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vein. |
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Activity-4 |
Let us perform the following activities to observe arteries and veins. |
Sit on a table with one leg dangling and the other resting on it so that the |
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back of one knee rests on the knee of the other. After a time you will see and |
feel the leg which is on top give a series of small movements with each heart |
beat. If you do it for long you will reduce the blood flow to the leg and so |
develop ‘pins and needles’. Discuss with your teacher about reasons. |
Swing your arm round several times to fill the veins with blood, hold |
the arm vertically downwards and gently press your finger along a prominent |
vein-stroking it in the reverse direction to the blood flow, i.e., towards the |
Free distribution by T.S. Government 2019-20 57 |
hand. Can you see the swellings where you have pushed blood against the |
valves? Discuss with your teacher about reasons. |
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A |
Think and discuss |
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AN |
Artery walls are very strong and elastic. why? |
Why we compare arteries like tree which divides into smaller and smaller branches. |
The lumen size is bigger in vein when compared with artery. Why? |
The cardiac cycle |
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NG |
The human heart starts beating around 21st day during the |
embryonic development (refer reproduction chapter). If it stops |
beating, it results in the death of a person. |
One contraction and one relaxation of atria and ventricles |
is called one cardiac cycle. |
LA |
1. We start with the imagination that all the four chambers of |
1. Imaginary relaxation the heart are in relaxed state (diastole). |
of atria and ventricles. |
2. Blood from venacava and pulmonary veins enters the right |
and left atria respectively. |
3. Now the atria contract, forcing the blood to enter into the |
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ventricles. |
4. When the ventricles are filled with blood they start |
contracting and atria start relaxing. The aperture between |
2. Blood flows into atria. |
the atria and ventricles is closed by valves. On ventricular |
contraction due to pressure the blood moves into the aorta |
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and pulmonary artery. When the valves are closed forcibly, |
we can listen to the first sharp sound of the heart lub. |
ER |
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5. When the ventricles start relaxing the pressure in the |
ventricles is reduced. The blood which has entered the |
3. Contraction of atria and arteries tries to come back into the ventricles. The valves |
flow of blood into ventricles. which are present in the blood vessels are closed to prevent |
backward flow of blood into the ventricles. Now we can |
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listen to a dull sound of the heart dub. The atria are filled up |
with blood and are ready to pump the blood into the |
ventricles. |
The sequential events in the heart which are cyclically |
4. Contraction of ventricles. repeated are called cardiac cycle. The cardiac cycle includes an |
A.V. Valves closed (Lub) active phase systole and a resting phase the diastole of atria and |
blood flows into arteries. ventricles. |
58 X Class Transportation - The circulatory system |
The time needed for atrial contraction (atrial systole) is 0.11- |
0.14 seconds. The time needed for ventricular contraction |
(ventricular systole) is 0.27-0.35 seconds. The time needed for |
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A |
relaxation of both auricles and ventriculars i.e. joint diastole is about |
0.4 seconds. The whole process is completed in approximately 0.8 |
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