Difference between revisions of "Erection - Anatomy & Physiology"

From WikiVet English
Jump to navigation Jump to search
(New page: == 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 p...)
 
 
(52 intermediate revisions by 3 users not shown)
Line 1: Line 1:
 
 
== 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 [[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.
 
* Erection requires that blood be trapped within the cavernous sinus of the penis.
 
* 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.
 
* Increased blood flow to the penis is brought about by vasodilation of the arterioles supplying it.
 +
 +
 +
== 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 Fibroelastic Penis ==
 
  
  
 
== 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]]

Latest revision as of 13:40, 5 July 2012

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

The Fibroelastic Penis in a Flaccid State

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.