Excretory Products and Their Elimination – Complete NEET UG 2026 Guide
MOST IMPORTANT POINTS (NEET REVISION GOLD)
Nitrogenous Wastes (VERY FREQUENT)
- Ammonia (NH₃) → most toxic, needs more water
- Urea → less toxic (humans)
- Uric acid → least toxic (birds, reptiles)
Shortcut:
“Ammonia → Aquatic, Urea → Humans, Uric → Birds”
Types of Animals (Direct Questions आते हैं)
| Type | Waste | Example |
|---|---|---|
| Ammonotelic | Ammonia | Fish |
| Ureotelic | Urea | Humans |
| Uricotelic | Uric acid | Birds |
Trick:
“AQUA → AMMONIA, LAND → UREA/URIC”
Human Excretory System (Diagram Based)
- Kidney (2)
- Ureter (2)
- Urinary bladder
- Urethra
Kidney facts:
- Length: 10–12 cm
- Weight: 120–170 g
- Nephrons: ~1 million/kidney
Nephron (MOST IMPORTANT TOPIC)
Structure:
- Glomerulus
- Bowman’s capsule
- PCT → Loop of Henle → DCT → Collecting duct
Mnemonic:
“BPHDC” → Bowman’s → PCT → Henle → DCT → Collecting
Urine Formation (SUPER IMPORTANT)
3 Steps:
- Glomerular Filtration
- Reabsorption
- Secretion
Trick:
“FRS → Filter, Reabsorb, Secrete”
Important Values (Direct MCQ)
- GFR = 125 ml/min
- Filtrate/day = 180 L
- Urine/day = 1–1.5 L
- Reabsorption = 99%
Tubular Functions (High Weightage)
| Part | Functions |
|---|---|
| PCT | Max Reabsorbtion (70-80%) |
| Henle Loop | Concentration |
| DCT | Conditional Reabsorbtion |
| Collecting Duct | Final Concentration |
Trick:
“PCT = Power House”
Counter Current Mechanism (VERY IMPORTANT)
- Henle loop + Vasa recta
- Maintains osmotic gradient (300 → 1200 mOsm)
Key concept:
- Descending → Water out
- Ascending → Salt out
Hormonal Control (VERY IMPORTANT)
| Hormone | Functions |
|---|---|
| ADH | Water Reabsorbtion |
| Aldosteron | Sodium Reabsorbtion |
| ANF | Reducing BP |
Trick:
“ADH → Anti Diuresis (Less urine)”
Disorders (Frequently Asked)
- Uremia
- Kidney stone
- Glomerulonephritis
- Hemodialysis
2. MAJOR MISTAKES STUDENTS MAKE
Confusing:
- Ascending vs Descending limb
- Reabsorption vs Secretion
Forgetting:
- Exact GFR value (125 ml/min)
- 99% reabsorption fact
Wrong assumptions:
- The thinking kidney only removes urea
(Also CO₂, water, ions via other organs)
Ignoring:
- Hormones (ADH, RAAS, ANF)
100% MCQ guaranteed
3. SUPER SHORT TRICKS / MNEMONICS
Nephron Flow
“BowPCTHenDCTCD”
Urine Formation
“Filtration → Reabsorption → Secretion”
Hormones
“AAA”
- ADH → Water
- Aldosterone → Na⁺
- ANF → BP ↓
Loop of Henle
- “Down → Water Out”
- “Up → Salt Out”
Excretory Organs
“KLLS”
- Kidney
- Lungs
- Liver
- Skin
4. ANALYTICAL QUESTIONS (NEET LEVEL)
Q1: Why urine volume is only 1.5 L when the filtrate is 180 L?
Answer:
Because 99% reabsorption occurs in the nephron.
Q2: What happens if ADH is absent?
Answer:
- Less water reabsorption
- More dilute urine
- Condition: Diabetes insipidus
Q3: Why is the ascending limb impermeable to water?
Answer:
To maintain an osmotic gradient → helps the concentration mechanism
Q4: Why are proteins not filtered in the glomerulus?
Answer:
- Large size
- The filtration barrier prevents passage
Q5: How does the counter-current mechanism concentrate urine?
Answer:
- Opposite flow in Henle loop + vasa recta
- Creates an osmotic gradient
- Helps water reabsorption
Q6: Why is PCT called the “reabsorption center”?
Answer:
- Reabsorbs ~70–80% water & solutes
- Active + passive transport
5. LAST 5 YEARS NEET TREND
Most asked topics:
✔ Nephron structure
✔ Counter-current mechanism
✔ Hormonal regulation
✔ GFR values
✔ Tubular functions
FINAL REVISION STRATEGY
- Read NCERT line by line (VERY IMPORTANT)
- Revise diagrams daily
- Practice assertionreason questions
- Memorize values + hormones
- Focus on concept clarity (not ratta)