question: Why is it harder for guys to urinate when they have an erection compared to when they’re flaccid?
comment: Simply put, there's a series of inflatable chambers around the urine hose from the bladder. When flaccid, these chambers are empty, which allows pee to flow through the hose easily. The erection happens because those chambers are filled with blood. And that pressure squeezes down on the hose making it very difficult to pass pee through. A much greater pressure than normal must build up to squeeze through.
passages: BULLET::::- the post void residual volume (PVR, ml) was significantly decreased
  
  BULLET::::- the maximum urinary flow (Qmax, ml/s) was increased
  
  BULLET::::- the voiding time (VT, s) was decreased
  
  This urodynamic profile is related to a lower risk of urologic complications, such as cystitis and bladder stones.
  
  Section::::Physiological functions.:Erection.
   In Figure 1, the neutral (i.e. active) base is green, and the depleted base regions are hashed light green. The neutral emitter and collector regions are dark blue and the depleted regions hashed light blue. Under increased collector–base reverse bias, the lower panel of Figure 1 shows a widening of the depletion region in the base and the associated narrowing of the neutral base region.
   During sexual arousal, arterial blood flow to the clitoris is increased, and within the clitoris, the arteries further branch to supply the erectile tissues. The trabecular smooth muscles of the erectile tissue relax increasing blood flow to fill the vascular spaces, expanding the erectile tissues until they are fully engorged with blood. The ischiocavernosus and bulbocavernosus muscles contract, compressing the dorsal vein of the clitoris. This compression of the vein restricts drainage of the erectile structures, trapping the blood. This process stretches the tunica albuginea. As a result, the clitoris becomes tumescent to accommodate the increased intracavernosus pressure. The tunica albuginea of the clitoris is made up of one layer making it more elastic than the tunica albuginea of the penis, which is composed of two layers. Erick Janssen (2007) elaborates on this reporting that "the corpora cavernosa of the clitoris are essentially similar to that of the penis except that there is no subalbugineal layer interposed between the tunica albuginea and the erectile tissue. In the penis, this tissue engorges with blood during sexual arousal and becomes compressed against the unyielding tunica, creating penile rigidity --a true erection. The lack of this plexus in the clitoris indicates that while the organ can become tumescent or engorged, it cannot, like the penis become stiffly erect. The clitoris thus does not really become erect with sexual excitement, but engorged." In addition, the tunica albuginea around the glans is thinner than around the shaft in both the clitoris and penis. This gives the glans less firmness relative to the shaft. The extrusion of the glans clitoridis and thinning of the skin enhances sensitivity to physical contact. After a female has orgasmed, the erection usually ends, but this may take time.
   The circumference of the base of the glans forms a rounded projecting border, the corona of glans penis, overhanging a deep retroglandular sulcus, behind which is the neck of the penis.
  
  Section::::Function.
  
  The function of the corpus spongiosum in erection is to prevent the urethra from pinching closed, thereby maintaining the urethra as a viable channel for ejaculation. To do this, the corpus spongiosum remains pliable during erection while the corpora cavernosa penis becomes engorged with blood.
  
  Section::::See also.
  
  BULLET::::- Corpus cavernosum penis
  
  BULLET::::- Spongy urethra
  
  BULLET::::- Trabeculae of corpus spongiosum of penis
  
  Section::::External links.
   In some circumstances, release of nitric oxide precedes relaxation of muscles in the corpora cavernosa and corpus spongiosum, in a process similar to female arousal. The spongy tissue fills with blood, from arteries down the length of the penis. A little blood enters the corpus spongiosum; the remainder engorges the corpora cavernosa, which expand to hold 90% of the blood involved in an erection, increasing both in length and in diameter. The function of the corpus spongiosum is to prevent compression of the urethra during erection.
   Bulls have a fibro-elastic penis. Given the small amount of erectile tissue, there is little enlargement after erection. The penis is quite rigid when non-erect, and becomes even more rigid during erection. Protrusion is not affected much by erection, but more by relaxation of the retractor penis muscle and straightening of the sigmoid flexure.
   The restriction of blood flow can also be used in specialized tissues to cause engorgement, resulting in an erection of that tissue; examples are the erectile tissue in the penis and clitoris.
  
  Another example of a hydraulic function is the jumping spider, in which blood forced into the legs under pressure causes them to straighten for a powerful jump, without the need for bulky muscular legs.
  
  Section::::Physiology.:Invertebrates.
   The mammalian penis is a hydrostatic organ. The hydrostatic fluid, in this case blood, fills the penis during an erection. Unlike the hydrostatic skeletons of many invertebrates, which use the bending of the animal for locomotion, the penis must resist bending and shape changes during sexual intercourse. Instead of connective fibers arranged in a helical shape, the penis contains a layer called the corpus cavernosum. The corpus cavernosum contains connective fibers arranged both parallel and perpendicular to the longitudinal axis. These fibers remain folded when the penis is flaccid, but unfold as the penis fills with blood during an erection, which allows the penis to resist bending. The penises of turtles are structured similarly, although they evolved separately.
   Section::::Interpretation.:Blood CO levels may not be negligible.:Any change in formula_25 alters formula_19.
   Earlier techniques used a bone graft as part of reconstruction. Long-term follow-up studies from Germany and Turkey of more than 10 years proved that these reconstructions maintain their stiffness without later complications. Unfortunately, the reconstructed penis cannot become flaccid again without breaking the internal bone graft.
   If the patient chooses to have the urethra extended to the glans of the neophallus, it is formed by the following steps:
  
  BULLET::::- The labia minora is injected with a mixture of saline and epinephrine.
  
  BULLET::::- It is then split open and layers separated using sharp and blunt dissection.
  
  BULLET::::- The layers are wrapped around a catheter and stitched.
   Cold work also serves to harden the material's surface. This makes cracks less likely to form at the surface and provides resistance to abrasion. When a metal undergoes strain hardening its yield strength increases but its ductility decreases. Strain hardening actually increases the number of dislocations in the crystal lattice of the material. When a material has a great number of dislocations, plastic deformation is hindered, and the material will continue to behave in an elastic way well beyond the elastic yield stress of the non-strain hardened material.
  
  Section::::Residual strain / stretching.
   Recently hemodynamic studies were conducted in both fresh and defrosted human cadavers in which a rigid erection was without exception attainable despite cavernosal tissue having lost its extensibility in cadaveric sinusoids. This implies a rigid penile erection is just a mechanical event and, consequently, that penile veins play a pivotal role in achieving a rigid erection. This is clearly a ramification of endorsing the determinant role of the erection-related veins in human erectile function. 
   Section::::Shear behavior: stiffness and strength.:Drained and undrained shear.
  
  The presence of nearly incompressible fluids such as water in the pore spaces affects the ability for the pores to dilate or contract.
  
  If the pores are saturated with water, water must be sucked into the dilating pore spaces to fill the expanding pores (this phenomenon is visible at the beach when apparently dry spots form around feet that press into the wet sand).
  
  Similarly, for contractive soil, water must be squeezed out of the pore spaces to allow contraction to take place.
   BULLET::::5. the glandular tissue is surrounded by a muscularis to facilitate expulsion of secretory products into the urethra,
  
  BULLET::::6. seasonal changes in echidna glandular development, whereby in aspermatogenic animals the glandular tissue surrounding the urethra is less developed (Figure 1) than during the breeding season when the secretory glands surrounding the urethra of spermatogenic animals appear well developed (Figure 2) coinciding with elevated levels of testosterone and active spermatogenesis.
  
  In aggregate, these characteristics of glandular tissue surrounding the urethra identify a rudimentary disseminate prostate in monotremes.
   Trabeculae of corpus spongiosum of penis
  
  The fibrous envelope of the corpus cavernosum urethrae is thinner, whiter in color, and more elastic than that of the corpora cavernosa penis. It is called the trabeculae of corpus spongiosum of penis.
  
  The trabeculae are more delicate, nearly uniform in size, and the meshes between them smaller than in the corpora cavernosa penis: their long diameters, for the most part, corresponding with that of the penis.
   Venous drainage is performed by the deep and superficial dorsal veins of the penis. The dorsal arteries of the penis are located adjacent to the deep dorsal vein and a cavernous artery is located in the center of each corpus cavernosum. On color Doppler, the cavernous arteries present single phase flow. In the flaccid penis (Figure 3), the normal cavernous arteries show a systolic peak between 11 and 20 cm/s. At the beginning of erection, the systolic and diastolic flows undergo progressive increases. When vein occlusion begins, the diastolic flow decreases progressively, and once stiffness is established, it becomes negative.
   "Intensity" is a key parameter of the shot peening process. After some development of the process, an analog was needed to measure the effects of shot peening. John Almen noticed that shot peening made the side of the sheet metal that was exposed begin to bend and stretch. He created the Almen strip to measure the compressive stresses in the strip created by the shot peening operation. One can obtain what is referred to as the "intensity of the blast stream" by measuring the deformation on the Almen strip that is in the shot peening operation. As the strip reaches a 10% deformation, the Almen strip is then hit with the same intensity for twice the amount of time. If the strip deforms another 10%, then one obtains the intensity of the blast stream.
   In contrast to the serum anion gap equation, the bicarbonate is excluded. This is because urine is acidic, so the bicarbonate level would be negligible.
  
  Section::::Uses.
   BULLET::::- the penis, within the prepuce, also known as the "sheath". Stallions have a vascular penis. When non-erect, it is quite flaccid and contained within the prepuce (foreskin, or sheath). The retractor penis muscle is relatively underdeveloped. Erection and protrusion take place gradually, by the increasing tumescence of the erectile vascular tissue in the "corpus cavernosum penis". When not erect, the penis is housed within the prepuce, long and in diameter with the distal end . The retractor muscle contracts to retract the penis into the sheath and relaxes to allow the penis to extend from the sheath. When erect, the penis doubles in length and thickness and the glans increases by 3 to . The urethra opens within the urethral fossa, a small pouch at the distal end of the glans. A structure called the urethral process projects beyond the glans.
   When peening is used to induce residual stress or work-harden an object, care needs to be taken with thin parts not to stretch the work-piece. Where stretching is unavoidable then allowances may need to be made in the part design or process application.
  
  Section::::Use with welding.
   Coverage is affected by shot geometry and the shot and workpiece chemistry. The size of the shot controls how many impacts there are per pound, where smaller shot produces more impacts per pound therefore requiring less exposure time. Soft shot impacting hard material will take more exposure time to reach acceptable coverage compared to hard shot impacting a soft material (since the harder shot can penetrate deeper, thus creating a larger impression).
   The presence of Glycymeris's valves turns out to be very frequent in a context of life outdoors of the final Neolithic / Chalcolitic of the central region of the peninsular Mediterranean, where they appear in a high number of remains, between 51 and 87%. Good part of the valves they are affected by the marine erode in major or minor measure, indicative fact of which his withdrawal goes away to carry out in the beach, once died the animal.
   Section::::History and further developments.
  
  It was common practice for blacksmiths to hammer peen the concave side of leaf springs, which enhanced their life, although the exact mechanism was unknown. The maximum tensile stresses are located on the surface of the concave portion of leaf springs; the peening effectively offset the maximum tensile stresses, also located on the surface, when the compressive stresses were induced by peening with a ball peen hammer.
   Section::::Compressive residual stress.
  