Difference between revisions of "Erection - Anatomy & Physiology"

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<big><center>[[ Reproductive System |'''BACK TO REPRODUCTIVE SYSTEM''']]</center></big>
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<big><center>[[ Reproductive_System#Reproductive_Behaviour |'''BACK TO REPRODUCTIVE BEHAVIOUR''']]</center></big>
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<big><center>[[ Reproductive_Behaviour_-_Pre-copulatory_Behaviour_-_Anatomy_%26_Physiology|'''BACK TO PRE-COPULATORY BEHAVIOUR''']]</center></big>
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== Introduction ==
 
== Introduction ==
  
 
* 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]].
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* 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 ==
  
[[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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[[Image:Erection of the Fibroelastic Penis.jpg|thumb|right|150px|<p>Erection of the Fibroelastic Penis</p><sup> Copyright Nottingham University 2008.</sup>]]
  
 
* Bull,Ram and Boar
 
* Bull,Ram and Boar
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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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* Stimuli cause afferent sensory nerves to fire.
 
* Stimuli cause afferent sensory nerves to fire.
* Terminals synapse with neurons in the ''''behaviour centre'''' in the [[Hypothalamus_- Anatomy & Physiology#Hypothalamus|Hypothalamus]].
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* Terminals synapse with neurons in the ''''behaviour centre'''' in the [[Endocrine_System_-_Hypothalamus_-_Anatomy_%26_Physiology#Hypothalamus|Hypothalamus]].
 
* Hypothalamic neurones synapse with parasympathetic and sympathetic efferent neurons that control penile vascular smooth muscle (vascular tone).
 
* 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.
 
* Firing of '''Nonadrenergic, noncholinergic (NANC) parasympathetic neurones''' causes erection.
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** Venous outflow blocked
 
** Venous outflow blocked
 
* Penile erection maintained for as long as vasodilation of corporal smooth muscle takes place.
 
* Penile erection maintained for as long as vasodilation of corporal smooth muscle takes place.
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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.
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* 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.
 
[[Category:Reproductive Behaviour]]
 
[[Category:Bullet Points]]
 

Revision as of 08:20, 31 July 2008

BACK TO REPRODUCTIVE SYSTEM
BACK TO REPRODUCTIVE BEHAVIOUR
BACK TO PRE-COPULATORY BEHAVIOUR


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

Erection of the Fibroelastic Penis

Copyright Nottingham University 2008.
  • 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.
  • 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.