Renal Physiology Practice Questions

Q: What is the principal stimulus for vasopressin secretion?

Hyperosmolality. ***Hyperosmolality*** - An increase in **plasma osmolality**, even by a small percentage (1-2%), is the **most potent and PRINCIPAL stimulus** for ADH (vasopressin) release. - This is detected by **osmoreceptors** in the hypothalamus (particularly in the organum vasculosum of the lamina terminalis), which are extremely sensitive and respond rapidly. - This response is the primary mechanism for day-to-day regulation of water balance. *Hypovolemia* - A significant decrease in **blood volume** (typically >10%) also stimulates vasopressin release, but it is **much less sensitive** than hyperosmolality and serves as a secondary/backup mechanism. - This response is mediated by **baroreceptors** in the carotid sinuses and aortic arch. - Only activated during substantial volume loss (hemorrhage, severe dehydration). *Hypoosmolality* - **Decreased plasma osmolality** actively **inhibits** vasopressin secretion as the body aims to excrete excess water. - This helps to prevent overhydration and maintain proper fluid balance. *Hypervolemia* - **Increased blood volume** (hypervolemia) **inhibits** vasopressin secretion, as the body needs to excrete excess fluid. - This contributes to diuresis and the lowering of blood pressure.

Q: A healthy 22-year-old female medical student with normal kidneys decreases her sodium intake by 50% for a period of 2 months. Which of the following parameters is expected to increase in response to the reduction in sodium intake?

Renin release. ***Renin release*** - A reduction in **sodium intake** leads to decreased extracellular fluid volume and **reduced renal perfusion pressure**, which stimulates **renin release** from the juxtaglomerular cells. - Renin initiates the **renin-angiotensin-aldosterone system (RAAS)**, leading to **angiotensin II** formation and increased **aldosterone** secretion, aimed at sodium and water retention. *Atrial natriuretic peptide release* - **Atrial natriuretic peptide (ANP)** release is stimulated by **atrial stretch** due to increased blood volume and pressure, which would decrease with reduced sodium intake. - Therefore, ANP release would likely **decrease** or remain unchanged, not increase, in response to chronic sodium restriction. *Extracellular fluid volume* - A decrease in sodium intake directly leads to a **reduction in total body sodium**, which is the primary determinant of **extracellular fluid volume**. - The body attempts to maintain fluid balance, but chronic sodium restriction will ultimately lead to a **decrease** in extracellular fluid volume as the kidneys excrete less water to match the lower sodium intake. *Arterial pressure* - Reduced sodium intake typically leads to a **decrease in extracellular fluid volume** and **cardiac output**, which in turn causes a **reduction in arterial blood pressure**. - The activation of the RAAS aims to mitigate this drop but usually does not fully compensate to increase pressure above baseline in this scenario.

Q: Escape phenomenon in mineralocorticoid excess occurs due to:

ANP (Atrial Natriuretic Peptide). ***ANP (Atrial Natriuretic Peptide)*** - The **escape phenomenon** in mineralocorticoid excess is an adaptive mechanism where initial sodium and water retention is followed by a return to near-normal sodium balance, primarily due to increased release of **ANP**. - **ANP** promotes natriuresis (sodium excretion) and diuresis (water excretion), counteracting the effects of prolonged mineralocorticoid action. *Angiotensin II* - **Angiotensin II** stimulates aldosterone secretion and promotes sodium and water reabsorption, directly opposing the "escape" from mineralocorticoid-induced fluid retention. - Its actions would exacerbate, rather than mitigate, the effects of mineralocorticoid excess. *Renin* - In mineralocorticoid excess, high sodium and fluid volume typically **suppress renin secretion**, which would lead to decreased angiotensin II and aldosterone production. - Suppressed renin is a *consequence* of mineralocorticoid excess, not the mechanism for escape. *Mineralocorticoid-like action of cortisol* - While **cortisol** can exert mineralocorticoid effects, especially at high concentrations or in conditions like apparent mineralocorticoid excess, it would perpetuate rather than resolve the issues of sodium and water retention. - The escape phenomenon describes the body's adaptation *despite* the continued presence of mineralocorticoid activity.

Q: Parathormone increases calcium reabsorption by acting at -

DCT. ***DCT*** - Parathormone (PTH) primarily increases **calcium reabsorption** in the kidneys by acting on the **distal convoluted tubule (DCT)**. - This action involves stimulating the activity of **calcium channels** and pumps in the apical and basolateral membranes of DCT cells. *Loop of Henle* - The loop of Henle is mainly involved in establishing the **osmotic gradient** in the kidney and reabsorbing water and some ions like sodium and chloride, but not significantly calcium under PTH control. - While some calcium reabsorption occurs in the thick ascending limb, it is not the primary site of **PTH-mediated calcium absorption**. *PCT* - The **proximal convoluted tubule (PCT)** is the primary site for reabsorbing filtered substances like glucose, amino acids, and a large portion of sodium and water. - While about 60-70% of filtered calcium is reabsorbed here, this process is largely **PTH-independent**. *Collecting duct* - The collecting duct is mainly involved in fine-tuning water reabsorption (controlled by **ADH**) and potassium and acid-base balance. - It plays a minor role in calcium reabsorption, and its activity is not a primary target for **PTH's calcium-regulating effects**.

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.

Question 1

What is the principal stimulus for vasopressin secretion?

Accepted Answer

Hyperosmolality

Answer

Hypovolemia

Answer

Hypoosmolality

Answer

Hypervolemia

Question 2

A healthy 22-year-old female medical student with normal kidneys decreases her sodium intake by 50% for a period of 2 months. Which of the following parameters is expected to increase in response to the reduction in sodium intake?

Accepted Answer

Renin release

Answer

Atrial natriuretic peptide release

Answer

Extracellular fluid volume

Answer

Arterial pressure

Question 3

Escape phenomenon in mineralocorticoid excess occurs due to:

Accepted Answer

ANP (Atrial Natriuretic Peptide)

Answer

Angiotensin II

Answer

Renin

Answer

Mineralocorticoid-like action of cortisol

Question 4

Which of the following rightly describes the mechanism of "Vasopressin Escape" in SIADH?

Accepted Answer

Characterized by sudden increase in urine volume with decrease in urine osmolality independent of circulating vasopressin levels.

Answer

Characterized by sudden decrease in urine volume with increase in urine osmolality independent of circulating vasopressin levels.

Answer

Characterized by sudden decrease in urine volume with increase in urine osmolality dependent on circulating vasopressin levels.

Answer

Characterized by sudden increase in urine volume with decrease in urine osmolality dependent on circulating vasopressin levels.

Question 5

Parathormone increases calcium reabsorption by acting at -

Accepted Answer

DCT

Answer

Loop of Henle

Answer

PCT

Answer

Collecting duct

Question 6

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 7

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

Accepted Answer

DCT

Answer

Glomerulus

Answer

Loop of Henle

Answer

PCT

Question 8

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 9

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 10

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

Renal Physiology — MCQs

Renal Physiology — MCQs

On this page

Practice by Chapter

Want unlimited practice?