Difference between revisions of "Erection - Anatomy & Physiology"

Revision as of 09:51, 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.

@@ Line 3: / Line 3: @@
 * 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 [[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.
 * Increased rigidity is the result of increase in arterial inflow of blood compared to venous outflow.
@@ Line 9: / Line 9: @@
 * 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'''.
+* 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.
 == 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]]

Difference between revisions of "Erection - Anatomy & Physiology"

Revision as of 09:51, 10 July 2008

Introduction

Erection of the Fibroelastic Penis

Erection of the Musculovascular Penis

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