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37–2 Blood and the Lymphatic System
Section 37–2
1 FOCUS
J
ust as a plumbing system carries water through a series of
pipes to different parts of a house, the circulatory system
carries blood through a series of blood vessels to different parts
of the body. Blood is a type of connective tissue containing both
dissolved substances and specialized cells. Blood collects oxygen
from the lungs, nutrients from the digestive tract, and waste
products from tissues. Blood helps to regulate factors in the
body’s internal environment, such as body temperature. In
addition, components in blood help to fight infections. Blood can
even form clots to repair damaged blood vessels.
Blood Plasma
The human body contains 4 to 6 liters of blood, which is about 8
percent of the total mass of the body. As Figure 37–7 shows,
about 45 percent of the volume of blood consists of cells, which
are suspended in the other 55 percent—a straw-colored fluid
called plasma. Plasma is about 90 percent water and 10
percent dissolved gases, salts, nutrients, enzymes, hormones,
waste products, and proteins called plasma proteins.
Plasma proteins, which perform a variety of functions, are
divided into three groups: albumins, globulins, and fibrinogen.
Albumins and globulins transport substances such as fatty
acids, hormones, and vitamins. Albumins also help to regulate
osmotic pressure and blood volume. Some globulins fight viral
and bacterial infections. Fibrinogen is the protein responsible
for the ability of blood to clot.
Objectives
Key Concepts
• What is the function of each
type of blood cell?
• What is the function of the
lymphatic system?
Vocabulary
plasma
hemoglobin
lymphocyte
platelet
lymph
37.2.1 Describe blood plasma.
37.2.2 Explain the functions of red
blood cells, white blood
cells, and platelets.
37.2.3 Describe the role of the lymphatic system.
Vocabulary Preview
Reading Strategy:
Asking Questions Before
you read, rewrite the headings
in the sections as how, why, or
what questions about blood and
the lymphatic system. As you
read, write brief answers to the
heading questions.
! Figure 37–7
Blood consists of
plasma, blood cells, nutrients,
hormones, waste products, and
plasma proteins. Interpreting
Graphics When a whole blood
sample is placed in a centrifuge, as
shown below, what is the result?
Have students preview new vocabulary by skimming the section and
listing the highlighted, boldface
terms. They should leave space to
make notes as they read the section.
Reading Strategy
Suggest that students preview section
content by studying the figures and
reading the captions. They should
write down any unfamiliar terms and
try to find the meanings as they read.
2 INSTRUCT
Blood Plasma
Use Community Resources
Plasma
Platelets
White blood
cells
Red blood
cells
Whole Blood Sample
Sample Placed in Centrifuge
Have students contact their local
chapter of the American Red Cross to
learn about blood banks and blood
drives in their community. Suggest
that they try to find out who can and
cannot donate blood, how donations
are made, and what happens to the
donated blood. Urge students to
share what they learn with the class.
Blood Sample That
Has Been Centrifuged
SECTION RESOURCES
• Teaching Resources, Lesson Plan 37–2,
Adapted Section Summary 37–2, Adapted
Sav37–2,
Worksheets 37–2, Section Summary
e
e
Worksheets 37–2, Section Review 37–2
• Reading and Study Workbook A,
Section 37–2
• Adapted Reading and Study Workbook B,
Section 37–2
• Investigations in Forensics, Investigation 10
• iText, Section 37–2
• Transparencies Plus, Section 37–2
Tim
Technology:
r
Print:
Answer to . . .
Figure 37–7 The cellular portion and
the plasma portion of blood separate.
Circulatory and Respiratory Systems
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Blood Cells
37–2 (continued)
The cellular portion of blood consists of red blood cells, white
blood cells, and platelets. Red blood cells transport oxygen,
white blood cells perform a variety of protective functions, and
platelets help in the clotting process. Platelets are actually
fragments of cells derived from larger cells in bone marrow.
Blood Cells
Build Science Skills
Calculating Help students appreciate the relative proportions of red
and white cells in blood. Point out
that a milliliter of blood contains
about 5 million red blood cells
(about 5.2 million cells in males and
about 4.7 million cells in females)
and that red blood cells outnumber
white blood cells about 1000 to 1.
Ask: How many white blood cells
are there in a milliliter of blood?
(About 7000) If a milliliter of blood
was found to have 20,000 white
blood cells, what might explain
this increase? (An infection)
Use Community Resources
(magnification: 2342!)
! Figure 37–8
Red blood
cells transport oxygen. White
blood cells fight invasions of
foreign substances, cells, and
organisms. Red blood cells and a
single white blood cell are shown in
this scanning electron micrograph.
Arrange for interested students to
visit a clinic or hospital laboratory
where they can observe blood counts
being performed. If possible, have a
lab technician or supervisor explain
why blood counts are performed and
what can be learned from them.
Other topics the technician or supervisor might address include the
importance of accuracy in blood
counts and the safety precautions
that must be taken when handling
blood samples. Have students report
to the class on what they learn.
NS TA
Download a worksheet
on blood cells for students to complete, and find additional teacher
support from NSTA SciLinks.
N S TA
For: Links on blood
cells
Visit: www.SciLinks.org
Web Code: cbn-0372
Red Blood Cells The most numerous cells in the blood are the
red blood cells, or erythrocytes (eh-RITH-roh-syts).
Red
blood cells transport oxygen. They get their color from
hemoglobin. Hemoglobin is the iron-containing protein that
binds to oxygen in the lungs and transports it to tissues throughout the body where the oxygen is released.
Red blood cells, like those shown in Figure 37–8, are
shaped like disks that are thinner in the center than along the
edges. These cells are produced from cells in red bone marrow.
As these cells gradually become filled with hemoglobin, their
nuclei and other organelles are forced out. Thus, mature red
blood cells do not have nuclei. Red blood cells circulate for an
average of 120 days before they are worn out from squeezing
through narrow capillaries. Old red blood cells are destroyed
in the liver and spleen.
White Blood Cells White blood cells, or leukocytes (LOO-
koh-syts), do not contain hemoglobin. They are much less common than red cells, which outnumber them almost 1000 to 1.
Both white and red blood cells are produced from the same
population of blood-forming stem cells found in the bone marrow. Unlike red blood cells, however, white blood cells contain
nuclei. They may live for days, months, or even years.
White blood cells are the “army” of the circulatory
system—they guard against infection, fight parasites, and
attack bacteria. There are many types of white blood cells, and
they perform a wide variety of important functions. Some protect
the body by acting as phagocytes, or “eating cells,” that engulf and
digest bacteria and other disease-causing microorganisms. Some
white blood cells react to foreign substances by releasing chemicals known as histamines. These chemicals increase blood flow
into the affected area, producing redness and swelling that are
often associated with allergies. Other white blood cells, known as
lymphocytes, are involved in the immune response. B lymphocytes produce antibodies. Antibodies are essential to fighting
infection and help to produce immunity to many diseases.
T lymphocytes help fight tumors and viruses. You will learn
more about lymphocytes in Chapter 40.
White blood cells are not confined to the circulatory system.
Many white blood cells are able to slip out of capillary walls,
travel through the lymphatic system, and attack invading
organisms in the tissues of the body. In many ways, white blood
cells are the first lines of defense when the body is invaded by
disease-causing organisms.
UNIVERSAL ACCESS
Inclusion/Special Needs
Help students grasp the material on blood cells
by helping them organize the details in a compare/contrast table. Use headings for type of
blood cell, number, size, shape, functions, presence/absence of nucleus, source, and life span.
Then, call on volunteers to fill in the table with a
row for red blood cells and a row for white
blood cells. Have students save their tables to
use as study guides.
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Chapter 37
Advanced Learners
Challenge students to find out how hemophilia
is inherited and why it occurs primarily in males.
Have them focus on hemophilia in the family of
Queen Victoria of England. They should find a
family tree showing which of Victoria’s descendants had the disease or carried the defective
gene. Ask volunteers to explain to the class how
hemophilia is inherited, using the family tree to
illustrate their explanation.
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Demonstration
Like an army with units in reserve, the body
is able to increase the number of white blood
cells dramatically when a “battle” is underway. A
sudden increase in the white blood cell count is
one of the ways in which physicians can tell that
the body is fighting a serious infection.
Break in Capillary Wall
Platelets and Blood Clotting Blood is
essential to life. An injury can cause the body to
lose this essential fluid. Fortunately, blood has an
internal mechanism to slow bleeding and begin
healing. A minor cut or scrape may bleed for a
few seconds or minutes, but then it stops. Clean
it up with soap and water, cover it with a bandage, and it begins to heal. Have you ever wondered why the bleeding stops?
The answer is that blood has the ability to
form a clot. Figure 37–9 summarizes the process.
Blood clotting is made possible by
plasma proteins and cell fragments called
platelets. There are certain large cells in bone
marrow that can break into thousands of small
pieces. Each fragment of cytoplasm is enclosed in
a piece of cell membrane and released into the
bloodstream as a platelet.
When platelets come into contact with the
edges of a broken blood vessel, their surfaces
become very sticky, and a cluster of platelets
develops around the wound. These platelets
then release proteins called clotting factors.
The clotting factors start a series of chemical
reactions that are quite complicated. In one
reaction, a clotting factor called thromboplastin
(thrahm-boh-PLAS-tin) converts prothrombin,
which is found in blood plasma, into thrombin.
Thrombin is an enzyme that helps convert the
soluble plasma protein fibrinogen into a sticky
mesh of fibrin filaments. These filaments stop
the bleeding by producing a clot. Figure 37–10
shows the tangle of microscopic fibers in an
actual blood clot.
Use a microprojector to display prepared slides of red blood cells, white
blood cells, and platelets. Have students make a sketch of each
structure. Then, call on students to
describe the size, shape, and general
appearance of each structure.
Use Visuals
Clumping of Platelets
Clot Forms
Figure 37–9 Check students’ comprehension of the figure by having
them identify each of the following in
the drawings: red blood cells (red),
platelets (pink), and fibrin filaments
(blue). Then, ask: What is the main
role of platelets in blood clotting?
(The production of clotting factors such
as thromboplastin) What role do calcium and vitamin K play in blood
clotting? (They help convert prothrombin to thrombin.)
! Figure 37–9
Blood clotting is made
possible by a number of plasma proteins and cell
fragments called platelets. Calcium and vitamin K
aid in converting prothrombin into thrombin.
What are platelets?
"
Figure 37–10 Strands of fibrin trap
blood cells, forming a net that prevents blood
from leaving a damaged blood vessel.
Using Analogies How is a blood clot similar
to a screened-in porch?
(magnification: 3000!)
FACTS AND FIGURES
Red blood cell shapes
Normal red blood cells are disk-shaped, but
some people have red blood cells with abnormal shapes, such as spherical, oval, or sickle
shapes. People with spherical red blood cells
have an inherited disorder called spherocytosis.
Because of their shape, the red cells become
trapped and destroyed by the spleen, leading to
anemia. Treatment may include removal of the
spleen, which corrects the anemia but not the
abnormal shape of the red cells. People with
oval red blood cells have the inherited disorder
elliptocytosis. This sometimes causes mild anemia but usually requires no treatment. People
with sickle-shaped red blood cells have sickle
cell disease, another inherited disorder and the
most serious of the three disorders. Sickle cell
disease can cause severe anemia, organ damage, deformities, and even death.
Answers to . . .
Platelets are cell fragments that form a cluster around a
wound and release clotting factors.
Figure 37–10 It is similar in forming
a mesh barrier that prevents blood
from leaving a damaged vessel (or that
keeps insects out).
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Blood Transfusions
37–2 (continued)
Blood Type
of Donor
Blood Transfusions
Tell students that the first successful
blood transfusions were performed in
the early 1800s by a British physician
named James Blundell. At least half of
Blundell’s patients benefited from the
transfusions, but many others had
severe reactions to the transfused
blood, and most of these died. In
1900, an Austrian physician, Karl
Landsteiner, discovered the ABO
blood group. Knowledge of ABO
blood types explained Blundell’s
results and, in general, why some
transfusions are successful and others
are not.
Answers
1. Type O is sometimes referred to as
the “universal donor.” Type AB is
sometimes referred to as the “universal recipient.”
2. Yes, because people with type A
blood can safely receive type O
blood, but people with type O blood
cannot safely receive type A blood.
3. Student answers should reflect an
understanding of blood groups and
genetics. Suggested answer: People
who have type O blood do not produce blood antigens and therefore
can donate blood to any of the other
blood groups safely. Because the
alleles for type A and B are codominant, people with type AB blood can
receive blood from all groups.
Although the first successful transfusions of human
blood were carried out in the 1820s, many recipients
had severe reactions to the transfused blood, and
several died. Today we know why. We inherit one of
four blood types—A, B, AB, or O—which are determined by antigens on our blood cells. Antigens are
substances that trigger an immune response. People
with blood type A have A antigens on their cells,
those with type B have B antigens, those with AB
blood have both A and B, and those with type O have
neither A nor B antigens.
When blood types match, the transfusion is successful. However, transfusions are successful in some
cases even when the blood types of the donor and
the recipient do not match. Use the table to answer
the questions that follow.
Chapter 37
A
!
X
!
X
B
X
!
!
X
AB
X
X
!
X
O
!
!
!
!
X = Unsuccessful transfusion ! = Successful transfusion
1. Drawing Conclusions Which blood type is
sometimes referred to as the “universal donor”?
Which is known as the “universal recipient”?
2. Drawing Conclusions In a transfusion involving
the A and O blood types, does it make a difference
which blood type belongs to the recipient and
which to the donor?
3. Applying Concepts Write a brief explanation
for the results in the chart using information about
phenotypes and genotypes in blood group genes.
(Hint: Review Section 14–1 if needed.)
The Lymphatic System
As blood circulates, some fluid leaks from the blood into the
surrounding tissues. This isn’t an altogether bad thing. A steady
flow of fluid helps to maintain an efficient movement of nutrients
and salts from the blood into the tissues. However, more than 3
liters of fluid leak from the circulatory system into surrounding
tissues every day! If this leakage continued unchecked, the body
would begin to swell with fluid—not a very pleasant prospect.
Fortunately, the interrelationship between two body systems
does not allow this to happen.
A network of vessels,
nodes, and organs called the lymphatic system collects
the fluid that is lost by the blood and returns it back to
the circulatory system. The fluid is known as lymph (LIMF).
Build Science Skills
954
Blood Type of Recipient
AB
B
O
Blood Clotting Problems If the wound is small, within a
few minutes the mesh of platelets and fibrin seals the wound, and
bleeding stops. Most of the time, this clotting reaction works so
well that we take it for granted. However, if one of the clotting
factors is missing or defective, the clotting process does not work
well. Hemophilia is a genetic disorder that results from a defective
protein in the clotting pathway. People with hemophilia cannot
produce blood clots that are firm enough to stop even minor
bleeding. They must take great care to avoid injury. Fortunately,
hemophilia can be treated by injecting extracts containing the
missing clotting factor.
The Lymphatic
System
Applying Concepts Tell students
that both malaria and sickle cell anemia are diseases that damage red
blood cells. Ask: Why do people
with malaria or sickle cell anemia
often have enlarged spleens?
(Damaged red blood cells are removed
by the spleen. It becomes enlarged
when there are many damaged cells.)
A
FACTS AND FIGURES
Lymphatic System Facts
The thymus is the primary lymphoid organ
and the site where lymphocytes acquire their
antigen receptors. It attains its full size by age
two, then decreases in size until puberty, after
which it almost disappears. Secondary lymphoid organs include the spleen and tonsils.
Most antibodies are made in the spleen. It
consists of white pulp, where T cells are stimulated by antigen, and red pulp, where old red
blood cells are removed. The red pulp also
manufactures new red blood cells when too
many are lost during illness. Tonsils are small
pieces of lymphatic tissue in the throat. Their
primary role is to trap and destroy bacteria
that enter the respiratory tract. One set of tonsils protrudes from each side of the pharynx
behind the mouth. Another set, commonly
called adenoids, is located higher up in the
pharynx behind the nose.
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Lymph collects in lymphatic capillaries and slowly flows into
larger and larger lymph vessels. Like large veins, lymph
vessels contain valves that prevent lymph from flowing
backward. Ducts collect the lymph and return it to the
circulatory system through two openings in the superior
vena cava. The openings are under the left and right clavicle
bones just below the shoulders. Figure 37–11 shows the
lymphatic system.
Along the length of the lymph vessels are small beanshaped enlargements called lymph nodes. Lymph nodes
act as filters, trapping bacteria and other microorganisms
that cause disease. When large numbers of microorganisms are trapped in the lymph nodes, the nodes become
enlarged. If you have ever had “swollen glands,” you
actually had swollen lymph nodes.
Lymph vessels do not merely return excess fluid to the
circulation. They also play a very important role in nutrient
absorption. Lymph vessels lie near the cells that line the
intestines, where they absorb fats and fat-soluble vitamins
from the digestive tract and carry them to the blood. Lymph
moves through the lymphatic system under osmotic pressure
from the blood and is pushed along by the contractions of
nearby skeletal muscles. It is important that there is a
steady flow of lymph. Edema, a swelling of the tissues due to
the accumulation of excess fluid, can occur when lymphatic
vessels are blocked due to injury or disease.
In addition to the lymph vessels and lymph nodes, the
thymus and spleen also have important roles in the
lymphatic system. The thymus is located beneath the
sternum. Certain lymphocytes called T cells mature in the
thymus before they can function in the immune system.
T cells are the cells that recognize foreign “invaders” in
the body. The spleen helps to cleanse the blood and
removes damaged blood cells from the circulatory system.
The spleen also harbors phagocytes that engulf and
destroy bacteria and other microorganisms.
Use Visuals
Superior
vena cava
Thymus
Heart
Thoracic
duct
Spleen
Lymph
nodes
Lymph
vessels
3 ASSESS
Evaluate Understanding
! Figure 37–11
The lymphatic
system collects and returns fluid that leaks
from blood vessels. The spleen is an organ
whose main function is to destroy damaged
red blood cells and platelets. Certain white
blood cells called T lymphocytes, or T cells,
mature in the thymus gland, which produces
hormones that promote their development.
37–2 Section Assessment
1.
Key Concept List the
main function of red blood cells,
white blood cells, and platelets.
2.
Key Concept Describe the
role of the lymphatic system.
3. What types of materials are
dissolved in plasma?
4. Explain how blood clots.
Figure 37–11 Have students compare the distribution of lymphatic
vessels with the distribution of blood
vessels, shown in Figure 37–3. Then,
ask: How are the lymphatic and circulatory systems related? (The
lymphatic system collects fluid that
seeps into the tissues from blood and
returns it to the circulatory system.)
Point out that the vein where this
fluid is returned to the blood is called
the superior vena cava. Have students find the superior vena cava in
the figure. Also have them locate the
clusters of lymph nodes. Ask: If you
have a sore throat because of an
infection, which lymph nodes
might become swollen? (The lymph
nodes in the neck)
5. Critical Thinking Inferring
Sometimes lymph nodes must be
surgically removed. Although
more lymph vessels eventually
grow, what result would you
expect to see immediately after
surgery?
Constructing a
Concept Map
Construct a concept map that
shows the components of
blood. Include information
about the functions of the
different components. (Be
sure to include the different
types of white blood cells.)
Call on students at random to name
each component of the blood. Call
on other students to describe the
function of each component.
Reteach
Using the chalkboard or a transparency, work with students to create
a concept map of the functions of
blood based on information in the
opening paragraph of the section.
Then, have students identify the
parts of the blood involved in each
function.
Students’ concept maps should
show that blood consists of plasma, platelets, red blood cells, and
white blood cells, of which there
are five main types: neutrophils,
eosinophils, basophils, monocytes,
and lymphoctyes.
37–2 Section Assessment
1. Red blood cells carry oxygen; white blood
cells fight infection; platelets help blood to
clot.
2. Its role is to collect fluid lost by blood and
return it to the circulatory system.
3. Gases, salts, nutrients, enzymes, hormones,
waste products, and plasma proteins
4. When platelets come in contact with the
broken edges of a blood vessel, their surfaces become sticky. A cluster of platelets
develops around the wound. The platelets
release clotting factors, which start reactions
that produce a blood clot.
5. Areas without lymph nodes and vessels
would retain excess fluid and become
swollen immediately after surgery.
If your class subscribes to the iText,
use it to review the Key Concepts in
Section 37–2.
Circulatory and Respiratory Systems
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