Urinary System and Skin
Your cells constantly produce waste, and getting rid of it is just as important as taking in food and oxygen. The urinary system and the skin both help remove waste and keep your internal environment balanced. This topic, called excretion, is a clear and testable part of human biology.
This lesson covers the urinary system and the skin’s role in excretion.
Excretion is the removal of waste products from the body. The urinary system, led by the kidneys, filters waste from the blood and removes it as urine. The skin also excretes waste and water through sweat, and it helps control body temperature.
How does the urinary system work?
The stars of the urinary system are the kidneys, two bean-shaped organs that filter the blood. They remove waste, especially a substance called urea, along with excess water and salts, producing urine. The urine travels down tubes called ureters to the bladder, which stores it until it leaves the body. Beyond removing waste, the kidneys carefully balance the body’s water and salt levels, a key part of homeostasis.
| Organ | Job |
|---|---|
| Kidneys | Filter blood, make urine |
| Ureters | Carry urine to the bladder |
| Bladder | Stores urine |
How does the skin help?
The skin is the body’s largest organ, and it does more than cover you. Through sweat, it excretes water, salts, and a small amount of waste. Sweating also cools you down: as sweat evaporates, it carries heat away, helping control body temperature. The skin also acts as a protective barrier against germs and injury, tying it to both excretion and defense.
Watch: A Short Video Lesson
Mr Catterson walks through this skill clearly in a few minutes. It is a helpful companion to the reading above:
A routine for excretion questions
- Define excretion: removing waste from the body.
- Recall the kidneys filter blood and make urine.
- Trace urine: kidneys, ureters, bladder.
- Remember the skin excretes through sweat and cools the body.
- Connect the kidneys to water and salt balance (homeostasis).
Practice questions
- What is excretion?
- Which organs filter waste from the blood?
- What waste substance do the kidneys remove in urine?
- How does sweating help cool the body?
- Besides making urine, what balance do the kidneys maintain?
- True or false: the skin plays no role in excretion.
Answers:
- The removal of waste products from the body.
- The kidneys.
- Urea (along with excess water and salts).
- As sweat evaporates, it carries heat away from the body.
- Water and salt balance.
- False. The skin excretes water, salts, and waste through sweat.
Where this fits
Excretion keeps the internal balance tied to homeostasis, and the kidneys clean the blood moved by the circulatory system. It is one of the major human body systems. Find all topics on the ASVAB General Science Learning Hub.
Recommended Prep Books
These study guides and practice books help you keep building momentum as you prepare:
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