Short Notes: Excretion in Humans
1.0 Core Concepts
- Excretion: Removal of chemical metabolic wastes from the body.
- Homeostasis: Maintaining a constant internal environment (water/salt balance).
- Metabolic Wastes: Urea, Uric acid, CO₂, and excess salts.
2.0 Organs & Waste Products
| Organ | Main Waste Removed |
|---|---|
| Kidneys | Urea, excess water, salts (as Urine) |
| Lungs | CO₂ and Water vapor |
| Skin | Water, salts, traces of urea (as Sweat) |
| Liver | Converts ammonia to Urea |
3.0 The Urinary System
Flow of Urine:
Kidneys → Ureters → Urinary Bladder → Urethra
- Kidneys: Filter blood and form urine.
- Ureters: Transport tubes from kidney to bladder.
- Bladder: Temporary storage sac for urine.
- Urethra: Final canal for urine exit.
💡 Revision Tip: The Kidney Pelvis is the central funnel where urine collects before entering the ureter.
4.0 Functional Unit: The Nephron
Each kidney contains ~1 million Nephrons.
- Bowman's Capsule: Cup-shaped start of the nephron.
- Glomerulus: Network of capillaries inside the capsule (site of filtration).
- Renal Tubule: Coiled tube for reabsorbing useful substances.
5.0 How Urine is Formed
Step 1: Ultrafiltration
Blood pressure forces water, urea, and glucose out of the Glomerulus into the Bowman’s Capsule.
Blood pressure forces water, urea, and glucose out of the Glomerulus into the Bowman’s Capsule.
Step 2: Selective Reabsorption
Useful things (Glucose, salts, water) are taken back into the blood from the Renal Tubule.
Useful things (Glucose, salts, water) are taken back into the blood from the Renal Tubule.
6.0 Composition of Urine
| Constituent | Percentage |
|---|---|
| Water | 95% |
| Urea | 2.5% |
| Other wastes (Salts/Uric Acid) | 2.5% |
Pigment: Urochrome (gives urine its yellow color).
Daily Volume: Average adult passes 1.0 - 1.8 Litres.
💡 Memory Aid: Filtration happens first, then Reabsorption (First Run).
7.0 Common Disorders
- 💎 Kidney Stones: Small, hard mineral deposits (calcium/uric acid) that block urine flow. Cause: Dehydration.
- 🦠 UTI (Urinary Tract Infection): Bacterial infection in any part of the system. Symptoms: Painful or frequent urination.
- ⚠️ Kidney Failure: When kidneys lose the ability to filter waste. Can be fatal if not treated.
8.0 Dialysis & Transplantation
When kidneys fail, medicine provides two main alternatives:
- 🩺 Dialysis (Artificial Kidney): A machine filters the patient's blood to remove urea and salts. It works on the principle of Diffusion.
- 🏥 Kidney Transplantation: A surgical procedure to replace a damaged kidney with a healthy one from a donor.
9.0 Maintaining Kidney Health
💧
Drink 8+ glasses
of water
Drink 8+ glasses
of water
🧂
Lower salt
intake
Lower salt
intake
🥗
Eat balanced
diet
Eat balanced
diet
REVISION COMPLETE
Excretion in Humans: Short Notes finished.