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Urine
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<p>Urine is a liquid <a href="/facts/By-product/qDosnqoD">by-product</a> of <a href="/facts/Metabolism/WxDrm8k5">metabolism</a> in humans and many other animals. In <a href="/facts/Placental_mammal/xegVWIRG">placental mammals</a>, urine flows from the <a href="/facts/Kidney_(vertebrates)/HkG2xISn">kidneys</a> through the <a href="/facts/Ureter/VIfEGI2c">ureters</a> to the <a href="/facts/Urinary_bladder/g8Khaf7A">urinary bladder</a> and exits the <a href="/facts/Urethra/THkvxu0d">urethra</a> through the <a href="/facts/Penile_meatus/KEpC3DKX">penile meatus</a> (males) or urethral meatus of the <a href="/facts/Vulva/ECayW89s">vulva</a> (females) during <a href="/facts/Urination/H4qYz02K">urination</a>. In other <a href="/facts/Vertebrate/tT54FSTT">vertebrates</a>, urine is excreted through the <a href="/facts/Cloaca/e5rv15PI">cloaca</a>. </p><p>Urine contains water-soluble <a href="/facts/By-product/qDosnqoD">by-products</a> of <a href="/facts/Cell_(biology)/bLM9UQvy">cellular</a> metabolism that are rich in <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a> and must be <a href="/facts/Clearance_(medicine)/RqI64paT">cleared</a> from the <a href="/facts/Circulatory_system/WXwudzzc">bloodstream</a>, such as <a href="/facts/Urea/6j84AoCG">urea</a>, <a href="/facts/Uric_acid/gPMSfLcT">uric acid</a> and <a href="/facts/Creatinine/gkebqj2L">creatinine</a>. A <a href="/facts/Urinalysis/PeS2UfIG">urinalysis</a> can detect <a href="/facts/Nitrogenous_waste/qGH5b3od">nitrogenous wastes</a> of the <a href="/facts/Mammal/phSwTzBo">mammalian</a> body. </p><p>Urine plays an important role in the earth's <a href="/facts/Nitrogen_cycle/0X1z74dN">nitrogen cycle</a>. In balanced <a href="/facts/Ecosystem/kVE8mSmR">ecosystems</a>, urine fertilizes the <a href="/facts/Soil/5Ddpr3QM">soil</a> and thus helps <a href="/facts/Plant/X5BMDMvS">plants</a> to grow. Therefore, <a href="/facts/Reuse_of_excreta/A4FUhsdv">urine can be used</a> as a <a href="/facts/Fertilizer/ysh3r6NJ">fertilizer</a>. Some animals use it to <a href="/facts/Territory_(animal)/T15S7XeD">mark their territories</a>. Historically, aged or fermented urine (known as <a href="/facts/Lant/DdgjvQID">lant</a>) was also used for <a href="/facts/Gunpowder/AEcB6HCR">gunpowder</a> production, household cleaning, <a href="/facts/Tanning_(leather)/NqL8LFrg">tanning</a> of leather, and <a href="/facts/Dyeing/6I8w1TyN">dyeing</a> of textiles. </p><p>Human urine and <a href="/facts/Human_feces/E55Ym1Cl">feces</a> are collectively referred to as <a href="/facts/Human_waste/FkBVmLgc">human waste</a> (or human excreta), and are managed via <a href="/facts/Sanitation/NLGqBs2T">sanitation</a> systems. <a href="/facts/Livestock/Quhv6GvP">Livestock</a> urine and feces also require proper management if the <a href="/facts/Concentrated_animal_feeding_operation/t8S3UPvn">livestock population density is high</a>. </p>