These tissues are characterized by highly permeable, often fenestrated vessels 24 ... angiogenic factor responsible for proliferation of capillaries and neovascularization of the corpus luteum.
It is returned to the heart in the veins. The capillaries connect the two types of blood vessel, and molecules are exchanged between the blood and the cells across their walls.
Microscopic – walls are one cell thick, this allows for the diffusion of substances into the cells from the capillaries and out of the cells into the capillaries. Very low blood pressure.