LESSON
13
What is blood made of?
In first aid, you learn how to help people who are hurt. A n important
first-aid rule is: "Treat Serious Bleeding First/' A person can die very
quickly f r o m a .loss of blood.
What is blood made of? Why is it so important to life?
Blood is the tissue of transport in your body. It carries needed materials to
the cells. It also carries waste materials away f r o m the cells.
Blood has a liquid part and a solid part. The liquid part of blood is called
plasma [PLAZ-muh]. The solid part of blood is made up of blood cells.
PLASMA
Plasma is 90% water. It is straw colored. Digested food, important
chemicals, and certain waste products are dissolved in plasma. These
substances are carried to the cells by the plasma. The waste materials are
carried away f r o m the cells.
B L O O D CELLS
Your blood is made up of three kinds of blood cells: red blood cells, w h i t e
blood cells, and platelets [PLAYT-lits]. These blood cells are carried in the
flowing plasma.
Red blood cells contain a substance called hemoglobin [HEE-moh-glohbin]. Hemoglobin is red. It gives blood its color.
Oxygen links up with hemoglobin. Red blood cells carry this oxygen to all
parts of the body. The same hemoglobin also picks up most of the carbon
dioxide waste that is made by the cells.
White blood cells fight disease and infection. They destroy harmful germs
in the body.
Platelets are tiny, colorless pieces of cells. They help stop bleeding.
Platelets give off a chemical that helps blood clot.
BLOOD COMPOSITION
Figure A shows the composition of blood. Study Figure A, then answer the questions.
1.
What percent of blood is liquid?
2.
What is the name of the liquid part
plasma 55%
of blood?
3.
a) The liquid part of blood is made
white blood cells
2%
up mostly of
, . .
(If you need help, look back to
the reading.)
red blood cells
43%
b) What percent?
4.
A l l of the blood cells together make
up
Figure A
Make-up
.
,
percent of
of blood
blood.
5.
Red blood cells make up
percent of blood; white blood cells
make up
percent.
B L O O D C E L L S — T H E I R SIZES A N D N U M B E R S
Figure B w i l l give you an idea of the sizes and numbers of red and white blood cells found in
your body. Study Figure B. Then answer the questions.
Figure B
1.
Which blood cells are the largest?
2.
Which type of blood cell is most numerous? _
3.
Which cells are shaped like "pinched" disks?
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Study Figures C and D. Then answer the
questions about each picture.
4.
What kind of blood cell is
shown?
5.
Describe briefly what is happening
in Figure C.
Figure C
A white blood cell at work.
Look at Figure D. Then answer the questions.
6.
When you cut yourself, which part of the blood helps you stop bleeding?
7.
White blood cells also come to the area of a cut. Why?
8.
Take a guess! What happens to the number of white blood cells when germs are in
the body?
^
Figure D
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germs
Blood clots when your skin is cut.
MORE ABOUT R E D BLOOD CELLS
Answer the following questions about red blood cells.
1.
Oxygen is
2.
Which blood cells pick up and carry oxygen?
needed by the cells, a cell waste
red blood cells, white blood cells, platelets
3.
What substance in red blood cells joins w i t h oxygen?
4.
Where does the blood pick up this oxygen?
a) in the heart
b) in the arteries and veins
c) in the lungs
5.
What gives blood its color?
T O OR AWAY?
Blood has been called the "River of Life." Blood carries to the cells materials the cells need. In
turn, blood carries away waste materials made by the cells.
Ten substances carried by the blood are listed i n the chart below. Indicate whether each
substance is carried to the cells or away f r o m the cells. Place a check (W) i n the proper boxes.
SUBSTANCE CARRIED BY THE BLOOD
1.
digested food
2.
oxygen
3.
carbon dioxide
4.
enzymes
5.
hormones (used by the cells to
regulate chemical reactions)
6.
heat
7.
harmful chemicals
8.
extra (waste) water
9.
vitamins and minerals
10.
CARRIED TO
THE CELLS
CARRIED AWAY
FROM THE CELLS
proteins
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SOME I N T E R E S T I N G FACTS A B O U T B L O O D
1.
Blood makes up about 9% of a person's body weight. For example, if you weigh 100
pounds, 9 pounds is blood. (Figure out how many pounds of blood your body has.)
2.
A n adult has about 12 pints of blood.
Figure E Blood makes up about 9% of a
person's weight. If you weigh 45 kilograms
(100 pounds), 4 kilograms (9 pounds) is blood.
Figure F A grownup has about 5.7 liters (12
pints) of blood.
3.
There are about 600 red blood cells for every white blood cell in your blood. Just
one drop of blood contains about 5 million red blood cells. There are about 25
trillion red blood cells i n the body of the average adult.
4.
Red blood cells and white blood cells are produced i n the marrow of
bones—especially i n the ribs, breast bone, and backbone.
5.
It is estimated that f r o m 1 to 2 million red blood cells die every second. New cells
are made to take their place.
6.
Blood cells are carried by the flowing plasma. White blood cells, however, can also
move by themselves.
7.
White cells also can pass through tiny holes i n the blood vessels. They move into
surrounding tissues. White blood cells are like good soldiers. They seek out and
destroy enemies (harmful germs).
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