1. The Urinary System
The organs, tubes, muscles, and nerves that work together to create, store, and carry urine are the urinary system. The urinary system includes two kidneys, two ureters, the bladder, two sphincter muscles, and the urethra.

2. Excretion
Excretion is the process of removing wastes and excess products from the body
Three of your body systems are involved in excretion:
Your skin releases waste products and water when you sweat
Your lungs expel carbon dioxide and water when you exhale
Your urinary system removes waste products from your blood

3. Cleaning the blood
Your blood is like a supply train that comes into a town to drop off supplies and take away garbage
The train has to find a way to get rid of the garbage before it can load up with more supplies.
If the garbage is not removed, the townspeople will be in a very unhealthy environment

4. Kidneys
The kidneys are a pair of bean-shaped organs that constantly clean the blood.
Your kidneys filter about 2,000 liters of blood each day
Your body only holds 5.6 liters of blood, so your blood cycles through the kidneys about 350 times a day

5. Inside the Kidney
Inside each kidney are more than 1 million microscopic filters called nephrons
Nephrons remove a variety of harmful substances from the body.

6. How the Kidneys Filter Blood
A large artery brings blood into each kidney
Tiny blood vessels branch off the main artery and pass through part of each nephron
Water and other substances are forced out of the blood vessels and into the nephrons

7. Nephrons
As these substances flow through the nephrons, most of the water and some nutrients are moved back into blood vessels
A concentrated mixture of waste materials is left behind in the nephrons
The cleased blood leaves each kidney in a large vein to recirculate in the body

8. Urination
The yellow fluid that remains in the nephrons is called urine
Urine leaves each kidney through a slender tube called the ureter and flows into the urinary bladder
Urine leaves the body through another tube called the urethra
Urination is the process of expelling urine from the body.

9. Water In, Water Out
Our bodies would swell up with excess water if we did not excrete as much water as we take in.
The balance of fluids is controlled by chemical messengers in the body called hormones

10. Sweat and Thirst
When you get hot, you lose more water in the form of sweat
The evaporation of water from your skin cools you down
As the water content of the blood drops, the salivary glands produce less saliva
This is one of the reasons you feel thirsty.

11. Antidiuretic Hormone
When you get thirsty, other parts of your body react to the water shortage
A hormone called antidiuretic hormone, or ADH, is released
ADH signals the kidneys to take back water from the nephrons and return it to the bloodstream, thereby making less urine
When your blood is too watery, smaller amounts of ADH are released
The kidneys react by allowing more water to stay in the nephron and leave the body as urine

12. Diuretics When you are thirsty, your tissues are asking for more water
Some beverages contain caffeine, which is a diuretic
Diuretics cause the kidneys to make more urine, which decreases the amount of water in the blood
So instead of giving your body more water, caffeinated beverages cause additional water to be lost in urine

13. Urinary System Ailments
Since the urinary system regulates body fluids and removes wastes from the blood, any malfunction can become life-threatening
Some common urinary system disorders are:
Bacterial infections
Kidney stones
Kidney disease

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Bacterial Infections
Bacteria can get into the bladder and ureters through the urethra and cause painful infections
It is important to treat such an infection early because it could spread to the kidneys and lead to permanent damage
Drinking six-eight 8 oz glasses of water can help prevent these infections

15. Kidney Stones
Sometimes salts and wastes collect inside the kidneys and form kidney stones.
Kidney stones interfere with urine flow and cause pain
Most kidney stones pass naturally from the body, but sometimes a medical procedure is necessary

16. Kidney Disease
Damage to nephrons can prevent normal kidney functioning, leading to kidney disease
If the kidneys do not function properly, a kidney machine can be used to filter waste from the blood.
The machine pumps blood from an artery in the forearm or wrist to a kidney machine, where it is filtered.
The cleaned blood is then pumped back into a vein in the arm.