FMGE 2025 - Physiology FMGE Practice Questions and MCQs
Question 1: Which segment of the nephron has the lowest osmolality under the influence of antidiuretic hormone (ADH)?
- A. Descending limb of the loop of Henle
- B. Collecting duct
- C. Late distal tubule
- D. Early distal tubule (Correct Answer)
Explanation: ***Early distal tubule***
- This segment is known as the **cortical diluting segment** because it actively reabsorbs solutes (Na+ and Cl-) via the **Na+-Cl- cotransporter** while being impermeable to water.
- This mandatory solute removal ensures the tubular fluid is maximally diluted (hypoosmolar, often around 100 mOsm/L), a process that is independent of **ADH** levels.
*Descending limb of the loop of Henle*
- This segment is highly permeable to **water** but largely impermeable to solutes, causing water to flow out into the surrounding hypertonic medulla.
- Consequently, the osmolality of the tubular fluid **increases** significantly as it moves down toward the loop hairpin turn, making it highly concentrated, not dilute.
*Collecting duct*
- The influence of **ADH** is to insert **aquaporin 2** channels into the apical membrane, making this segment highly permeable to water.
- This allows massive water reabsorption out of the tubule, concentrating the urine and leading to a **high osmolality** within the tubule lumen, especially near the end.
*Late distal tubule*
- While the fluid here is dilute, some water reabsorption is possible in the presence of **ADH** due to ADH-sensitive aquaporins, similar to the collecting duct.
- This water movement slightly increases the osmolality compared to the maximally dilute fluid produced earlier in the **early distal tubule**.
Question 2: Which of the following is the afferent limb of the corneal reflex?
- A. Facial nerve
- B. Trigeminal nerve (Correct Answer)
- C. Trochlear nerve
- D. Optic nerve
Explanation: ***Trigeminal nerve***- The **Trigeminal nerve (CN V)**, specifically its **ophthalmic division (V1)**, detects the tactile sensation on the cornea, making it the sensory input (afferent limb) of the reflex arc.- Sensory impulses travel through the nasociliary nerve (a branch of V1) to the **principal sensory nucleus of CN V** in the pons.*Optic nerve*- The **Optic nerve (CN II)** is crucial for the sense of **vision** and serves as the afferent limb for the **pupillary light reflex**.- It transmits light stimuli, whereas the corneal reflex is triggered by **tactile stimuli** (touch or pain).*Facial nerve*- The **Facial nerve (CN VII)** serves as the **efferent (motor) limb** of the reflex, responsible for causing the blink via innervation of the **orbicularis oculi** muscle.- It carries the motor command *away* from the nucleus to the muscle, contrasting with the afferent nerve which carries sensation *to* the nucleus.*Trochlear nerve*- The **Trochlear nerve (CN IV)** is a motor nerve responsible for innervating the **superior oblique muscle**, which controls eye movement (depression and intorsion).- It has no role in the sensation of the cornea or the motor response (blinking) that characterizes the corneal reflex.
Question 3: Which of the following changes occurs during muscle contraction while exercising, as shown in the image?
- A. M length increase
- B. M length increase and I decrease
- C. A length decrease
- D. I length decrease (Correct Answer)
Explanation: ***I length decrease***
- The **I band** is the region of the sarcomere containing only **thin filaments (actin)**. During contraction, these thin filaments slide over the thick filaments, causing the I band to shorten.
- The shortening of the I band, along with the H zone, results in the **Z lines** moving closer together, which constitutes the shortening of the entire **sarcomere**.
*M length increase*
- The **M line** is a protein structure in the center of the H zone that anchors the **thick filaments (myosin)**. It is a line, not a band, and its own length does not change.
- The region surrounding the M line, the **H zone**, actually *decreases* in width during contraction, it does not increase.
*A length decrease*
- The **A band** represents the entire length of the **thick myosin filaments**. The length of these filaments does not change during the sliding filament process of muscle contraction.
- Because the thick filaments do not shorten, the length of the **A band remains constant** during both muscle contraction and relaxation.
*M length increase and I decrease*
- This option is partially correct, as the **I band** does decrease in length during contraction.
- However, it is incorrect because the **M line** does not increase in length; it remains constant. The overall statement is therefore false.