MCQ on Excretory System

🟢 Easy Level (1–20)

1. The main organ of the human excretory system is:
   A) Liver
   B) Kidney ✅
   C) Lung
   D) Heart
   Explanation: Kidneys filter blood to remove waste.
2. Urine is stored in the:
   A) Kidney
   B) Urethra
   C) Urinary bladder ✅
   D) Ureter
   Explanation: The bladder temporarily stores urine.
3. The functional unit of the kidney is:
   A) Alveolus
   B) Nephron ✅
   C) Neuron
   D) Glomerulus
   Explanation: Nephrons perform filtration, reabsorption, and secretion.
4. Which blood vessel brings blood to the kidney?
   A) Renal vein
   B) Hepatic artery
   C) Renal artery ✅
   D) Pulmonary vein
   Explanation: Renal artery carries oxygenated blood to the kidney.
5. The urethra carries urine from:
   A) Kidney to ureter
   B) Ureter to bladder
   C) Bladder to outside of body ✅
   D) Ureter to kidney
   Explanation: Urethra is the final pathway for urine excretion.
6. What is the main nitrogenous waste in human urine?
   A) Ammonia
   B) Uric acid
   C) Creatinine
   D) Urea ✅
   Explanation: Urea is the primary nitrogenous waste in urine.
7. Which part of the nephron filters blood?
   A) Loop of Henle
   B) Glomerulus ✅
   C) Collecting duct
   D) Bowman’s capsule
   Explanation: The glomerulus is a network of capillaries for filtration.
8. Urine formation does NOT involve:
   A) Filtration
   B) Reabsorption
   C) Assimilation ✅
   D) Secretion
   Explanation: Assimilation is related to digestion, not excretion.
9. Which hormone increases water reabsorption in kidneys?
   A) Insulin
   B) ADH ✅
   C) Glucagon
   D) Oxytocin
   Explanation: ADH helps conserve water by increasing reabsorption.
10. The outer region of the kidney is called:
    A) Medulla
    B) Cortex ✅
    C) Pelvis
    D) Hilum
    Explanation: The cortex contains glomeruli and proximal/distal tubules.
11. Which structure connects kidneys to the bladder?
    A) Urethra
    B) Loop of Henle
    C) Ureters ✅
    D) Collecting duct
    Explanation: Ureters transport urine from kidneys to bladder.
12. What is the normal pH of urine?
    A) 2
    B) 5–6 ✅
    C) 7.5
    D) 9
    Explanation: Urine is slightly acidic under normal conditions.
13. Which organ removes carbon dioxide from the blood?
    A) Kidney
    B) Lung ✅
    C) Skin
    D) Liver
    Explanation: Lungs excrete carbon dioxide through exhalation.
14. Excess water is excreted through:
    A) Lungs
    B) Skin
    C) Kidneys ✅
    D) Liver
    Explanation: Kidneys regulate water balance through urine.
15. The tube that carries urine from kidneys is the:
    A) Urethra
    B) Ureter ✅
    C) Nephron
    D) Bladder
    Explanation: Each kidney connects to the bladder via a ureter.
16. Which waste product is excreted by the liver into bile?
    A) Urea
    B) Bilirubin ✅
    C) Ammonia
    D) Carbon dioxide
    Explanation: Bilirubin is a bile pigment formed from hemoglobin breakdown.
17. Which organ excretes sweat?
    A) Kidney
    B) Skin ✅
    C) Lung
    D) Liver
    Explanation: Sweat glands in the skin help excrete salts and water.
18. Which part of the nephron forms a cup-like structure?
    A) Glomerulus
    B) Bowman’s capsule ✅
    C) Loop of Henle
    D) Collecting duct
    Explanation: Bowman’s capsule surrounds the glomerulus for filtration.
19. Which of the following is NOT a function of the kidneys?
    A) Regulation of pH
    B) Production of insulin ✅
    C) Blood pressure regulation
    D) Waste elimination
    Explanation: Insulin is produced by the pancreas.
20. What is the color of normal urine due to?
    A) Hemoglobin
    B) Melanin
    C) Urobilin ✅
    D) Chlorophyll
    Explanation: Urobilin is a yellow pigment derived from bilirubin.

🟡 Moderate Level (21–40)

21. The loop of Henle is mainly involved in:
    A) Filtration
    B) Water reabsorption ✅
    C) Protein digestion
    D) Urine storage
    Explanation: The loop concentrates urine by reabsorbing water and salts.
22. Which part of the nephron is responsible for selective reabsorption?
    A) Bowman’s capsule
    B) Proximal convoluted tubule ✅
    C) Loop of Henle
    D) Ureter
    Explanation: The proximal tubule reabsorbs glucose, salts, and water.
23. High levels of urea in blood is called:
    A) Uremia ✅
    B) Glycosuria
    C) Albuminuria
    D) Hematuria
    Explanation: Uremia indicates kidney failure or dysfunction.
24. Which hormone regulates sodium reabsorption in kidneys?
    A) ADH
    B) Aldosterone ✅
    C) TSH
    D) FSH
    Explanation: Aldosterone increases Na+ reabsorption, affecting fluid balance.
25. What does the renal pelvis do?
    A) Filters blood
    B) Reabsorbs glucose
    C) Collects urine ✅
    D) Regulates hormones
    Explanation: It channels urine into the ureter.
26. Presence of glucose in urine is termed:
    A) Hematuria
    B) Glycosuria ✅
    C) Ketosis
    D) Polyuria
    Explanation: Glycosuria is a common symptom of diabetes mellitus.
27. Which structure in the nephron is impermeable to water?
    A) Descending limb
    B) Ascending limb of loop of Henle ✅
    C) Collecting duct
    D) Proximal tubule
    Explanation: This limb allows salt transport but not water.
28. Which blood vessel carries filtered blood from the kidney?
    A) Renal artery
    B) Renal vein ✅
    C) Vasa recta
    D) Glomerular capillary
    Explanation: Renal vein returns deoxygenated, filtered blood to circulation.
29. Which metabolic waste is formed from amino acid breakdown?
    A) Glucose
    B) Urea ✅
    C) Glycerol
    D) Oxygen
    Explanation: Deamination of amino acids forms urea in the liver.
30. Which of the following does NOT pass into the glomerular filtrate?
    A) Glucose
    B) Plasma proteins ✅
    C) Urea
    D) Ions
    Explanation: Proteins are too large to be filtered through glomeruli.
31. The kidney is located in the:
    A) Thoracic cavity
    B) Abdominal cavity ✅
    C) Cranial cavity
    D) Pelvic cavity
    Explanation: Kidneys lie on either side of the spine in the abdomen.
32. Excretion through skin is called:
    A) Perspiration ✅
    B) Filtration
    C) Evaporation
    D) Digestion
    Explanation: Perspiration helps in temperature regulation and excretion.
33. Which part of the nephron is highly coiled?
    A) Loop of Henle
    B) Proximal convoluted tubule ✅
    C) Collecting duct
    D) Renal artery
    Explanation: Its coiled structure maximizes absorption surface area.
34. Which ion is critical for acid-base balance in kidneys?
    A) Na⁺
    B) Cl⁻
    C) H⁺ ✅
    D) Mg²⁺
    Explanation: Kidneys excrete or retain H⁺ to maintain pH.
35. Juxtaglomerular apparatus regulates:
    A) Blood glucose
    B) Blood pressure ✅
    C) Filtrate color
    D) Sweating
    Explanation: It senses blood pressure and releases renin.
36. Which disease is associated with crystal deposition in joints due to uric acid?
    A) Osteoporosis
    B) Gout ✅
    C) Arthritis
    D) Rickets
    Explanation: Gout results from hyperuricemia and urate crystal formation.
37. Which of these is NOT excreted by the kidneys?
    A) Urea
    B) Creatinine
    C) Bile pigments ✅
    D) Salts
    Explanation: Bile pigments are excreted by the liver into feces.
38. The fluid entering Bowman’s capsule is called:
    A) Urine
    B) Filtrate ✅
    C) Plasma
    D) Lymph
    Explanation: This filtrate undergoes further modification to form urine.
39. Which condition is caused by failure of kidneys?
    A) Anemia
    B) Uremia ✅
    C) Hypoxia
    D) Dyspepsia
    Explanation: Uremia results in accumulation of waste in blood.
40. The kidney’s filtering capacity per minute is called:
    A) Renal absorption
    B) Glomerular filtration rate (GFR) ✅
    C) Blood pressure
    D) Renal clearance
    Explanation: GFR indicates how much filtrate is produced per minute.

🔴 Hard Level (41–50)

41. Which component is actively secreted into distal tubule?
    A) Na⁺
    B) K⁺ ✅
    C) Glucose
    D) Albumin
    Explanation: Potassium ions are secreted to maintain electrolyte balance.
42. Which enzyme triggers the renin-angiotensin system?
    A) Aldosterone
    B) Renin ✅
    C) ADH
    D) Erythropoietin
    Explanation: Renin initiates the cascade that increases blood pressure.
43. Which process helps concentrate urine in the loop of Henle?
    A) Countercurrent mechanism ✅
    B) Active transport only
    C) Ultrafiltration
    D) Osmosis alone
    Explanation: The countercurrent multiplier concentrates the filtrate.
44. Which protein is produced by kidneys to stimulate RBC formation?
    A) Insulin
    B) Erythropoietin ✅
    C) Renin
    D) Albumin
    Explanation: Erythropoietin stimulates bone marrow to produce RBCs.
45. In chronic kidney disease, dialysis is used to:
    A) Cure diabetes
    B) Remove waste from blood ✅
    C) Deliver insulin
    D) Produce urine
    Explanation: Dialysis artificially filters blood in place of kidneys.
46. Which condition results from kidney’s inability to concentrate urine?
    A) Diabetes insipidus ✅
    B) Diabetes mellitus
    C) Glomerulonephritis
    D) Pyelonephritis
    Explanation: ADH deficiency causes dilute urine in diabetes insipidus.
47. What happens during renal autoregulation?
    A) GFR stays constant ✅
    B) GFR drops quickly
    C) Urine stops forming
    D) Glucose is reabsorbed
    Explanation: Kidneys maintain a constant GFR despite blood pressure changes.
48. What is the minimum urine output needed to remove waste?
    A) 100 mL
    B) 300 mL
    C) 400 mL ✅
    D) 800 mL
    Explanation: Called “obligatory water loss,” about 400 mL/day is needed.
49. Which cells monitor blood pressure in kidneys?
    A) Podocytes
    B) Macula densa
    C) Juxtaglomerular cells ✅
    D) Epithelial cells
    Explanation: These cells secrete renin in response to low BP.
50. Which of the following is used to assess kidney function?
    A) Blood pressure
    B) Urine volume
    C) Creatinine clearance ✅
    D) Pulse rate
    Explanation: Creatinine clearance estimates GFR and kidney efficiency.