Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: thedoc on 29/04/2012 11:27:02

Title: How does my heart generate enough pressure to circulate my blood?
Post by: thedoc on 29/04/2012 11:27:02

Richard Almand  asked the Naked Scientists:
   
Hi Guys,

I love listening to your show (http://www.thenakedscientists.com/HTML/podcasts/).

My question is:
How does my heart, which is I presume average size (not having seen it) generate enough pressure to circulate all of my blood around all of my circulatory system. Some of those capillaries get pretty small and as they say blood is thicker than water.

Cheers

Richard Almand (from New Zealand)

What do you think?

Title: Re: How does my heart generate enough pressure to circulate my blood?
Post by: Nizzle on 30/04/2012 11:58:29

In the arteries and some arterioles, there is a flow back protection called valves. These make the blood flow in only one way. Also when going from heart -> arteries -> arterioles -> cappilaries, the combined diameter of the vascular system increases, so there's "more room" for the blood. After the blood has passed the cappilaries, it enters the venous system where the pressure is close to "0" and the blood gets 'pushed in the back' to the heart by new blood from the cappilaries.

Title: Re: How does my heart generate enough pressure to circulate my blood?
Post by: Lmnre on 30/04/2012 14:47:01

Quote from: Nizzle on 30/04/2012 11:58:29

After the blood has passed the cappilaries, it enters the venous system where the pressure is close to "0" and the blood gets 'pushed in the back' to the heart by new blood from the capillaries.

More technically, it's differential pressure that moves blood (or any fluid). You could subject a fluid to a million PSI, but it won't move if no pressure gradient exists. Muscular activity combined with some veins having one-way valves (http://www.jobst-usa.com/en/leghealth/veinsandvalves/page.html) also helps to push blood back to the heart ... thus keeping the venous pressure low, which allows the arterial blood to flow.

Title: Re: How does my heart generate enough pressure to circulate my blood?
Post by: cheryl j on 11/05/2012 04:06:14

In addition to the pumping action of the heart, pressure is also regulated by changing the diameter of arteries and arterioles. They have a layer of muscle in them, and when this muscle is stimulated either by nerves or hormones (adrenaline, noradrenaline) they will narrow in diameter, driving pressure up, or widen to allow more blood to flow to a particular area in the body.