Excretion: Urinary System
13.2 Urinary System
Organs Of The Urinary System
- Kidneys – filter blood, form urine (remove urea, excess salts, excess water).
- Ureters – carry urine from kidneys to bladder.
- Bladder – stores urine.
- Urethra – carries urine out of body.
Need For Excretion
- Urea = toxic if it builds up.
- Must be removed to maintain safe internal conditions.
Structure Of Nephron
| Part | Function |
|---|---|
| Bowman’s capsule + glomerulus | Ultrafiltration of blood → water, ions, glucose, urea forced out |
| Proximal tubule | Reabsorption of glucose, amino acids, most water and ions |
| Loop of Henle | Concentrates urine by reabsorbing water |
| Distal tubule | Further ion and water balance |
| Collecting duct | Final water reabsorption, urine formation |
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course
Liver And Excretion
- Assimilation: converts amino acids into proteins.
- Deamination: removal of nitrogen-containing part of excess amino acids.
- Forms ammonia → converted to urea → excreted in urine.
Urine Composition
- Urea, excess water, excess salts.
- No glucose or protein in healthy urine.
Key Points To Remember
- Kidneys regulate water and salt balance (osmoregulation).
- Damage to kidneys → urea builds up → dangerous.
- Dialysis/artificial kidney machines used if kidneys fail.
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course