NEET-PG 2012 - Physiology Practice Questions

Q: What does Einthoven's law state regarding the relationship between the electrical potentials of the limb leads?

I + III = II. ***I + III = II*** - Einthoven's law describes the relationship between the three **bipolar limb leads** (I, II, and III) in an **electrocardiogram (ECG)**. - It states that the electrical potential of Lead II is equal to the sum of the potentials of Lead I and Lead III (Lead II = Lead I + Lead III). - This can also be expressed as **I + III = II**, which is the **correct mathematical representation** of Einthoven's law. *I - III = II* - This equation is **incorrect** and does not represent Einthoven's law. - The correct relationship involves **addition** of Leads I and III, not subtraction. *I + II + III = 0* - This equation is **incorrect** as written with all positive signs. - Einthoven's law can be rearranged as **I + III - II = 0** (not I + II + III = 0). - The equation shown suggests adding all three leads to get zero, which is **mathematically inconsistent** with the correct formulation (I + III = II). *I + III = avL* - This equation is incorrect and does not relate to Einthoven's law. - **avL (augmented vector left)** is one of the augmented unipolar limb leads calculated as: avL = I - (II/2), not as a direct sum of Leads I and III.

Q: Which of the following statements about gastric secretion is true?

Increased by stomach distention. ***Increased by stomach distention*** - **Stomach distention** activates local reflexes and the **vagovagal reflex**, leading to the release of **acetylcholine** and **gastrin**, which stimulate gastric acid secretion during the gastric phase. - This is a physiological response that prepares the stomach for digestion of incoming food. *Inhibited by curare* - **Curare** is a **nicotinic acetylcholine receptor antagonist** that primarily affects neuromuscular junctions, causing muscle paralysis. - It does not directly inhibit the primary mechanisms of gastric acid secretion, which are largely mediated by **muscarinic acetylcholine receptors**, histamine, and gastrin. *Stimulated by nor adrenaline* - **Noradrenaline** (norepinephrine) is a neurotransmitter of the **sympathetic nervous system**, which generally **inhibits** gastric motility and secretion. - Activation of alpha-2 adrenergic receptors can decrease gastric acid secretion. *Stimulated by an increase in tonic activity* - This statement is vague; "tonic activity" can refer to various physiological processes. If it refers to **sympathetic nervous system** tonic activity, it would **inhibit** gastric secretion. - If it implies increased vagal tone (parasympathetic activity), then secretion would be stimulated, but the phrasing is not precise enough to be unequivocally true for gastric secretion in general.

Q: What is the definition of preload in the context of cardiac physiology?

Volume of blood in the ventricles at the end of diastole. ***Volume of blood in the ventricles at the end of diastole*** - Preload represents the **initial stretching** of the cardiac myocytes prior to contraction, largely determined by the **volume of blood filling the ventricles** at the end of relaxation (diastole). - This **end-diastolic volume** directly correlates with the ventricular muscle fiber length at the start of systole, influencing the force of contraction according to the **Frank-Starling mechanism**. *Volume of blood in the ventricles at the end of systole* - This describes the **end-systolic volume**, which is the amount of blood remaining in the ventricle after it has contracted and ejected blood. - End-systolic volume is a determinant of the **ejection fraction** but does not define preload. *Amount of blood pumped by the heart per beat* - This refers to the **stroke volume**—the volume of blood ejected from the left ventricle with each heartbeat. - While preload influences stroke volume, stroke volume itself is not the definition of preload. *Resistance to blood flow in the arteries* - This describes **afterload**, which is the pressure or resistance the ventricle must overcome to eject blood during systole. - Afterload primarily affects the *force* needed for contraction, rather than the initial stretch or filling volume of the heart.

Q: Substance that is completely reabsorbed from the kidney?

Glucose. ***Glucose*** - In a healthy individual, **virtually all filtered glucose** is reabsorbed in the proximal convoluted tubule via **sodium-glucose cotransporters (SGLTs)**. - This complete reabsorption ensures that this vital energy source is conserved and not excreted in the urine. *Na+* - While a large proportion of filtered **Na+** is reabsorbed to maintain fluid and electrolyte balance, not all of it is reabsorbed; some is excreted in urine. - The reabsorption of Na+ is **regulated** by hormones like **aldosterone** to fine-tune its excretion based on the body's needs. *K+* - **K+** undergoes both reabsorption and secretion in different parts of the nephron, and its excretion is tightly regulated. - Net reabsorption of K+ is not complete; its handling ensures appropriate plasma levels are maintained for muscle and nerve function. *Urea* - Approximately **50% of filtered urea undergoes reabsorption** in the renal tubules, while the other half is excreted. - Urea reabsorption is important for generating the **medullary osmotic gradient**, which is essential for concentrating urine, but it is never completely reabsorbed.

Q: Gastric secretions are essential for absorption of -

Cobalamin. ***Cobalamin*** - **Intrinsic factor**, secreted by gastric parietal cells, is crucial for the absorption of **vitamin B12 (cobalamin)** in the terminal ileum [1]. - Without sufficient intrinsic factor, **pernicious anemia** can develop due to impaired B12 absorption [2]. *Fat* - Fat digestion primarily occurs in the **small intestine** with the help of **bile salts** and **pancreatic lipases**. - While gastric lipase begins some fat digestion, it's not essential for overall fat absorption. *Thiamine* - **Thiamine (vitamin B1)** is absorbed in the jejunum and ileum, primarily via **active transport** and passive diffusion. - Gastric secretions do not play a direct, essential role in its absorption. *Folic acid* - **Folic acid** is absorbed in the **duodenum and jejunum** as monoglutamates after being deconjugated from polyglutamate forms. - This process is not directly dependent on gastric secretions [2].

Q: What triggers the cephalic phase of gastric secretion?

On seeing food. ***On seeing food*** - The **cephalic phase** of gastric secretion is initiated by sensory input such as the sight, smell, taste, or even the thought of food. - This phase is mediated by the **vagus nerve**, stimulating gastric acid and enzyme secretion in anticipation of food arrival. *On food entering stomach* - This describes the initiation of the **gastric phase** of digestion, where mechanical stretch and chemical presence of food in the stomach stimulate further secretions. - The gastric phase primarily involves local reflexes and hormonal mechanisms (like **gastrin** release), rather than purely sensory input from the head. *On food entering intestine* - This marks the beginning of the **intestinal phase** of digestion, which involves both stimulatory and inhibitory signals for gastric secretion. - The primary role of the intestinal phase is to regulate the rate at which chyme enters the small intestine and to coordinate bile and pancreatic enzyme release. *On stress* - While stress can impact digestive function, it typically affects the **autonomic nervous system** in a generalized way, often leading to inhibition of digestion or altered motility. - Stress does not specifically trigger the cephalic phase of gastric secretion, which is a physiological response linked to nutrient anticipation.

Q: A wave in ERG is due to activity of:

Rods and cones. ***Rods and cones*** - The **electroretinogram (ERG)** measures the electrical responses of various retinal cells to light stimuli. - The **a-wave** of the ERG primarily reflects the activity of the **photoreceptors (rods and cones)** as they hyperpolarize in response to light. *Pigmented epithelium* - The **retinal pigmented epithelium (RPE)** plays a crucial role in photoreceptor health and function but does not directly generate the primary electrical waves measured by the standard ERG. - Its dysfunction can lead to secondary changes in ERG, but its activity is not the direct source of the a-wave. *Ganglion cell* - **Ganglion cells** are the output neurons of the retina, transmitting visual information to the brain. - Their activity is generally not well-represented in the standard ERG, which primarily assays outer and middle retinal layers. *Bipolar cell* - **Bipolar cells** transmit signals from photoreceptors to ganglion cells and contribute to the **b-wave** component of the ERG. - The b-wave, not the a-wave, is largely generated by the depolarizing activity of bipolar cells and Müller cells.

Q: What is the characteristic of the second Purkinje image in relation to eye movement?

Erect and moves in same direction. ***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.

Q: Which structure of the eye has the maximum refractive power?

Anterior surface of cornea. ***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.

Q: What does colostrum have compared to normal milk?

Increased proteins. ***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 1

What does Einthoven's law state regarding the relationship between the electrical potentials of the limb leads?

Accepted Answer

I + III = II

Answer

I - III = II

Answer

I + II + III = 0

Answer

I + III = avL

Question 2

Which of the following statements about gastric secretion is true?

Accepted Answer

Increased by stomach distention

Answer

Inhibited by curare

Answer

Stimulated by nor adrenaline

Answer

Stimulated by an increase in tonic activity

Question 3

What is the definition of preload in the context of cardiac physiology?

Accepted Answer

Volume of blood in the ventricles at the end of diastole

Answer

Volume of blood in the ventricles at the end of systole

Answer

Amount of blood pumped by the heart per beat

Answer

Resistance to blood flow in the arteries

Question 4

Substance that is completely reabsorbed from the kidney?

Accepted Answer

Glucose

Answer

Na+

Answer

K+

Answer

Urea

Question 5

Gastric secretions are essential for absorption of -

Accepted Answer

Cobalamin

Answer

Fat

Answer

Thiamine

Answer

Folic acid

Question 6

What triggers the cephalic phase of gastric secretion?

Accepted Answer

On seeing food

Answer

On food entering stomach

Answer

On food entering intestine

Answer

On stress

Question 7

A wave in ERG is due to activity of:

Accepted Answer

Rods and cones

Answer

Pigmented epithelium

Answer

Ganglion cell

Answer

Bipolar cell

Question 8

What is the characteristic of the second Purkinje image in relation to eye movement?

Accepted Answer

Erect and moves in same direction

Answer

Inverted and moves in same direction

Answer

Inverted and moves in opposite direction

Answer

Erect and moves in opposite direction

Question 9

Which structure of the eye has the maximum refractive power?

Accepted Answer

Anterior surface of cornea

Answer

Anterior surface of lens

Answer

Posterior surface of lens

Answer

Posterior surface of cornea

Question 10

What does colostrum have compared to normal milk?

Accepted Answer

Increased proteins

Answer

Decreased potassium

Answer

Decreased sodium

Answer

Decreased calories

NEET-PG 2012 — Physiology