Difference between revisions of "Erection - Anatomy & Physiology"
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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 [[ | + | * 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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* Bull,Ram and Boar | * Bull,Ram and Boar | ||
* Involves increased blood flow with subsequent increase in pressure and simultaneous relaxation of the '''retractor penis muscles'''. | * 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'''. | + | * Erection and [[Reproductive_Behaviour_-_Pre-copulatory_Behaviour_-_Anatomy_%26_Physiology#Penile_Protrusion|protrusion]] involve straightening of the penis to eliminate the '''sigmoid flexure'''. |
* Does not increase significantly in diameter during erection. | * 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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* Engorgement with blood plays a significant role in the highly vascular penis. | * Engorgement with blood plays a significant role in the highly vascular penis. | ||
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== Mechanism == | == Mechanism == | ||
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* Very high pressure results. | * Very high pressure results. | ||
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== Sensory Input and Local Vascular Response == | == Sensory Input and Local Vascular Response == | ||
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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. | * 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'''. | ** Extrinsic stimuli are called '''erotogenic stimuli'''. | ||
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* Stimuli cause afferent sensory nerves to fire. | * Stimuli cause afferent sensory nerves to fire. | ||
| − | * Terminals synapse with neurons in the ''''behaviour centre'''' in the [[ | + | * Terminals synapse with neurons in the ''''behaviour centre'''' in the [[Endocrine_System_-_Hypothalamus_-_Anatomy_%26_Physiology#Hypothalamus|Hypothalamus]]. |
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| + | '''''Local Vascular Component''''' | ||
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== Vascular and Biochemical Control of Erection == | == Vascular and Biochemical Control of Erection == | ||
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| − | * For more information on anatomy of the penis follow this link. | + | * For more information on anatomy of the penis follow [[this link]]. |
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* Pressure compresses the venules through which blood exits the penis. | * Pressure compresses the venules through which blood exits the penis. | ||
* Blood trapped within the penis causing an erection. | * Blood trapped within the penis causing an erection. | ||
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Revision as of 10:53, 10 July 2008
Introduction
- 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.
- Erection of the penis is necessary for copulation and deposition of semen in the female reproductive tract.
- 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.
- Erection requires that blood be trapped within the cavernous sinus of the penis.
- Increased blood flow to the penis is brought about by vasodilation of the arterioles supplying it.
Erection of the Fibroelastic Penis
- 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
- 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.
Local Vascular Component
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.