Blood pressure

[Anura]

Can anyone tell me why having high blood pressure is dangerous? What exactly is going on?

[Ahsan Iqbal]

By definition, blood pressure is the force exerted by the blood on the walls of the blood vessels per unit area. So high blood pressure means that your blood is exerting more force per unit area on walls of your blood vessels. Most common cause of high blood pressure is atherosclerosis (normally occurs in old age). Atherosclerosis means hardening of your blood vessels, your blood vessels loose the elasticity. So when blood rushes with great velocity and force in blood vessels (especially arteries) the loss of elasticity of blood vessels prevent them to expand and in this way with less volume available, the force per unit area of blood on blood vessels is increases.

I think I have made it a little complicated. Let me explain what normally happens. During systole when the heart pushes blood into arteries, the amount of blood, force behind the blood and its velocity are all greater than can be accommodated in arteries, so to accommodate the extra amount of blood, the arteries expand (and that is what is called pulse). Then during diastole, when heart is not pumping any blood, the arteries return to their normal state and the extra blood flows into circulation. This all happens too quickly, (0.8 second for all the effects to take place). So the arteries because of their elasticity, eliminate the extra force of blood but in atherosclerosis, the elasticity is lost and arteries cannot expand so not only the force per unit area is increased but the rate of flow of blood is also increased.

 

The consequences of high blood pressure include the rupturing of blood vessels. failure of organs like the kidneys and heart failure. If you want me to explain why these occur with high blood pressure, let me know.

[Mrs Zeta]

The problem with high blood pressure is that it is often associated with other seemingly unrelated conditions such as diabetes, high cholesterol etc.

[lemur]

Imagine you have two balloons. One is very new and uniformly elastic and the other has gotten old and lost its elasticity. Now you pump air into each balloon with the same amount of pressure. The newer balloon will be able to expand more uniformly, which causes the air-pressure to distribute more evenly and get dissipated as the overall volume of the balloon increases. The stiffer balloon resists expanding, which causes the pressure to be greater within the more constrained volume and, as you probably know, high pressure seeks weak-points to expand, which could cause the balloon to rupture or put extra pressure on the parts of it that are still elastic enough to stretch. I don't know if this is a perfect analogy to what happens with your circulatory system, but I hope you can basically see how a more constrained (i.e. more inelastic) container dissipates pressure-fluctuations less uniformly than one that is more rigid.

Edited December 25, 2010 by lemur

[Marat]

Here's an interesting problem: Giraffes are mammals just like humans and their retinas, kidneys, and other highly vascularized organs are essentially like our own. But while our organs would fall apart from the stresses of severe hypertension, giraffes normally have extreme hypertension, since that is necessary to supply their brain with sufficient blood at the end of such a long neck, yet they don't experience the same sort of damage to their organs as we do from hypertension. Why?

[lemur]

Here's an interesting problem: Giraffes are mammals just like humans and their retinas, kidneys, and other highly vascularized organs are essentially like our own. But while our organs would fall apart from the stresses of severe hypertension, giraffes normally have extreme hypertension, since that is necessary to supply their brain with sufficient blood at the end of such a long neck, yet they don't experience the same sort of damage to their organs as we do from hypertension. Why?

Why don't our legs and feet suffer more from hypertension than our arms and heads?

 

 

 

[Anura]

@ahsan iqbal, very well explained.

 

@lemur, very good analogy with the balloons.

Edited December 28, 2010 by Anura

[Ahsan Iqbal]

Imagine you have two balloons. One is very new and uniformly elastic and the other has gotten old and lost its elasticity.

 

A great way of explanation. However, I wonder, how would a balloon lose its elasticity.

[lemur]

A great way of explanation. However, I wonder, how would a balloon lose its elasticity.

They dry out, in my experience. You try to inflate them and they pop easily. I think it's because certain parts of the balloon become more brittle than others, thus making that part of the material more susceptible to breakage. Fresher balloons are more uniformly elastic, I think, and you can enhance their elasticity by stretching them in various directions before inflating them. Think of elastic materials like chains. The weakest link breaks, and the more force the other links can take, the more the force the weakest link is going to be subject to.

[Ahsan Iqbal]

They dry out, in my experience. You try to inflate them and they pop easily. I think it's because certain parts of the balloon become more brittle than others, thus making that part of the material more susceptible to breakage. Fresher balloons are more uniformly elastic, I think, and you can enhance their elasticity by stretching them in various directions before inflating them. Think of elastic materials like chains. The weakest link breaks, and the more force the other links can take, the more the force the weakest link is going to be subject to.

 

Thankyou for making an addition to my little knowledge. I had no idea of how a balloon could lose elasticity.