What is the characteristic of the second Purkinje image in relation to eye movement?
Which structure of the eye has the maximum refractive power?
What does colostrum have compared to normal milk?
Lesion of globus pallidus causes
In the context of blunt trauma affecting the entire body, what is the estimated daily nitrogen loss in grams due to protein metabolism?
Which of the following is used for the diagnosis of asthma?
What is the primary mechanism underlying hyperthermia?
Tetany is seen in
In pregnancy, plasma volume increase is maximum at what gestational age?
Narcolepsy is due to abnormality in ?
NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs
Question 81: What is the characteristic of the second Purkinje image in relation to eye movement?
- A. Inverted and moves in same direction
- B. Inverted and moves in opposite direction
- C. Erect and moves in same direction (Correct Answer)
- D. Erect and moves in opposite direction
Explanation: ***Erect and moves in same direction*** - The second Purkinje image (P2) is formed by reflection from the **posterior surface of the cornea**. - This surface acts as a convex mirror, producing a **virtual, erect, and diminished image**. - The image moves in the **same direction** as the eye movement, characteristic of reflections from the first three Purkinje images (P1, P2, P3). - P2 is clinically used in keratometry and assessment of corneal curvature. *Erect and moves in opposite direction* - While the image orientation (erect) would apply to P2, the direction of movement is incorrect. - Only the **fourth Purkinje image (P4)**, formed by the **posterior lens surface**, moves in the opposite direction to eye movement. - P4 is the only inverted Purkinje image due to reflection from the concave posterior lens surface. *Inverted and moves in same direction* - The second Purkinje image is **erect, not inverted**. - All Purkinje images are erect except P4, which is inverted due to reflection from the concave posterior lens surface. - This combination (inverted + same direction) does not correspond to any Purkinje image. *Inverted and moves in opposite direction* - This describes the **fourth Purkinje image (P4)**, not the second. - P4 is formed by reflection from the **posterior surface of the lens** (concave surface), which produces an inverted image. - The second Purkinje image (P2) is always erect, being formed by the posterior corneal surface.
Question 82: Which structure of the eye has the maximum refractive power?
- A. Anterior surface of lens
- B. Posterior surface of lens
- C. Anterior surface of cornea (Correct Answer)
- D. Posterior surface of cornea
Explanation: ***Anterior surface of cornea*** - The **cornea** accounts for approximately two-thirds of the eye's total refractive power due to the large difference in refractive index between air and the corneal tissue. - The **anterior surface of the cornea** is the primary site of light refraction as light enters the eye from the air. *Anterior surface of lens* - The **lens** contributes significantly to accommodation, but its overall refractive power is less than that of the cornea in the unaccommodated state. - The change in refractive index between the aqueous humor and the lens is less pronounced compared to the air-cornea interface. *Posterior surface of lens* - The **posterior surface of the lens** also contributes to the focusing power of the lens, but its curvature and refractive index difference are typically less than the anterior surface of the cornea. - Its contribution to total refractive power is secondary to the anterior corneal surface and the anterior lens surface. *Posterior surface of cornea* - The **posterior surface of the cornea** has a much smaller refractive power compared to the anterior surface due to the smaller difference in refractive index between the cornea and the aqueous humor. - This interface does contribute to refraction but is not the primary focusing component.
Question 83: What does colostrum have compared to normal milk?
- A. Increased proteins (Correct Answer)
- B. Decreased potassium
- C. Decreased sodium
- D. Decreased calories
Explanation: ***Increased proteins*** - **Colostrum** is rich in **immunoglobulins (antibodies)** like IgA, IgG, and IgM, which are proteins crucial for passive immunity in the newborn, making its protein content **2-3 times higher** than mature milk (approximately 2.3 g/100 mL vs 0.9 g/100 mL). - These high protein levels also include **lactoferrin** and **growth factors**, which support the development of the infant's gut and immune system. - This is the **most clinically significant** distinguishing feature of colostrum. *Decreased potassium* - **Potassium (K)** levels in colostrum are actually **similar to or slightly higher** than mature milk (approximately 74 mg/100 mL vs 51 mg/100 mL). - This option is incorrect as potassium is not decreased. *Decreased sodium* - **Sodium (Na)** levels are actually **significantly higher** in colostrum than in mature milk (approximately 48 mg/100 mL vs 15 mg/100 mL). - This elevated sodium gives colostrum a distinct salty taste, differentiating it from mature milk. - This option is incorrect as sodium is increased, not decreased. *Decreased calories* - While colostrum has a **lower fat content** than mature milk, leading to somewhat lower caloric density (54-58 kcal/100 mL vs 65-70 kcal/100 mL), this is not the primary distinguishing characteristic. - The most important feature of colostrum is its **high protein and immunoglobulin content** for immune protection, not its caloric value.
Question 84: Lesion of globus pallidus causes
- A. Chorea
- B. Athetosis (Correct Answer)
- C. Hemibalismus
- D. Dystonia
Explanation: ***Athetosis*** - **Athetosis** is the **classic movement disorder** associated with lesions of the **globus pallidus**, often occurring with **putamen** involvement. - It is characterized by **slow, writhing, involuntary movements**, particularly affecting the **distal extremities** (hands and feet). - Commonly seen in **kernicterus** (bilirubin-induced damage to basal ganglia), **cerebral palsy**, and **status marmoratus** of the basal ganglia. - When combined with chorea, it forms **choreoathetosis**. *Chorea* - **Chorea** is predominantly associated with dysfunction of the **caudate nucleus** and **putamen**, as seen in **Huntington's disease**. - It involves brief, irregular, unpredictable, **involuntary movements** that flow from one body part to another. *Hemibalismus* - **Hemibalismus** is most commonly caused by a lesion in the **subthalamic nucleus** (nucleus of Luys), often due to a **lacunar stroke**. - It involves large-amplitude, **involuntary flinging movements** of the limbs on **one side of the body**. *Dystonia* - **Dystonia** involves sustained or repetitive muscle contractions leading to twisting movements or abnormal fixed postures. - It results from dysfunction of **multiple basal ganglia structures** including the globus pallidus internal segment, putamen, and thalamus, but is **not the classic presentation** of isolated globus pallidus lesions.
Question 85: In the context of blunt trauma affecting the entire body, what is the estimated daily nitrogen loss in grams due to protein metabolism?
- A. Approximately 35 grams (Correct Answer)
- B. Approximately 45 grams
- C. Approximately 55 grams
- D. Approximately 65 grams
Explanation: ***Approximately 35 grams*** - In **severe trauma**, such as blunt trauma affecting the entire body, the body undergoes a significant stress response leading to marked **protein catabolism**. Approximately **35 grams of nitrogen** can be lost daily under such conditions. - This represents a highly catabolic state where muscle protein is broken down to provide amino acids for energy and synthesis of acute-phase proteins, impacting overall nitrogen balance. *Approximately 45 grams* - While severe trauma does lead to substantial nitrogen loss, **45 grams** would typically indicate an even more extreme or prolonged catabolic state, which is less common in the initial stages of post-trauma protein metabolism than 35 grams. - Such a high nitrogen loss might be seen in very extensive burns or sepsis, which are different clinical contexts. *Approximately 55 grams* - A daily nitrogen loss of **55 grams** is beyond what is commonly observed even in severe, whole-body blunt trauma. This level of catabolism would likely be unsustainable or indicative of a rare, super-catabolic condition. - This magnitude of protein breakdown would lead to rapid and severe muscle wasting and organ dysfunction if sustained. *Approximately 65 grams* - Losing **65 grams of nitrogen** per day is an exceptionally high rate of protein catabolism, rarely, if ever, observed in blunt trauma alone. - This level of protein breakdown would represent a profound and life-threatening metabolic derangement, far exceeding typical post-trauma responses.
Question 86: Which of the following is used for the diagnosis of asthma?
- A. Measurement of tidal volume
- B. End expiratory flow rate
- C. Total lung capacity
- D. FEV1 (Correct Answer)
Explanation: ***FEV1*** - **Forced expiratory volume in 1 second (FEV1)** is the gold standard spirometric parameter for asthma diagnosis - Key diagnostic criteria include: - Reduced **FEV1/FVC ratio** (<0.70 or <0.75-0.80 in adults) - **Bronchodilator reversibility**: ≥12% and ≥200 mL increase in FEV1 after inhaled short-acting β2-agonist - This reversibility distinguishes asthma from fixed obstructive diseases like COPD - Serial **peak expiratory flow (PEF)** monitoring can also demonstrate variability characteristic of asthma *Measurement of tidal volume* - **Tidal volume** measures the amount of air inhaled or exhaled during normal breathing (typically ~500 mL at rest) - Not a diagnostic parameter for asthma as it doesn't assess **airway obstruction** or **hyperresponsiveness** - May be reduced during acute exacerbations but lacks specificity for asthma diagnosis *End expiratory flow rate* - Not a standard diagnostic parameter for asthma - While **mid-expiratory flow rates** (FEF25-75%) and **peak expiratory flow (PEF)** are assessed, **FEV1** remains the primary diagnostic measure - FEV1 provides better reproducibility and standardization for diagnosis *Total lung capacity* - **Total lung capacity (TLC)** represents total lung volume after maximal inhalation - May be normal or increased in asthma due to **air trapping** and hyperinflation - Not used as a primary diagnostic criterion as asthma diagnosis focuses on demonstrating **reversible airflow limitation**, not lung volumes
Question 87: What is the primary mechanism underlying hyperthermia?
- A. Temperature > 40°C with autonomic dysfunction
- B. Failure of thermoregulation (Correct Answer)
- C. Temperature > 41.5°C
- D. No change in hypothalamic set point
Explanation: ***Failure of thermoregulation*** - **Hyperthermia** is fundamentally caused by the body's inability to dissipate heat effectively, leading to an uncontrolled rise in core body temperature. - This differentiates it from fever, where the **hypothalamic set point** is elevated, and the body actively tries to reach that higher temperature. *Temperature > 41.5°C* - While a temperature exceeding **41.5°C** is often seen in severe hyperthermia, it is a *consequence* of the failure of thermoregulation, not its primary cause. - This extreme temperature indicates a critical state, but the underlying problem is the body's inability to control internal heat. *Temperature > 40°C with autonomic dysfunction* - A temperature above **40°C** combined with **autonomic dysfunction** (e.g., altered mental status, seizures) describes a severe *manifestation* of hyperthermia, often seen in heat stroke. - This is a symptom complex resulting from, rather than the primary cause of, the body's thermoregulatory failure. *No change in hypothalamic set point* - This statement is a *characteristic* of hyperthermia, distinguishing it from fever, where the **hypothalamic set point** is elevated. - However, the *absence* of this change is not the primary cause; rather, the underlying issue is the body's inability to manage its heat load despite a normal set point.
Question 88: Tetany is seen in
- A. Respiratory alkalosis (Correct Answer)
- B. Respiratory acidosis
- C. Metabolic acidosis
- D. Hyperkalemia
Explanation: ***Respiratory alkalosis*** - **Respiratory alkalosis** is caused by **hyperventilation**, which leads to a decrease in arterial partial pressure of carbon dioxide (**PaCO2**). - This decrease in PaCO2 causes an increase in pH (alkalemia) and a shift in the albumin-bound calcium equilibrium, reducing the amount of **ionized calcium** in the blood, leading to symptoms of **hypocalcemia** such as tetany. *Respiratory acidosis* - **Respiratory acidosis** is characterized by an increase in PaCO2 and a decrease in pH due to inadequate ventilation, which would not typically cause tetany. - In fact, the acidosis would tend to increase **ionized calcium** levels, thereby counteracting any tendency towards symptoms of hypocalcemia. *Metabolic acidosis* - **Metabolic acidosis** involves a decrease in bicarbonate concentration and pH, often due to conditions like diabetic ketoacidosis or lactic acidosis. - Similar to respiratory acidosis, the acidic environment of **metabolic acidosis** tends to increase **ionized calcium** levels, making tetany unlikely. *Hyperkalemia* - **Hyperkalemia** refers to elevated potassium levels in the blood, which primarily affects cardiac and neuromuscular function. - While it can cause muscle weakness and cardiac arrhythmias, it does not directly lead to **tetany**, which is a sign of **hypocalcemia**.
Question 89: In pregnancy, plasma volume increase is maximum at what gestational age?
- A. 10 wks
- B. 20 wks
- C. 25 wks
- D. 30 wks (Correct Answer)
Explanation: ***30 wks*** - **Plasma volume** typically reaches its maximum expansion around **30-34 weeks of gestation**, increasing by approximately 40-50% compared to pre-pregnancy levels. - This increase is crucial for supporting the **fetoplacental unit**, enhancing nutrient delivery, and protecting against supine hypotension. *10 wks* - At **10 weeks**, the increase in plasma volume is still modest, with significant expansion primarily occurring in the **second trimester**. - Most of the rapid expansion begins after the **first trimester**, around the 12-week mark. *20 wks* - While plasma volume is significantly increasing by **20 weeks**, it has not yet reached its peak. - The continuous expansion continues through the **third trimester** before stabilizing. *25 wks* - At **25 weeks**, plasma volume is substantially elevated, but the maximum expansion is usually observed a few weeks later. - The peak is generally in the **early third trimester**, around 30-34 weeks.
Question 90: Narcolepsy is due to abnormality in ?
- A. Hypothalamus (Correct Answer)
- B. Neocortex
- C. Cerebellum
- D. Medulla oblongata
Explanation: **Hypothalamus** - Narcolepsy is primarily caused by the loss of **orexin (hypocretin)** producing neurons in the **hypothalamus**, which are crucial for maintaining wakefulness. - This deficiency leads to dysregulation of **sleep-wake cycles**, causing excessive daytime sleepiness and other narcolepsy symptoms. *Neocortex* - The neocortex is involved in higher-level cognitive functions, sensory perception, and voluntary movement, but it is not the primary site of pathology in narcolepsy. - While sleep stages involve cortical activity, the core deficit in narcolepsy does not originate here. *Cerebellum* - The cerebellum is mainly responsible for motor control, coordination, and balance. - Its dysfunction is associated with ataxic gait and coordination problems, not the sleep disturbances characteristic of narcolepsy. *Medulla oblongata* - The medulla oblongata controls vital autonomic functions like breathing, heart rate, and blood pressure. - While involved in sleep regulation pathways, it is not the primary anatomical location affected in narcolepsy.