Question

The loose skin of the ___________ allows for expansion during erection. corona penile glans penile shaft foreskin

Answer 1

Penile shaft

During erection, blood flows into the spaces, causing distention and elevation of the penis. The amount of blood entering the penis can be increased by physical or psychological stimulation. As blood enters, there is a temporary reduction in the rate and volume of blood leaving the penis. The arteries carrying blood to the penis dilate; this, in turn, causes tissue expansion. The veins leading from the penis have funnel-shaped valves that reduce the outflow of blood. As the erectile tissue begins to enlarge, the additional pressure causes the veins to be squeezed against the surrounding fibrous tissue, and this further diminishes the outflow of blood. Essentially, blood becomes temporarily trapped in the organ.

Answer 2

The answer is penile shaft. 

The penile shaft has 3 erectile columns. There are 2 corpus cavernosum and 1 corpus spongiosum. The skin is loose because those columns fill with blood and the skin will stretch and that's why it hardens. It is the changes in blood flow in the penis that results in an erection.