MadSci Network: Medicine |
Thank you for your question: From the web site, http://www.sexualrecords.com , Jamison and Gebhard, (Journal for Sex Research 24: 177-183. 1988) used data from the Kinsey report to generate these numbers. Flaccid penis length (mean +/- SEM: inches).......3.89 +/- 0.73 Erect penis length ...............................6.21 +/- 0.77 Flaccid penis circumference.......................3.75 +/- 0.65 Erect penis circumference.........................4.85 +/- 0.71 Erectile increase in length.......................2.30 +/- 0.71 Erectile increase in circumference................1.11 +/- 0.52 There appears to be no direct relationship between flaccid length and erect length. Moreover, very small flaccid penises often reach about the same size when erect as large flaccid penises. The human penis is of the vascular type. That is, there are spongy areas within the penis that will engorge with blood during periods of sexual excitment (often in 5 - 30 seconds after the onset of sexual stimulation). There are two cylindrical bodies along the dorsal (top) aspect of the penis called the corpora cavernosa (cavernous bodies) and a single corpus spongiosum which encirles the urethra (the tube through which urine and semen exit the body). Erection results when blood is trapped in these regions of the penis. This is accomplished by small arteries dilating as a result of neural input. The increase in blood entering the penis causes an increased volume which passively will occlude veins carrying blood away adding to the engorgement. The neurotransmitter nitric oxide is important in the dilation of the arteries as it ultimately stimulates the production of cyclic guanylyl monophosphate (cGMP) which leads to arterial dilation. This is the basis for the drug sildenafil's (Viagra) action {Viagra blocks the enzyme responsible for degrading cGMP, therefore, helps keep cGMP concentrations high for a longer period of time which results in the likelihood of erection during sexual stimulation. The penis usually reaches final adult size during puberty. Penis size is often the source of much worry by men. There seems to be a perception that "bigger is better". Certainly "adult entertainment" films and videos feature "actors" with extarordinarly large penises, adding to the concern men may feel that they are too small. Considering that the average vaginal size is 3 to 4 inches in length (when sexually excited) and 2 to 2.5 inches in diameter, AND that the clitoris (equivalent to the penis head) is an exterior structure, most men have no problem resulting from the size of their penis. I hope this helps. David Mallory, Ph.D. Associate Professor of Biology Marshall University Huntington, WV
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