Facts About Blood Pressure - April 22, 2010 by admin

Higher animals found it expedient to separate themselves not only from the external but also from the internal ocean by providing themselves with a closed circulatory system. However, this problem has as yet not been completely solved. The main channel of the internal river, i. e. the cardiovascular system in mammals, is a closed one, but it takes in many streamlets, lymphatic vessels, through which the fluids from the interstitial and intercellular spaces flow.

This means that the tissues and organs completely blocked themselves off from the waters of the internal ocean, but reserved the right to pour their waters into this mobile reservoir. Of course, the isolation of this internal ocean is only relative. In the arterial part of the capillaries, the walls of which are fairly thin, but the blood pressure is still high, a certain amount of liquid seeps into the intercellular spaces. This leakage would be still greater since the banks cannot withhold it sufficiently, if it were not the high oncotic pressure of the blood (caused by the proteins dissolved in it), which prevents the water from leaving the dissolved proteins.

In a resting state a small amount of water percolates into the tissues, but it all returns to the venous section of the capillary where the blood pressure is lower than the oncotic pressure of the plasma; the liquid starts to be actively attracted into the plasma by the proteins dissolved in it. The force which acts inside the venous section of the capil­lary and makes the liquid return to the blood stream is about twice that in the arterial section which forces the liquid into the interstitial spaces. This is why it is all returned.

However, during periods of work it is quite another mat­ter. In this case the blood pressure in the arterial section of the capillary will be so high that its walls will be able to retain neither water nor proteins. In the venous section of the capillary the blood pressure will remain fairly high, while the oncotic pressure will drop owing to loss of proteins; the liquid will have neither the stimulus nor the opportunity to return to the blood stream. The only alternative left to it will be to enter the lymphatic system. Thus, in the body the lymphatic system acts in a way similar to the system of drains in towns which prevents the streets and squares from becoming flooded during heavy rainfall.