Editing Normal Erectile Physiology (section)

== Hemodynamics and Mechanisms of Erection and Detumescence ==

=== Corpora cavernosa ===
* 7 phases of erection/detumesence: 
**0, flaccid
**1, latent
**2, tumescence
**3, full erection
**4, rigid erection
**5, initial detumescence
**6, slow detumescence
**7, fast detumescence

==== '''<span style="color:#ff0000">Flaccid state''' ====
*'''<span style="color:#ff0000">In contrast to many other smooth muscles, the cavernous smooth muscle and the smooth muscles of the arteriolar and arterial wall are in a contracted state most of the time, allowing only a small amount of arterial flow into the corpora.'''
** '''Maintenance of the intracorporeal smooth muscle in a semicontracted (flaccid) state likely results from 3 factors:'''
**# '''Intrinsic myogenic activity'''
**# '''Adrenergic neurotransmission'''
**# '''Endothelium-derived contracting factors such as angiotensin II, PGF2α, and endothelin-1'''
** Smooth muscle has the ability to maintain tension for prolonged periods with minimal energy expenditure. This efficiency has been termed the latch state and is critical for sustaining the "basal" tone of the smooth muscle.

==== '''<span style="color:#ff0000">Transition to erection/tumescence</span>''' ====
*'''<span style="color:#ff0000">Sexual stimulation triggers release of neurotransmitters from the parasympathetic cavernous nerve terminals.</span>''' 
*'''This release of neurotransmitters (see above) results in relaxation of these smooth muscles and the following events:'''
*# '''Dilation of the arterioles and arteries''' by increasing blood flow in the diastolic and systolic phases
*# Trapping of the incoming blood by the expanding sinusoids
*# '''Compression of the subtunical venous plexuses''' between the tunica albuginea and the peripheral sinusoids, '''decreasing venous outflow'''
*# Stretching of the tunica to its capacity, which '''occludes the emissary veins''' between the inner circular and outer longitudinal layers and further decreases venous outflow
*# '''Increase in PO2 (≈90 mm Hg) and intracavernous pressure (≈100 mm Hg),''' which raises the penis from the dependent position to the erect state (the full erection phase).
* '''Erection involves sinusoidal relaxation, arterial dilation (increased inflow), and venous compression (decreased outflow)'''
*See [[commons:File:Erection_Development.jpg|Figure demonstrating the development of an erection]]
[[File:Figure 28 01 06.jpg|alt=Anatomic representation of changes to penis during erection.|thumb|582x582px|Anatomic representation of changes to penis during erection. Source: [[commons:File:Figure_28_01_06.jpg|Wikipedia]]|center]]

==== '''<span style="color:#ff0000">Transition to detumescence</span>''' ====
*'''<span style="color:#ff0000">3 phases of detumescence:</span>'''
*# '''<span style="color:#ff0000">Transient intracorporeal pressure increase, indicating the beginning of smooth muscle contraction against a closed venous system</span>'''
*# '''<span style="color:#ff0000">Slow pressure decreases</span>''', suggesting a slow reopening of venous channels with resumption of the basal level of arterial flow
*# '''<span style="color:#ff0000">Fast pressure decrease</span>''' with fully restored venous outflow capacity
*'''<span style="color:#ff0000">Detumescence after erection may be a result of (3):</span>'''
*# '''<span style="color:#ff0000">Cessation of NO release</span>'''
*# '''<span style="color:#ff0000">Breakdown of cGMP by PDEs</span>'''
*# '''<span style="color:#ff0000">and/or sympathetic discharge during ejaculation</span>'''
=== Corpus spongiosum and glans penis ===
* '''During erection, the arterial flow increases in a similar manner; however, the pressure in the corpus spongiosum and glans is only 1/3-1/2 that in the corpora cavernosa because the spongiosum lacks the outer longitudinal layer of the tunica albuginea,''' resulting in minimal venous occlusion (Chapter 26 suggests tunica albuginea absent from corpus spongiosum but Chapter 21 specifies that outer longitudinal layer is absent)