Renal Physiology Practice Questions

Q: Atrial natriuretic peptide causes:

All of the options. ***All of the options*** - **Atrial natriuretic peptide (ANP)** has multiple integrated effects on the cardiovascular and renal systems, making all the listed options correct. **Vasodilation** - ANP causes **vasodilation** of both afferent and efferent renal arterioles (with greater effect on afferent), as well as systemic blood vessels - This vasodilation directly reduces systemic vascular resistance and blood pressure - Mediated through cGMP-dependent mechanisms **Promotes natriuresis by inhibiting sodium reabsorption** - ANP directly **inhibits sodium reabsorption** in the collecting duct by: - Antagonizing aldosterone effects - Inhibiting epithelial sodium channels (ENaC) - Reducing sodium transport in the distal nephron - This promotes natriuresis (sodium excretion) and diuresis (water excretion) **Increases glomerular filtration rate by acting via mesangial cells** - ANP increases **GFR** through multiple mechanisms: - Causes **relaxation of mesangial cells**, which increases glomerular capillary surface area available for filtration - Dilates afferent arteriole more than efferent, increasing glomerular capillary hydrostatic pressure - These combined effects significantly enhance glomerular filtration *Vasodilation alone* - While vasodilation is one important effect of ANP, it is not the only mechanism by which ANP regulates blood volume and pressure *Promotes natriuresis by inhibiting sodium reabsorption alone* - While natriuresis through sodium reabsorption inhibition is a key mechanism, ANP has additional important effects *Increases GFR by acting via mesangial cells alone* - While the mesangial cell relaxation and GFR increase are correct, ANP's actions are more comprehensive

Q: Aldosterone acts chiefly on which of the following parts of the nephron:

DCT. ***DCT*** - Aldosterone primarily acts on the **principal cells** in the **distal convoluted tubule (DCT)** and collecting duct. - Its main roles are increasing **sodium reabsorption** and **potassium secretion** from the tubular fluid. *Glomerulus* - The glomerulus is responsible for **filtration** of blood, not hormonal regulation of electrolyte reabsorption. - It is where the initial filtrate is formed, based on pressure gradients. *Loop of Henle* - The Loop of Henle is crucial for establishing the **medullary osmotic gradient**, primarily through reabsorption of water (descending limb) and solutes (ascending limb). - It does not have significant receptors for aldosterone regulation. *PCT* - The proximal convoluted tubule (PCT) is the primary site for the **non-regulated reabsorption** of most filtered solutes, including a large percentage of sodium, glucose, and amino acids. - Its reabsorptive functions are largely independent of aldosterone.

Q: Which of the following substances is not typically excreted in urine under normal physiological conditions?

HCO3-. ***HCO3-*** - Under normal physiological conditions, almost all **filtered bicarbonate** is reabsorbed in the renal tubules to maintain the body's **acid-base balance**. - Its presence in significant amounts in urine would indicate a disorder of acid-base regulation, such as **renal tubular acidosis**. *Creatinine* - **Creatinine** is a waste product of muscle metabolism that is freely filtered by the glomeruli and **not reabsorbed** or further metabolized. - It is consistently excreted in urine, making it a useful marker for **glomerular filtration rate (GFR)**. *Uric acid* - **Uric acid** is a metabolic by-product of **purine metabolism** that is both filtered and secreted by the kidneys, although a significant portion is reabsorbed. - Excretion of uric acid in urine is normal and important for preventing its accumulation, which can lead to conditions like **gout**. *Sodium* - **Sodium** is a major electrolyte whose excretion in urine is tightly regulated by the kidneys to maintain **fluid balance** and **blood pressure**. - While most filtered sodium is reabsorbed, the amount excreted in urine varies depending on dietary intake and hormonal influences such as **aldosterone**.

Q: In Bartter's syndrome there is a defect in

Thick ascending limb of LOH. ***Thick ascending limb of LOH*** - **Bartter's syndrome** is characterized by a genetic defect affecting the **Na-K-2Cl cotransporter (NKCC2)** located in the thick ascending limb of the loop of Henle. - This defect impairs the reabsorption of sodium, potassium, and chloride ions, leading to significant **electrolyte imbalances** such as hypokalemia, metabolic alkalosis, and hyperreninemia. *Descending limb of LOH* - The descending limb is primarily permeable to **water** due to aquaporin channels, and impermeable to solutes. - Defects in this segment are not typically associated with the electrolyte derangements seen in Bartter's syndrome. *DCT* - The **distal convoluted tubule (DCT)** is where fine-tuning of sodium and calcium reabsorption occurs, primarily through the Na-Cl cotransporter (NCC) and active calcium transport. - Defects in the DCT are characteristic of **Gitelman's syndrome**, which has similar but generally milder symptoms compared to Bartter's syndrome. *PCT* - The **proximal convoluted tubule (PCT)** is responsible for the bulk reabsorption of filtered substances, including glucose, amino acids, bicarbonate, and about 65-70% of filtered sodium. - While defects here can lead to various syndromes (e.g., Fanconi syndrome), they do not directly cause the specific electrolyte abnormalities seen in Bartter's syndrome.

Q: Which of the following results in increased ADH activity?

Hypovolemia. ***Hypovolemia*** - **Hypovolemia** (decreased blood volume) is a potent stimulus for antidiuretic hormone (ADH) release, as the body attempts to conserve water and increase blood volume. - Reduced **stretch receptor activity** in the atria and great vessels due to decreased blood volume signals the posterior pituitary to release ADH. *Hypervolemia* - **Hypervolemia** (increased blood volume) would lead to a *decrease* in ADH activity, as the body tries to excrete excess water to normalize blood volume. - Increased stretch receptor activity in the atria inhibits ADH release. *Hypertension* - **Hypertension** (high blood pressure) generally *reduces* ADH secretion because the increased stretch on baroreceptors signals to decrease fluid volume. - This typically promotes diuresis rather than water retention. *Decrease osmolarity* - A **decrease in plasma osmolarity** (more dilute blood) inhibits ADH release, as the body aims to excrete excess water to bring osmolarity back to normal. - **Osmoreceptors** in the hypothalamus are sensitive to changes in plasma osmolarity and are the primary regulators of ADH secretion.

Q: Calcitriol is formed in:

PCT. ***PCT*** - The final step in calcitriol (active vitamin D) synthesis, 1-alpha hydroxylation, primarily occurs in the **proximal convoluted tubule (PCT)** cells of the kidney. - This enzymatic step converts **25-hydroxyvitamin D** into the potent hormone **1,25-dihydroxyvitamin D (calcitriol)**, which regulates calcium and phosphate homeostasis. *Glomerulus* - The **glomerulus** is primarily responsible for **filtering blood** to form ultrafiltrate, not for hormone synthesis. - While vitamin D precursors are filtered, the enzymatic conversion to calcitriol does not occur here. *Bowman's capsule* - **Bowman's capsule** surrounds the glomerulus and collects the filtered fluid, acting as a passive receiver. - It plays no direct role in the synthesis or metabolism of vitamin D. *DCT* - The **distal convoluted tubule (DCT)** is involved in fine-tuning reabsorption of ions like calcium and sodium, responding to hormones. - It is not the primary site for the **1-alpha hydroxylation** required for calcitriol synthesis.

Q: Which of the following does not have a Tm value?

Creatinine. ***Creatinine*** - **Creatinine** is freely filtered at the glomerulus but is **not reabsorbed** by the renal tubules. - Since there is **no reabsorption mechanism** for creatinine, there is no tubular maximum (Tm) for reabsorption. - A small amount of creatinine is secreted in the proximal tubule, but secretion mechanisms are distinct from the Tm concept which applies to reabsorption. - This makes creatinine an excellent marker for **glomerular filtration rate (GFR)** assessment. *Glucose* - **Glucose** has a well-defined **tubular maximum (Tm)** of approximately **375 mg/min** in adults. - It is reabsorbed via specific carrier proteins (**SGLT2** in early proximal tubule, **SGLT1** in late proximal tubule). - When plasma glucose exceeds the renal threshold (~180 mg/dL), the carriers become saturated and glucose appears in urine (glucosuria). *Urea* - **Urea** undergoes passive reabsorption driven by concentration gradients, particularly in the proximal tubule (~50%) and collecting duct. - While primarily passive, urea transporters (UT-A1, UT-A3) facilitate its movement and can exhibit **saturation kinetics**. - Some sources consider urea to have a form of Tm, though it's less clearly defined than glucose. *Na+* - **Na+** reabsorption occurs via multiple carrier-mediated mechanisms including **Na-K-ATPase**, Na-H exchangers, and various cotransporters. - These carrier systems **do exhibit saturation kinetics** and can be considered to have Tm characteristics, particularly in the proximal tubule where ~65% of filtered Na+ is reabsorbed. - However, Na+ handling is also heavily regulated by hormones (aldosterone, ANP) and hemodynamic factors, making its Tm less clinically apparent than glucose.

Q: Immediately after kidney donation what happens to the creatinine level in the donors?

Increases. ***Increases*** - Following the donation of one kidney, the remaining kidney experiences a temporary **reduction in overall renal mass** and a subsequent **transient decrease in glomerular filtration rate (GFR)**. - This immediate post-operative decrease in GFR leads to a **temporary rise in serum creatinine** as the body adjusts to the function of a single kidney. *Level is independent of the donation* - This statement is incorrect because the GFR is directly related to the total functional renal mass, which changes significantly after **nephrectomy**. - Renal function, as measured by creatinine, is undeniably affected by the **loss of a kidney**. *Decreases* - Creatinine levels would decrease if the **GFR of the remaining kidney improved significantly** or if there was an underlying condition causing an already elevated creatinine to normalize post-donation, neither of which is the immediate physiological response. - A decrease in creatinine after donation would imply improved kidney function or reduced burden, which is not what occurs acutely. *Remains Same* - This is unlikely because the removal of one kidney immediately **reduces the total filtration capacity** of the body by approximately half, even if there's rapid compensatory hypertrophy. - While the remaining kidney will undergo **compensatory hypertrophy and hyperfiltration** in the long term, the immediate effect is a reduction in overall GFR.

Q: Aldosterone mainly acts upon

Distal renal tubule. ***Distal renal tubule*** - Aldosterone primarily acts on the **principal cells** of the **distal convoluted tubule** and collecting duct. - Its main function is to promote **sodium reabsorption** and **potassium excretion** in these segments. *Loop of Henle* - The Loop of Henle is primarily involved in establishing the **medullary osmotic gradient** and reabsorbing water and solutes, but it is **not the primary site** of aldosterone action. - While some sodium is reabsorbed here, this process is largely independent of aldosterone's direct influence. *PCT* - The **proximal convoluted tubule (PCT)** is responsible for the bulk reabsorption of filtered substances, including about 65% of sodium and water. - Aldosterone has **minimal to no direct effect** on the reabsorptive processes occurring in the PCT. *Glomerulus* - The **glomerulus** is the site of **ultrafiltration**, where blood is filtered to form a protein-free filtrate. - Aldosterone has no direct action on the filtration barrier or the cells of the glomerulus.

Question 1

Atrial natriuretic peptide causes:

Accepted Answer

All of the options

Answer

Vasodilation

Answer

Promotes natriuresis by inhibiting sodium reabsorption

Answer

Increases glomerular filtration rate by acting via mesangial cells

Question 2

Aldosterone acts chiefly on which of the following parts of the nephron:

Accepted Answer

DCT

Answer

Glomerulus

Answer

Loop of Henle

Answer

PCT

Question 3

Which of the following substances is not typically excreted in urine under normal physiological conditions?

Accepted Answer

HCO3-

Answer

Creatinine

Answer

Uric acid

Answer

Sodium

Question 4

Which statement about antidiuretic hormone (ADH) is true?

Accepted Answer

It increases water reabsorption in the collecting tubules and ducts

Answer

It is synthesized in the posterior pituitary gland

Answer

It decreases both urine and plasma osmolality

Answer

It stimulates thirst

Question 5

In Bartter's syndrome there is a defect in

Accepted Answer

Thick ascending limb of LOH

Answer

Descending limb of LOH

Answer

DCT

Answer

PCT

Question 6

Which of the following results in increased ADH activity?

Accepted Answer

Hypovolemia

Answer

Hypervolemia

Answer

Hypertension

Answer

Decrease osmolarity

Question 7

Calcitriol is formed in:

Accepted Answer

PCT

Answer

Glomerulus

Answer

Bowman's capsule

Answer

DCT

Question 8

Which of the following does not have a Tm value?

Accepted Answer

Creatinine

Answer

Urea

Answer

Glucose

Answer

Na+

Question 9

Immediately after kidney donation what happens to the creatinine level in the donors?

Accepted Answer

Increases

Answer

Level is independent of the donation

Answer

Decreases

Answer

Remains Same

Question 10

Aldosterone mainly acts upon

Accepted Answer

Distal renal tubule

Answer

Loop of Henle

Answer

PCT

Answer

Glomerulus

Renal Physiology — MCQs

Renal Physiology — MCQs

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