BACKGROUND:
Blood is composed of a solid portion and a liquid portion.
The liquid portion or plasma provides a medium in which the solid portion
can be transported. Within plasma are found many substances, including
water, inorganic salts, proteins, nitrogen bearing substances including
fats, cholesterol, sugars, hormones, and dissolved gases. The cellular
solid portion includes red blood cells, a variety of different types of
white blood cells and platelets.
Four major parts to blood are plasma, red blood cells, white
blood cells, and platelets. On the worksheet the students will identify
each of the components after you discuss the characteristics of each part.
About 55% of blood is plasma. Plasma is about 90%
water. Food, nutrients, and oxygen are dissolved in plasma.
Plasma also contains antibodies. Antibodies help fight disease.
Red blood cells are saucer shaped cells found in the plasma that
carry oxygen. They are the most plentiful blood cells found in the
human body. Red blood cells are also called erythrocytes. White
blood cells are used by the blood to destroy harmful germs. White
blood cells are also called leukocytes.
Platelets are smaller than red blood cells and colorless.
Platelets help stop bleeding by producing blood clots that stop blood
from escaping a blood vessel.
Blood travels through veins and arteries. On the students'
worksheets they will measure the widths of the various blood vessels and
rank them in order of largest width to smallest width. The largest
artery (aorta) and the two largest veins (vena cava) measure about 2-3
cm wide. Because of their muscle tissue, the walls of arteries are
thicker and firmer than those of veins.
PROCEDURE:
- Give students the worksheet and have them measure
the different cross sections of arteries and veins. See if
the students know what each of the cross sections represent before you
give them the answer.
- Remind students that when you measure in metric you can record
in decimal by recording the whole number, place decimal, and then count
the spaces. The answers are in centimeters. However, students
can record .1 cm as 1 mm.
ANSWERS:
1. aorta - 2.8 cm
2. large artery - 1.3 cm
3. small artery
- .5 cm
4. arteriole - .2 cm
5. capillary - .1 cm
6. venule - .2 cm
7. small vein - .3 cm
8. small vein 1.2 cm
9. vena cava - 2 cm
- The second picture goes over the names of the arteries
and veins. Notice that veins have “v” in front of the name and arteries
have “a” in front of the name. Students are fascinated with an understanding
of the different parts of the body. The names may be difficult, but
they represent a part of their body.
