The Circulatory System is the system of organs in the human beings and other animals which is responsible for transport of materials inside the body. It consists of heart, arteries, veins, capillaries and blood. The heart acts as a pump to push out blood. The arteries, veins and capillaries act as pipes or tubes through which the blood flows. These tubes carries blood are called blood vessels. So, there are three types of blood vessels in the human body: arteries, veins and capillaries. Now in detail we will understand all the parts of the circulatory system.
Roughly the shape of the heart is triangular and is made up of special muscle called cardiac muscle. The heart has four compartments known as ‘chambers’ inside it. The upper two chambers of heart are known as atria (in singular atrium) and the lower two chambers of heart are called ventricles. From two main veins these two atria receives blood. And the two ventricles transport blood to the entire body and the lungs. The left atrium is connected to the left ventricle through a valve V1. Similarly, the right atrium is connected to the right ventricle through another valve V2. These valves prevent the back flow of blood in to atria when ventricles contract to pump blood out of the heart to the rest of the body. This is because when the ventricles contract, the valves V1 and V2 close automatically so that the blood may not go back to atria. So, heart pumps blood around our body. All the atria and veins contract and relax and make heart to pump blood. Since ventricles have to pump blood in to various organs with high pressure, they have thicker walls than atria.
A sheath of tissue called ‘pericardium’ protects the muscular heart and the chambers of the heart are separated by a partition called septum. Now, before describing the circulation of blood in the human body it is necessary to know more about arteries, veins and capillaries.
The main difference between artery and vein is that an artery carries blood from the heart to the body organs whereas a vein carries blood from the body organs back to the heart. The blood which carries oxygen is called oxygenated blood and the blood which does not carry oxygen is called deoxygenated blood, however carries carbon dioxide in it.
Also when blood circulates in our body it supplies oxygen, digested food and other chemicals like hormones to all the cells of the body. It also carries back waste products like carbon dioxide etc. from the body cells.
Process of blood circulation in humans
This whole process is repeated continuously.
So, now we can say that a circulatory system is that in which the blood travels twice through the heart in one complete cycle of the body called double circulation. In human circulatory system the pathway of blood from the heart to the lungs and back to the heart is called pulmonary circulation and the pathway of blood from the heart to rest of the body and back to the heart is called systemic circulation. And these two together make double circulation.
One complete contraction and relaxation of the heart is called a heart beat. The heart beat usually beats about 70 to 72 times in a minute when we are resting. A stethoscope is an apparatus due to which doctors listens our heart beat. The heart beat faster during and after exercise because the body needs more energy under these conditions.
The pressure at which blood is pumped around the body by the heart is called blood pressure. The maximum pressure at which the blood leaves the heart through the main artery during contraction phase is called the systolic pressure and the minimum pressure in the arteries during the relaxation phase of heart is called diastolic pressure.
Systolic pressure: 120 mm Hg
Diastolic pressure: 80 mm Hg
So, the normal blood pressure is 120/80 and is measured by an instrument called sphygmomanometer.