main types of cells in your
blood are red blood cells, commonly shortened to RBCs, and white blood cells,
commonly shortened to WBCs. Also found in your blood are small
cell fragments called platelets. And all three of these components
are suspended in an amber-colored liquid called plasma. And this heterogeneous mixture is
what we refer to as blood.
All of the blood in your body is
contained within your circulatory system, which consists of your heart, which pumps
the blood, and the complex closed network of blood vessels that carry the blood from
place to place. Blood has several important
functions. Its primary function is
transport. Blood transports gases like oxygen
and carbon dioxide. It transports nutrients like
glucose. It also transports waste products
and hormones. Blood also helps to prevent
infection. It helps your body to maintain a
uniform and appropriate temperature. Your blood also helps to maintain
fluid and chemical balance within the body. The red blood cells, white blood
cells, platelets, and plasma are all adapted to allow the blood to carry out these
Next, let’s take a closer look at
each of these four components. First, we have red blood cells,
also called erythrocytes. Erythro- is a prefix that means
red, and -cyte is a word part that means cell. The primary function of
erythrocytes is to carry oxygen from the lungs to the rest of the tissues of the
body. These cells are the most numerous
in your blood, and they have several adaptations that allow them to carry out their
Most notably, they have a distinct
red color. This color comes from a molecule
called hemoglobin, which is rich in iron. Hemoglobin is a molecule that helps
the red blood cells to carry oxygen. Another important feature of mature
red blood cells is that they do not possess a nucleus. They also don’t have mitochondria
or many other organelles. They’re basically just sacs filled
with cytoplasm that’s rich in hemoglobin.
This lack of a nucleus gives red
blood cells their distinct shape. They’re shaped like a disk with
indents on each side. This shape is called biconcave. Bi- is a prefix that means two, and
concave is what we call an indented shape. I like to remember this because
caves are like indents in rocks. This shape increases the surface
area of the cell in relation to the cytoplasm inside, which allows more oxygen to
diffuse into the cell more quickly. These special features in the
structure of the red blood cell directly support their function of carrying oxygen
throughout the body.
Next, let’s look at some of the
special features of platelets. Platelets are also scientifically
known as thrombocytes. Thrombo- is a word part that means
clot, and platelets serve the purpose of causing blood clotting. And -cyte does mean cell, but
platelets are technically small fragments of much larger cells. If you were to injure yourself and
tear a blood vessel, causing bleeding, the damaged epithelial cells would release
chemical signals, which activate the platelets in your bloodstream, causing them to
stick together and form a plug over the wound.
This plug serves two purposes. First, it prevents you from
bleeding indefinitely and losing too much of your blood too quickly. Secondly, it prevents pathogens
from entering the bloodstream, where they could cause a serious infection. Blood clotting is an important
adaptation that helps to protect our bodies. But sometimes blood clots can be
dangerous. Sometimes blood vessels become
damaged because of disease. If a blood clot occurs in the blood
vessels that carry oxygenated blood to the heart or to the brain, it can cause a
heart attack or a stroke, which is one of the reasons why it’s so important to keep
your circulatory system healthy.
Next, let’s take a closer look at
white blood cells. White blood cells are also called
leukocytes. Leuko- is a word part that means
white, and I’m sure you know by now that -cyte means cell. White blood cells, unlike platelets
and red blood cells, actually possess a nucleus. White blood cells are responsible
for protecting our bodies from infection by identifying and destroying antigens. They’re an important part of our
There are many different types of
white blood cells, which each play a specific role in our immune response. One of these types is called a
lymphocyte. These cells are more common in our
lymphatic system than in our blood. And they play a wide range of roles
when it comes to fighting infection. Another important type of white
blood cell is called phagocytes. And these cells are able to
surround and engulf foreign particles that are found in the blood.
Now that we’ve investigated red
blood cells, which carry oxygen, platelets, which are responsible for blood
clotting, and white blood cells that fight infection, let’s take a look at the
material that holds it all together, blood plasma. Our blood plasma is an
amber-colored liquid that’s mostly water. And it serves the purpose of
carrying the red blood cells, white blood cells, and platelets throughout the blood
Besides water, plasma contains and
transports many materials our body relies on to function properly. These include electrolytes,
proteins, hormones, nutrients, and waste products on their way to be removed from
the body. The average human adult has about
one and a half gallons, or around five liters, of blood circulating throughout their
body. If we were to separate blood into
its components, about 45 percent of the blood would consist of red blood cells,
about one percent would be platelets and white blood cells, and about 55 percent of
your blood would be plasma.
Now that we’ve learned about the
components of our blood and the adaptations that allow them to carry out their
function, let’s try a practice question.
Which of the following is not a
major component of blood in humans? (A) Epithelial cells, (B) red blood
cells, (C) white blood cells, (D) plasma, or (E) platelets.
This question is asking us to
recall the major components of blood and then choose the response that is not one of
those components. So first, let’s recall that there
are four major components to human blood. We’ll briefly review them before we
select our answer.
Here we have a diagram of a blood
vessel. And we’ve exposed a view of the
lumen so that we can see the blood flowing through it. The blood vessel has an inner
lining composed of a layer of epithelial cells. The main component of our blood is
plasma, an amber-colored liquid.
Plasma transports electrolytes,
proteins, hormones, nutrients, and waste from place to place in the body. It also carries the different types
of blood cells. Red blood cells are cells that are
specifically adapted to transport oxygen. White blood cells are immune cells
that help our bodies to identify and fight off pathogens. And platelets are small cell
fragments that form blood clots in order to prevent bleeding and infection. Red blood cells, white blood cells,
platelets, and plasma are the four components that make up human blood. Epithelial cells are lining cells
and not a part of the blood itself.
Returning to our answer choices,
which of the following is not a major component of blood in humans? Well, epithelial cells are not a
component of our blood.
Let’s try one more practice
What is the scientific name given
to red blood cells in humans? (A) Phagocytes, (B) hemocytes, (C)
lymphocytes, (D) erythrocytes, or (E) oocytes.
This question is asking us to
select the option that’s telling us the scientific name that we use for red blood
cells. This is where being familiar with
the different parts that make up scientific words really comes in handy. We can break the words in our
answer choices down into five different prefixes and just one suffix. The word part -cyte means cell,
which tells us that all of our choices actually name different types of cells.
Phago- is a word part that means
eating. And phagocytes are cells that are
able to surround and engulf particles or other cells. Hemo- is a word that means
pertaining to the blood. And hemocyte is a general term for
blood cells. It applies to more than one type of
cell in more than one type of organism. Lympho- is a word that means
pertaining to the lymphatic system. Lymphocytes are a type of immune
cell. Erythro- is a word part that means
red. So an erythrocyte would be a red
cell. That sounds right, but let’s keep
going. Oo- is a word part that means
egg. So oocytes are egg cells.
Let’s return to our answer
choices. Some of these are obviously
incorrect. And on first glance, you might be
tempted to choose hemocytes, especially if you remember that red blood cells contain
hemoglobin. But hemocyte is a general term for
all blood cells and actually usually refers to the blood of invertebrates, not
humans. Erythro- is a word part that means
red. So the correct scientific name
given to red blood cells is erythrocytes.
Let’s go ahead and wrap up our
lesson by reviewing what it is we’ve learned. In this lesson, we learned about
the function of blood. We learned about the four
components of blood: red blood cells, white blood cells, platelets, and plasma. And we learned about the scientific
names, adaptations, and different functions of each of these components.