Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

Unit 4: Maintaining life

Excretion In Humans — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 9 of 10 2 quizzes

📚 HIA International - Grade 8 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

Excretion in humans — HIA INTERNATIONAL notes: Describe what excretion is, what humans excrete and how the kidneys and urinary system work.Excretion = getting rid of waste materials made in body cells, plus substances in excess that have been part of the body.Not faeces — waste f…

  • Blood vessels
  • Reabsorption
  • Water balance
  • Urea and urine
  • Ureter and urethra
  • Not faeces — waste from the digestive system never was part of the body, so it is not excretion

Part 1 of 6What excretion is

Excretion
Excretion getting rid of waste materials made in body cells, plus substances in excess that have been part of the body.
Not faeces
  • Not faeces waste from the digestive system never was part of the body, so it is not excretion.
Egestion
  • Egestion removal of undigested food (faeces).

Part 2 of 6What humans excrete

SubstanceWhere it comes fromHow it is removed
Carbon dioxideRespiration in body cellsBreathed out through the lungs
UreaLiver cells break down excess proteinKidneys, in urine
Excess waterNot needed by the bodyKidneys in urine, and skin in sweat

Part 3 of 6Making urea

1
Proteins in food are broken down to smaller molecules in the digestive system.
2
The small molecules enter the blood and go to the liver.
3
If there is more protein than needed, liver cells change the molecules into urea.
4
Urea is poisonous, so it is removed from the liver in the blood and taken to the kidneys.
  • Plants
    • do not need to excrete urea because they make their own proteins.

Part 4 of 6The urinary (renal) system

The urinary (renal) system
Renal
Renal to do with the kidneys.
Kidneys
  • Kidneys filter the blood, removing urea and excess water.
Urine
Urine urea dissolved in excess water.
Ureters
  • Ureters tubes that carry urine from each kidney to the bladder.
Bladder
  • Bladder stores urine.
Urethra
  • Urethra carries urine out of the body.
Blood vessels
  • Blood vessels an artery brings blood to each kidney and a vein takes it away.

Part 5 of 6Kidney function

Kidney function
Filtering
  • Filtering small molecules such as water, glucose, salts and urea pass out of the blood into kidney tubules;
    • blood cells and proteins stay in the blood.
Reabsorption
  • Reabsorption useful substances such as all the glucose, much of the water and needed salts return to the blood.
Water balance
  • Water balance when dehydrated the kidneys make a small volume of concentrated urine;
    • after drinking a lot, a large volume of dilute urine.
Failure
  • Failure treated by dialysis or a kidney transplant.

Part 6 of 6Remembering the words

Urea and urine
  • Urea and urine urea is the waste chemical and urine is the liquid containing it.
Ureter and urethra
  • Ureter and urethra the ureter goes from kidney to bladder and the urethra from bladder to outside.

Key terms

TermMeaning
ExcretionGetting rid of waste materials made in body cells.
UreaA poisonous waste made in the liver from excess protein.
UrineA solution of urea in excess water.
KidneyAn organ that filters the blood to remove urea and excess water.
UreterA tube carrying urine from a kidney to the bladder.
BladderThe organ that stores urine.
UrethraThe tube carrying urine out of the body.

Avoid these mistakes

1
Faeces are excreted — they were never part of the body, so removing them is egestion.
2
Urea and urine are the same — urine is a solution containing urea.
3
The ureter carries urine out of the body — the urethra does that.
4
Glucose is excreted in urine — it is reabsorbed into the blood.

Last updated: