Histological structure of nephron and filtering membrane, glomerular filtration, counter current exchanger and multiplier. Physiological mechanism of tubular reabsorption and secretion. Diuresis. JG apparatus.
- The glomerular filtration barrier’s size selectivity is primarily due to:
(a) Podocyte foot processes
(b) Basement membrane collagen IV mesh
(c) Fenestrated endothelium
(d) Slit diaphragm nephrin
Answer: (b) Basement membrane collagen IV mesh
Explanation: Basement membrane (BM) pores (5–10 nm) block molecules >70 kDa (e.g., albumin). Fenestrations allow passage but BM is key size barrier. - In tubuloglomerular feedback, macula densa detects:
(a) Low pH
(b) High NaCl delivery
(c) Low K⁺ concentration
(d) High urea levels
Answer: (b) High NaCl delivery
Explanation: Macula densa senses ↑[NaCl] in DCT → ATP/adenosine release → afferent arteriole constriction ↓ GFR. - The primary force opposing glomerular filtration is:
(a) Glomerular hydrostatic pressure
(b) Bowman’s capsule colloid osmotic pressure
(c) Plasma oncotic pressure (πₚ)
(d) Capsular hydrostatic pressure
Answer: (c) Plasma oncotic pressure (πₚ)
Explanation: πₚ (~25 mmHg) pulls fluid back into capillaries; major opposition to filtration (normal net filtration pressure: 10 mmHg). - Countercurrent multiplication establishes a corticopapillary gradient via:
(a) Active NaCl transport in thick ascending limb
(b) Water reabsorption in collecting duct
(c) Urea recycling in inner medulla
(d) Vasa recta flow reversal
Answer: (a) Active NaCl transport in thick ascending limb
Explanation: TAL actively pumps NaCl without water → interstitial hypertonicity → drives water exit from descending limb. - Glucose reabsorption saturation occurs at:
(a) Renal threshold (~180 mg/dL)
(b) TmG (375 mg/min)
(c) GFR 125 mL/min
(d) Plasma glucose 100 mg/dL
Answer: (a) Renal threshold (~180 mg/dL)
Explanation: SGLT transporters saturate at plasma glucose ≥180 mg/dL → glycosuria begins. - Which segment is impermeable to water regardless of ADH?
(a) Proximal tubule
(b) Thin descending limb
(c) Thick ascending limb
(d) Collecting duct
Answer: (c) Thick ascending limb
Explanation: The thick ascending limb actively reabsorbs Na⁺/K⁺/Cl⁻ but is impermeable to water even in the presence of ADH. - Which transporter reabsorbs Na⁺ and glucose in the proximal tubule?
(a) SGLT2
(b) ENaC
(c) Na⁺/K⁺ ATPase
(d) NKCC2
Answer: (a) SGLT2
Explanation: SGLT2 co-transports glucose and Na⁺ in the early proximal tubule using Na⁺ gradient. - Aldosterone increases Na⁺ reabsorption in:
(a) Thick ascending limb
(b) Early proximal tubule
(c) Distal convoluted tubule
(d) Principal cells of collecting duct
Answer: (d) Principal cells of collecting duct
Explanation: Aldosterone acts on principal cells → ↑ENaC expression → ↑Na⁺ reabsorption. - Aquaregulation (water permeability) in collecting ducts is mediated by:
(a) Na⁺/K⁺ ATPase
(b) Aquaporin-1
(c) Aquaporin-2
(d) Aquaporin-3
Answer: (c) Aquaporin-2
Explanation: ADH inserts AQP2 into luminal membrane of collecting ducts → water reabsorption. - In severe dehydration, maximal urine concentration is due to:
(a) Glomerular vasodilation
(b) Increased GFR
(c) ADH-mediated water reabsorption
(d) Decreased medullary osmolarity
Answer: (c) ADH-mediated water reabsorption
Explanation: ADH inserts AQP2 → water reabsorption → concentrated urine (~1200 mOsm/kg). - The site of action of loop diuretics is:
(a) Early proximal tubule
(b) Late distal tubule
(c) Collecting duct
(d) Thick ascending limb of loop of Henle
Answer: (d) Thick ascending limb of loop of Henle
Explanation: Loop diuretics (e.g., furosemide) inhibit NKCC2 in the TAL → ↑Na⁺ excretion. - A fall in blood pressure activates renin release by:
(a) Proximal tubule cells
(b) Intercalated cells
(c) Juxtaglomerular cells
(d) Podocytes
Answer: (c) Juxtaglomerular cells
Explanation: JG cells in afferent arteriole release renin in response to ↓BP or ↓NaCl sensed by macula densa. - Angiotensin II causes:
(a) Efferent arteriole dilation
(b) Proximal tubule bicarbonate excretion
(c) Increased GFR
(d) Preferential efferent arteriole constriction
Answer: (d) Preferential efferent arteriole constriction
Explanation: Ang II preferentially constricts efferent arteriole → maintains GFR during hypotension. - Which of the following increases GFR?
(a) Constriction of afferent arteriole
(b) Constriction of efferent arteriole
(c) Decreased glomerular hydrostatic pressure
(d) Increased plasma oncotic pressure
Answer: (b) Constriction of efferent arteriole
Explanation: Moderate efferent constriction ↑ glomerular pressure → ↑GFR. - The renal clearance of inulin is used to measure:
(a) Renal blood flow
(b) Tubular reabsorption
(c) Glomerular filtration rate
(d) Renal plasma flow
Answer: (c) Glomerular filtration rate
Explanation: Inulin is freely filtered, not reabsorbed/secreted → ideal marker for GFR. - Which statement about PAH (para-aminohippuric acid) is true?
(a) Reabsorbed in PCT
(b) Freely filtered and fully reabsorbed
(c) Clearance equals renal blood flow
(d) Used to estimate GFR
Answer: (c) Clearance equals renal blood flow
Explanation: PAH is filtered and actively secreted → almost all cleared → used to estimate renal plasma flow. - Which hormone reduces renal Na⁺ reabsorption?
(a) Aldosterone
(b) Angiotensin II
(c) ADH
(d) Atrial natriuretic peptide
Answer: (d) Atrial natriuretic peptide
Explanation: ANP dilates afferent and constricts efferent arterioles → ↑GFR and ↓Na⁺ reabsorption. - Which cell in the collecting duct secretes H⁺?
(a) Principal cell
(b) Type A intercalated cell
(c) Macula densa
(d) Podocyte
Answer: (b) Type A intercalated cell
Explanation: Type A cells secrete H⁺ via H⁺-ATPase → important for acid-base regulation. - In acidosis, the kidney responds by:
(a) Decreasing ammoniagenesis
(b) Increasing bicarbonate excretion
(c) Secreting more H⁺
(d) Decreasing reabsorption of HCO₃⁻
Answer: (c) Secreting more H⁺
Explanation: In acidosis, kidneys ↑ H⁺ secretion and ↑ HCO₃⁻ reabsorption. - Which structure does not contribute to the juxtaglomerular apparatus?
(a) Macula densa
(b) Juxtaglomerular cells
(c) Mesangial cells
(d) Podocytes
Answer: (d) Podocytes
Explanation: Podocytes are part of filtration barrier, not JGA. - The kidneys help regulate blood pH by:
(a) Retaining urea
(b) Excreting bicarbonate
(c) Secreting ammonia
(d) Inhibiting carbonic anhydrase
Answer: (c) Secreting ammonia
Explanation: Ammonia binds H⁺ to form NH₄⁺, which is excreted → helps eliminate acid. - Proximal tubule reabsorbs the largest fraction of:
(a) Na⁺ only
(b) Water only
(c) Bicarbonate only
(d) All filtered solutes
Answer: (d) All filtered solutes
Explanation: ~65–70% of filtered Na⁺, water, and solutes are reabsorbed in PCT. - Which part of nephron is most susceptible to ischemia?
(a) Glomerulus
(b) Thick ascending limb
(c) Proximal straight tubule
(d) Distal convoluted tubule
Answer: (c) Proximal straight tubule
Explanation: High metabolic activity, low oxygen tension → vulnerable to hypoxic injury. - Which component creates medullary hypertonicity?
(a) Urea recycling
(b) Albumin filtration
(c) Podocyte function
(d) ANP secretion
Answer: (a) Urea recycling
Explanation: Urea reabsorbed from inner medullary collecting duct contributes to hypertonicity. - Most renal oxygen consumption is for:
(a) Urine concentration
(b) H⁺ secretion
(c) Na⁺ reabsorption
(d) EPO synthesis
Answer: (c) Na⁺ reabsorption
Explanation: Na⁺/K⁺ ATPase uses ATP → high oxygen requirement in PCT. - Renal compensation for respiratory acidosis involves:
(a) Secreting less H⁺
(b) Decreasing bicarbonate reabsorption
(c) Increasing bicarbonate reabsorption
(d) Inhibiting ammoniagenesis
Answer: (c) Increasing bicarbonate reabsorption
Explanation: Kidneys retain more HCO₃⁻ and excrete H⁺ to buffer acid. - The following substance has a clearance greater than GFR:
(a) Inulin
(b) Glucose
(c) Creatinine
(d) PAH
Answer: (d) PAH
Explanation: PAH is secreted → total clearance exceeds GFR → approximates RPF. - Creatinine is not ideal for GFR because it is:
(a) Filtered and reabsorbed
(b) Filtered only
(c) Filtered and secreted
(d) Bound to albumin
Answer: (c) Filtered and secreted
Explanation: Small amount of tubular secretion → overestimates GFR slightly. - Which pressure promotes filtration in the glomerulus?
(a) Bowman’s space hydrostatic pressure
(b) Plasma oncotic pressure
(c) Glomerular capillary hydrostatic pressure
(d) Tubular pressure
Answer: (c) Glomerular capillary hydrostatic pressure
Explanation: Main force driving filtration (~60 mmHg). - Which of the following is true for the vasa recta?
(a) Active transport of solutes
(b) Removes solutes from medulla
(c) Maintains osmotic gradient
(d) Impermeable to water
Answer: (c) Maintains osmotic gradient
Explanation: Countercurrent exchange in vasa recta preserves medullary gradient without washout. - Which enzyme catalyzes the formation of bicarbonate in the kidney?
(a) Renin
(b) Carbonic anhydrase
(c) ACE
(d) Aldolase
Answer: (b) Carbonic anhydrase
Explanation: Carbonic anhydrase catalyzes CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻, critical for acid-base regulation. - Glucose is normally completely reabsorbed in the:
(a) Proximal convoluted tubule
(b) Loop of Henle
(c) Distal convoluted tubule
(d) Collecting duct
Answer: (a) Proximal convoluted tubule
Explanation: Glucose is reabsorbed by SGLT2 and SGLT1 transporters in PCT. - Which of the following increases urea reabsorption in the inner medullary collecting duct?
(a) Aldosterone
(b) ANP
(c) ADH
(d) Renin
Answer: (c) ADH
Explanation: ADH increases urea permeability in the inner medullary collecting duct → helps medullary hypertonicity. - Which part of the nephron is responsible for establishing the corticomedullary gradient?
(a) Proximal tubule
(b) Loop of Henle
(c) Distal tubule
(d) Collecting duct
Answer: (b) Loop of Henle
Explanation: Countercurrent multiplication by Loop of Henle creates the corticomedullary osmotic gradient. - What is the renal threshold for glucose?
(a) 100 mg/dL
(b) 150 mg/dL
(c) 180 mg/dL
(d) 220 mg/dL
Answer: (c) 180 mg/dL
Explanation: When plasma glucose exceeds ~180 mg/dL, transporters saturate, and glucose appears in urine. - Which of the following is filtered but neither reabsorbed nor secreted?
(a) Creatinine
(b) PAH
(c) Inulin
(d) Glucose
Answer: (c) Inulin
Explanation: Inulin is ideal for GFR measurement because it is freely filtered and neither reabsorbed nor secreted. - Which nephron segment reabsorbs calcium under control of PTH?
(a) Proximal tubule
(b) Thin descending limb
(c) Thick ascending limb
(d) Distal convoluted tubule
Answer: (d) Distal convoluted tubule
Explanation: PTH increases Ca²⁺ reabsorption in the DCT. - Which is not a function of the kidney?
(a) Gluconeogenesis
(b) Erythropoietin secretion
(c) Vitamin C activation
(d) Acid-base balance
Answer: (c) Vitamin C activation
Explanation: Kidneys activate vitamin D (calcitriol), not vitamin C. - Which electrolyte imbalance is most likely with chronic renal failure?
(a) Hypokalemia
(b) Hyperkalemia
(c) Hypercalcemia
(d) Hypophosphatemia
Answer: (b) Hyperkalemia
Explanation: Impaired K⁺ excretion leads to hyperkalemia in chronic renal failure. - Which structure senses NaCl concentration in the distal tubule?
(a) Podocytes
(b) Juxtaglomerular cells
(c) Macula densa
(d) Mesangial cells
Answer: (c) Macula densa
Explanation: Macula densa in the DCT senses tubular NaCl and regulates renin release. - During dehydration, which hormone is secreted to increase water reabsorption?
(a) Aldosterone
(b) ADH
(c) ANP
(d) Renin
Answer: (b) ADH
Explanation: ADH increases water permeability in collecting ducts → water retention. - Which of the following is a marker for renal plasma flow?
(a) Glucose
(b) Urea
(c) PAH
(d) Creatinine
Answer: (c) PAH
Explanation: PAH is filtered and secreted → nearly all removed in one pass → estimates renal plasma flow. - Which of the following is freely filtered but fully reabsorbed under normal conditions?
(a) Creatinine
(b) Inulin
(c) Urea
(d) Glucose
Answer: (d) Glucose
Explanation: Under normal blood glucose levels, all filtered glucose is reabsorbed in the proximal tubule. - Renal tubular acidosis type I is due to:
(a) Increased bicarbonate reabsorption
(b) Defective H⁺ secretion in distal tubule
(c) Increased ammonia excretion
(d) Defective glucose transport
Answer: (b) Defective H⁺ secretion in distal tubule
Explanation: Type I (distal) RTA involves failure of H⁺ secretion → inability to acidify urine. - A patient has a high serum creatinine. This indicates:
(a) Low GFR
(b) High GFR
(c) Increased secretion
(d) Dehydration
Answer: (a) Low GFR
Explanation: High serum creatinine suggests impaired filtration → decreased GFR. - Which of the following is not found in Bowman’s space?
(a) Water
(b) Glucose
(c) Albumin
(d) Urea
Answer: (c) Albumin
Explanation: Albumin is too large and negatively charged → not filtered in significant amounts. - The term “countercurrent multiplier” refers to function of:
(a) Glomerulus
(b) Loop of Henle
(c) Collecting duct
(d) Vasa recta
Answer: (b) Loop of Henle
Explanation: Loop of Henle establishes the osmotic gradient via countercurrent multiplication. - What is the effect of sympathetic stimulation on the kidney?
(a) Vasodilation of afferent arteriole
(b) Decreased Na⁺ reabsorption
(c) Increased renin release
(d) Inhibition of ADH
Answer: (c) Increased renin release
Explanation: SNS stimulation → vasoconstriction and ↑ renin from JG cells. - Clearance of a substance is defined as:
(a) Volume of plasma filtered per minute
(b) Amount of substance secreted
(c) Volume of plasma cleared of a substance per minute
(d) Amount of substance reabsorbed
Answer: (c) Volume of plasma cleared of a substance per minute
Explanation: Clearance reflects how much plasma is “cleared” of a solute in a given time. - The major factor determining GFR is:
(a) Plasma osmolarity
(b) Renal blood flow
(c) Glomerular capillary hydrostatic pressure
(d) Tubular backpressure
Answer: (c) Glomerular capillary hydrostatic pressure
Explanation: This pressure pushes fluid across the filtration membrane → primary determinant of GFR. - Which nephron segment is impermeable to water?
(a) Proximal tubule
(b) Thin descending limb
(c) Thick ascending limb
(d) Collecting duct
Answer: (c) Thick ascending limb
Explanation: The thick ascending limb actively reabsorbs Na⁺, K⁺, and Cl⁻ but is impermeable to water. - Which ion is secreted into the tubule in exchange for Na⁺ in the distal nephron?
(a) Ca²⁺
(b) HCO₃⁻
(c) H⁺
(d) Cl⁻
Answer: (c) H⁺
Explanation: H⁺ is secreted in exchange for Na⁺ reabsorption in distal nephron segments, helping with acid-base balance. - Which hormone stimulates Na⁺ reabsorption and K⁺ secretion?
(a) ADH
(b) PTH
(c) ANP
(d) Aldosterone
Answer: (d) Aldosterone
Explanation: Aldosterone increases Na⁺ reabsorption and K⁺ secretion in the distal tubule and collecting duct. - Angiotensin II exerts all the following effects except:
(a) Vasoconstriction
(b) Aldosterone release
(c) ADH inhibition
(d) Increased Na⁺ reabsorption
Answer: (c) ADH inhibition
Explanation: Angiotensin II stimulates ADH secretion, not inhibition. - Which factor increases renin secretion?
(a) Increased afferent arteriole pressure
(b) High Na⁺ delivery to macula densa
(c) Sympathetic stimulation
(d) Increased blood volume
Answer: (c) Sympathetic stimulation
Explanation: β1-receptor activation on juxtaglomerular cells enhances renin release. - Which segment of nephron has the highest osmolarity of tubular fluid?
(a) Proximal tubule
(b) Tip of loop of Henle
(c) Distal tubule
(d) Collecting duct
Answer: (b) Tip of loop of Henle
Explanation: Water is reabsorbed in the descending limb, concentrating the tubular fluid at the tip. - What is the effect of ADH on the collecting duct?
(a) Decreased urea reabsorption
(b) Increased water permeability
(c) Inhibits Na⁺ reabsorption
(d) Promotes K⁺ secretion
Answer: (b) Increased water permeability
Explanation: ADH inserts aquaporins in the collecting duct, allowing water reabsorption. - In which condition is glucose found in urine despite normal blood glucose?
(a) Diabetes mellitus
(b) Renal glycosuria
(c) Nephrotic syndrome
(d) Cushing’s syndrome
Answer: (b) Renal glycosuria
Explanation: Due to defective glucose transporters in the PCT, glucose appears in urine even with normal blood glucose. - What happens to GFR if the efferent arteriole constricts moderately?
(a) Decreases
(b) Increases
(c) No change
(d) Fluctuates
Answer: (b) Increases
Explanation: Moderate efferent constriction increases glomerular pressure and GFR. - Which of the following is a function of the proximal tubule?
(a) Active Na⁺ secretion
(b) Passive glucose excretion
(c) Reabsorption of 65% of filtered Na⁺
(d) H⁺ generation
Answer: (c) Reabsorption of 65% of filtered Na⁺
Explanation: The proximal tubule reabsorbs about 65% of filtered sodium and water. - Which hormone causes insertion of aquaporins in the collecting duct?
(a) ANP
(b) Aldosterone
(c) PTH
(d) ADH
Answer: (d) ADH
Explanation: ADH (vasopressin) inserts aquaporin-2 channels in the collecting duct. - In a normal person, which is the major site of phosphate reabsorption?
(a) Loop of Henle
(b) Collecting duct
(c) Proximal tubule
(d) Distal tubule
Answer: (c) Proximal tubule
Explanation: Around 80% of phosphate reabsorption occurs in the proximal tubule via Na⁺-phosphate cotransporters. - Which statement is true about urea handling by the kidney?
(a) Fully reabsorbed
(b) Fully secreted
(c) Partially reabsorbed
(d) Not filtered
Answer: (c) Partially reabsorbed
Explanation: Urea is filtered, partly reabsorbed in the PCT, and ADH increases reabsorption in the collecting duct. - Renin is secreted from:
(a) Macula densa
(b) Afferent arteriole granular cells
(c) Collecting duct
(d) Glomerular capillary endothelium
Answer: (b) Afferent arteriole granular cells
Explanation: Renin is released by juxtaglomerular (granular) cells of the afferent arteriole. - Most bicarbonate is reabsorbed in:
(a) Loop of Henle
(b) Proximal tubule
(c) Distal tubule
(d) Collecting duct
Answer: (b) Proximal tubule
Explanation: ~80–90% of filtered bicarbonate is reabsorbed in the proximal tubule. - Which substance is used to estimate GFR accurately?
(a) Creatinine
(b) Urea
(c) Inulin
(d) PAH
Answer: (c) Inulin
Explanation: Inulin is ideal for GFR measurement as it is filtered but neither reabsorbed nor secreted. - ANP causes all except:
(a) Natriuresis
(b) Vasodilation
(c) Decreased renin secretion
(d) Increased Na⁺ reabsorption
Answer: (d) Increased Na⁺ reabsorption
Explanation: ANP inhibits Na⁺ reabsorption, promotes natriuresis and vasodilation. - What is the renal effect of PTH?
(a) Increase phosphate reabsorption
(b) Decrease calcium reabsorption
(c) Increase calcium reabsorption
(d) Stimulate water retention
Answer: (c) Increase calcium reabsorption
Explanation: PTH increases Ca²⁺ reabsorption and decreases phosphate reabsorption in the kidney. - Which of the following does not influence GFR?
(a) Glomerular capillary pressure
(b) Tubular backpressure
(c) Plasma oncotic pressure
(d) Renal pelvis pressure
Answer: (d) Renal pelvis pressure
Explanation: While it may reflect obstruction, renal pelvis pressure doesn’t directly control GFR under normal conditions. - What happens to GFR in severe hypotension?
(a) Increases
(b) Decreases
(c) No change
(d) Initially increases, then drops
Answer: (b) Decreases
Explanation: Low perfusion pressure reduces glomerular filtration due to decreased hydrostatic pressure. - What is the primary site for potassium secretion in the nephron?
(a) Proximal tubule
(b) Loop of Henle
(c) Distal tubule
(d) Glomerulus
Answer: (c) Distal tubule
Explanation: Principal cells in the distal tubule and collecting duct secrete K⁺ under aldosterone influence. - The macula densa senses:
(a) Na⁺ and Cl⁻ concentration in tubular fluid
(b) Glomerular filtration pressure
(c) Urea concentration
(d) Blood glucose level
Answer: (a) Na⁺ and Cl⁻ concentration in tubular fluid
Explanation: The macula densa detects changes in NaCl concentration in the distal tubule to regulate GFR via tubuloglomerular feedback. - Which structure acts as the countercurrent exchanger?
(a) Loop of Henle
(b) Collecting duct
(c) Vasa recta
(d) Distal tubule
Answer: (c) Vasa recta
Explanation: The vasa recta preserves medullary osmotic gradient by passive exchange of solutes and water. - Which of the following favors water reabsorption in the collecting duct?
(a) Low medullary interstitial osmolality
(b) Presence of ADH
(c) Absence of aquaporins
(d) High tubular flow
Answer: (b) Presence of ADH
Explanation: ADH increases water permeability via aquaporins, promoting reabsorption in the hyperosmotic medulla. - In which part of the nephron is glucose completely reabsorbed (under normal conditions)?
(a) Distal tubule
(b) Collecting duct
(c) Loop of Henle
(d) Proximal tubule
Answer: (d) Proximal tubule
Explanation: All filtered glucose is reabsorbed in the early proximal tubule via SGLT transporters under normal conditions. - PAH is used to estimate renal plasma flow because it is:
(a) Freely filtered and not secreted
(b) Partially filtered and reabsorbed
(c) Freely filtered and completely secreted
(d) Not handled by the nephron
Answer: (c) Freely filtered and completely secreted
Explanation: PAH is both filtered and secreted, so nearly all entering plasma is cleared of PAH. - Which segment of the nephron is responsible for generating medullary hypertonicity?
(a) Proximal tubule
(b) Thick ascending limb
(c) Collecting duct
(d) Distal tubule
Answer: (b) Thick ascending limb
Explanation: The thick ascending limb actively reabsorbs Na⁺, K⁺, and Cl⁻, contributing to medullary hypertonicity without water movement. - Which of the following is the main buffer system in the kidney?
(a) Bicarbonate
(b) Ammonia
(c) Phosphate
(d) Protein
Answer: (b) Ammonia
Explanation: Ammonia buffering is critical in excreting H⁺ in the distal nephron, especially under acidotic conditions. - What is the role of the Na⁺/K⁺ ATPase in the renal tubule?
(a) Secretes potassium into the lumen
(b) Reabsorbs glucose
(c) Maintains electrochemical gradient
(d) Reabsorbs urea
Answer: (c) Maintains electrochemical gradient
Explanation: Na⁺/K⁺ ATPase on the basolateral membrane pumps Na⁺ out and K⁺ in, facilitating secondary active transport. - The clearance of a substance that is filtered and reabsorbed is:
(a) Equal to GFR
(b) Less than GFR
(c) More than GFR
(d) Equal to renal blood flow
Answer: (b) Less than GFR
Explanation: Reabsorption reduces the amount excreted, so clearance becomes less than GFR. - Which hormone acts via V2 receptors in the kidney?
(a) Aldosterone
(b) PTH
(c) ADH
(d) ANP
Answer: (c) ADH
Explanation: ADH acts on V2 receptors in the collecting duct to insert aquaporin-2 channels and promote water reabsorption. - Which part of the nephron absorbs the largest fraction of filtered sodium?
(a) Proximal tubule
(b) Loop of Henle
(c) Distal tubule
(d) Collecting duct
Answer: (a) Proximal tubule
Explanation: About 65–70% of filtered sodium is reabsorbed in the proximal tubule. - The kidney produces which hormone involved in erythropoiesis?
(a) Renin
(b) ADH
(c) Erythropoietin
(d) Aldosterone
Answer: (c) Erythropoietin
Explanation: The kidney releases erythropoietin in response to hypoxia to stimulate RBC production. - Which is true about filtered load of glucose?
(a) Decreases with increased GFR
(b) Exceeds reabsorptive capacity in diabetes
(c) Is secreted into the tubule
(d) Inversely proportional to plasma glucose
Answer: (b) Exceeds reabsorptive capacity in diabetes
Explanation: When plasma glucose > 200 mg/dL, reabsorption saturates, and glucose appears in urine. - What is the approximate GFR in a healthy adult?
(a) 30 mL/min
(b) 60 mL/min
(c) 90 mL/min
(d) 125 mL/min
Answer: (d) 125 mL/min
Explanation: Normal GFR is ~125 mL/min in adults, depending on age, sex, and body size. - Which process occurs primarily in the distal convoluted tubule?
(a) Glucose reabsorption
(b) Passive water reabsorption
(c) Calcium reabsorption regulated by PTH
(d) Urea secretion
Answer: (c) Calcium reabsorption regulated by PTH
Explanation: The distal tubule is a major site for calcium reabsorption under PTH influence. - Which pressure opposes filtration in the glomerulus?
(a) Glomerular capillary hydrostatic pressure
(b) Bowman’s space oncotic pressure
(c) Glomerular capillary oncotic pressure
(d) Afferent arteriole pressure
Answer: (c) Glomerular capillary oncotic pressure
Explanation: Plasma proteins exert oncotic pressure opposing filtration. - Which transporter is responsible for Na⁺, K⁺, and 2Cl⁻ reabsorption in the thick ascending limb?
(a) Na⁺/H⁺ exchanger
(b) SGLT-2
(c) NKCC2
(d) ENaC
Answer: (c) NKCC2
Explanation: The NKCC2 cotransporter is located in the thick ascending limb and is blocked by loop diuretics. - Which segment of the nephron is impermeable to water even in the presence of ADH?
(a) Proximal tubule
(b) Descending loop
(c) Thick ascending loop
(d) Collecting duct
Answer: (c) Thick ascending loop
Explanation: The thick ascending limb is always impermeable to water. - What causes metabolic acidosis in chronic kidney disease?
(a) Increased ammonia production
(b) Increased phosphate excretion
(c) Decreased H⁺ secretion
(d) Increased bicarbonate reabsorption
Answer: (c) Decreased H⁺ secretion
Explanation: Reduced nephron function leads to impaired acid excretion and HCO₃⁻ reabsorption. - Clearance of inulin is used to estimate:
(a) Renal plasma flow
(b) Renal blood flow
(c) Glomerular filtration rate
(d) Tubular secretion
Answer: (c) Glomerular filtration rate
Explanation: Inulin is neither reabsorbed nor secreted, making it ideal for measuring GFR. - Which is an effect of atrial natriuretic peptide (ANP)?
(a) Increased renin secretion
(b) Increased Na⁺ reabsorption
(c) Vasodilation of afferent arteriole
(d) Increased aldosterone secretion
Answer: (c) Vasodilation of afferent arteriole
Explanation: ANP increases GFR by vasodilating afferent arteriole and reducing Na⁺ reabsorption. - What is the renal threshold for glucose?
(a) 100 mg/dL
(b) 150 mg/dL
(c) 180 mg/dL
(d) 220 mg/dL
Answer: (c) 180 mg/dL
Explanation: Above this plasma concentration, glucose begins to appear in urine. - Which of the following is not filtered by the glomerulus?
(a) Water
(b) Sodium
(c) Albumin
(d) Glucose
Answer: (c) Albumin
Explanation: Albumin is a large protein and normally not filtered due to size and charge barriers. - Where is the main site of bicarbonate regeneration in acidosis?
(a) Proximal tubule
(b) Collecting duct
(c) Loop of Henle
(d) Glomerulus
Answer: (b) Collecting duct
Explanation: Intercalated cells of the collecting duct secrete H⁺ and regenerate bicarbonate. - In response to acidosis, which ion exchange increases in the nephron?
(a) Na⁺ for Cl⁻
(b) H⁺ for Na⁺
(c) K⁺ for Cl⁻
(d) Ca²⁺ for Na⁺
Answer: (b) H⁺ for Na⁺
Explanation: H⁺ is secreted in exchange for Na⁺ to eliminate excess acid. - Which condition decreases GFR?
(a) Efferent arteriole constriction (moderate)
(b) Low plasma protein
(c) Hypotension
(d) Decreased afferent arteriole resistance
Answer: (c) Hypotension
Explanation: Decreased systemic pressure reduces glomerular hydrostatic pressure and thus GFR. - Which structure monitors tubular fluid composition?
(a) Juxtaglomerular cells
(b) Macula densa
(c) Podocytes
(d) Mesangial cells
Answer: (b) Macula densa
Explanation: The macula densa senses NaCl in the distal tubule and regulates renin release. - Which is reabsorbed in the proximal tubule via secondary active transport?
(a) Urea
(b) Glucose
(c) Albumin
(d) K⁺
Answer: (b) Glucose
Explanation: Glucose is reabsorbed with Na⁺ using SGLT transporters in the proximal tubule. - In which nephron segment does aldosterone act?
(a) Proximal tubule
(b) Loop of Henle
(c) Collecting duct
(d) Glomerulus
Answer: (c) Collecting duct
Explanation: Aldosterone promotes Na⁺ reabsorption and K⁺ secretion in the late distal tubule and collecting duct.
