https://fitose.com/vital-progenix/

When a man is sexually aroused, mental signals cause the valves of each penile reservoir to expand, allowing blood circulation to pour into these swollen chambers. The chambers are fixed in place by connective, Vital Progenix sponge-like tissue and as they swell by means of pressure from inside, the male reproductive organ becomes erect and hard. Pressure detectors regulate the amount of circulation, and balance the erection, and degree of rigidity. Afterwards when that man has ejaculated, the muscle relaxes. The blood flow return to normal and the male reproductive organ goes limp.