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