NEET-PG 2012 - Physiology Practice Questions

Q: Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?

An increase in arterial carbon dioxide tension. ***An increase in arterial carbon dioxide tension*** - An increase in **arterial PCO2** (hypercapnia) leads to a rapid decrease in the **pH of the cerebrospinal fluid (CSF)**, which strongly stimulates **central chemoreceptors** in the medulla. - While overwhelmingly driven by central chemoreceptors, a significant increase in **arterial PCO2** also causes a slight decrease in **arterial pH**, which can additionally stimulate **peripheral chemoreceptors** in the carotid and aortic bodies, leading to increased ventilation. *A decrease in arterial oxygen content* - A decrease in **arterial oxygen content** (e.g., due to anemia or carbon monoxide poisoning) without a significant drop in **arterial PO2** primarily affects oxygen delivery to tissues. - It does not directly stimulate peripheral chemoreceptors, which are sensitive to **PO2**, not content, nor does it affect central chemoreceptors directly to increase ventilation in this manner. *A decrease in arterial blood pressure* - A decrease in **arterial blood pressure** is sensed by **baroreceptors** and primarily triggers cardiovascular reflexes (e.g., increased heart rate and vasoconstriction) to restore blood pressure. - It does not directly stimulate peripheral or central chemoreceptors to significantly increase ventilation unless severe hypoperfusion leads to significant changes in arterial blood gases. *A decrease in arterial oxygen tension* - A decrease in **arterial oxygen tension (PO2)**, especially when it falls below approximately 60 mmHg, acts as a potent stimulus for **peripheral chemoreceptors**. - However, **central chemoreceptors** are primarily sensitive to **PCO2** and CSF pH, and a decrease in **arterial PO2** alone has little direct effect on their activity.

Q: Transpulmonary pressure is the difference between:

Pressure in alveoli and intrapleural pressure. ***Pressure in alveoli and intrapleural pressure*** - Transpulmonary pressure is the **pressure gradient** across the lung wall, which is essential for maintaining alveolar inflation. - It is calculated as the **alveolar pressure minus the intrapleural pressure**. *The pressure in the bronchus and atmospheric pressure* - This difference would represent the pressure driving airflow through the **bronchial tree**, not the pressure across the lung wall itself. - It's a measure relevant to **airway resistance**, not lung distension. *The difference between atmospheric pressure and intrapleural pressure* - This difference is related to the **intrathoracic pressure**, which influences venous return and cardiac function, but not directly the distension of the lungs. - It does not account for the **alveolar pressure**, which is the primary internal pressure expanding the lung. *The difference between atmospheric pressure and intraalveolar pressure* - This difference is the **driving pressure for airflow** into or out of the lungs. - It represents the pressure gradient that causes air to move between the **atmosphere and the alveoli** during inspiration and expiration.

Q: Which of the following components are included in microcirculation?

Capillaries, venules, and arterioles. ***Capillaries, venules, and arterioles*** - **Microcirculation** is the portion of the **circulatory system** that includes the **smallest blood vessels**, specifically the **arterioles**, **capillaries**, and **venules**. - These vessels are crucial for the **delivery of oxygen** and **nutrients** to tissues and the removal of waste products. *Capillaries* - While **capillaries** are a vital part of **microcirculation** and the primary site of nutrient and waste exchange, they alone do not encompass the entire microcirculatory unit. - The microcirculation also includes the vessels that feed into and drain from the capillaries: the **arterioles** and **venules**. *Aorta* - The **aorta** is the **largest artery** in the body, part of the **macrocirculation**, which distributes blood from the heart to the systemic circulation. - It is not considered part of the **microcirculation** due to its large size and primary function as a high-pressure conduit rather than a site of exchange. *Arteries and veins* - **Arteries** and **veins** are primarily components of the **macrocirculation**, responsible for transporting blood to and from the systemic and pulmonary circuits. - While arterioles and venules (small arteries and veins) are part of the microcirculation, the broader terms "arteries" and "veins" typically refer to the larger vessels and do not exclusively define the microcirculatory network.

Q: Mean arterial pressure is calculated as:

(SBP+2DBP)/3. ***(SBP+2DBP)/3*** - This formula accurately calculates **mean arterial pressure (MAP)**, emphasizing the longer duration of diastole compared to systole in the cardiac cycle. - The diastolic blood pressure (**DBP**) is weighted twice as much as the systolic blood pressure (**SBP**) to reflect this physiological difference. *(DBP+2SBP)/3* - This formula incorrectly weighs the diastolic pressure less and the systolic pressure more, which does not reflect the **physiological duration of the cardiac cycle**. - While it attempts to average pressures, it does not correctly represent the **mean perfusion pressure**. *(SBP+3DBP)/2* - This formula is inaccurate for calculating MAP as the **denominator should be 3**, not 2, to account for the three components being averaged (one SBP and two DBP). - It also disproportionately weights **DBP** too high relative to the standard physiological formula. *(DBP+3SBP)/2* - This formula is incorrect as it applies an **excessive weighting to SBP** and uses an incorrect denominator. - It would yield a significantly higher and inaccurate value for **mean arterial pressure**.

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: Neurotransmitter involved in nigrostriatal pathway is?

Dopamine. ***Dopamine*** - The **nigrostriatal pathway** is a major dopaminergic pathway in the brain, originating in the **substantia nigra pars compacta** and projecting to the striatum. - It is crucial for the control of voluntary movement, and its degeneration is a hallmark of **Parkinson's disease**. *Serotonin* - Serotonin (5-HT) is primarily involved in mood, sleep, appetite, and cognition, and is not the primary neurotransmitter of the **nigrostriatal pathway**. - Serotonergic pathways originate in the **raphe nuclei** and project widely throughout the brain. *Acetylcholine* - Acetylcholine is a key neurotransmitter in the periphery (neuromuscular junction, autonomic nervous system) and in the central nervous system, involved in learning and memory. - Cholinergic neurons in the **basal forebrain** project to the cortex and hippocampus, but acetylcholine is not the neurotransmitter of the **nigrostriatal pathway**. *Norepinephrine* - Norepinephrine (noradrenaline) is involved in arousal, attention, and the fight-or-flight response, with pathways originating in the **locus coeruleus**. - While it plays a role in modulating motor circuits, it is not the main neurotransmitter of the **nigrostriatal pathway**.

Q: What is a key difference between smooth muscle and skeletal muscle physiology?

Troponin is absent in smooth muscle.. ***Troponin is absent in smooth muscle.*** * Smooth muscle contraction is regulated by **calcium-calmodulin complex** and subsequent activation of **myosin light chain kinase (MLCK)**, in contrast to skeletal muscle's reliance on the troponin-tropomyosin system. * **Troponin** is a calcium-binding protein found in skeletal and cardiac muscle, which plays a critical role in regulating muscle contraction by initiating the movement of tropomyosin, thereby exposing myosin-binding sites on actin. *Calcium is required for contraction.* * While calcium is indeed required for contraction in both smooth and skeletal muscle, the **mechanism of its action** differs, making this statement insufficiently discriminative as a *key difference*. * In both muscle types, an increase in intracellular **calcium** initiates the contractile process, but the downstream signaling pathways diverge significantly. *Myosin is essential for contraction.* * **Myosin** is a fundamental motor protein essential for contraction in *all* muscle types, including skeletal, cardiac, and smooth muscle. * This statement highlights a similarity, not a key difference, as **actin-myosin cross-bridge cycling** is the basis of force generation in all muscle tissues. *Potassium is required for contraction.* * **Potassium ions** are crucial for maintaining the resting membrane potential and for repolarization following an action potential, which is necessary for muscle excitability, but they do not directly trigger muscle contraction. * The influx of calcium (or release from intracellular stores) is the direct trigger for contraction, not potassium.

Q: When the tension in a muscle fibre is maximum, its length is called?

Optimum length. ***Optimum length*** - This is the muscle length at which the **maximum number of cross-bridges** can form between actin and myosin filaments. - At this length, the sarcomere allows for the **greatest overlap** of thick and thin filaments without excessive stretching or compression, leading to peak tension generation. *Equilibrium length* - This term usually refers to the **resting length** of a muscle fiber when no external forces are acting upon it. - At equilibrium, the tension generated by the muscle may not necessarily be at its maximum. *Initial length* - This is a general term that refers to the **starting length** of a muscle fiber before it contracts or is stretched. - It does not specifically denote the length at which maximum tension is achieved. *None of the options* - This option is incorrect because **optimum length** accurately describes the muscle length yielding maximum tension.

Q: Which of the following is the MOST accurate statement about CSF?

Formed by the choroid plexus in the ventricles.. ***Formed by the choroid plexus in the ventricles.*** * The **choroid plexus**, located in the ventricles of the brain, is primarily responsible for the production of **cerebrospinal fluid (CSF)**. * Specialized epithelial cells of the choroid plexus filter blood plasma to produce CSF, which then circulates through the central nervous system. *Normally contains no neutrophils* * Normal CSF should contain **virtually no neutrophils**; their presence typically indicates an inflammatory or infectious process, such as **bacterial meningitis**. * While normal CSF doesn't have neutrophils, this option isn't as broadly accurate as the choroid plexus statement because the presence of other cell types like lymphocytes in small numbers is normal. *pH is less than that of plasma* * The pH of CSF is typically **slightly lower than that of plasma** (around 7.31 compared to 7.40), but the statement "less than" is broad and the degree of difference can be variable and is a less defining characteristic than its formation site. * This slight difference in pH is important for regulating **respiration** through chemoreceptors, but it's not the most accurate or fundamental statement about CSF properties. *Removal of CSF during dural tap can cause a headache due to the change in pressure.* * A **post-dural puncture headache** (PDPH) is a well-known complication of a dural tap (lumbar puncture), caused by the leakage of CSF from the puncture site, leading to **intracranial hypotension**, not simply a change in pressure. * This decrease in CSF volume and pressure causes a traction on pain-sensitive structures within the cranium, resulting in a headache that is typically **worse when upright** and relieved by lying down.

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.

Question 1

Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?

Accepted Answer

An increase in arterial carbon dioxide tension

Answer

A decrease in arterial oxygen content

Answer

A decrease in arterial blood pressure

Answer

A decrease in arterial oxygen tension

Question 2

Transpulmonary pressure is the difference between:

Accepted Answer

Pressure in alveoli and intrapleural pressure

Answer

The pressure in the bronchus and atmospheric pressure

Answer

The difference between atmospheric pressure and intrapleural pressure

Answer

The difference between atmospheric pressure and intraalveolar pressure

Question 3

Which of the following components are included in microcirculation?

Accepted Answer

Capillaries, venules, and arterioles

Answer

Capillaries

Answer

Aorta

Answer

Arteries and veins

Question 4

Mean arterial pressure is calculated as:

Accepted Answer

(SBP+2DBP)/3

Answer

(DBP+3SBP)/2

Answer

(SBP+3DBP)/2

Answer

(DBP+2SBP)/3

Question 5

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 6

Neurotransmitter involved in nigrostriatal pathway is?

Accepted Answer

Dopamine

Answer

Acetylcholine

Answer

Serotonin

Answer

Norepinephrine

Question 7

What is a key difference between smooth muscle and skeletal muscle physiology?

Accepted Answer

Troponin is absent in smooth muscle.

Answer

Calcium is required for contraction.

Answer

Myosin is essential for contraction.

Answer

Potassium is required for contraction.

Question 8

When the tension in a muscle fibre is maximum, its length is called?

Accepted Answer

Optimum length

Answer

None of the options

Answer

Initial length

Answer

Equilibrium length

Question 9

Which of the following is the MOST accurate statement about CSF?

Accepted Answer

Formed by the choroid plexus in the ventricles.

Answer

Normally contains no neutrophils

Answer

pH is less than that of plasma

Answer

Removal of CSF during dural tap can cause a headache due to the change in pressure.

Question 10

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

NEET-PG 2012 — Physiology