BACKGROUND:
The circulatory system is responsible
for the transport of body fluids such as blood and lymph and for the
temperature regulation. The heart pumps blood through a network of
arteries and
veins spread throughout the body. For your own knowledge, the
lymphatic circulatory system is structurally and functionally related to
the blood circulatory system. Lymph vessels are widely distributed
throughout the body, but they are concerned with the transport of lymph
which is concerned with immune defenses.
Blood is a mixture of solid material and liquid.
The liquid portion, or plasma, provides a medium in which the solid portion
can be transported. Within the plasma are many substances, including
water, inorganic salts, proteins, nitrogen bearing substances (urea), fats,
cholesterol, sugars, hormones, and dissolved gases. (Note: do not confuse
plasma, a state of matter with this meaning.) The cellular solid
portion includes red blood cells and variety of white blood cells and platelets.
This lab emphasizes how blood moves
in our body. Students will learn about the heart rate and how body position
affects the heart rate.
The heart is a mechanical device whose function
is to pump blood through the body to replenish oxygen lacking blood cells
with oxygen. The importance of constant circulation of blood throughout
the body cannot be overemphasized. Without blood, life would not
exist. If blood does not reach the brain for just five seconds an
individual loses consciousness; after 15-20 seconds the body begins to
convulse (shake uncontrollably); and if nine minutes pass, irreparable
damage to the brain results.
The strong contraction of the heart muscle
forces blood into the arteries in two ways: the first expands the
muscular walls of the arteries and the second pushes the blood through
the arteries to regions of the body away from the heart. This rhythm
makes the arteries expand and produce a pulse. In the wrist, the
pulse is detected by a throbbing sensation near the surface. The
heart is composed of four chambers, two upper chambers, the right and left
atria, and two lower ones, the right and left ventricles.
PROCEDURE:
- There are three parts to
this lab. Use the worksheet to show students the pattern of the circulatory
system. Make sure they note that it is a closed network. You
may want them to trace some of the "lines" to see how
complicated it is.
- The second part of the lab has students
mixing some "blood" by filling half a glass of water with a few drops of
red food coloring. Ask students how this blood moves through the
body. Many students may not be aware that blood moves through a network
of tubes (arteries and veins). Note that a child thinks that blood
is just moving around in their bodies. It is conceptually difficult
to understand veins, arteries and capillaries in our bodies. Capillaries
are a net work of "roads" that allow communication between arteries and
veins. When a tube is cut, we bleed. Give students an empty
cup and a little less than a meter of (3 feet) plastic tubing (approximately
1 cm (½ inch) thick). The problem is to get the liquid from
the head (top) to the toes (bottom).
Place the cup with the liquid about 1-3 feet
higher than the empty cup. Have the students siphon the tube so the
liquid begins to flow to the bottom cup. Many students have never
seen a siphon, so demonstrate and guide them. When you suck at one
end you are forcing the liquid to flow. Gravity then continues the
flow until no more liquid can flow or no more liquid is left. Although
the tube is open compared to a closed blood network, it does show the students
how blood moves. Students love to "siphon."
- The third part of the lab is for students
to see the model heart. Ask them what the "beating" is all about
in their chest. The heart is the pump that will bring the blood back
up so it can circulate through the body. The model heart can show
students the different parts. Students can disassemble the heart
and put it back.
This lab is just to expose students to how
blood moves through their body. Just learning the words "artery"
and "vein" will help students to begin to understand circulation.
