FMGE 2025 - Physiology Practice Questions

Q: Hormone responsible for milk ejection reflex in the image shown?

Oxytocin. ***Oxytocin*** - The image shows a baby breastfeeding, which involves the **suckling reflex**. This reflex triggers the release of oxytocin from the posterior pituitary gland. - Oxytocin is crucial for the **milk ejection reflex** (or let-down reflex), as it causes the contraction of myoepithelial cells surrounding the alveoli in the mammary glands, expelling milk. *TSH* - Thyroid-Stimulating Hormone (TSH) is released from the anterior pituitary and its primary role is to stimulate the **thyroid gland** to produce thyroid hormones. - It is involved in regulating the body's **metabolism** and is not directly responsible for lactation. *GH* - Growth Hormone (GH) is secreted by the anterior pituitary and is essential for overall **somatic growth**, particularly of bones and muscles. - While it contributes to mammary gland development, it does not mediate the immediate process of milk ejection during breastfeeding. *FSH* - Follicle-Stimulating Hormone (FSH) is an anterior pituitary hormone that plays a key role in the reproductive cycle. - It stimulates the growth of **ovarian follicles** in females and **spermatogenesis** in males, and is not involved in lactation.

Q: What best describes step 3 in the given diagram?

Efflux of K ions. ***Efflux of K ions*** - Step 3 represents the **repolarization** phase of the action potential. This is caused by the opening of voltage-gated **K+ channels** and the inactivation of voltage-gated Na+ channels. - The opening of these channels allows a rapid **efflux** (outward flow) of positively charged K+ ions, which makes the membrane potential decrease from its positive peak back towards the negative resting potential. *Efflux of Na ions* - An efflux of Na+ ions is primarily driven by the **Na+/K+ pump** to maintain the resting potential over time, not to cause the rapid repolarization seen in step 3. - The significant movement of Na+ during the action potential is an **influx** during depolarization (step 2), not an efflux. *Influx of Na ions* - The influx of Na+ ions through voltage-gated channels is responsible for the **depolarization** phase (step 2), the rapid rising phase of the action potential. - During step 3, the voltage-gated **Na+ channels are inactivated**, preventing the influx of Na+ ions and allowing repolarization to occur. *Influx of K ions* - K+ ions move **outward** (efflux) during repolarization, not inward. - An influx of K+ would make the membrane potential more negative, but this is not the mechanism of repolarization in step 3.

Q: Which of the following ion movements is primarily responsible for the repolarization phase (Phase 3) of an action potential, as depicted in the image?

Efflux of K ions. ***Efflux of K ions*** - Phase 3, the **repolarization** or falling phase, is initiated by the opening of voltage-gated **potassium (K+) channels** as the membrane potential peaks. - The outflow of positive K+ ions from the cell, known as **efflux**, causes the membrane potential to become negative again, returning it towards the resting state. *Efflux of Na ions* - The electrochemical gradient for **sodium (Na+)** strongly favors its movement into the cell (influx), not out of it (efflux). - While the **Na+/K+ pump** does move Na+ out of the cell, this is a slow, active process to maintain resting potential, not the cause of rapid repolarization. *Influx of Na ions* - The rapid influx (inflow) of **Na+** ions through voltage-gated channels is responsible for the **depolarization** phase (Phase 0), the sharp upstroke of the action potential. - During repolarization (Phase 3), these voltage-gated **Na+ channels** become inactivated, stopping the influx. *Resting membrane potential is maintained by the Na-K pump* - The **Na+/K+ pump** is crucial for establishing and maintaining the ion gradients for the **resting membrane potential** (Phase 4), not for the rapid repolarization phase itself. - Repolarization is a passive process resulting from ion flow through channels, which is much faster than the action of the Na+/K+ pump.

Q: Which among the following hormones, in a lactating mother, is responsible for the maintenance and proliferation of milk-secreting breast tissue?

Prolactin. ***Prolactin***- **Prolactin** is the key hormone responsible for establishing and maintaining **lactation** (milk production), and it drives the final proliferation and differentiation of the **alveolar epithelial cells** during the later stages of pregnancy and postpartum state.- While other hormones contribute to overall breast development, Prolactin ensures the functional readiness and continued growth/maintenance of the glandular tissue necessary for milk synthesis.*Oxytocin*- **Oxytocin** is responsible for the **milk ejection reflex** (let-down), causing the contraction of **myoepithelial cells** around the alveoli.- It does not promote the proliferative growth or differentiation of the secretory breast tissue itself.*Estrogen*- **Estrogen** is primarily responsible for the growth and development of the **ductal system** of the breast during puberty and pregnancy.- High levels of estrogen during pregnancy actively **inhibit** the full secretory function of prolactin until after delivery.*Progesterone*- **Progesterone** is crucial for the development of the **lobular-alveolar system** during pregnancy.- Its rapid decline after delivery is essential to remove the inhibitory block, allowing **prolactin** to fully initiate and manage milk secretion in the lactating phase.

Q: A 35-year-old man wakes up after sleeping with his arm draped over a chair and complains of pain. Which of the following accurately describes the order of susceptibility of nerve fibers in the given condition?

A > B > C. ***A > B > C***- The clinical scenario describes **neuropraxia** (transient functional block) due to **compression and ischemia**, such as in 'Saturday night palsy'.- A fibers have the largest diameter and the heaviest myelination, making them the most vulnerable to conduction block resulting from **focal demyelination** caused by mechanical stress. *A B > A*- This order represents the susceptibility of nerve fibers to **local anesthetic agents** (pharmacologic block), not mechanical compression. - Local anesthetics preferentially block smaller, unmyelinated C fibers (pain and temperature sensation), followed by B and then A fibers (motor/proprioception). *C B fibers > C fibers) to compression injury.

Q: A woman from Delhi travels to Ladakh, a high-altitude region. Soon after arrival, she develops symptoms such as breathlessness, headache, and lightheadedness. What is the primary underlying mechanism responsible for her symptoms?

Respiratory alkalosis. ***Respiratory alkalosis***- Acute exposure to high altitude decreases the **partial pressure of inspired oxygen ($P_{I}O_2$)**, leading to **hypoxemia**, which stimulates the peripheral chemoreceptors (carotid bodies) to increase the respiratory drive (hyperventilation).- This hyperventilation causes a massive *washout* of **carbon dioxide ($ ext{CO}_2$)**, resulting in low arterial $ ext{P}_{ ext{a}} ext{CO}_2$ (hypocapnia) and an immediate increase in blood $ ext{pH}$ (alkalosis).*Respiratory acidosis*- This condition is characterized by **hypoventilation** resulting in the retention of $ ext{CO}_2$ and a resultant drop in $ ext{pH}$.- Acute high altitude exposure leads to increased ventilation (hyperventilation), making this mechanism incorrect.*Metabolic alkalosis*- This state results from excess plasma **bicarbonate ($ ext{HCO}_3^{-})$** or significant loss of $ ext{H}^{+}$ (e.g., protracted vomiting, loop diuretics).- This is not the primary acid-base disturbance leading to acute mountain sickness (AMS) symptoms.*Metabolic acidosis*- This state is the **delayed renal compensatory mechanism** for respiratory alkalosis, where the kidneys increase the excretion of $ ext{bicarbonate}$.- While it occurs, it is a secondary compensation that takes 24–48 hours and is not the *primary underlying mechanism* responsible for the immediate symptoms upon arrival.

Q: As a neuron’s diameter increases, what effect manifests?

Conduction velocity increases. ***Conduction velocity increases*** - Increasing the diameter of an axon decreases the **internal (axial) resistance** ($R_i$) to passive current flow longitudinal to the axon. - Reduced internal resistance allows local current loops to spread further and faster, significantly increasing the **length constant**, thereby increasing conduction velocity. *Conduction velocity decreases* - This is incorrect, as larger diameter decreases internal resistance, leading directly to a **faster electrotonic spread** of depolarization and a higher conduction speed. - Decreased conduction velocity is typically observed in **small-diameter** or **demyelinated** axons where internal resistance is higher or membrane capacitance is altered. *Membrane resistance increases* - Membrane resistance ($R_m$) is determined by the density and activity of **leak ion channels** within the cell membrane, which is independent of the overall axon diameter. - While the total membrane area increases, the **specific membrane resistance** (resistance per unit area) does not change with diameter. *Action potential amplitude increases* - Action potential (AP) conduction is an **all-or-none** phenomenon, meaning the amplitude is fixed and determined by the electrochemical gradient of **voltage-gated sodium channels**. - Changes in axon diameter influence the **speed** of propagation (conduction velocity), but they do not alter the required peak voltage (amplitude) of the action potential.

Question 1

Hormone responsible for milk ejection reflex in the image shown?

Accepted Answer

Oxytocin

Answer

GH

Answer

TSH

Answer

FSH

Question 2

What best describes step 3 in the given diagram?

Accepted Answer

Efflux of K ions

Answer

Efflux of Na ions

Answer

Influx of Na ions

Answer

Influx of K ions

Question 3

Which of the following ion movements is primarily responsible for the repolarization phase (Phase 3) of an action potential, as depicted in the image?

Accepted Answer

Efflux of K ions

Answer

Influx of Na ions

Answer

Efflux of Na ions

Answer

Resting membrane potential is maintained by the Na-K pump

Question 4

Which among the following hormones, in a lactating mother, is responsible for the maintenance and proliferation of milk-secreting breast tissue?

Accepted Answer

Prolactin

Answer

Estrogen

Answer

Oxytocin

Answer

Progesterone

Question 5

A 35-year-old man wakes up after sleeping with his arm draped over a chair and complains of pain. Which of the following accurately describes the order of susceptibility of nerve fibers in the given condition?

Accepted Answer

A > B > C

Answer

C < B < A

Answer

A < B < C

Answer

C > B > A

Question 6

A woman from Delhi travels to Ladakh, a high-altitude region. Soon after arrival, she develops symptoms such as breathlessness, headache, and lightheadedness. What is the primary underlying mechanism responsible for her symptoms?

Accepted Answer

Respiratory alkalosis

Answer

Metabolic alkalosis

Answer

Metabolic acidosis

Answer

Respiratory acidosis

Question 7

As a neuron’s diameter increases, what effect manifests?

Accepted Answer

Conduction velocity increases

Answer

Conduction velocity decreases

Answer

Membrane resistance increases

Answer

Action potential amplitude increases

FMGE 2025 — Physiology