Which layer of the typical vessel can be regulated to constrict or dilate the lumen?

TUNICA MEDIA is the layer of the typical vessel that can be regulated to constrict or dilate the lumen.

The constriction and dilation is done to adjust the volume of blood released to the tissues according to its needs.

Other layers of the typical vessels are tunica intima (inner tunic) and tunica externa (external tunic). Tunica media is found between these two layers. 

Atp is is our little "pocket" of energy. of course, if you have too little, then it means you have too little energy, and you'll pass out. the way to not have enough, is to have no energy sources (glucose, fats, proteins). you can't have too many atp molecules. cycles like the krebs cycle produce it, but if you have too much of any substrate (or too little for that matter), the cycle stops and atp is no longer made (it stops until substrate levels are such that the process can go on). in any case, this is unlikely since atp is constantly hydrolyzed and remade, even while you're asleep. you won't have too much. if you have zero, you are dead or dying.