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Erection - Anatomy & Physiology (view source)
Revision as of 13:40, 5 July 2012
, 13:40, 5 July 2012→Vascular and Biochemical Control of Erection
* When sexual receptivity of the female is established and sufficient arousal is accomplished in the male, erection and protrusion of the penis ensue.
* When sexual receptivity of the female is established and sufficient arousal is accomplished in the male, erection and protrusion of the penis ensue.
* Successful penile erection requires a complex series of neural and vasomotor reactions.
* Successful penile erection requires a complex series of neural and vasomotor reactions.
* Erection of the penis is necessary for copulation and deposition of [[Copulation_-Sperm_in_the_Female_Tract_-_Anatomy_%26_Physiology|semen in the female reproductive tract]].
* Erection of the penis is necessary for copulation and deposition of [[Sperm in the Female Tract - Anatomy & Physiology|semen in the female reproductive tract]].
* Erection is characterized by a marked increase in rigidity of the penis.
* Erection is characterized by a marked increase in rigidity of the penis.
* Increased rigidity is the result of increase in arterial inflow of blood compared to venous outflow.
* Increased rigidity is the result of increase in arterial inflow of blood compared to venous outflow.
* Increased blood flow to the penis is brought about by vasodilation of the arterioles supplying it.
* Increased blood flow to the penis is brought about by vasodilation of the arterioles supplying it.
== Erection of the Fibroelastic Penis ==
== Erection of the Fibroelastic Penis ==
[[Image:Erection of the Fibroelastic Penis.jpg|thumb|right|150px|<p>The Fibroelastic Penis in a Flaccid State</p><sup> Copyright Nottingham University 2008.</sup>]]
* Bull,Ram and Boar
* Involves increased blood flow with subsequent increase in pressure and simultaneous relaxation of the '''retractor penis muscles'''.
* Erection and protrusion involve straightening of the penis to eliminate the '''sigmoid flexure'''.
* Does not increase significantly in diameter during erection.
== Erection of the Musculovascular Penis ==
== Erection of the Musculovascular Penis ==
* Stallion
* Increases in diameter during erection.
* '''Retractor penis muscle''' still relaxes during erection, but '''no sigmoid flexure'''.
* Engorgement with blood plays a significant role in the highly vascular penis.
== Mechanism ==
Erection of the penis requires:
* Elevated arterial inflow
* Dilation of '''corporal sinusoids'''
* Restricted venous outflow
* Elevated intrapenile pressure
* Relaxation of '''retractor penis muscles'''
* Engorgement of cavernous sinuses causes a blockage of venous circulation from the penis.
* Contractions of ischiocavernous muscles cause compression of the penile veins.
** Intermittent contractions of the muscles around the two '''crura''' create a pump-like action at the base of the penis.
** Result in the build up of blood within the '''corpus cavernosum'''.
* Very high pressure results.
== Sensory Input and Local Vascular Response ==
'''''Nervous Component'''''
* Arousal driven
* Must be appropriate sensory stimuli (tactile, visual, olfactory, auditory) in order for the central nervous system to be stimulated for efferent events to cause erection.
** Extrinsic stimuli are called '''erotogenic stimuli'''.
* Stimuli cause afferent sensory nerves to fire.
* Terminals synapse with neurons in the ''''behaviour centre'''' in the [[Hypothalamus_- Anatomy & Physiology#Hypothalamus|Hypothalamus]].
* Hypothalamic neurones synapse with parasympathetic and sympathetic efferent neurons that control penile vascular smooth muscle (vascular tone).
* Firing of '''Nonadrenergic, noncholinergic (NANC) parasympathetic neurones''' causes erection.
** Release '''nitric oxide (NO)''' from their terminals.
** NO is the principle neurotransmitter that drives the erectile process.
** NO activates the enzyme '''guanylate cyclase'''.
** Guanylate cyclase converts guanylate triphosphate (GTP) into cyclic guanyosine monophosphate (cGMP).
* Causes corporal smooth muscle relaxation (vasodilation) and results in erection.
* Under nonerotogenic conditions, cGMP is acted upon by '''PDE5 (phosphodiesterase 5)'''.
* PDE5 promotes conversion of cGMP to GMP.
* Breakdown causes increased vascular tone.
** Tonic contraction of arterial and corporal smooth muscles.
** Outflow of blood from '''corpora cavernosa'''.
* Loss of erection and return to usual flaccid state.
'''''Local Vascular Component'''''
* When corporal smooth muscles relax because of cGMP, resistance to blood flow by penile arterioles and '''corporal sinusoids''' decreases.
* Blood flow to the penis triples or quadruples.
* When erection occurs, sinusoid pressure is so great that '''emissary veins''' are collapsed.
** Venous outflow blocked
* Penile erection maintained for as long as vasodilation of corporal smooth muscle takes place.
== Vascular and Biochemical Control of Erection ==
'''''Anatomy'''''
* '''Shaft''' of the Penis consists of two dorso-lateral '''corpora cavernosa''' and the '''corpus spongiosum'''.
* Arterial blood is supplied by the '''internal pudendal artery''' that supplies '''dorsal and deep cavernosal arteries'''.
* '''Corporal sinusoids''' are supplied by '''helicine arteries'''.
* '''Deep dorsal vein''' and '''superficial dorsal vein''' drain the erectile tissues.
* For more information on anatomy of the penis follow this link.
'''''Flaccid Penis'''''
* Sinusoids are flattened because adrenergic nerves secrete noradrenaline (norepinephrine) that causes '''vasoconstriction'''.
* Blood flow to cavernous tissue is low.
* No erotogenic stimuli present
* Nonadrenergic noncholinergic (NANC) parasympathetic neurons do not fire.
* No release of Nitric Oxide (NO)
* Vasoconstriction takes precedence over vasodilation.
'''''Erect Penis'''''
* Erotogenic stimuli present
* NANC neurones fire and release NO from their terminals.
* NO activates the enzyme guanylate cyclase.
* Guanylate cyclase converts guanylate triphosphate (GTP) into cyclic guanyosine monophosphate (cGMP).
* Causes smooth muscle of '''corporal sinusoids''' to relax (vasodilation).
* '''Cavernous sinusoids''' engorge with blood.
* Intracorporal pressure increases dramatically.
* Pressure compresses the venules through which blood exits the penis.
* Blood trapped within the penis causing an erection.
[[Category:Reproductive Behaviour]]
[[Category:Bullet Points]]