All right, guys. You
almost stumped me with this one. It's quite hard (no pun!):tongue: to get info on this question without being a member of certain medical journal sites.
But after
much searching, I have learned the following:
The average blood volume in a flaccid penis (average sized penis) at any given time is about 5 1/2 milliliters.
I found two sets of statistics (and don't know which is right). When you get an erection, the blood volume in your penis will increase to either:
6 to 7 times normal (erect blood volume of 33-38.5 mL for average penis) or
8 to 10 times normal (erect blood volume of 44-55 mL for average penis)
Of course, the amount of blood in the penis at any given time is never static. Just for shits and grins, I've included some info on what causes an erection, as well as some info about penile anatomy with an accompanying diagram. (Hey -- I found the stuff, so I might as well post it).
The Mystery of an Erection
Simply stated, an erection is a result of an increased flow of blood into the penis and a decreased outflow.
When a man is sexually stimulated, either physically or mentally, two nerve pathways are activated. The first pathway causes a reflex erection through the sacral spinal cord (lower end of spinal cord). No connection to the brain needs to occur, which explains why a man with a spinal cord injury is often still capable of producing an erection. The second nerve pathway occurs between the brain and the multitude of nerves within the penis. When stimulated, these nerve cells create nitric oxide, which causes the penis to form a chemical called cyclic guanosine monophosphate, commonly referred to as cyclic GMP or simply cGMP.
Cyclic GMP dilates (opens and broadens) the blood vessels within the penis allowing it to engorge with blood. The result is a rigid and erect penis. In normal circumstances, a man continues to produce abundant amounts of cGMP for the duration of the sexual stimulation in order to maintain sufficient rigidity for penetration. Simultaneously, another chemical known as Phosphodiesterase-5, or PDE-5, diminishes the effects of cGMP and creates an equilibrium between the two chemicals. This balancing act allows the erection to continue.
Once a man's sexual arousal dies down, or stimulation ceases, cGMP production comes to a halt. With PDE 5 as the predominant chemical, the penis returns to its flaccid state.
The Penis Contains:
Two cylinder shaped chambers called the corpora cavernosa, which run the length of the penis and contain a maze of blood vessels.
The urethra, the channel in which urine and sperm flow, which runs along the underside of the corpora cavernosa.
Erectile tissue, which surrounds the urethra, two main arteries and several veins and nerves
The shaft, the longest part of the penis.
The head (glans), located at the end of the shaft.
The meatus, the opening at the tip of the head where urine and semen are discharged.