Part 3: Urine Formation – Ultrafiltration, Reabsorption, Secretion

Q1. The first step in urine formation is:

a) Tubular secretion
b) Ultrafiltration
c) Tubular reabsorption
d) Active transport

Answer: b) Ultrafiltration

Explanation:

(a) Secretion – later step.
✅ (b) Ultrafiltration – occurs in Bowman’s capsule.
(c) Reabsorption – second step.
(d) Active transport – mechanism, not step.

Q2. Which of the following does not pass through the glomerular filter?

a) Urea
b) Glucose
c) Plasma proteins
d) Amino acids

Answer: c) Plasma proteins

Explanation:

(a) Urea – small, freely filtered.
(b) Glucose – filtered.
✅ (c) Plasma proteins – too large to pass.
(d) Amino acids – filtered.

Q3. Glomerular filtration is:

a) Active process
b) Passive process
c) Osmotic process
d) Secretion process

Answer: b) Passive process

Explanation:

(a) Wrong – does not require ATP.
✅ (b) Passive – driven by hydrostatic pressure.
(c) Osmotic – partly involved but not main.
(d) Not secretion.

Q4. Which pressure mainly causes filtration at glomerulus?

a) Oncotic pressure
b) Glomerular hydrostatic pressure
c) Capsular pressure
d) Osmotic pressure of filtrate

Answer: b) Glomerular hydrostatic pressure

Explanation:

(a) Oncotic – opposes filtration.
✅ (b) Hydrostatic – main driving force (~55 mmHg).
(c) Capsular pressure – opposes filtration.
(d) Osmotic pressure of filtrate – not major.

Q5. Filtration slits are formed by:

a) Endothelial cells
b) Podocytes
c) Basement membrane
d) Vasa recta

Answer: b) Podocytes

Explanation:

(a) Endothelium – fenestrated, not slit diaphragm.
✅ (b) Podocytes – form filtration slits.
(c) Basement membrane – barrier but no slits.
(d) Vasa recta – blood vessels.

Q6. The normal GFR (glomerular filtration rate) in humans is about:

a) 50 L/day
b) 100 L/day
c) 180 L/day
d) 500 L/day

Answer: c) 180 L/day

Explanation:

(a), (b), (d) – incorrect.
✅ (c) GFR = ~125 ml/min = ~180 L/day.

Q7. Which of the following substances is completely reabsorbed in a healthy kidney?

a) Glucose
b) Urea
c) Sodium
d) Creatinine

Answer: a) Glucose

Explanation:

✅ (a) Glucose – 100% reabsorbed under normal conditions.
(b) Urea – partially reabsorbed.
(c) Sodium – mostly but not fully reabsorbed.
(d) Creatinine – not reabsorbed.

Q8. In which part of nephron does maximum reabsorption occur?

a) Bowman’s capsule
b) PCT
c) Loop of Henle
d) DCT

Answer: b) PCT

Explanation:

(a) Bowman’s capsule – filtration only.
✅ (b) PCT – ~65–70% of filtrate reabsorbed.
(c) Loop of Henle – water & salt.
(d) DCT – selective reabsorption.

Q9. Which of the following is not reabsorbed at all?

a) Glucose
b) Creatinine
c) Amino acids
d) Sodium

Answer: b) Creatinine

Explanation:

(a) Glucose – 100% reabsorbed.
✅ (b) Creatinine – neither reabsorbed nor secreted significantly.
(c) Amino acids – completely reabsorbed.
(d) Sodium – reabsorbed substantially.

Q10. Selective reabsorption occurs mainly in:

a) Loop of Henle
b) PCT
c) Collecting duct
d) Ureter

Answer: b) PCT

Explanation:

(a) Loop of Henle – countercurrent role.
✅ (b) PCT – major selective reabsorption.
(c) Collecting duct – some reabsorption of water.
(d) Ureter – only conduction, no reabsorption.

Q11. Water reabsorption in PCT is:

a) Obligatory
b) Facultative
c) Independent of solute
d) Hormone-controlled

Answer: a) Obligatory

Explanation:

✅ (a) Obligatory – always happens in PCT.
(b) Facultative – occurs in DCT/collecting duct.
(c) Wrong – depends on solute gradient.
(d) Wrong – not hormone-controlled in PCT.

Q12. Which hormone increases reabsorption of water in collecting ducts?

a) Aldosterone
b) ADH
c) Renin
d) ANF

Answer: b) ADH

Explanation:

(a) Aldosterone – Na+ reabsorption, indirectly water.
✅ (b) ADH – directly increases water reabsorption.
(c) Renin – regulates angiotensin.
(d) ANF – promotes excretion.

Q13. Tubular secretion occurs mainly in:

a) PCT and DCT
b) Loop of Henle
c) Bowman’s capsule
d) Collecting duct

Answer: a) PCT and DCT

Explanation:

✅ (a) Secretion of ions, drugs, H+, K+ in PCT & DCT.
(b) Loop of Henle – no secretion.
(c) Bowman’s – only filtration.
(d) Collecting duct – mainly reabsorption, not secretion.

Q14. Urea reabsorption in nephron is:

a) Complete
b) Partial
c) Absent
d) Hormone-dependent

Answer: b) Partial

Explanation:

(a) Complete – false.
✅ (b) Partial – ~50% reabsorbed, rest excreted.
(c) Absent – false.
(d) Not hormone-dependent.

Q15. Which of the following is secreted into renal tubule?

a) Sodium
b) Glucose
c) Hydrogen ions
d) Amino acids

Answer: c) Hydrogen ions

Explanation:

(a) Sodium – reabsorbed, not secreted.
(b) Glucose – reabsorbed.
✅ (c) H+ ions secreted for pH regulation.
(d) Amino acids – reabsorbed.

Q16. Which of the following is an indicator of kidney function?

a) Creatinine clearance
b) Hemoglobin concentration
c) Glucose concentration in urine
d) Serum bilirubin

Answer: a) Creatinine clearance

Explanation:

✅ (a) Creatinine clearance – used to estimate GFR.
(b) Hemoglobin – unrelated.
(c) Glucose in urine – indicates diabetes, not normal function.
(d) Bilirubin – liver function.

Q17. Active secretion of drugs into urine occurs at:

a) Glomerulus
b) Bowman’s capsule
c) PCT
d) Loop of Henle

Answer: c) PCT

Explanation:

(a), (b), (d) – not correct.
✅ (c) PCT actively secretes drugs & organic ions.

Q18. Which of the following is excreted by tubular secretion?

a) Urea
b) Uric acid
c) H+ and K+ ions
d) Glucose

Answer: c) H+ and K+ ions

Explanation:

(a) Urea – filtered & partially reabsorbed.
(b) Uric acid – filtered & reabsorbed partly.
✅ (c) H+ and K+ actively secreted.
(d) Glucose – reabsorbed.

Q19. Which process is absent in Bowman’s capsule?

a) Filtration
b) Reabsorption
c) Secretion
d) Both b and c

Answer: d) Both b and c

Explanation:

(a) Filtration – present.
(b) Reabsorption – not here.
(c) Secretion – not here.
✅ (d) Both b and c absent.

Q20. Obligatory water reabsorption occurs in:

a) PCT and descending limb of Henle
b) Ascending limb of Henle
c) DCT
d) Collecting duct only

Answer: a) PCT and descending limb of Henle

Explanation:

✅ (a) Obligatory water reabsorption in PCT & descending loop.
(b) Ascending loop – impermeable to water.
(c) DCT – facultative water reabsorption.
(d) Collecting duct – hormone-controlled water reabsorption.

Q21. Which process helps in maintaining acid-base balance?

a) Tubular secretion
b) Ultrafiltration
c) Osmosis
d) Passive reabsorption

Answer: a) Tubular secretion

Explanation:

✅ (a) H+ ion secretion regulates blood pH.
(b) Ultrafiltration – nonspecific.
(c) Osmosis – water movement.
(d) Passive reabsorption – not main.

Q22. Which condition occurs if glucose is present in urine?

a) Glycosuria
b) Ketonuria
c) Hematuria
d) Albuminuria

Answer: a) Glycosuria

Explanation:

✅ (a) Glycosuria – glucose in urine, seen in diabetes.
(b) Ketonuria – ketone bodies in urine.
(c) Hematuria – blood in urine.
(d) Albuminuria – protein in urine.

Q23. Which part of nephron is impermeable to water?

a) Descending loop of Henle
b) Ascending loop of Henle
c) PCT
d) Collecting duct

Answer: b) Ascending loop of Henle

Explanation:

(a) Descending loop – permeable to water.
✅ (b) Ascending loop – impermeable to water, actively transports NaCl.
(c) PCT – permeable.
(d) Collecting duct – permeable under ADH.

Q24. Which process ensures that useful substances are not lost in urine?

a) Filtration
b) Reabsorption
c) Secretion
d) Micturition

Answer: b) Reabsorption

Explanation:

(a) Filtration – nonspecific.
✅ (b) Reabsorption – reclaims glucose, amino acids, water, etc.
(c) Secretion – adds waste.
(d) Micturition – expulsion only.

Q25. Which is the last step in urine formation?

a) Tubular reabsorption
b) Tubular secretion
c) Ultrafiltration
d) Counter-current mechanism

Answer: b) Tubular secretion

Explanation:

(a) Reabsorption – intermediate step.
✅ (b) Secretion – last before urine is finalized.
(c) Filtration – first step.
(d) Counter-current – mechanism, not direct step.

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Part 3: Urine Formation – Ultrafiltration, Reabsorption, Secretion