Red blood cell Much of this potential appears to be contributed by the exposed sialic acid residues in the membrane: their removal results in zeta potential of −6.06 mV. When red blood cells undergo shear stress in constricted vessels, they release ATP, which causes the vessel walls to relax and dilate so as to promote normal blood flow. When their hemoglobin molecules are deoxygenated, red blood cells release S-nitrosothiols, which also act to dilate blood vessels, thus directing more blood to areas of the body depleted of oxygen. Red blood cells can also synthesize nitric oxide enzymatically, using L-arginine as substrate, as do
Blood red dark red state, but quickly oxygenates upon exposure to air, turning a brighter shade of red. This happens more quickly with smaller volumes of blood such as a pinprick and less quickly from cuts or punctures that cause greater blood flows such as a puncture in the basilic vein: all blood collected during a phlebotomy procedure is deoxygenated blood, and it does not usually have a chance to become oxygenated upon leaving the body. Arterial blood, which is already oxygenated, is also already a brighter shade of red— this is the blood see from a pulsating neck, arm, or leg