Renal Physiology Practice Questions

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).

Q: What percentage of total nephrons are juxtamedullary nephrons?

15%. **Explanation:** In the human kidney, nephrons are classified into two distinct types based on their location and structural characteristics: **Cortical nephrons** and **Juxtamedullary nephrons**. 1. **Why 15% is correct:** Approximately **15%** (range 12–15%) of all nephrons are juxtamedullary nephrons. Their glomeruli are located in the inner third of the renal cortex, near the medulla. They possess long Loops of Henle that descend deep into the renal medulla, often reaching the tips of the renal papillae. Their primary physiological role is the **concentration of urine** via the countercurrent multiplier system. 2. **Why other options are incorrect:** * **85% (Inverse of Option A):** This represents the majority of nephrons, which are **Cortical nephrons**. These have short loops and are primarily responsible for waste excretion and nutrient reabsorption. * **50%, 70%, and 90%:** These values do not correspond to any standard anatomical distribution of nephron types in a healthy human kidney. **High-Yield Facts for NEET-PG:** * **Vasa Recta:** Juxtamedullary nephrons are uniquely associated with the *vasa recta* (specialized peritubular capillaries), which are essential for maintaining the medullary osmotic gradient. * **Concentrating Capacity:** Species living in arid environments (like the kangaroo rat) have a much higher percentage of juxtamedullary nephrons to conserve water. * **Renin Content:** Juxtamedullary nephrons generally contain higher amounts of renin compared to cortical nephrons. * **Blood Flow:** Although juxtamedullary nephrons are vital for concentration, the majority of renal blood flow (approx. 90%) is directed to the renal cortex.

Q: Which of the following is not a correct association regarding the renin-angiotensin-aldosterone system?

Renin - liver. ### Explanation The **Renin-Angiotensin-Aldosterone System (RAAS)** is a critical hormonal cascade for blood pressure regulation and fluid balance. **Why Option A is the correct answer:** **Renin** is an enzyme synthesized, stored, and secreted by the **Juxtaglomerular (JG) cells** of the afferent arterioles in the **kidney**, not the liver. Its primary role is to cleave Angiotensinogen into Angiotensin I. Therefore, the association of Renin with the liver is incorrect. **Analysis of other options:** * **B. Renin - kidney:** This is a correct association. JG cells (modified smooth muscle cells) in the kidney release renin in response to low perfusion pressure, sympathetic stimulation, or decreased sodium delivery to the macula densa. * **C. Renin substrate - liver:** This is a correct association. **Angiotensinogen** (the substrate for renin) is a plasma protein synthesized and continuously released into the circulation by the **liver**. * **D. ACE - lung endothelium:** This is a correct association. **Angiotensin-Converting Enzyme (ACE)** is primarily located on the luminal surface of vascular endothelial cells, with the highest concentration found in the **pulmonary capillaries**. **High-Yield NEET-PG Pearls:** * **Rate-limiting step:** The release of **Renin** is the rate-limiting step of the RAAS pathway. * **Stimuli for Renin release:** 1. Decreased renal perfusion (Baroreceptor mechanism), 2. Decreased NaCl at Macula Densa, 3. Increased Sympathetic activity ($\beta_1$ receptors). * **ACE Inhibitors:** Common side effect is a dry cough due to the accumulation of **Bradykinin** in the lungs, as ACE is also responsible for bradykinin degradation. * **Angiotensin II:** A potent vasoconstrictor that also stimulates the **Zona Glomerulosa** of the adrenal cortex to secrete **Aldosterone**.

Q: Maximum absorption of NaCl in the proximal convoluted tubule occurs due to the effect of:

Angiotensin II. **Explanation:** The **Proximal Convoluted Tubule (PCT)** is the primary site for the reabsorption of water and solutes (approximately 65-70% of the filtered load). **Angiotensin II** is the most potent stimulator of NaCl and water reabsorption in the PCT. **Why Angiotensin II is correct:** Angiotensin II acts on the **NHE3 (Sodium-Hydrogen Exchanger)** on the apical membrane and the **Na+/K+ ATPase** on the basolateral membrane of the PCT cells. By stimulating these transporters, it directly increases sodium reabsorption. Additionally, by constricting the efferent arteriole, it increases the filtration fraction, leading to increased peritubular capillary oncotic pressure, which further facilitates fluid reabsorption from the PCT. **Why other options are incorrect:** * **ADH (Vasopressin):** Primarily acts on the **Collecting Ducts** (V2 receptors) to increase water permeability via Aquaporin-2 channels. It has minimal effect on NaCl reabsorption in the PCT. * **Aldosterone:** Acts on the **Principal cells of the Late Distal Tubule and Collecting Duct**. It promotes Na+ reabsorption and K+ secretion by upregulating ENaC channels and Na+/K+ ATPase. * **Atrial Natriuretic Peptide (ANP):** This is a "natriuretic" hormone; it **inhibits** Na+ reabsorption in the medullary collecting duct and inhibits the secretion of Renin and Aldosterone to decrease blood pressure. **High-Yield Clinical Pearls for NEET-PG:** * **PCT** is the site for 100% reabsorption of Glucose and Amino acids. * **Carbonic Anhydrase inhibitors (Acetazolamide)** act specifically on the PCT. * **Angiotensin II** is unique because it maintains GFR (via efferent constriction) while simultaneously increasing Na+ reabsorption to expand ECF volume.

Q: Osmoreceptors are located in which of the following areas?

Supraoptic nuclei. **Explanation:** The regulation of water balance is primarily governed by **osmoreceptors**, which are specialized neurons that detect changes in plasma osmolarity. **1. Why Supraoptic Nuclei (SON) is correct:** The osmoreceptors are primarily located in the **anterior hypothalamus**, specifically within the **Supraoptic Nuclei (SON)** and the **Organum Vasculosum of the Lamina Terminalis (OVLT)**. When plasma osmolarity increases (e.g., dehydration), these receptors shrink, triggering an action potential. This stimulates the synthesis and release of **Antidiuretic Hormone (ADH/Vasopressin)** from the SON, which then travels via the hypothalamo-hypophyseal tract to the posterior pituitary for secretion into the blood. **2. Why other options are incorrect:** * **Paraventricular nuclei (PVN):** While the PVN also produces ADH, its primary function is the synthesis of **Oxytocin**. It is less involved in osmoreception compared to the SON. * **Anterior hypothalamus:** While the SON is *located* in the anterior hypothalamus, the question asks for the specific site. In NEET-PG, the most specific anatomical structure (SON) is preferred over the general region. * **Lateral hypothalamus:** This area is known as the **"Feeding Center."** Stimulation leads to hunger, while lesions lead to aphagia and weight loss. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Stimulus for ADH:** A mere 1% change in osmolarity triggers ADH release. * **Thirst Center:** Located in the lateral preoptic area. * **Circumventricular Organs:** The OVLT and SFO (Subfornical Organ) lack a blood-brain barrier, allowing them to sense systemic osmolarity directly. * **Diabetes Insipidus:** Damage to the SON or the tract leads to Central DI, characterized by polyuria and low urine osmolarity.

Question 1

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 2

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 3

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 4

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 5

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

Question 6

What percentage of total nephrons are juxtamedullary nephrons?

Accepted Answer

15%

Answer

50%

Answer

70%

Answer

90%

Question 7

Which of the following is not a correct association regarding the renin-angiotensin-aldosterone system?

Accepted Answer

Renin - liver

Answer

Renin - kidney

Answer

Renin substrate - liver

Answer

ACE - lung endothelium

Question 8

Maximum absorption of NaCl in the proximal convoluted tubule occurs due to the effect of:

Accepted Answer

Angiotensin II

Answer

ADH

Answer

Aldosterone

Answer

Atrial natriuretic peptide

Question 9

Osmoreceptors are located in which of the following areas?

Accepted Answer

Supraoptic nuclei

Answer

Paraventricular nuclei

Answer

Anterior hypothalamus

Answer

Lateral hypothalamus

Question 10

Which of the following renal alterations would most likely preserve the Glomerular Filtration Rate (GFR)?

Accepted Answer

Decreased intrarenal nitric oxide

Answer

Defect in the elimination of hydrogen ions in the distal tubule

Answer

Luminal obstruction by renal tubular casts

Answer

Increased interstitial pressure

Renal Physiology — MCQs

Renal Physiology — MCQs

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