Circulatory System

All the living organisms need nutrients, gases, liquids etc., for growth and maintenance of the body.

All the organisms would need to send these materials to all parts of their body whether they are unicellular organisms or multicellular

In lower organisms like amoeba, hydra etc., all the materials are transported through a simple processes like diffusion, osmosis etc.,

This specialized system that is developed by organisms is called ‘the circulatory system’.

The heart is divided into four parts by grooves.

Two upper parts are called atria (auricles), and the lower ones axe called Ventricles.

The atrium and ventricle are smaller when compared to that of right atrium and ventricle blood vessels found in the walls of the heart are coronary vessels which supply blood to the muscles of the heart.

The walls of the ventricles are relatively thicker than atrial walls.

In our observation we found that the heart has four chambers in it. On the left side two chambers are present, one is anterior and the other is the posterior. On the right side also two chambers present, one upper (anterior), and one lower (posterior).

The relatively smaller one is pulmonary artery which carries blood from the heart to the lungs. The less rigid vessels are the veins, which bring blood from all body parts to the heart.

The vein which is at the anterior end of the right side of the heart is Superior venacava (precaval vein), which collects blood from anterior parts (head and neck) of the body.

The vein which is coming from posterior part of the heart is inferior Venacava (postcaval vein), collecting blood from posterior part (hand and legs) of the body.

The two atria and the two ventricles are separated from each other by muscular partitions called septa. The openings between atria and ventricles are guarded by valves.

The valve present on the Right Auriculo-ventricular septum between Right Artery and Right Ventricle is referred to as “Tricuspid Valve”. The valve present on the right Auriculo-Ventricular septum between right atrium and right ventricle is referred as Bicuscid volve or Mitral valve. A major blood vessel that originate from right ventricle is Pulmonary aorta. The valves present at the region of Pulmonary aorta are called “Pulmonary valves”. A major blood vessel originates from left ventrical is systemic aorta. The valves present at the region of systemic aorta are called Systemic valves.

In the right atrium we can observe the openings of superior and inferior venacava. in the left atrium, we can observe the openings of pulmonary veins, that bring blood from lungs.

From the upper part of the left ventricle, a thick blood vessel called aorta arises, it supplies oxygenated blood to the body parts. From the upper part of the right ventricle pulmonary artery arises that supplies deoxygenated blood to the lungs. After careful examination we can observe valves in the pulmonary artery and aorta as well.

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.

Blood capillaries

Blood capillaries are the microscopic vessels made of single layer of cells. They allow diffusion of various substances. The leucocytes (WBC) can squeeze out of the capillary wall. They establish continuity between arteries and veins.

The cardiac cycle

The human heart starts beating around 21 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.

1. We start with the imagination that all the four chambers of the heart are in relaxed state (diastole).

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 ventricles.

4. When the ventricles are filled with blood they start contracting and atria start relaxing. The aperture between the atria and ventricles is closed by valves. On ventricular contraction due to pressure the blood moves into the aorta arid pulmonary artery. When the valves are closed forcibly, we can listen to the first sharp sound of the heart lub.

5. When the ventricles start relaxing the pressure in the ventricles is reduced. The blood which has entered the arteries tries to come back into the ventricles. The valves which are present in the blood vessels are closed to prevent backward flow of blood into the ventricles. Now we C311 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 repeated are called cardiac cycle. The cardiac cycle includes an active phase systole and a resting phase the diastole of atria and Ventricles. The whole process is completed in approximately second.

We know that blood flows in the blood vessels. To keep the blood moving the heart pumps it continuously. The blood that is pumped by the heart reaches the body parts and comes back to the heart. But course taken by the blood is not the same in all the animals.

Move in the direction of arrow. Note down the parts which are in the way in cyclical form.

(Try to identify different parts of the body in both figures.)

If blood flows through heart only once for completing one circulation it is called single circulation.

If the blood flows through the heart twice for completing one circulation it is called double circulation.

Blood pressure (B.P)

To move the blood through this network of vessels, a great deal of force is required. The force is provided by the heart and is at its highest when the ventricles contract, forcing the blood out of the heart and into the arteries. Then there is a drop in the pressure as the ventricles refill with blood for the next beat.

B.P. is always measured in the upper arm artery. B.P. varies throughout the body, so a standard place must be used so that a person’s blood pressure can be compared over a period of time. Doctors measure the blood pressure (B.P.) with a device called sphygmomanometer.

There are two pressure readings. One measures the strongest pressure during the time blood is forced out of the ventricles. This is called systolic pressure. For a healthy young adult it will be 120 mm of Hg. The second reading is taken during the resting period, as the ventricles refill with blood. This is called diastolic pressure. It will be 80 mm of Hg.

B.P. will change according to the activity in which the person is engaged, such as resting, walking and running. People who have high B.P. during resting period are said to have hypertension. Discuss with your teacher about low blood pressure.

Coagulation of blood

Another important part in the story of blood is coagulation. Only because of this character animals survive when they meet severe injuries.

When there is an injury blood clots in 3-6 minutes. How does the blood clot? What chemistry involved in blood coagulation. You know that when you cut yourself, the blood flows out of the wound for only a short time. Then the cut is filled with a reddish solid material. This solid is called a blood clot. If blood did not clot, anyone with even a slight wound bleeds profusely.

• When the blood flows out, the platelets release an enzyme called thrombokinase.

• Thrombokinase acts on another substance present in the blood called pro-thrombin converting it into thrombin.

• Thrombin acts on another substance called fibrin that is present in dissolved state converting it into insoluble fibrin.

• The blood cells entangle in the fibrin fibers forming the clot.

• The fibrin fibers are attached to the edges of the wound and pull them together.

This straw yellowish coloured fluid portion after formation of the clot is serum.

                        Thrombrokinase
Prothrombrin -------------------------> Thrombin

                         Thrombin
Fibrinogen ----------------------------> Fibrin

Discuss with your teacher about vitamin K in relation to coagulation of blood.

·         The pulse rate is equal to heart beat. We can count the heart beat without the aid of any instrument.

·         Rene Laennec discovered the first stethoscope.

·         The heart is covered with two pericardial membranes filled with pericardia] fluid which protects it from shocks.

·         Rigid blood vessels attached to the heart are called arteries. The two rigid blood vessels are arteries which supplies blood to body parts and lungs.

·         The less rigid vessels are veins, which brings blood from body parts.

·         Heart has four chambers, two upper atria and two lower ventricles.

·         Atrium and ventricle of the same side are connected by atrio ventricular aperture.

·         Atria are separated from each other by interatrial septum, ventricles by interventricular septum.

·         The atrioventricular apertures are guarded by valves. There are valves in the aorta and pulmonary arteiy also.

·         The right side of heart receives blood from body and sends to lungs.

·         The left side of the body receives blood from lungs and sends it to body parts.

·         The arteries carry oxygenated blood except pulmonary artery. The veins carry deoxygenated blood except pulmonary veins.

·         One contraction and relaxation of heart is called cardiac cycle.

·         If the blood goes to heart only once before it reaches all the body parts. It is called single circulation.

·         If it goes twice it is called double circulation.

·         Vitamin K deficiency leads to delayed coagulation of blood.

·         Plants absorb soil water through roots by the process of osmosis.

·         Water travels through xylem vessels and food material travels through phloem tissues.

·         There is a relation between transportation and transpiration in plants.

·         Biologists studied about phloem tubes with the help of aphids.

Thalassemia

Thalassemia is a group of inherited blood disorders characterized by mild to severe anemia caused by haemoglobin deficiency in the red blood cells. In individuals with thalassemia, the production of the oxygen carrying blood pigment haemoglobin is abnormally low. There are two main types of thalassemia: alpha thalassemia and beta thalassemia. In each variant a different part of the haemoglobin protein is defective. Individuals with mild thalassemia may have symptoms, such as anemia, enlarged liver and spleen, increased susceptibility to infections, slow growth, thin and brittle bones, and heart failure.

Facts about Thalassemia

·       Thalassemia is a serious Inherited Blood Disorder.

·      4.5% of world population (250 million) suffering with thalassemia minor.

·      There are over 35 million Indians are carriers of the abnormal Gene for Thalassemia.

·      It is estimated that about 1,00,000 infants are born with major Haemoglobinopathies every year in the world.

·       10,000 — 12,000 Thalassemic children are born every year in our country.

·      Survival depends upon repeated blood transfusion and costly medicines. Thalassemia can be prevented by awareness, pre marital or pre conceptual screening followed by antenatal diagnosis is required.