Education Always

Level: JHS, Basic 9  |  Subject: Integrated Science  |  Strand: Systems  |  Topic: The Excretory System (Skin, Lungs, Kidneys)

Curriculum reference: B9.3.1.1 Understand the circulatory and excretory systems in humans. Indicator B9.3.1.1.2: Explain the excretory mechanism and organs (skin, lungs, kidneys). All the exemplars are merged into one set of notes.

1. What Is Excretion?

Excretion is the removal of waste products made by the body’s chemical reactions (metabolism). It is different from egestion, which is the removal of undigested food (faeces) from the gut.

2. Waste Products and Organs

Organ	Waste removed
Lungs	Carbon dioxide and water vapour (when we breathe out)
Skin	Sweat: water, salts and a little urea
Kidneys	Urine: water, urea and extra salts
Liver	Breaks down proteins to make urea (sent to the kidneys) and bile pigments from old red blood cells

Urea is a poisonous waste made in the liver when excess amino acids (from proteins) are broken down.

3. The Urinary System

• Kidneys (two): bean-shaped organs at the back of the abdomen. They filter the blood.
• Renal artery: brings blood to the kidney. Renal vein: takes cleaned blood away.
• Ureter: a tube that carries urine from each kidney to the bladder.
• Bladder: stores urine.
• Urethra: the tube that carries urine out of the body.

4. How the Kidney Works

Each kidney has about a million tiny filters called nephrons.

1. Filtration: blood enters the nephron under pressure. Water, urea, salts, glucose and amino acids pass out of the blood. Blood cells and big proteins stay in.
2. Reabsorption: all the glucose, most of the water and useful salts are taken back into the blood.
3. Urine formation: the water, urea and extra salts left behind form urine, which goes to the bladder through the ureter.

The kidneys also control the amount of water and salt in the body (osmoregulation). On a hot day we sweat more and pass less, darker urine. On a cool day we pass more, paler urine.

5. The Skin

Sweat glands take water, salts and urea from the blood and release sweat through pores. Sweating also cools the body as it evaporates. The skin has other jobs: protection, feeling touch and making vitamin D.

6. Kidney Problems and Care

• Kidney stones: hard lumps from salts that cause pain.
• Kidney failure: the kidneys stop cleaning the blood. Treatments are dialysis (a machine cleans the blood) and a kidney transplant.
• Care: drink enough clean water, avoid too much salt, do not take drugs without a doctor’s advice, treat infections early and check blood pressure.

Remember: Lungs remove carbon dioxide, skin removes sweat, and kidneys remove urea and control water balance.

Education Always (education.inspiringalways.com). Original notes written to follow the NaCCA Basic 9 Integrated Science curriculum.