Diameter 100 - 500 nm depending on vesicle content. The protein clathin is attached to the outer membrane of the vesicle. SVs are rather numerous in nerve cells at locations where the latter contact other cells forming synapses. SVs are only present in the presynaptic cell. After stimulation their membrane attaches to the cell membrane for release of the neurotransmitters into the synaptic cleft.
Capillaries serve for exchange of substances including blood gases.