Now, we know that blood circulates in the blood vessels.
But how did the scientists find out that blood moves in blood
vessels? Is it possible to demonstrate the movement of blood
in vessels without damaging the vessels?
Let us repeat the classical experiment to demonstrate
the movement of blood in veins conducted by William Harvey
in early 17th century, when there was no compound
microscope or any other modern equipment.
1. Tie a tornquit just above the elbow of a person as shown
in fig-8(b) whose blood vessels are prominent in the hand.
2. Ask him/her to hold the fist with a piece of cloth rolled
in the hand. Now the blood vessels can be seen more
prominently.
3. Find undivided blood vessel, where we have to work for
the next few minutes.
4. At the end of the vessel farthest from the elbow apply
steady pressure, so as to close its cavity.
5. Now apply pressure from elbow towards the palm slowly
and observe the changes in the blood vessels. (Take the
help of the figures given here.) Observe changes and
discuss in your class.
Answer the following:
In which blood vessels valves are found? What do you think is the
function of the valves in them?
Why do sub-cutaneous blood vessels bulge on the side away from
the heart when the hand is tied?
The deep seated blood vessels (the arteries) bulge on the side
towards the heart when tied. What do you understand from it?
There are valves in the heart between atria and ventricles. Is the
purpose of valves in the veins and heart same?
Why the arteries are deeply seated in the body?
Where as veins are
seated on peripheral part of the body?
Arteries and veins
There are two types of blood vessels called arteries and veins. Arteries
carry blood from the heart to body parts. Whereas, veins carry blood from
body organs to heart. Let us observe the structural and functional
differences between arteries and veins.
