Urination

It is also known medically as micturition,[4] voiding, uresis, or, rarely, emiction, and known colloquially by various names including peeing, weeing, pissing, and euphemistically number one.

The process of urination is under voluntary control in healthy humans and other animals, but may occur as a reflex in infants, some elderly individuals, and those with neurological injury.

Brain centres that regulate urination include the pontine micturition center, periaqueductal gray, and the cerebral cortex.

Part of the urethra is surrounded by the male or female external urethral sphincter, which is innervated by the somatic pudendal nerve originating in the cord, in an area termed Onuf's nucleus.

The state of the reflex system is dependent on both a conscious signal from the brain and the firing rate of sensory fibers from the bladder and urethra.

Individual ready to urinate consciously initiates voiding, causing the bladder to contract and the outlet to relax.

During the storage phase, the internal urethral sphincter remains tense and the detrusor muscle relaxed by sympathetic stimulation.

This phenomenon is a manifestation of the law of Laplace, which states that the pressure in a spherical viscus is equal to twice the wall tension divided by the radius.

Action potentials carried by sensory neurons from stretch receptors in the urinary bladder wall travel to the sacral segments of the spinal cord through the pelvic nerves.

Diuresis (production of urine by the kidney) occurs constantly, and as the bladder becomes full, afferent firing increases, yet the micturition reflex can be voluntarily inhibited until it is appropriate to begin voiding.

Bladder afferent signals ascend the spinal cord to the periaqueductal gray, where they project both to the pontine micturition center and to the cerebrum.

The firing of these neurons causes the wall of the bladder to contract; as a result, a sudden, sharp rise in intravesical pressure occurs.

The pontine micturition center also causes inhibition of Onuf's nucleus, resulting in relaxation of the external urinary sphincter.

[25] Another possibility is the excitation or disinhibition of neurons in the pontine micturition center, which causes concurrent contraction of the bladder and relaxation of the sphincter.

In humans with lesions in the superior frontal gyrus, the desire to urinate is reduced and there is also difficulty in stopping micturition once it has commenced.

When the afferent and efferent nerves are both destroyed, as they may be by tumors of the cauda equina or filum terminale, the bladder is flaccid and distended for a while.

Some paraplegic patients train themselves to initiate voiding by pinching or stroking their thighs, provoking a mild mass reflex.

A common technique used in many developing nations involves holding the child by the backs of the thighs, above the ground, facing outward, in order to urinate.

[30] A puer mingens[31] is a figure in a work of art depicted as a prepubescent boy in the act of urinating, either actual or simulated.

[33][full citation needed] It is socially more accepted and more environmentally hygienic for those who are able, especially when indoors and in outdoor urban or suburban areas, to urinate in a toilet.

Examples (depending on circumstances) include activities such as camping, hiking, delivery driving, cross country running, rural fishing, amateur baseball, golf, etc.

[39] Public urination still remains more accepted by males in the UK, although British cultural tradition itself seems to find such practices objectionable.

[43] Women generally need to urinate more frequently than men, but as opposed to the common misconception, it is not due to having smaller bladders.

Women averting contact with a toilet seat may employ a partial squatting position (or "hovering"), similar to using a female urinal.

For example, centuries ago the standard English word (both noun and verb, for the product and the activity) was "piss", but subsequently "pee", formerly associated with children, has become more common in general public speech.

[citation needed] Other expressions include "squirting" and "taking a leak", and, predominantly by younger persons for outdoor female urination, "popping a squat", referring to the position many women adopt in such circumstances.

[60] Australian English has coined "I am off to take a Chinese singing lesson", derived from the tinkling sound of urination against the China porcelain of a toilet bowl.

[62] One of the most common, albeit old-fashioned, euphemisms in British English is "to spend a penny", a reference to coin-operated pay toilets, which used (pre-decimalisation) to charge that sum.

In 2008 in London, a person died when they were urinating alongside a railway track at a train station and they received an electric shock.

For example, the urine of birds and reptiles is whitish, consisting of a pastelike suspension of uric acid crystals, and discharged with the feces of the animal via the cloaca, whereas mammals' urine is a yellowish colour, with mostly urea instead of uric acid, and is discharged via the urethra, separately from the feces.