The main organ involved in sexual dysfunction is the penis.58 It is the male sex organ which contains two chambers called the corpora cavernosa that runs the length of the upper side of the penis while the corpus spongiosum lies ventral to the two cavernosa muscles.38 The corpus cavernosa and the bulbo spongiosum originated from the pubic bones and join (terminated) at the head of penis. The urethra which is the channel of urine and ejaculate runs along the underside of the copora cavernosa to the tip of the penis.58 Arteries originates from internal pudendal artery while veins drains blood from the superficial intermediate and deep veins to internal pudendal veins.58 The corpora cavernosa is a spongy tissue consisting of smooth muscle and arteries.
Tunica albuginea is a membrane that surrounds the corpora cavernosa which drains blood out of the penis to the internal pudendal veins58
The arterial supply of the penile skin originates from the left and right superficial external pudendal arteries while the ventral part of the penis is from the arterial supply of deep structures of the pelvis.59 The arterial supply to the penile muscles originates from the common penile artery which is a branch of the internal pudedal artery.59 The common penile artery branches into
VASCULO GENIC Arterial insufficiency venous leak
Atherosclerosis Arteriosclerosis
ENDOCRINOLOGIC Hypogonadism
Psychogenic
ANATOMIC Peyronie’s Disease NEUROLOGIC
Spinal cord injury Peripheral neuropathy Diabetes
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the dorsal, bulbo urethral and cavernous arteries.59 The dorsal artery is responsible for the engorgement of the glands during erection while the bulbo-urethral branch supplies the corpus spongiosiom and the bulb of the penis. The carvenous branch supplies the corpus cavernosal muscles which affects tumulscence and responsible for erection principally. It also supplies the trabeculae erectile tissues and the sinusoids.59
The venous drainage originates from the venules of the sinusoids beneath the tunica albuginea, these veins form the emissary veins of the penis.35 The primary nerve fibres to the penis originated from the dorsal nerve of the penis which is a branch of the pudendal nerve. The cavernous nerves of the penis serve both sympathetic and parasympathetic stimulus as part of the autonomic nervous system. They enter the copora cavernosa and the corpus spongiosum through the prostate to regulate blood flow in the penis during sexual stimulation.39 The pudendal nerve also gives a branch (dorsal somatic nerves) which is responsible for penile sensation .35,59
Penile erection is a vascular event primarily which can be impaired in conditions that end with endothelial dysfunction.13 Therefore physiological alteration related to hormonal changes together with sedentary lifestyles have been implicated in erectile dysfunction.47
During intercourse, the penis must sustain an erection which is the state of rigidity induced in erectile tissues of the penis as a result of engorgement of the tissues with blood in response to sexual arousal or during sleep.60 This results from the combination of neurotransmitters and vascular smooth muscles response largely due to impulse from the brain which stimulates the flow of blood from arteries leading to engorgement of the penis.60
Erection occurs with specific sequence of events involving nerve impulse from the brain, spinal column, muscles, penis, fibrous tissues, arteries and veins.61 The mechanism of erection begins with sexual stimulation which can either be tactile or mental.61 Sexual stimulation generates
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electrical impulses along the nerves going to the penis. This causes the nerves to release nitric oxide which in turn increase the production of cyclic guanosine monophosphate (cGMP) in the smooth muscle of the copora cavernosa. The cGMP causes the smooth muscle of the copora cavernosa to relax and allow rapid flow into the penis.61
The incoming blood fills the corpora carvernosa making the penis to expand, the pressure from the expanding penis compresses the veins in the tunica albugeneae helping to trap the blood in the corpora carvernosa thereby sustaining the erection.61 Erection is reversed when cGMP levels in the corpora cavernosa falls.62 This causes the smooth muscle of the corpora carvernosa to contract stopping inflow of blood and opening veins that drain blood away from the penis.62 The level of the cGMP in the corpora cavernosa falls because It is destroyed by an enzyme called phosphodiesterase type 5 (PDE5).62
E n d o l l e l i a l c e l l a n d n e u r o n e
P D E 5
5 G M T ( in a c tiv e ) C G M P
C G M P - d e p e n d e n t ( p r o te in k in a s e ) G u s n ily l
c y la s e G T P
P r o te in s
P h o s p h o p r o te in s ( in c lu d e s c a r tt p u m p s
R e d u c e c y to p la s m ic c a tt
R e la x a tio n - in c r e a s e b lo o d flo w - e r e c tio n
S m o o th m u s c le s N itr ic o x id e
F IG U R E 1
P D S 5 in h ib ito r s
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Erectile dysfunction is commoner in older men because of hormonal changes which occur as a result of changes in testicular size, hence a decline in sex hormones.63