FMGE 2025 — Physiology

Q: Which segment of the nephron has the lowest osmolality under the influence of antidiuretic hormone (ADH)?

Early distal tubule. ***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**. [Practice more Physiology PYQs on OnCourse]

Q: Which of the following is the afferent limb of the corneal reflex?

Trigeminal nerve. ***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. [Practice more Physiology PYQs on OnCourse]

Q: Which of the following changes occurs during muscle contraction while exercising, as shown in the image?

I length decrease. ***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. [Practice more Physiology PYQs on OnCourse]

Q: During spermatogenesis, which of the following hormones inhibits Follicle-Stimulating Hormone (FSH) secretion?

Inhibin. ***Inhibin*** - **Inhibin** is produced by **Sertoli cells** in the seminiferous tubules, acting as a crucial regulator of spermatogenesis. - It specifically targets the anterior pituitary gland to implement a **negative feedback loop**, reducing the secretion of **FSH** (Follicle-Stimulating Hormone) when sperm production levels are adequate. *Testosterone* - **Testosterone** is the primary androgen required for the maintenance and stimulation of spermatogenesis within the seminiferous tubules. - High systemic levels of testosterone primarily inhibit the secretion of **GnRH** (from the hypothalamus) and **LH** (from the pituitary), rather than specifically inhibiting FSH production. *Luteinizing Hormone (LH)* - **LH** acts on the **Leydig cells** in the testes, stimulating them to produce testosterone. - It does not directly inhibit FSH; rather, it is part of the **Hypothalamic-Pituitary-Gonadal (HPG) axis** regulation system. *Estrogen* - While small amounts of **estrogen** are produced in males (via aromatization of testosterone), it does not play a primary role in the negative feedback inhibition of FSH during spermatogenesis. - In males, **inhibin** is the specific hormone that directly targets FSH secretion from the anterior pituitary. [Practice more Physiology PYQs on OnCourse]

Q: Dehydration is more severe in infants compared to adults. What is the PRIMARY reason for this increased susceptibility?

Total body water in infants is more than in adults. ***Total body water in infants is more than in adults*** - Newborn infants have a significantly higher percentage of **Total Body Water (TBW)**, approximately **75-80%** of their body weight, compared to adults (~60%). - This large volume of water, combined with their greater **surface area-to-volume ratio** and higher **metabolic rate**, necessitates rapid fluid turnover, dramatically increasing their risk of severe dehydration. - This is the **primary physiological reason** why infants are more vulnerable to dehydration compared to adults. *Intracellular fluid (ICF) is more than extracellular fluid (ECF)* - This fluid distribution pattern is characteristic of **adults and older children**, not infants. - In young infants, the **ECF** compartment is actually greater than or nearly equal to the **ICF** compartment. - This represents the adult fluid distribution pattern, not the infant pattern. *Extracellular fluid (ECF) is more than intracellular fluid (ICF)* - While this statement is **anatomically true** for newborns (who have a disproportionately large ECF volume), it does not explain the **primary mechanism** of increased dehydration risk. - The ECF:ICF ratio changes with age, but the overall higher **total body water percentage** is the fundamental reason for severe dehydration susceptibility. - This is a characteristic of infant fluid distribution but not the main answer to why dehydration is more severe. *Extracellular fluid equals intracellular fluid* - In normal physiological states, the volume of the **ECF** compartment rarely equals the volume of the **ICF** compartment at any age. - In infants, ECF typically exceeds ICF; in adults, ICF exceeds ECF. - This statement is not accurate for either infants or adults. [Practice more Physiology PYQs on OnCourse]

17 Previous Year Questions with Answers & Explanations

Questions

Which segment of the nephron has the lowest osmolality under the influence of antidiuretic hormone (ADH)?

Which of the following is the afferent limb of the corneal reflex?

Which of the following changes occurs during muscle contraction while exercising, as shown in the image?

During spermatogenesis, which of the following hormones inhibits Follicle-Stimulating Hormone (FSH) secretion?

Dehydration is more severe in infants compared to adults. What is the PRIMARY reason for this increased susceptibility?

Scientists administered norepinephrine to guinea pigs, resulting in an increase in systolic and diastolic blood pressure and a decrease in heart rate. What mechanism explains this response?

A patient presents with high blood pressure accompanied by a decrease in heart rate. What is the most likely physiological mechanism responsible for this response?

Which of the following describes the chloride ion exchange in red blood cells, where bicarbonate ions are exchanged for chloride ions to maintain electrical neutrality?

Which of the following factors causes a rightward shift in the oxygen-hemoglobin dissociation curve?

Q10

In the jugular venous pressure (JVP) waveform, the "a" wave corresponds to:

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.

Question 4: During spermatogenesis, which of the following hormones inhibits Follicle-Stimulating Hormone (FSH) secretion?

A. Luteinizing Hormone (LH)
B. Testosterone
C. Inhibin (Correct Answer)
D. Estrogen

Explanation: ***Inhibin*** - **Inhibin** is produced by **Sertoli cells** in the seminiferous tubules, acting as a crucial regulator of spermatogenesis. - It specifically targets the anterior pituitary gland to implement a **negative feedback loop**, reducing the secretion of **FSH** (Follicle-Stimulating Hormone) when sperm production levels are adequate. *Testosterone* - **Testosterone** is the primary androgen required for the maintenance and stimulation of spermatogenesis within the seminiferous tubules. - High systemic levels of testosterone primarily inhibit the secretion of **GnRH** (from the hypothalamus) and **LH** (from the pituitary), rather than specifically inhibiting FSH production. *Luteinizing Hormone (LH)* - **LH** acts on the **Leydig cells** in the testes, stimulating them to produce testosterone. - It does not directly inhibit FSH; rather, it is part of the **Hypothalamic-Pituitary-Gonadal (HPG) axis** regulation system. *Estrogen* - While small amounts of **estrogen** are produced in males (via aromatization of testosterone), it does not play a primary role in the negative feedback inhibition of FSH during spermatogenesis. - In males, **inhibin** is the specific hormone that directly targets FSH secretion from the anterior pituitary.

Question 5: Dehydration is more severe in infants compared to adults. What is the PRIMARY reason for this increased susceptibility?

A. Total body water in infants is more than in adults (Correct Answer)
B. Intracellular fluid (ICF) is more than extracellular fluid (ECF)
C. Extracellular fluid (ECF) is more than intracellular fluid (ICF)
D. Extracellular fluid equals intracellular fluid

Explanation: ***Total body water in infants is more than in adults*** - Newborn infants have a significantly higher percentage of **Total Body Water (TBW)**, approximately **75-80%** of their body weight, compared to adults (~60%). - This large volume of water, combined with their greater **surface area-to-volume ratio** and higher **metabolic rate**, necessitates rapid fluid turnover, dramatically increasing their risk of severe dehydration. - This is the **primary physiological reason** why infants are more vulnerable to dehydration compared to adults. *Intracellular fluid (ICF) is more than extracellular fluid (ECF)* - This fluid distribution pattern is characteristic of **adults and older children**, not infants. - In young infants, the **ECF** compartment is actually greater than or nearly equal to the **ICF** compartment. - This represents the adult fluid distribution pattern, not the infant pattern. *Extracellular fluid (ECF) is more than intracellular fluid (ICF)* - While this statement is **anatomically true** for newborns (who have a disproportionately large ECF volume), it does not explain the **primary mechanism** of increased dehydration risk. - The ECF:ICF ratio changes with age, but the overall higher **total body water percentage** is the fundamental reason for severe dehydration susceptibility. - This is a characteristic of infant fluid distribution but not the main answer to why dehydration is more severe. *Extracellular fluid equals intracellular fluid* - In normal physiological states, the volume of the **ECF** compartment rarely equals the volume of the **ICF** compartment at any age. - In infants, ECF typically exceeds ICF; in adults, ICF exceeds ECF. - This statement is not accurate for either infants or adults.

Question 6: Scientists administered norepinephrine to guinea pigs, resulting in an increase in systolic and diastolic blood pressure and a decrease in heart rate. What mechanism explains this response?

A. Baroreceptor stimulation (Correct Answer)
B. Alpha-1 receptor blockade
C. Beta-1 receptor blockade
D. Baroreceptor inhibition

Explanation: ***Baroreceptor stimulation***- The administration of **norepinephrine** causes a massive increase in **systemic vascular resistance (SVR)** via activation of **alpha-1 receptors**, leading to severe hypertension (increased SBP and DBP).- This sudden rise in blood pressure activates arterial **baroreceptors** (in the carotid sinus and aortic arch), triggering a robust compensatory increase in **vagal tone** (parasympathetic outflow), which results in reflex **bradycardia**. *Beta-1 receptor blockade*- Beta-1 receptor blockade would decrease cardiac output and prevent the direct chronotropic effect of norepinephrine, but it would also lead to a **decrease** in SBP rather than the observed rise.- This mechanism cannot explain the severe **hypertension** observed, as norepinephrine's primary pressor effect (vasoconstriction) is mediated by **alpha-1 receptors**. *Alpha-1 receptor blockade*- Alpha-1 receptor blockade would prevent **vasoconstriction**, leading to a significant **drop** in both systolic and diastolic blood pressure, which directly contradicts the finding of increased SBP and DBP.- The hypertensive effect observed requires the potent activation of **alpha-1 receptors** by norepinephrine. *Baroreceptor inhibition*- If the baroreceptors were inhibited, the reflex mechanism would be absent, and the direct effect of norepinephrine on cardiac **beta-1 receptors** would dominate.- This direct stimulation would cause **tachycardia** (increased heart rate), which is the opposite of the observed physiological response.

Question 7: A patient presents with high blood pressure accompanied by a decrease in heart rate. What is the most likely physiological mechanism responsible for this response?

A. Inhibition of baroreceptors
B. Stimulation of chemoreceptors
C. Bezold-Jarisch reflex (J reflex)
D. Stimulation of baroreceptors (Correct Answer)

Explanation: ***Stimulation of baroreceptors*** - High blood pressure causes stretching of the arterial walls (especially the **carotid sinus** and **aortic arch**), leading to robust activation of the **baroreceptors**. - This activation sends inhibitory signals to the vasomotor center, resulting in increased **parasympathetic (vagal) tone** to the heart, which causes reflex **bradycardia** (decreased heart rate). *Inhibition of baroreceptors* - Inhibition occurs when **blood pressure is low**; decreased stretch signals lead to increased sympathetic output. - This response typically causes **tachycardia** and peripheral vasoconstriction in an effort to raise the blood pressure, which contradicts the observed bradycardia. *Bezold-Jarisch reflex (J reflex)* - This reflex is triggered by intense chemical or mechanical stimulation of intracardiac receptors, usually resulting in **hypotension** and **bradycardia**. - It is frequently associated with conditions like **myocardial ischemia** or severe cardiac depressant drugs, but does not explain hypertension. *Stimulation of chemoreceptors* - Peripheral chemoreceptors are primarily stimulated by conditions such as **hypoxia**, severe acidosis, or hypercapnia. - While stimulation causes systemic vasoconstriction (raising BP) and reflex bradycardia, the baroreceptor mechanism is the most direct and primary regulator linking elevated BP to decreased HR.

Question 8: Which of the following describes the chloride ion exchange in red blood cells, where bicarbonate ions are exchanged for chloride ions to maintain electrical neutrality?

A. Root effect
B. Chloride shift (Correct Answer)
C. Bohr effect
D. Haldane effect

Explanation: ***Chloride shift***- This is the term for the exchange of a **bicarbonate ion** ($ ext{HCO}_3^-$) moving out of the red blood cell for a **chloride ion** ($ ext{Cl}^-$) moving into the cell to maintain **electrical neutrality**. - It is essential for the efficient transport of **carbon dioxide** ($ ext{CO}_2$) from peripheral tissues to the lungs in the form of dissolved bicarbonate. *Haldane effect* - Describes the process where the unloading of **oxygen** in peripheral tissues increases the affinity of hemoglobin for **carbon dioxide** ($ ext{CO}_2$) and $ ext{H}^+$ (and vice versa in the lungs). - It primarily relates to the interaction between $ ext{O}_2$ saturation and $ ext{CO}_2$ binding, not the ion exchange itself. *Root effect* - This effect describes the decrease in the **oxygen carrying capacity** of hemoglobin caused by a drop in pH, often seen in fish. - It is a specialized form of the **Bohr effect**, but specifically refers to the non-sigmoidal shape of the $ ext{O}_2$-Hb curve at low pH. *Bohr effect* - This phenomenon explains that an increase in $ ext{PCO}_2$ or a decrease in pH (more **acidity**) shifts the oxygen-hemoglobin dissociation curve to the **right**. - This shift promotes the release of **oxygen** from hemoglobin to active tissues where $ ext{CO}_2$ production is high.

Question 9: Which of the following factors causes a rightward shift in the oxygen-hemoglobin dissociation curve?

A. Increase in O₂
B. Increase in CO₂ (Correct Answer)
C. Decrease in CO₂
D. Decrease in temperature

Explanation: ***Increase in CO₂*** - An increase in the partial pressure of **carbon dioxide (PCO₂)** in the blood leads to a decrease in pH (increased H⁺ concentration), a phenomenon known as the **Bohr effect**. - This acidic environment stabilizes the **taut (T) state** of hemoglobin, reducing its affinity for oxygen and facilitating oxygen unloading to metabolically active tissues, thus causing a **rightward shift**. *Increase in O₂* - An increase in the partial pressure of **oxygen (PO₂)** represents a movement *along* the existing curve to the right, leading to a higher hemoglobin saturation percentage. - It does not alter the intrinsic affinity of hemoglobin for oxygen and therefore does not cause a shift of the entire curve. *Decrease in CO₂* - A decrease in **PCO₂** leads to an increase in blood pH (respiratory alkalosis), which increases hemoglobin's affinity for oxygen. - This increased affinity impairs oxygen release to tissues and causes a **leftward shift** of the curve, promoting oxygen uptake in the lungs. *Decrease in temperature* - A decrease in body **temperature** (hypothermia) increases the affinity of hemoglobin for oxygen. - This makes it more difficult for hemoglobin to release oxygen to the tissues, resulting in a **leftward shift** of the curve.

Question 10: In the jugular venous pressure (JVP) waveform, the "a" wave corresponds to:

A. Tricuspid valve bulging into Right atria
B. Right Atrial contraction (Correct Answer)
C. Right Atrial relaxation
D. Right atrial filling

Explanation: ***Right Atrial contraction*** - The **'a' wave** is the first positive deflection in the JVP waveform and is produced by the increase in right atrial pressure during **atrial systole** (contraction). - This wave occurs just before the first heart sound (S1) and is notably absent in conditions like **atrial fibrillation** where coordinated atrial contraction is lost. *Tricuspid valve bulging into Right atria* - The bulging of the closed **tricuspid valve** into the right atrium at the beginning of ventricular systole contributes to the **'c' wave**. - The 'c' wave follows the 'a' wave and also reflects the transmitted pulsation from the adjacent **carotid artery**. *Right Atrial relaxation* - Right atrial relaxation leads to a fall in pressure, which is represented by the **'x' descent**. - This descent follows the 'c' wave and is caused by both atrial relaxation and the downward pulling of the atrial floor during ventricular contraction. *Right atrial filling* - The **'v' wave** represents the rise in right atrial pressure due to passive venous filling from the vena cavae while the tricuspid valve is closed. - This wave peaks just before the tricuspid valve opens at the beginning of diastole.