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 [[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.
  
 +
----
  
 
== 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
 
* 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.
  
 
+
----
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
== 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.
  
 +
 +
----
  
 
== Mechanism ==
 
== Mechanism ==
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* Very high pressure results.
 
* Very high pressure results.
  
 +
 +
----
  
 
== 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'''.
 
 
 
* 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]].
+
* 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.
 
  
 +
'''''Local Vascular Component'''''
  
* 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 ==
 
== 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]].
 +
 
  
  
 
'''''Flaccid Penis'''''
 
'''''Flaccid Penis'''''
  
* Sinusoids are flattened because adrenergic nerves secrete noradrenaline (norepinephrine) that causes '''vasoconstriction'''.
+
* Sinusoids are flattened because adrenergic nerves secrete noradrenaline (norepinephrine)that causes '''vasoconstriction'''.
 
* Blood flow to cavernous tissue is low.
 
* Blood flow to cavernous tissue is low.
 
* No erotogenic stimuli present
 
* No erotogenic stimuli present
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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 10:49, 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.