Download Respiration and Circulation Blood Functions of Blood

Respiration and Circulation
Blood
Functions of Blood
Have your ever had an injury that caused bleeding? Blood
is a red liquid that is a little thicker than water. You learned
that your circulatory system works closely with all your
other body systems to maintain homeostasis. Blood is the
link that connects the circulatory system with all the other
body systems. Blood transports substances around your
body. It helps protect your body from infection. Blood also
helps keep your body’s temperature steady.
Transportation
Protection
Some blood cells fight infection. They help protect you
from harmful organisms, such as bacteria, viruses, fungi, and
parasites. Blood also contains materials that help repair torn
blood vessels and heal wounds. When you get a cut or a
scrape, materials in your blood help protect your body from
losing too much blood.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Blood transports many substances through your body.
You have read that blood carries oxygen to and carbon
dioxide from your lungs. Blood also picks up nutrients in the
small intestine and carries them to all body cells. It transports
hormones that are produced by the endocrine system. Blood
carries waste products to the excretory system. Most of the
substances are dissolved in the liquid part of blood.
Temperature Regulation
Blood helps your body stay at a temperature of about 37°C.
When your body temperature is too high, blood vessels near the
surface of your skin widen. This increases blood flow to your
skin’s surface and releases more thermal energy into the air.
Your body cools down. When your body temperature lowers,
blood vessels at your skin’s surface get narrower. This decreases
blood flow to your skin’s surface and reduces the amount of
thermal energy that is lost to the air. Your body warms up.
Parts of Blood
Blood is a tissue because it is made up of different kinds of
cells that work together. The figure shows blood’s four main
parts: red blood cells, white blood cells, platelets, and plasma.
Most adults have about 70 mL of blood per kilogram of body
weight. An average adult has about five to six liters of blood.
Platelets
Red blood cells
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
White blood
cells
Plasma
Red Blood Cells
Every cubic milliliter of your blood contains four to six
million red blood cells, or erythrocytes (ih RITH ruh sites).
Red blood cells are made mostly of iron-rich protein
molecules called hemoglobin (HEE muh gloh bun). In the
alveoli of the lungs, oxygen attaches to the hemoglobin. The
hemoglobin releases the oxygen when red blood cells enter
the capillaries and get close to body cells.
Look at the red blood cells in the figure above. How
would you describe their shape? You might say that they
look like doughnuts without holes. This flattened disk shape
gives red blood cells more surface area. They can carry more
oxygen than they could if they were round like a ball. Red
blood cells wear out after a few months, so your body
produces new red blood cells all the time.
White Blood Cells
Your blood contains several kinds of white blood cells, or
leukocytes (LEW kuh sites). White blood cells protect your
body from illness and infection. Some attack viruses, bacteria,
fungi, and parasites that might invade your body.
Most white blood cells last only a few days. Your body is
always replacing them. You have fewer white blood cells—
5,000 to 10,000 per cubic millimeter—than red blood cells.
Platelets
What happens if you get a cut? The cut, or wound, bleeds
for a short time. Then the blood clots, as shown below.
Platelets are small, irregularly shaped pieces of cells in the blood
that plug wounds and stop bleeding. Platelets produce proteins
that help make the plug stronger. Without platelets, blood
would not stop flowing through the wound. Your blood
contains 150,000 to 440,000 platelets per cubic millimeter.
Step 1
Platelets rush to the tear
and form a plug to stop
the bleeding.
Red
blood
cells
Step 2
A web of fibrin forms
around the platelets to
hold them in place.
Activated
platelets
Step 3
More platelets and red
blood cells are caught in
the fibrin web, forming
a blood clot.
Plasma
The yellowish, liquid part of blood, called plasma, transports blood
cells. Plasma is 90 percent water. It helps thin the blood.
Blood has to be thin to move through small blood vessels.
Plasma contains many dissolved molecules that travel along
in the blood. They include salts, vitamins, sugars, minerals,
proteins, and cellular wastes.
Plasma also helps control the activities of cells in your
body. Plasma carries chemical messengers that control the
amounts of salts and glucose that enter cells.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
White
blood
cell
Blood Types
Do you know someone who has donated blood? Doctors
use donated blood to help people who have lost too much
blood from an injury or surgery. A blood transfusion is the
transfer of one person’s blood to another person. All human
blood has the same four parts—red blood cells, white blood
cells, platelets, and plasma. But you cannot receive a blood
transfusion from just anyone. Different people have different
blood types.
The ABO System
You inherited your blood type from your parents. Blood
type refers to the type of proteins, or antigens, on red blood
cells. The table below shows the four human blood types:
A, B, AB, and O. As you can see, type A blood cells have the
A antigen. Type B blood cells have the B antigen. Type AB
blood cells have both A and B antigens. Type O blood cells
have no antigens.
Blood Type
Type A
Antigens on red blood cells
A
A
A
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Type B
Type AB
B
B
A
B
A
B
Type O
B
A
B
B
A
B
A
B
A
Percentage of US population
with this blood type
42
10
4
44
Clumping proteins in plasma
Anti-B
Anti-A
None
Anti-A and anti-B
Blood type(s) that can be
RECEIVED in a transfusion
A or O
B or O
A or B or AB or O
O only
This blood type can DONATE
TO these blood types
A or AB
B or AB
AB only
A or B or AB or O
If different antigens are introduced through a blood
transfusion, the red blood cells will clump together and no
longer function. Clumps form because of clumping proteins
in blood plasma, shown in the table above. The type of
clumping proteins in your blood determines what blood
type you could safely get in a transfusion.
A, B, and O blood types have clumping proteins in their
plasma. A person with type A blood has anti-B clumping
proteins that attack type B antigens and cause type B red
blood cells to clump together. Type AB blood has no
clumping proteins. People with type AB blood can receive
any blood type because it has no clumping proteins. Type O
blood has anti-A and anti-B proteins. People with type O
blood can donate blood to anyone.
The Rh Factor
Another protein found on red blood cells is a chemical marker called
the Rh factor. Some people have this protein on their red
blood cells. People who have this protein are Rh positive.
People without this protein are Rh negative. If Rh positive
blood mixes with Rh negative blood, clumping can result.
Blood types usually have a plus (+) or a negative (–) sign to
show whether the person is Rh positive or negative. For
example, a person with an A+ blood type has red blood cells
with A antigens and the Rh factor. Someone with O– blood
has no antigens and no Rh factor.
Blood Disorders
Sometimes a person’s blood does not function as it
should. People with hemophilia do not have a protein
needed to clot blood. They bleed at the same rate as other
people. However, their bleeding does not stop as quickly as
it does for other people.
People with anemia have low numbers of red blood cells
or have red blood cells that do not contain enough
hemoglobin. Their blood might not carry as much oxygen
as their bodies need.
People who inherit sickle-cell disease have red blood cells
shaped like crescents, or sickles (old-fashioned farm tools
with curved blades). As shown in the figure below, sickleshaped cells do not move through blood vessels as easily
as normal, disk-shaped cells do. They form clumps that can
block blood vessels. Sickle cells can keep oxygen from
reaching tissues and cause sickle-cell anemia.
Normal red blood cells
Sickle cells
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Bone marrow is the soft tissue in the center of bones. It
produces red blood cells. Cancer of the bone marrow
is called leukemia. Leukemia can slow or prevent blood cell
formation. Leukemia can lead to anemia and a damaged
immune system.