Okay, so veins have valves to help counteract the pull of gravity. I'm wondering, do the veins in the head have this same adaptation, seeing as these veins are simply bringing blood down to the heart, and are not pulling against gravity.
No. They wouldn't work... Valves only allow blood to flow one way. If the valve allowed flow out if the head then it would always be open (unless you went upside down), so they wouldn't be needed. If they stopped blood flowing out if the head...well...you'd have a big purple bloaty head.
Valves counteract the pull of gravity. They also prevent blood clotting. Yes, because if they didn't, the blood could flow too fast and pool in your veins, which causes blood clots, which isn't good. So to monitor the amount of blood going through veins in the head or neck, the valves close, and open. Hope I helped. -Selene
