Urine

Urine is the fluid excreted by the kidneys of vertebrates to clear the bloodstream of excess water and metabolic by-products including urea, uric acid, and creatinine. In mammals, urine travels from the kidneys via the ureters to the bladder for storage until urination. Placental mammals expel urine from the bladder through the urethra, whereas other vertebrates urinate through the cloaca.

Urine plays an important role in the earth's nitrogen cycle. In balanced ecosystems, urine fertilizes the soil and thus helps plants to grow. Therefore, urine can be used as a fertilizer. Some animals mark their territories with urine. Historically, aged or fermented urine (known as lant) was also used in gunpowder production, household cleaning, leather tanning, and textile dyeing.

Human urine and feces, called human waste or human excreta, are managed via sanitation systems. Livestock urine and feces also require proper management if the livestock population density is high.

Physiology

Main article: Renal physiology

Animals have systems to remove harmful wastes from their bodies. In humans, this is mainly done by the urinary system. The urinary system includes the kidneys, ureters, urinary bladder, and urethra. The kidneys clean the blood by removing wastes, extra water, and other substances. This creates urine, which then moves from the kidneys through the ureters, into the bladder, and out through the urethra.

Studies show that larger mammals usually urinate for about 21 seconds, no matter their size. Smaller animals like rodents and bats urinate differently, releasing urine in drops instead of a steady stream.

Characteristics

The adult human bladder usually holds between 300 and 500 ml of urine before needing to go, but it can hold more. On average, adults make about 1.4 liters of urine each day, usually going about 6 to 8 times a day. This can change based on how active you are, the weather, and what you eat and drink.

Urine is mostly water—about 91–96% of it. The rest includes salts, urea (a waste product from food), and other small compounds. The color and smell of urine can change depending on how hydrated you are, what you eat, and your health. For example, drinking a lot of water can make your urine look almost clear, while not drinking enough can make it darker. Certain foods like beets can turn urine pink, and asparagus can give it a strong smell.

Examination for medical purposes

Long ago, doctors looked at their patients' urine to help understand their health. They noticed that the color and other features of urine could show signs of certain illnesses. Today, doctors still check urine, but they use special tests that look at its color, smell, and what it contains. These tests can help find problems like infections in the parts of the body that make and pass urine.

The way urine looks can also tell doctors about a person's hydration. If urine is very clear, it usually means the person is drinking enough water. If it is dark, it might mean the person needs to drink more water.

Uses

Further information: Lant

Source of medications

Urine contains proteins and other helpful substances that are used in medicines. For example, urine from women who are no longer having periods has special proteins that can help with fertility treatments. Pregnant women’s urine also contains important substances that can be used to make medicine. Urine can also help scientists test for germs, like the virus that causes AIDS.

Urine can be used to make a medicine that helps dissolve blood clots.

Fertilizer

Cleaning

Because urine contains a substance that turns into a cleaning agent, it has been used for cleaning for a very long time. People in the past used urine to clean and even to whiten teeth.

Gunpowder

Main article: Potassium nitrate

Before factories made chemicals, people used urine to help make gunpowder. Urine was mixed with straw and let sit for a long time. The mixture was then washed and the crystals collected were used in making gunpowder.

Survival uses

Sometimes people have drunk urine when they had no other water, but experts advise against this because urine can actually make dehydration worse. In very hot weather, putting urine-soaked cloth on the head can help cool the body. During World War I, soldiers used urine-soaked pads to protect themselves from poisonous gases.

There are stories that urine can help with jellyfish stings, but this is not true and can sometimes make the sting worse.

Textiles

Urine has been used to treat wool before dyeing it.

Olfactory communication

Urine can send signals to other animals. For example, the urine of dangerous animals can warn other animals to stay away.

History

Long ago, people discovered that when urine sits and changes with help from tiny living things, it can be useful. They used this changed urine to clean clothes, soften animal skins for making things, color fabrics, and even clean rust off metal. In ancient Rome, leaders even made money by taxing the use of urine for cleaning.

Later, smart people tried to find valuable materials in urine. One person found a new kind of material by heating changed urine. Another discovered an important natural material by boiling urine until it was dry.

Language

The word urine comes from the Latin word urina, which is related to words in many old languages that talk about water, rain, and passing urine. For example, in Sanskrit, varṣati means “it rains,” and in Greek, ourein means “to urinate.”

The word piss is an older word for urine but is now seen as rude. People often use friendly words with children, like wee, pee, or number one, instead of the more direct terms. There is also a word, lant, which means very old urine and comes from an old English word for urine.