Renal Physiology Practice Questions

Q: The neonatal kidney achieves concentrating ability equivalent to the adult kidney by what age?

One year of age. **Explanation:** The neonatal kidney is anatomically complete at birth (nephrogenesis ends at 34-36 weeks of gestation), but it is functionally immature. The ability to concentrate urine depends on the **medullary osmotic gradient** and the responsiveness of the distal tubules to **Antidiuretic Hormone (ADH)**. **1. Why Option A is Correct:** While glomerular filtration rate (GFR) increases rapidly after birth, the concentrating capacity matures more slowly. At birth, a neonate can only concentrate urine to approximately 500–700 mOsm/L. This limitation is due to shorter Loops of Henle, lower urea concentration in the medulla, and relative insensitivity to ADH. By **one year of age**, the tubular function and medullary gradient mature sufficiently to reach the adult concentrating capacity of approximately **1200–1400 mOsm/L**. **2. Why Other Options are Incorrect:** * **Option B:** By 18 months, renal function is well-established, but the specific physiological milestone for adult-level concentration is typically reached by the first birthday. * **Option C:** At 3 to 6 months, GFR and some tubular functions are improving, but the kidney still cannot handle high solute loads as effectively as an adult kidney. * **Option D:** Puberty is far too late; most renal parameters (GFR, secretion, and concentration) reach adult levels between 1 and 2 years of age. **High-Yield Clinical Pearls for NEET-PG:** * **GFR Milestone:** GFR reaches adult levels (adjusted for body surface area) by **2 years of age**. * **Neonatal Vulnerability:** Because neonates cannot concentrate urine effectively, they are at a much higher risk of **dehydration** and hypernatremia during periods of fluid loss (e.g., diarrhea). * **Urea’s Role:** The lower concentrating ability in infants is partly due to their high anabolic state; they use dietary protein for growth, leaving less urea available to contribute to the medullary osmotic gradient.

Q: What is the primary function of vasopressin?

Water absorption in the collecting duct. ### Explanation **Correct Answer: C. Water absorption in the collecting duct** **Mechanism:** Vasopressin, also known as **Antidiuretic Hormone (ADH)**, is synthesized in the hypothalamus (supraoptic and paraventricular nuclei) and released from the posterior pituitary. Its primary action is to maintain water homeostasis. It acts on the **V2 receptors** located on the basolateral membrane of the **principal cells** in the **Late Distal Tubule and Collecting Ducts**. This triggers a cAMP-mediated signaling pathway that leads to the insertion of **Aquaporin-2 (AQP2)** water channels into the apical membrane. This increases the permeability of the collecting duct, allowing water to be reabsorbed back into the medullary interstitium via an osmotic gradient. **Why other options are incorrect:** * **Option A & D:** The **Proximal Convoluted Tubule (PCT)** is responsible for the bulk reabsorption (65%) of water and solutes (like Sodium). However, water reabsorption in the PCT is "obligatory" (follows solutes) and is **independent of ADH**. * **Option B:** The **Loop of Henle** (specifically the descending limb) is permeable to water, but this is driven by the countercurrent multiplier system, not by vasopressin. Vasopressin does, however, increase urea recycling in the medullary collecting duct to maintain this gradient. **High-Yield NEET-PG Pearls:** * **V1 Receptors:** Located on vascular smooth muscle; cause vasoconstriction (hence the name "Vasopressin"). * **Diabetes Insipidus (DI):** Deficiency of ADH (Central DI) or resistance to ADH (Nephrogenic DI) leads to polyuria and dilute urine. * **SIADH:** Excessive ADH secretion leads to water retention and **euvolemic hyponatremia**. * **Urea Transport:** ADH also increases the activity of **UT-A1 urea transporters** in the inner medullary collecting duct, contributing to the corticomedullary osmotic gradient.

Q: Injury to dorsal root nerve fibers in the sacral region of the spinal cord can cause which of the following conditions?

Atonic bladder. **Explanation:** The micturition reflex is an autonomic reflex mediated by the sacral segments of the spinal cord (**S2, S3, and S4**). The sensory (afferent) limb of this reflex consists of fibers traveling via the pelvic nerves to the **dorsal roots** of the spinal cord. These fibers carry stretch signals from the bladder wall to the CNS. **1. Why Atonic Bladder is Correct:** When the **dorsal root nerve fibers (sensory limb)** are injured, the brain and spinal cord no longer receive signals indicating that the bladder is full. Consequently, the micturition reflex is never initiated. The bladder continues to fill beyond its capacity, leading to a thin-walled, non-contractile, and distended bladder. This is known as an **Atonic Bladder** (or Sensory Neurogenic Bladder). Clinical manifestation includes **overflow incontinence**, where urine dribbles out only when the intravesical pressure exceeds urethral resistance. **2. Why other options are incorrect:** * **Automatic Bladder (Spastic Bladder):** This occurs due to a spinal cord injury **above the sacral level**. The reflex arc remains intact, but voluntary control from the brain is lost. The bladder empties reflexively whenever it fills. * **Neurogenic Bladder:** This is a broad, non-specific umbrella term for any bladder dysfunction caused by neurologic damage. While technically correct in a general sense, "Atonic Bladder" is the specific physiological consequence of sensory (dorsal root) interruption. **High-Yield Clinical Pearls for NEET-PG:** * **Tabes Dorsalis:** A classic cause of atonic bladder due to syphilis-induced damage to the dorsal roots. * **De-efferented Bladder:** Caused by damage to the **motor (parasympathetic)** fibers; the bladder is also atonic. * **Autonomous Bladder:** Occurs when the **entire sacral reflex center** (conus medullaris) is destroyed; the bladder lacks both sensory and motor innervation.

Q: All of the following statements about angiotensin II are TRUE, EXCEPT:

Secreted from endothelium. **Explanation:** The correct answer is **C (Secreted from endothelium)**. This statement is false because Angiotensin II is not "secreted" by the endothelium; rather, it is **formed in the pulmonary and renal circulation** via the action of Angiotensin-Converting Enzyme (ACE) on Angiotensin I. While ACE is located on the surface of vascular endothelial cells, the precursor (Angiotensinogen) is secreted by the liver and converted to Angiotensin I by Renin (secreted by the JGA). **Analysis of other options:** * **A. Autoregulation of GFR:** Angiotensin II plays a critical role in maintaining GFR during states of low renal perfusion pressure. By preferentially constricting the efferent arteriole, it increases glomerular hydrostatic pressure, thereby stabilizing GFR. * **B. Release aldosterone:** Angiotensin II acts directly on the **Zona Glomerulosa** of the adrenal cortex to stimulate the synthesis and secretion of aldosterone, which promotes sodium and water retention. * **D. Constriction of afferent arteriole:** While Angiotensin II is more potent at the efferent arteriole, in high concentrations (pathological states or severe hypovolemia), it also causes constriction of the **afferent arteriole**, leading to a decrease in both Renal Blood Flow (RBF) and GFR. **High-Yield Clinical Pearls for NEET-PG:** * **ACE Inhibitors/ARBs:** These drugs are contraindicated in **Bilateral Renal Artery Stenosis** because they block Angiotensin II-mediated efferent vasoconstriction, leading to a precipitous drop in GFR and acute renal failure. * **Potency:** Angiotensin II is one of the most potent vasoconstrictors in the body. * **Thirst:** It also acts on the **Subfornical Organ** in the brain to stimulate the thirst center and ADH release.

Q: Which of the following is NOT an action of the kidney?

Glycogenesis. The kidney is a multifunctional organ responsible for excretory, homeostatic, and endocrine activities. **Explanation of the Correct Answer:** **C. Glycogenesis:** This is the process of synthesizing glycogen from glucose for storage. While the kidney is capable of **Gluconeogenesis** (synthesizing glucose from non-carbohydrate sources like amino acids, especially during prolonged fasting), it does not perform glycogenesis to any significant degree. Glycogen storage is primarily a function of the **liver and skeletal muscles**. **Why the other options are incorrect (Functions of the Kidney):** * **A. Erythropoietin secretion:** The kidney (specifically the interstitial cells in the peritubular capillary bed) produces erythropoietin in response to hypoxia, which stimulates RBC production in the bone marrow. * **B. Regulation of 1,25-dihydroxyvitamin D3:** The kidney contains the enzyme **1-alpha-hydroxylase**, which converts 25-hydroxyvitamin D into its active form, Calcitriol (1,25-dihydroxycholecalciferol). * **D. Regulation of water and electrolyte balance:** This is the primary homeostatic function of the kidney, achieved through glomerular filtration, tubular reabsorption, and secretion (regulated by hormones like ADH and Aldosterone). **High-Yield Clinical Pearls for NEET-PG:** * **Gluconeogenesis:** During starvation, the kidney can contribute up to **20-25%** of the body's glucose production. * **Hormones secreted by Kidney:** Renin (by JG cells), Erythropoietin, and Calcitriol. * **Chronic Kidney Disease (CKD):** Patients often present with **anemia** (due to decreased Erythropoietin) and **renal osteodystrophy** (due to failure of Vitamin D activation).

Question 1

Impaired function of aquaporins results in which of the following conditions?

Accepted Answer

Nephrogenic diabetes insipidus

Answer

Liddle syndrome

Answer

Cystic fibrosis

Answer

Baer syndrome

Question 2

The neonatal kidney achieves concentrating ability equivalent to the adult kidney by what age?

Accepted Answer

One year of age

Answer

Eighteen months of age

Answer

Three to six months of age

Answer

Just before puberty

Question 3

Acute metabolic acidosis tends to _____ intracellular K+ concentration and _____ K+ secretion by the cortical collecting tubules?

Accepted Answer

Decrease, decrease

Answer

Increase, increase

Answer

Increase, decrease

Answer

Decrease, increase

Question 4

Activation of the renin stimulates which of the following?

Accepted Answer

Sodium retention

Answer

Water excretion

Answer

Potassium retention

Answer

Magnesium excretion

Question 5

What is the primary function of vasopressin?

Accepted Answer

Water absorption in the collecting duct

Answer

Water absorption in the proximal convoluted tubule (PCT)

Answer

Water absorption in the loop of Henle

Answer

Sodium (Na+) absorption in the PCT

Question 6

In renal vascular hypertension, which of the following is true?

Accepted Answer

All of the above

Answer

Increased Aldosterone

Answer

Increased Renin

Answer

Decreased Angiotensin II

Question 7

Injury to dorsal root nerve fibers in the sacral region of the spinal cord can cause which of the following conditions?

Accepted Answer

Atonic bladder

Answer

Neurogenic bladder

Answer

Automatic bladder

Answer

Any of the above

Question 8

All of the following statements about angiotensin II are TRUE, EXCEPT:

Accepted Answer

Secreted from endothelium

Answer

Autoregulation of GFR

Answer

Release aldosterone

Answer

Constriction of afferent arteriole

Question 9

Which of the following is NOT an action of the kidney?

Accepted Answer

Glycogenesis

Answer

Erythropoietin secretion

Answer

Regulation of 1,25-dihydroxyvitamin D3 production

Answer

Regulation of water and electrolyte balance

Question 10

What substances are involved in the countercurrent mechanism for maintaining the medullary osmotic gradient?

Accepted Answer

Sodium chloride (NaCl), Urea, and Water

Answer

Sodium chloride (NaCl)

Answer

Urea

Answer

Sodium chloride (NaCl) and Urea

Renal Physiology — MCQs

Renal Physiology — MCQs

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