veins take blood back to the heart. which gas would be most abundant in a vein that takes blood from the muscle cells in the arm back to the heart

answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;

the electromagnetic energy from the sun arrives in the form of visible and invisible light.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.