Renal Physiology Practice Questions

Q: Which of the following is not an effect of efferent arteriole constriction:

Decreased GFR. ***Decreased GFR*** - **Efferent arteriole constriction** typically *increases* GFR, not decreases it - Constriction raises **glomerular hydrostatic pressure** (PGC) by increasing resistance to outflow, which *enhances* the driving force for filtration - The initial and predominant effect is an **increase in GFR**, making "Decreased GFR" NOT a typical effect - Only with *severe* prolonged constriction might GFR eventually fall due to markedly reduced renal blood flow and extreme protein concentration *Increased glomerular hydrostatic pressure* - This IS an effect of efferent arteriole constriction - Constriction increases resistance to blood leaving the glomerulus, causing blood to "back up" and **raising hydrostatic pressure** in glomerular capillaries - This elevated pressure directly increases the filtration force *Decreased blood flow in peritubular vessels* - This IS an effect of efferent arteriole constriction - Blood exits the glomerulus through the efferent arteriole to reach peritubular capillaries - Constriction restricts this outflow, resulting in **reduced blood flow** to downstream peritubular vessels *Increased oncotic pressure in peritubular vessels* - This IS an effect of efferent arteriole constriction - As filtration increases due to higher glomerular pressure, plasma proteins (which cannot be filtered) become more concentrated in the blood - This concentrated blood flows into peritubular capillaries, resulting in **elevated oncotic pressure** that favors reabsorption

Q: Which of the following is the diluting segment of kidney?

Ascending thick loop of Henle. ***Ascending thick loop of Henle*** - The **thick ascending limb of the loop of Henle** is known as the *diluting segment* because it actively reabsorbs **solutes (Na+, K+, Cl-)** but is impermeable to **water**. - This action leads to a decrease in the osmolality of the tubular fluid, effectively *diluting* it entering the distal tubule. *Collecting duct* - The collecting duct is primarily involved in **water reabsorption** under the influence of **ADH**, which can concentrate the urine. - While it can reabsorb some solutes, its main role is to regulate **final urine concentration**. *Descending loop of Henle* - The descending loop of Henle is highly permeable to **water** but relatively impermeable to **solutes**. - As water leaves this segment, the tubular fluid becomes more **concentrated**, not diluted. *PCT* - The **proximal convoluted tubule (PCT)** reabsorbs a large percentage of both **water and solutes** in an isotonic manner. - Although it reduces the volume of filtrate, it does not significantly change its **osmolality** (i.e., it doesn't dilute the fluid).

Q: True about countercurrent multiplier system in the kidney except:

Involves collecting duct. ***Involves collecting duct*** - The **collecting duct** is *not* part of the countercurrent *multiplier* system but rather the countercurrent *exchange* system, - The collecting duct is the target of **ADH** where fine-tuning of water reabsorption occurs, influenced by the medullary osmotic gradient generated by the multiplier. *Occurs in Loop of Henle* - The **Loop of Henle**, specifically the ascending and descending limbs, is the anatomical site where the **countercurrent multiplier** system operates. - This structure's unique hairpin turn and differing permeabilities are crucial for establishing the osmotic gradient. *Requires NaCl transport* - Active transport of **NaCl** in the thick ascending limb of the Loop of Henle is the *driving force* for the countercurrent multiplication process. - This reabsorption of solutes without water permeability creates the initial osmotic gradient. *Creates hyperosmotic medulla* - The primary function of the **countercurrent multiplier** system is to establish and maintain a **hyperosmotic medullary interstitium**. - This high osmolarity is essential for subsequent water reabsorption from the collecting ducts, allowing for the concentration of urine.

Q: Where is the main site of sodium reabsorption in the nephron?

Proximal tubule. ***Proximal tubule*** - The **proximal tubule** reabsorbs approximately **65-70% of filtered sodium**, making it the primary site of sodium reabsorption. - This high rate of reabsorption is crucial for maintaining overall **fluid and electrolyte balance**. *Collecting duct* - The **collecting duct** reabsorbs a smaller, regulated amount of sodium, typically **2-5%**, under hormonal control by **aldosterone**. - Its main roles include **fine-tuning** water and electrolyte balance. *Loop of Henle* - The **loop of Henle** reabsorbs approximately **25%** of filtered sodium, primarily in its **thick ascending limb**. - Its main function is to create a **medullary osmotic gradient** for concentrated urine. *Distal tubule* - The **distal tubule** reabsorbs about **5%** of filtered sodium, which is also influenced by hormones like **aldosterone**. - It plays a role in **acid-base balance** and diluting or concentrating urine.

Q: A 40-year-old woman with chronic kidney disease presents with hyperkalemia. Which of the following represents the immediate effect of hyperkalemia on membrane physiology?

Depolarization of resting membrane potential. ***Depolarization of resting membrane potential*** - Hyperkalemia leads to an increase in extracellular potassium, which **decreases the transmembrane potassium gradient**. - This shifts the **resting membrane potential (RMP) toward zero (less negative)**, representing **depolarization** of the cell membrane. - This is the **immediate and direct effect** of elevated extracellular potassium on all excitable cells, based on the **Nernst equation for potassium**. *Prolonged action potential duration* - Hyperkalemia typically **shortens the action potential duration** in most excitable cells, not prolongs it. - This is primarily due to the increased potassium conductance, which hastens **repolarization**. *Decreased skeletal muscle contractility* - While this is a **clinical consequence** of hyperkalemia, it is a **secondary effect** resulting from persistent depolarization. - The initial membrane depolarization eventually leads to **sodium channel inactivation**, causing muscle weakness. - This is not the immediate membrane effect but rather a downstream consequence. *Decreased cardiac excitability* - This is also a **clinical consequence** of severe or prolonged hyperkalemia, not the immediate membrane effect. - The initial depolarization eventually leads to **persistent sodium channel inactivation**, depressing myocardial excitability and conduction. - This manifests as **bradycardia, widened QRS complexes, and potentially asystole**.

Q: A patient with chronic kidney disease is found to have hypertension and hyperkalemia. Which hormone's decreased levels could account for these findings?

Aldosterone. ***Aldosterone*** - **Aldosterone** normally promotes sodium reabsorption and potassium excretion in the kidneys [1]. Decreased aldosterone leads to **sodium wasting** and **potassium retention**, causing hyperkalemia [1]. - Reduced aldosterone also impairs the kidney's ability to excrete water, contributing to **fluid overload** and **hypertension** [4]. *Antidiuretic hormone* - **Antidiuretic hormone (ADH)** primarily regulates water balance by promoting water reabsorption in the collecting ducts, without directly impacting potassium levels. - Decreased ADH would lead to **diabetes insipidus**, characterized by polyuria and polydipsia, not hyperkalemia or hypertension in this context. *Cortisol* - **Cortisol** is a glucocorticoid involved in stress response, metabolism, and inflammation, and plays a minor role in electrolyte balance. - Decreased cortisol is associated with **adrenal insufficiency** (Addison's disease), which can cause hypotension and hyponatremia, not primarily hypertension and hyperkalemia [3]. *Insulin* - **Insulin** primarily regulates glucose metabolism and helps shift potassium into cells [2]. - Reduced insulin would lead to **hyperglycemia** and, when severe, can exacerbate hyperkalemia by preventing potassium uptake into cells. However, it's not the primary cause of hypertension and chronic hyperkalemia in CKD.

Q: A patient with severe dehydration presents with oliguria. What physiological mechanism is primarily responsible for the decreased urine output?

Increased release of antidiuretic hormone. ***Increased release of antidiuretic hormone*** - In **dehydration**, the body conserves water due to increased plasma osmolality and decreased blood volume, leading to the release of **antidiuretic hormone (ADH)** from the posterior pituitary. - ADH acts on the **collecting ducts** and **distal tubules** of the kidneys, increasing their permeability to water, thus promoting water reabsorption and reducing urine output (oliguria). *Increased glomerular filtration rate* - **Dehydration** typically leads to a **decreased glomerular filtration rate (GFR)** because reduced blood volume lowers renal blood flow and glomerular hydrostatic pressure. - A higher GFR would generally result in increased urine production, which contradicts the patient's symptom of **oliguria**. *Increased secretion of aldosterone* - While increased **aldosterone** secretion does occur in dehydration to conserve sodium and, subsequently, water, its primary role is to regulate **sodium reabsorption** in the distal tubules and collecting ducts, not directly reduce an existing large volume of filtered water. - Aldosterone's effect on water reabsorption is secondary to its effect on sodium, and it does not directly increase water permeability in the same way **ADH** does. *Increased reabsorption of sodium* - Increased **sodium reabsorption** is a compensatory mechanism in dehydration, driven primarily by **aldosterone**, to maintain extracellular fluid volume. - While water follows sodium reabsorption, the most direct and potent mechanism for reducing urine volume in the context of severe dehydration and oliguria is **ADH-mediated water reabsorption**.

Q: Which of the following hormones is most likely to increase during dehydration?

ADH. ***ADH*** - Dehydration leads to increased **plasma osmolality**, which is the primary stimulus for **ADH (vasopressin)** secretion from the posterior pituitary. - ADH acts on the **collecting ducts** of the kidneys to increase water reabsorption, concentrating urine and conserving body water. *Aldosterone* - While dehydration can indirectly stimulate **aldosterone** release via the **renin-angiotensin-aldosterone system** (due to decreased blood volume/pressure), its primary role is in **sodium reabsorption** and **potassium excretion**. - ADH is more directly and acutely responsive to changes in **plasma osmolality** which is a hallmark of dehydration. *ANP* - **Atrial natriuretic peptide (ANP)** is released in response to **atrial stretch** caused by **increased blood volume** or pressure. - Dehydration typically leads to **decreased blood volume** and pressure, thus ANP levels would likely decrease, or at least not increase significantly. *Cortisol* - **Cortisol** is a stress hormone released in response to various physical and physiological stressors, and it has some roles in fluid balance by influencing ADH. - However, it is not the **primary or most direct hormonal response** to dehydration for fluid conservation; ADH plays that crucial role.

Q: A patient presents with polyuria, polydipsia, and dilute urine. Which hypothalamic hormone deficiency is most likely responsible for these symptoms?

ADH (antidiuretic hormone). ***ADH (antidiuretic hormone)*** - **Deficiency of ADH**, also known as **vasopressin**, leads to **diabetes insipidus**, characterized by the kidneys' inability to reabsorb water, resulting in **polyuria** (excessive urination) and **polydipsia** (excessive thirst) to compensate for fluid loss [1],[2],[3]. - ADH plays a crucial role in maintaining **water balance** by stimulating water reabsorption in the renal tubules; its absence means large volumes of **dilute urine** are excreted [1]. *Oxytocin* - Primarily involved in **uterine contractions** during childbirth and **milk ejection** during lactation. - A deficiency would affect reproductive functions and milk release, not directly cause polyuria or polydipsia. *GnRH (gonadotropin-releasing hormone)* - Stimulates the release of **FSH (follicle-stimulating hormone)** and **LH (luteinizing hormone)** from the pituitary, which are essential for reproductive function. - Deficiency leads to hypogonadism, affecting fertility and sex hormone production, but not water balance. *CRH (corticotropin-releasing hormone)* - Stimulates the release of **ACTH (adrenocorticotropic hormone)** from the pituitary, which in turn regulates the adrenal glands' production of cortisol. - CRH deficiency would impact the stress response and cortisol levels, not fluid and electrolyte balance in the manner described.

Question 1

Which of the following is not an effect of efferent arteriole constriction:

Accepted Answer

Decreased GFR

Answer

Increased glomerular hydrostatic pressure

Answer

Decreased blood flow in peritubular vessels

Answer

Increased oncotic pressure in peritubular vessels

Question 2

Which of the following is the diluting segment of kidney?

Accepted Answer

Ascending thick loop of Henle

Answer

Collecting duct

Answer

Descending loop of Henle

Answer

PCT

Question 3

True about countercurrent multiplier system in the kidney except:

Accepted Answer

Involves collecting duct

Answer

Occurs in Loop of Henle

Answer

Requires NaCl transport

Answer

Creates hyperosmotic medulla

Question 4

Where is the main site of sodium reabsorption in the nephron?

Accepted Answer

Proximal tubule

Answer

Collecting duct

Answer

Loop of Henle

Answer

Distal tubule

Question 5

A 40-year-old woman with chronic kidney disease presents with hyperkalemia. Which of the following represents the immediate effect of hyperkalemia on membrane physiology?

Accepted Answer

Depolarization of resting membrane potential

Answer

Prolonged action potential duration

Answer

Decreased skeletal muscle contractility

Answer

Decreased cardiac excitability

Question 6

A patient with chronic kidney disease is found to have hypertension and hyperkalemia. Which hormone's decreased levels could account for these findings?

Accepted Answer

Aldosterone

Answer

Antidiuretic hormone

Answer

Cortisol

Answer

Insulin

Question 7

A patient with severe dehydration presents with oliguria. What physiological mechanism is primarily responsible for the decreased urine output?

Accepted Answer

Increased release of antidiuretic hormone

Answer

Increased glomerular filtration rate

Answer

Increased secretion of aldosterone

Answer

Increased reabsorption of sodium

Question 8

A patient with chronic hypertension is found to have elevated aldosterone levels. What is the impact of elevated aldosterone on renal sodium reabsorption and potassium excretion?

Accepted Answer

Increased sodium reabsorption and increased potassium excretion

Answer

Increased sodium reabsorption and decreased potassium excretion

Answer

Decreased sodium reabsorption and decreased potassium excretion

Answer

Decreased sodium reabsorption and increased potassium excretion

Question 9

Which of the following hormones is most likely to increase during dehydration?

Accepted Answer

ADH

Answer

Aldosterone

Answer

ANP

Answer

Cortisol

Question 10

A patient presents with polyuria, polydipsia, and dilute urine. Which hypothalamic hormone deficiency is most likely responsible for these symptoms?

Accepted Answer

ADH (antidiuretic hormone)

Answer

Oxytocin

Answer

GnRH (gonadotropin-releasing hormone)

Answer

CRH (corticotropin-releasing hormone)

Renal Physiology — MCQs

Renal Physiology — MCQs

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