Consider heart as water pump and blood vessels as net work of elastic rubber pipe networks. This will help you to understand what the blood pressure really means. It can be easily understood while the pump is pumping the maximum pressure is exerted on the wall of the tube, which is nearer to the pump. The furthest part has least pressure. The pressure also depends on the caliber of the tube,which is nearer to the pump.
The furthest part has least pressure. The pressure also depends on the caliber of the tube. Our heart has four chambers. Left ventricle actually pumps blood to the circulatory network at an average rate of 72/ min. The pump of heart works in different way than the water pump. It does not pump continuously. While beating at a rate of 75 per minute, it beats every 0.8 seconds. In this 0.8 sec, it pumps for 0.3 sec and rest 0.5 sec it relaxes to receive blood for pumping. Now you can understand the pressure in the blood vessels are not always equal. It is highest when the heart is pumping and lowest when it is receiving blood. Blood comes out through one large arched tube known as arch of aorta and then through divisions it comes to the arteries, which again divide and subdivide to arterioles and capillaries. Pressure is not equal in all these branches. For clinical purpose we measure blood pressure in arteries, precisely in the brachial artery in our arms.
You have noticed while doctors are telling the blood pressure, they are telling two values one is systolic that is on the higher side and one is diastolic that is on the lower side. The Systolic is the highest pressure exerted by blood on the wall of the arteries during contraction of the ventricle or systole and Diastolic is the lowest pressure exerted during relaxation or diastole. Normally the systolic blood pressure remains 120mm of mercury and the diastolic at 80 mm of mercury.
You may be wondered why the difference is so low and while the heart is relaxing why the lowest pressure is not 0! It is due to the elasticity of the artery which recoils during relaxation and expands during contraction and keeps the blood pressure to this limit, which is so essential for maintaining the perfusion of oxygen to the tissues.
If elasticity of the arteries is reduced it will increase the peak pressure and the gap between systolic and diastolic pressure will widen.
There are many other factors which maintain the normal blood pressure of our body. Few important factors are volume of blood, quality of blood, function of other organs like brain, kidney and other hormones. Altogether a complex phenomenon is maintaining the blood pressure, the pressure required to exchange nutrition and oxygen to the tissues.
This article is republished in India Study Channel
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