Urine

Urine is the fluid made by the kidneys of animals to remove extra water and waste from the bloodstream. This waste includes urea, uric acid, and creatinine. In mammals, urine moves from the kidneys through tubes called ureters to the bladder to be stored until it is passed out through a tube called the urethra. Other animals pass urine through a part of their body called the cloaca.

Urine helps the earth's nitrogen cycle. In nature, urine helps soil grow plants, so it can be used as a fertilizer. Some animals use urine to mark their areas. In the past, old or fermented urine, called lant, was used to make gunpowder, clean homes, treat leather, and color textiles.

Human urine and waste from the body are handled through sanitation systems. Livestock urine and waste also need good management when there are many animals in one place.

Physiology

Main article: Renal physiology

Animals have ways to get rid of harmful wastes from their bodies. In humans, this is done by the urinary system. The urinary system has the kidneys, ureters, urinary bladder, and urethra. The kidneys clean the blood by taking out wastes, extra water, and other substances. This makes urine. The urine moves from the kidneys through the ureters, into the bladder, and out through the urethra.

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

Urine containing uric acid crystals under the microscope

The adult human bladder usually holds about 300 to 500 ml of urine before you need 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.

Typical design values for the concentrations of constituents in fresh urine, based on data in Sweden and Switzerland^: 12
Parameter	Value
pH	6.2
Total nitrogen	8,830 mg/L
Ammonium/ammonia-N	460 mg/L
Nitrate and nitrite	0.06 mg/L
Chemical oxygen demand	6,000 mg/L
Total phosphorus	800–2,000 mg/L
Potassium	2,740 mg/L
Sulphate	1,500 mg/L
Sodium	3,450 mg/L
Magnesium	120 mg/L
Chloride	4,970 mg/L
Calcium	230 mg/L

Examination for medical purposes

A Doctor Examining Urine. Trophime Bigot.

Long ago, doctors looked at urine to learn about a person's health. They saw that the color and smell of urine could show signs of some illnesses. Today, doctors still check urine, but they use special tests. These tests look at the color, smell, and what is in the urine. They 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 how much water a person is drinking. 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

Medieval Welsh text from the Red Book of Hergest on uroscopy, called Ansoddau'r Trwnc (the 'Qualities of Urine'). Opening lines (translated):"Since it is through the qualities of the urine that a person's faults and his dangers and his diseases and his illness can be identified..."

Long ago, people found that when urine sits and changes with tiny living things, it can be useful. They used this changed urine to clean clothes, soften animal skins, color fabrics, and clean rust off metal. In ancient Rome, leaders taxed the use of urine for cleaning.

Later, smart people tried to find valuable materials in urine. One person found a new 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. This word is related to words in many old languages that talk about water and rain.

People often use friendly words with children, like wee or pee, instead of more direct terms.