From the website: 'The penis is composed of two functional compartments: the paired corpora cavernosa and the corpus spongiosum. Under the microscope, the tissue of the corpora cavernosa consists of bundles of smooth muscle fibers intertwined in a collagenous extracellular matrix. Interspersed within this tissue is a complex network of endothelial cell-lined sinuses, arteries and nerve terminals.

Figure 1. Anatomy and mechanism of penile erection. The cavernous nerves (autonomic), which travel postarterolaterally to the prostate, enter the corpora cavernosa and corpus spongiosum to regulate penile blood flow during erection and detumescence. The dorsal nerves (somatic), which are branches of the pudendal nerves, are primarily responsible for penile sensation. The mechanisms of erection and flaccidity are shown in the upper and lower insets, respectively. During erection, relaxation of the trabecular smooth muscle and vasodilatation of the arterioles results in a severalfold increase in blood flow, which expands the sinusoidal spaces to lengthen and enlarge the penis. The expansion of the sinusoids compresses the subtunical venular plexus against the tunica albuginea. In addition, stretching of the tunica compresses the emissary veins, thus reducing the outflow of blood to a minimum. In the flaccid state, inflow through the constricted and tortuous helicine arteries is minimal, and there is free outflow via the subtunical venular plexus. [Reproduced from T. F. Lue: N Engl J Med 342:1802–1813, 2000 (2 ). © Massachusetts Medical Society. All rights reserved.]
Male
Physiology - The Penis, Anatomy & Mechanism of Erections
http://edrv.endojournals.org/cgi/content/full/22/3/342#SEC2
A very interesting essay from the journal of Evolutionary Psychology on sperm competition and its role in shaping the human penis, (size, length, width, forceful ejaculation), evolutionary strategies for successful fertilization i.e. semen displacement and coagulation. On sexual intercourse and evolutionary benefits of deep penis thrusting, function of the foreskin and effects of circumcision, premature ejaculation, female reproductive strategies i.e. copulation with multiple partners, human sexual behaviour and wife rape (males having sex with their partner if suspecting them of infidelity).
Read More: Evolution, Human Reproduction & Fertilization: Sperm Competition, Semen Displacement & Penis
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Page Title: 'Male Reproductive System: Anatomy of Human Penis.
Sexual Health, Pictures, Erection, Orgasm, Sperm, Testicles'.
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