Micturition Physiology — MCQs
The reflex originating from the Golgi tendon organ to relax the responding muscle is a
An elderly female presented with dribbling of urine only on coughing and straining. What type of urinary incontinence is she suffering from
Stimulation of the nerves of the pelvic parasympathetic plexus results in:
Pine-tree bladder is a sign of.
Which of the following statements is true regarding the given cystometrogram?
A ventrolateral cordotomy is performed to produce relief of pain from the right leg. It is effective because it interrupts the
Pacinian corpuscle is stimulated by which of the following?
What is the primary site of bicarbonate reabsorption in the nephron?
What is true about calcium in the kidney?
What is the clearance of a substance if its concentration in plasma is 10 mg%, concentration in urine is 100 mg%, and urine flow is 2 ml/min?
Micturition Physiology Indian Medical PG Practice Questions and MCQs
Question 1: The reflex originating from the Golgi tendon organ to relax the responding muscle is a
- A. Disynaptic reflex (Correct Answer)
- B. Polysynaptic reflex
- C. Reflex with center in medulla oblongata
- D. Monosynaptic reflex
Explanation: ***Disynaptic reflex*** - The reflex arc originating from the **Golgi tendon organ** involves an afferent neuron synapsing with an inhibitory interneuron, which then synapses with the alpha motor neuron. - This two-synapse pathway (Golgi tendon organ sensory neuron to interneuron, then interneuron to alpha motor neuron) makes it a **disynaptic reflex**. *Monosynaptic reflex* - This type of reflex involves only **one synapse** between the afferent sensory neuron and the efferent motor neuron, such as the **stretch reflex**. - The Golgi tendon reflex requires an **interneuron** to inhibit the motor neuron, thus making it more complex than monosynaptic. *Polysynaptic reflex* - This term describes reflexes involving **multiple interneurons** and more than two synapses. - While the Golgi tendon reflex involves an interneuron, the primary direct inhibition of the motor neuron is achieved through a **single inhibitory interneuron**, making disynaptic a more precise description. *Reflex with center in medulla oblongata* - Reflexes centered in the **medulla oblongata** typically regulate vital functions such as breathing, heart rate, and blood pressure. - The **Golgi tendon reflex** is a spinal reflex with its neural circuitry located within the spinal cord segments associated with the involved muscle.
Question 2: An elderly female presented with dribbling of urine only on coughing and straining. What type of urinary incontinence is she suffering from
- A. Overflow incontinence
- B. Stress incontinence (Correct Answer)
- C. Urge incontinence
- D. Neurogenic bladder
Explanation: ***Stress incontinence*** - **Dribbling of urine** specifically with activities that increase intra-abdominal pressure like **coughing or straining** is the hallmark of stress incontinence. - This type of incontinence results from **weakness of the pelvic floor muscles** and/or intrinsic urethral sphincter deficiency. *Overflow incontinence* - This occurs when the bladder is **overfilled and unable to empty**, leading to constant dribbling or leakage. - Patients typically experience a **poor stream**, hesitancy, and a feeling of incomplete emptying, which are not described here. *Urge incontinence* - Characterized by a **sudden, strong urge to urinate** that is difficult to defer, often leading to involuntary leakage before reaching the toilet. - It is caused by **involuntary contractions of the detrusor muscle** and is not directly related to physical exertion like coughing. *Neurogenic bladder* - This refers to bladder dysfunction due to a **neurological condition** affecting bladder control, such as spinal cord injury or multiple sclerosis. - Symptoms can vary broadly (flaccid or spastic bladder) and are not limited to leakage with coughing alone.
Question 3: Stimulation of the nerves of the pelvic parasympathetic plexus results in:
- A. Contraction of the genital smooth muscle
- B. Penile erection (Correct Answer)
- C. Vasoconstriction
- D. Constriction of the internal urethral sphincter
Explanation: ***Penile erection*** - The **pelvic splanchnic nerves** (parasympathetic) innervate the penile erectile tissues, leading to the release of **nitric oxide**. - **Nitric oxide** causes relaxation of smooth muscle in the arteries supplying the penis, leading to increased blood flow and engorgement of the cavernous spaces, resulting in erection. *Vasoconstriction* - **Vasoconstriction** is primarily mediated by the **sympathetic nervous system** through the release of norepinephrine, causing smooth muscle contraction in blood vessel walls. - The **parasympathetic nervous system** generally promotes vasodilation in specific organs like the penis, rather than widespread vasoconstriction. *Contraction of the genital smooth muscle* - While some genital smooth muscle contraction (e.g., during emission and ejaculation) involves the nervous system, **erection** specifically requires relaxation of vascular smooth muscle. - Contraction of the **bulbospongiosus** and **ischiocavernosus muscles** (skeletal muscles) helps maintain erection and contributes to ejaculation, but this is distinct from direct parasympathetic smooth muscle contraction needed for erection itself. *Constriction of the internal urethral sphincter* - **Constriction of the internal urethral sphincter** is mediated by the **sympathetic nervous system** during ejaculation to prevent retrograde ejaculation into the bladder. - The **parasympathetic nervous system** is primarily involved in bladder emptying (micturition) by relaxing the internal sphincter and contracting the detrusor muscle.
Question 4: Pine-tree bladder is a sign of.
- A. Pelvic abscess
- B. Bilharziasis (Correct Answer)
- C. Intraperitoneal bladder rupture
- D. Neurogenic bladder
Explanation: ***Bilharziasis*** - The "pine-tree bladder" appearance on a retrograde cystogram is characteristic of **chronic bilharzial cystitis**, also known as **schistosomiasis of the bladder**. - This appearance results from **fibrosis**, **granulomas**, and **calcification** of the bladder wall leading to multiple irregular diverticula and trabeculations, which resemble pine-tree branches. *Pelvic abscess* - A pelvic abscess causes an **extrinsic compression** on the bladder, leading to mass effect or displacement, rather than intrinsic wall changes. - It would typically present with symptoms of infection, such as fever and localized pain, and imaging would show a fluid collection. *Intraperitoneal bladder rupture* - An intraperitoneal bladder rupture would lead to extravasation of urine into the peritoneal cavity, which would be visible on imaging as **free fluid** around abdominal organs. - The bladder itself would appear flaccid and potentially collapsed, without the characteristic "pine-tree" appearance. *Neurogenic bladder* - Neurogenic bladder is characterized by **detrusor-sphincter dyssynergia** or loss of bladder sensation, leading to features like **trabeculation**, cellules, and diverticula due to high intravesical pressure. - While it can cause some bladder wall changes, the specific "pine-tree" pattern is not its hallmark, and it is usually associated with neurological deficits.
Question 5: Which of the following statements is true regarding the given cystometrogram?
- A. Segment Ib reflects the bladder's ability to accommodate increasing volume without a significant rise in pressure. (Correct Answer)
- B. Micturition occurs in segment II; failure to micturate is not characteristic of this segment.
- C. Segment Ia represents the initial phase of bladder filling, not residual urine.
- D. The dotted line represents a reference point, not the occurrence of micturition.
Explanation: ***Segment Ib reflects the bladder's ability to accommodate increasing volume without a significant rise in pressure.*** - Segment Ib typically represents the **storage phase** of the bladder, where the detrusor muscle relaxes allowing for significant increases in volume with only a small increase in intravesical pressure. - This property is known as **compliance** and is crucial for normal bladder function, preventing premature urgency and high-pressure storage. - This is the **most clinically significant characteristic** that defines normal bladder function. *Micturition occurs in segment II; failure to micturate is not characteristic of this segment.* - While this statement is technically true, segment II represents the **micturition phase** with rapid rise in intravesical pressure as the detrusor contracts. - The statement is correct but less specific about the key functional property being tested in a cystometrogram. *Segment Ia represents the initial phase of bladder filling, not residual urine.* - This statement is also technically true; segment Ia represents the **initial filling phase** where the bladder begins to distend from baseline. - However, this is a basic anatomical description rather than a functionally significant characteristic. *The dotted line represents a reference point, not the occurrence of micturition.* - The dotted line typically shows a further increase in intravesical pressure, indicating **maximal pressure** the bladder can withstand or continued voiding attempt against resistance. - Segment II (solid line with rapid pressure increase) is where micturition actively occurs, making this a true but less significant observation.
Question 6: A ventrolateral cordotomy is performed to produce relief of pain from the right leg. It is effective because it interrupts the
- A. Left Dorsal Column
- B. Left Lateral Spinothalamic Tract (Correct Answer)
- C. Right Corticospinal Tract
- D. Right Lateral Spinothalamic Tract
Explanation: ***Left Lateral Spinothalamic Tract*** - A ventrolateral cordotomy is a surgical procedure that specifically targets the **spinothalamic tract** to relieve chronic, intractable pain. - Pain signals from the right leg cross over in the spinal cord and ascend via the **contralateral (left) lateral spinothalamic tract**. Therefore, interrupting this tract on the left side relieves pain from the right leg. *Left Dorsal Column* - The dorsal columns (fasciculus gracilis and cuneatus) primarily carry information about **fine touch, vibration, and proprioception**, not pain. - Interrupting the dorsal column would lead to deficits in these sensory modalities, not pain relief. *Right Corticospinal Tract* - The corticospinal tract is a **descending motor pathway** responsible for voluntary movement, originating from the cerebral cortex. - Interrupting this tract would result in **motor deficits** (paresis or paralysis), not pain relief. *Right Lateral Spinothalamic Tract* - The lateral spinothalamic tract carries pain and temperature sensation, but the fibers **cross over** at the segmental level of entry into the spinal cord. - Therefore, pain from the right leg ascends in the **left** lateral spinothalamic tract, making the right tract irrelevant for right leg pain relief through cordotomy.
Question 7: Pacinian corpuscle is stimulated by which of the following?
- A. Pain
- B. Temperature
- C. Touch
- D. Pressure (Correct Answer)
Explanation: ***Pressure*** - **Pacinian corpuscles** are rapidly adapting mechanoreceptors that detect **deep pressure** and **vibrations**. - Their layered, onion-like structure allows them to be very sensitive to rapid changes in pressure. *Pain* - **Pain** is primarily detected by **nociceptors**, which are free nerve endings, not Pacinian corpuscles. - Nociceptors respond to various noxious stimuli, including mechanical, thermal, and chemical. *Temperature* - **Temperature** changes are detected by **thermoreceptors**, such as Krause end bulbs for cold and Ruffini endings for warmth, not Pacinian corpuscles. - These receptors have specific temperature ranges over which they are active. *Touch* - **Touch** sensation is broadly detected by several mechanoreceptors, including **Meissner's corpuscles** (light touch), **Merkel discs** (sustained touch), and hair follicle receptors. - While Pacinian corpuscles contribute to sensing touch through deep pressure, they are not the primary receptors for general light or sustained touch.
Question 8: What is the primary site of bicarbonate reabsorption in the nephron?
- A. Proximal convoluted tubule (Correct Answer)
- B. Distal convoluted tubule
- C. Cortical collecting duct
- D. Medullary collecting duct
Explanation: **Explanation** The correct answer is **A. Proximal convoluted tubule (PCT)**. **1. Why the PCT is correct:** The Proximal Convoluted Tubule is the primary site for acid-base regulation in the kidney, responsible for reabsorbing approximately **80–90%** of the filtered bicarbonate ($HCO_3^-$). This process is mediated by the **Na⁺-H⁺ exchanger (NHE3)** on the apical membrane, which secretes $H^+$ into the lumen. The secreted $H^+$ combines with filtered $HCO_3^-$ to form $H_2CO_3$, which is then broken down by **carbonic anhydrase (type IV)** into $CO_2$ and $H_2O$. These molecules diffuse into the cell, are reconstituted into $HCO_3^-$, and transported into the blood via the **Na⁺-$HCO_3^-$ cotransporter (NBCe1)**. **2. Why the other options are incorrect:** * **B. Distal convoluted tubule (DCT):** While some transport occurs here, it is not the primary site. The DCT and collecting ducts handle the remaining 10–15% of bicarbonate. * **C & D. Collecting Ducts:** These segments are primarily responsible for the "fine-tuning" of acid-base balance. **Type A intercalated cells** secrete $H^+$ and reabsorb "new" bicarbonate during acidosis, but the bulk of the filtered load has already been reclaimed by the PCT. **3. High-Yield Clinical Pearls for NEET-PG:** * **Carbonic Anhydrase Inhibitors (Acetazolamide):** These drugs act specifically on the PCT to inhibit bicarbonate reabsorption, leading to alkaline urine and metabolic acidosis. * **Proximal RTA (Type 2):** Caused by a defect in the PCT's ability to reabsorb $HCO_3^-$. * **Threshold:** The renal threshold for $HCO_3^-$ reabsorption is approximately **24–26 mEq/L**; levels above this lead to bicarbonaturia.
Question 9: What is true about calcium in the kidney?
- A. Most reabsorption occurs in the distal convoluted tubule (DCT).
- B. The major regulating factor is parathormone. (Correct Answer)
- C. Parathormone decreases calcium absorption.
- D. Increased plasma phosphate decreases calcium resorption.
Explanation: ### Explanation **Correct Option: B. The major regulating factor is parathormone.** Calcium homeostasis is tightly regulated by **Parathyroid Hormone (PTH)**. In the kidneys, PTH acts primarily on the distal convoluted tubule (DCT) and the connecting tubule to increase the reabsorption of calcium from the tubular fluid back into the blood. It achieves this by increasing the expression and activity of apical calcium channels (TRPV5). **Analysis of Incorrect Options:** * **Option A:** Most calcium reabsorption (approx. **65-70%**) occurs in the **Proximal Convoluted Tubule (PCT)**, followed by the Thick Ascending Limb (TAL) of Henle’s loop (~20-25%). Only about 5-10% occurs in the DCT, though this is the site of active regulation. * **Option C:** PTH **increases** calcium reabsorption. It simultaneously decreases phosphate reabsorption in the PCT (phosphaturic effect), which helps prevent the formation of calcium-phosphate precipitates in the blood. * **Option D:** Increased plasma phosphate levels stimulate the secretion of PTH (secondary hyperparathyroidism), which subsequently **increases** calcium reabsorption in the kidney to maintain the calcium-phosphate product. **High-Yield Clinical Pearls for NEET-PG:** 1. **PCT Reabsorption:** Calcium reabsorption in the PCT is **passive** and follows sodium and water (paracellular). Therefore, volume expansion or loop diuretics (which inhibit Na+ reabsorption) can increase calcium excretion. 2. **Loop Diuretics vs. Thiazides:** Loop diuretics (Furosemide) cause hypercalciuria ("Loops lose calcium"), whereas Thiazides increase calcium reabsorption in the DCT and are used to treat hypercalciuric renal stones. 3. **Vitamin D:** Calcitriol ($1,25-(OH)_2D_3$) also promotes calcium reabsorption in the DCT, though its primary effect is on intestinal absorption.
Question 10: What is the clearance of a substance if its concentration in plasma is 10 mg%, concentration in urine is 100 mg%, and urine flow is 2 ml/min?
- A. 0.02 ml/min
- B. 0.2 ml/min
- C. 2 ml/min
- D. 20 ml/min (Correct Answer)
Explanation: ### Explanation **1. Understanding the Correct Answer (D)** Renal clearance is the volume of plasma that is completely cleared of a substance by the kidneys per unit time. It is calculated using the standard clearance formula: **$C = \frac{U \times V}{P}$** * **$U$ (Urine concentration):** 100 mg% (or 100 mg/100 ml) * **$V$ (Urine flow rate):** 2 ml/min * **$P$ (Plasma concentration):** 10 mg% (or 10 mg/100 ml) Plugging in the values: $C = \frac{100 \times 2}{10} = \frac{200}{10} = \mathbf{20\ ml/min}$ The units (mg%) cancel each other out, leaving the final result in ml/min. **2. Why Other Options are Incorrect** * **Option A (0.02 ml/min):** This is a mathematical error likely caused by incorrectly dividing the values or misplacing the decimal point by three places. * **Option B (0.2 ml/min):** This occurs if the formula is inverted ($P / (U \times V)$) or if the urine flow rate is ignored. * **Option C (2 ml/min):** This result would occur if the ratio of $U/P$ was 1, meaning the substance was neither concentrated nor diluted by the kidney. **3. NEET-PG High-Yield Clinical Pearls** * **Inulin Clearance:** The gold standard for measuring **GFR** because it is freely filtered but neither reabsorbed nor secreted. * **Creatinine Clearance:** Used clinically to estimate GFR; it slightly **overestimates** GFR because a small amount is secreted in the tubules. * **PAH (Para-aminohippuric acid) Clearance:** Used to measure **Effective Renal Plasma Flow (ERPF)** because it is both filtered and almost completely secreted. * **Glucose Clearance:** Normally **zero** because it is 100% reabsorbed in the proximal tubule (up to the transport maximum, $T_m$).
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