What makes a male's penis go up when he sees a girl?

blood rushing through it... if u don't want a homosexual answer.. for f..uck's sake .. get out of the lgbt section.

this is because of the chemical reaction which is triggered in your brain, thus causing your heart to beat fast and at the same time pushing the blood towards your thingy, which results in your thingy to go up. Its all natural, but don't thing a lot about sex or women. you seem to be still young, concentrate on your studies, don't watch a lot of TVs and Internet.

Vaso Congestion.

Heart pumping, blood flows to the penis quickly and an erection occurs. It could also occur for no random reason at all. You could just be sitting there at work/school and poof.

testasterone, hormones, chemicals in the brain Its not a phenomonon. Its just the way it is.

He gets aroused which releases hormones (like chemicals) in his blood. This makes the blood go faster and make the penis hard.

if you "don't want homosexual answers because it just feels wrong" then i suggest you post this in some other section, because if you haven't notice this is the Lesbian, Gay, Bisexual, and Transgender section!!

Well Tina Turner's legs.

Why did you post this in LGBT if you didn't want "homosexual comments"?

The same reason your penis goes up when you see a guy.