source of peripheral resistance

[superduper12]

Peripheral resistance is the impedance of blood flow in arterioles.

"This is caused because when the heart contracts, blood enters the arteries faster than it can leave...causing the vessels to strech from the pressure.The elastic walls of the arteries snap back during diastole, but the heart constracts again before enought blood has flowed into the arterioles to completely relieve pressure in the arteries. This impedance by the arterioles is called peripheral resistance."

Now wiki says that peripheral resistance is dependent on
- radius of vessel controlled by norepinephrine
- viscosity
- and capacitance of blood vessel

Can anyone expain the concept of source of peripheral resistance any further? I don't understand the viscosity and capacitance of blood vessel part.

Thanks.

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[xIcewind]

Viscosity refers to the thickness of blood -- thicker blood moves slower, the heart has to pump harder to move it.

The capacitance of blood vessels sort of relates to the radius, if it's what I'm thinking of. For example, build-up of plaque (the most... 'known' example) will increase the impedance, simply because it decreases the radius of vessel.