As long as you don't do it too tightly or hold it for too long. You can cause the blood vessels to rupture. Everyone does it just to see how hard it can get, but anything done too long usually causes a problem.
At the base of your penis is a donut-shaped muscle called the "penile sphincter." Blood flows into your penis through an artery deep inside. The blood flows back out through veins closer to the surface. When the penile sphincter tightens, it slows the flow of blood out of your penis and the tissue fills with blood. An erect penis can enter a woman's vagina, and the force of ejaculation pushes the semen through the relatively straight urethra (the tube inside the penis that urine also comes out of) with a lot of pressure. This helps the sperm get up the vaginal canal.
the lead may become jammed in the base and go into the blood stream which can ultimately end up contracting aids or if your lucky just a very violent and inflamed yeast infection
penis
Vacuum pumping to increase the size of the penis has been around for over a hundred years. Various gadgets and gizmos have been invented to apply negative pressure to the exterior of the penis, usually in a tube, to cause increase blood flow and congestion in the penis. Vacuum pumping is a valid, recognized therapy to increase the firmness of an erection in men who have diagnosed erectile dysfunction caused by damage or disease processes like diabetes and atherosclerosis. These diseases impair the blood flow to the spongy tissues of the penis that cause an erection when filled with blood. The vacuum pump is used to engorge the penis until it is erect, and then a silicone or rubber constricting ring is fitted around the base of the penis to restrict the outflow of blood. This maintains the erection until sexual activity has concluded, and must be removed shortly thereafter. Some men use pumping as a "fetish" activity, and strive to create massively large erections. There are some magazines devoted to practitioners of pumping and they offer various tips to maximize the experience. There are many dangers associated with pumping, mostly related to physical injury. Repeated or excessive pumping can result in ruptured blood vessels, and damage to the corpus cavernosa (the spongy erectile tissue of the penis). Injuries such as this threaten the circulation in the tissues, can result in necrosis and may require amputation. In short, pumping can be fun, but like anything, is definitely dangers when taken to extremes.
The Urethra.
A small firm lump under your skin at the base of your penis could be a cyst, but this should be confirmed with a doctor.
It's probably not swollen, when a dog has a full erection his penis will be quite large, often larger than a human's penis. The big lumps at the base of his penis is probably the part called the knot.
An "orgasm" in a male is the release of sperm from the tip of the penis. It is caused by spasmodic contraction of muscles at the base of the penis.
The root word for the adjective dangerous is the noun danger.
since im assuming ur a male and concious of your penis size, here are some basic foundations. Penis size is actually not that big of a deal as most men have enough "stuff" to please a woman already. The average size of and erect penis is 6.5 inches. If you really do want to enlargen you penis, try jelqing. This is a method of which with and erect penis, you create and OK sign with your hands and grasp the base of your penis with the "circle" (thumb and forefinger). Then slowly, slide your ok sign form the base to the tip of you penis. Ensure that a bit of pressure is maintained during this excercise. I do recommend using lubrication. This excercise works because it channels the blood near the top of your penis, enlargening the "spongy" chambers in it. Also, use this same techinque but in an upward, downward, left and right direction. happy enlarging :)
The base of a bull's penis (inside the bull) is a sigmoid flexture, which is curved in an S shape when retrated inside the bull, held by muscles that keep it that way. When the bull is sexually aroused and extends his penis to copulate a cow, the muscles relax and the sigmoid flexture straightens out allowing the penis to protude to copulate the cow he his mating with.
Usually during puberty your penis will grow a couple of inches, but since you have already passed that you can try natural penis lengtheners. Get a warm cloth and wrap it around your penis for thirty seconds. Do this three times. That will warm it up. Then, you pinch the base of your penis to allow blood flow through. Do this for a little while and then jack off. Then do the same cool off as you used to warm up with. Repeat daily.