What does it mean"microvessels act directly on local blood vessels,dilating or constricting them

what does it mean"microvessels act directly on local blood vessels,dilating or constricting them

They (endothelium of b.v)secret factors like prostaglandin (f2-constrict) or e(dilate) the vessel

Thank you✌️.So the microvessels(i.e-arterioles,capillaries)secrete these substances to control the amount of blood coming in to that part/organ through the regional/local artery of that place/organ;depending on the need of the organ.

Prostaglandin is produced from the cell wall itself,they will prepare it when they need it it’s like preparing meal when you are hungry