NEET-PG 2012 - Physiology Practice Questions

Q: Which of the following hormones does not mediate its action through cAMP?

Estrogen. ***Estrogen*** - **Estrogen** is a **steroid hormone** that mediates its action by binding to intracellular receptors, forming a complex that directly influences gene transcription. - Steroid hormones, due to their **lipophilicity**, can cross the cell membrane and do not typically rely on cell surface receptors or second messengers like cAMP. *Glucagon* - **Glucagon** acts on a **G protein-coupled receptor (GPCR)**, specifically a Gs-coupled receptor, leading to the activation of adenylyl cyclase. - This activation increases the intracellular concentration of **cAMP**, which then activates protein kinase A to mediate its effects, primarily on glucose metabolism. *Follicle stimulating hormone* - **FSH** binds to a **GPCR** on target cells, activating the Gs protein pathway. - This activation stimulates **adenylyl cyclase** and increases intracellular **cAMP** levels, which are critical for its role in gamete development. *Luteinizing hormone* - **LH**, like FSH, binds to a cell surface **GPCR** that activates the Gs protein. - This leads to the stimulation of **adenylyl cyclase** and an increase in **cAMP**, mediating its effects on steroidogenesis and ovulation.

Q: In which condition is venous blood most commonly observed to have a high hematocrit in routine clinical practice?

Dehydration. Dehydration - In **dehydration**, the total body water is reduced, leading to a decrease in plasma volume [1, 5]. This concentrates the red blood cells, resulting in a relatively **high hematocrit**. [3] - This is a common finding as the body attempts to conserve fluid, making it a primary cause of **elevated hematocrit** in clinical practice. *Anemia* - **Anemia** is characterized by a decrease in the number of red blood cells or a reduced hemoglobin concentration, which would lead to a **low hematocrit**, not a high one [2]. - This condition involves insufficient oxygen-carrying capacity due to a deficiency in red blood cells or hemoglobin [2]. *Hypervolemia* - **Hypervolemia** describes an excess of fluid in the blood, which would dilute the blood components, leading to a relatively **low hematocrit** [1]. - This condition is often associated with conditions like heart failure or kidney disease, where fluid retention is common. *Acute blood loss* - In **acute blood loss**, the loss of whole blood immediately after the event would initially reduce both red blood cells and plasma proportionally, not immediately raising hematocrit [2]. - As the body attempts to compensate by shifting extravascular fluid into the circulation, this would further dilute the blood, eventually leading to a **decreased hematocrit** [2].

Q: Lesion of preoptic nucleus of hypothalamus is associated with which of the following conditions?

Hyperthermia. ***Hyperthermia*** - The **preoptic nucleus** of the anterior hypothalamus is the primary **heat-loss center** containing warm-sensitive neurons. - Lesion of this area impairs **heat dissipation mechanisms** (sweating, cutaneous vasodilation), preventing the body from lowering its temperature. - Results in **hyperthermia** - a pathological elevation of core body temperature due to failure of heat dissipation, not a change in set point. - This is the **most specific and clinically accurate** term for this condition. *Impaired thermoregulation* - While technically true, this is too **broad and non-specific**. - Impaired thermoregulation could refer to inability to either increase or decrease temperature. - In medical terminology, we use more specific terms like "hyperthermia" to describe the actual clinical condition. *Increased body temperature* - This is a **general descriptive term** rather than a specific clinical diagnosis. - While the body temperature is indeed increased, **hyperthermia** is the precise medical term that indicates the mechanism (impaired heat dissipation). - Less specific than "hyperthermia" for exam purposes. *Normal thermoregulation* - Clearly incorrect - a lesion in the primary thermoregulatory center would **abolish normal temperature control**. - The preoptic nucleus is essential for detecting and responding to temperature changes.

Q: Tetanic contraction is due to accumulation of?

Ca 2+ . ***Ca 2+ *** - **Tetanic contraction** results from a rapid succession of muscle stimulations, leading to the sustained elevation of **intracellular calcium (Ca 2+ )** levels. - This persistent high Ca 2+ concentration in the sarcoplasm allows for continuous binding to **troponin**, maintaining the activation of cross-bridge cycling. *Na + * - **Sodium (Na + )** influx is primarily responsible for the **depolarization** of the muscle cell membrane, leading to an **action potential**. - While essential for initiating the contraction, Na + accumulation itself does not directly cause the sustained high Ca 2+ levels characteristic of tetany. *K + * - **Potassium (K + )** efflux is crucial for the **repolarization** of the muscle cell membrane after an action potential. - Accumulation of K + in the extracellular space can contribute to muscle fatigue and reduce excitability, but it does not directly lead to tetanic contraction. *Cl - * - **Chloride (Cl - )** ions play a significant role in stabilizing the resting membrane potential and contributing to muscle **repolarization**, particularly in skeletal muscle. - While important for muscle function, changes in Cl - concentration do not directly cause the sustained Ca 2+ release required for tetanic contraction.

Q: Nonshivering thermogenesis in adults is due to:

Brown fat between the shoulders. ***Brown fat between the shoulders*** - In adults, the primary **effector tissue** for **non-shivering thermogenesis** is **brown adipose tissue (BAT)**, with major depots located between the shoulders, around the neck, and along the spine. - **BAT** contains specialized mitochondria with **uncoupling protein 1 (UCP1)** that uncouples oxidative phosphorylation, generating heat instead of ATP. - This is the tissue where non-shivering thermogenesis actually occurs, making it the direct answer to what non-shivering thermogenesis is "due to." *Noradrenaline* - **Noradrenaline** is the key neurotransmitter that **activates brown fat** via **β3-adrenergic receptors** to initiate non-shivering thermogenesis. - While noradrenaline is the **trigger/stimulus**, the actual heat production occurs in brown adipose tissue. - Noradrenaline itself does not produce heat directly; it acts as the signal that activates the thermogenic machinery in BAT. *Thyroid hormone* - **Thyroid hormone** increases **basal metabolic rate** and can potentiate the thermogenic response by upregulating UCP1 expression in brown fat. - Its role is **permissive and long-term** rather than being the immediate effector of acute non-shivering thermogenesis. - It modulates overall cellular metabolism but is not the primary mechanism for rapid heat generation in cold exposure. *Muscle metabolism* - **Muscle contraction** during shivering generates heat through increased ATP hydrolysis, which is **shivering thermogenesis**. - **Non-shivering thermogenesis** specifically refers to heat production **without muscle contraction**, making muscle metabolism the mechanism for shivering, not non-shivering, thermogenesis.

Q: What is the primary physiological effect of increased 2,3-DPG on hemoglobin?

Decreased affinity of hemoglobin to oxygen. ***Decreased affinity of hemoglobin to oxygen*** - **2,3-Diphosphoglycerate (2,3-DPG)** binds to the beta subunits of deoxyhemoglobin, stabilizing the **deoxygenated state** and thus **reducing hemoglobin's affinity for oxygen**. - This is the **primary molecular mechanism** by which 2,3-DPG exerts its effect, facilitating **oxygen unloading** in peripheral tissues. - This decreased affinity manifests graphically as a **right shift** in the oxygen-hemoglobin dissociation curve. *Increased affinity of hemoglobin to oxygen* - This is incorrect because 2,3-DPG specifically works to **decrease hemoglobin's affinity** for oxygen, promoting oxygen release. - Increased affinity would mean oxygen is held more tightly, which is counterproductive for **oxygen delivery** to tissues. *Left shift of oxygen-hemoglobin dissociation curve* - A **left shift** indicates **increased affinity** of hemoglobin for oxygen, meaning oxygen is held more tightly. - Since 2,3-DPG decreases affinity, it causes a **right shift**, not a left shift. *Right shift of oxygen-hemoglobin dissociation curve* - While this is the **graphical representation** of 2,3-DPG's effect, it is a **consequence** of the primary molecular mechanism (decreased affinity). - A right shift signifies that for any given partial pressure of oxygen, hemoglobin is **less saturated** with oxygen, reflecting the decreased affinity caused by 2,3-DPG binding.

Q: Which of the following statements about volume receptors is NOT true?

They are located in carotid sinus. ***They are located in carotid sinus*** - Volume receptors, primarily **atrial stretch receptors** and receptors in the **pulmonary vessels**, are located in the low-pressure areas of the circulation, not the carotid sinus. - The carotid sinus primarily contains **baroreceptors** which detect changes in arterial pressure, not blood volume. *They are low pressure receptors* - This statement is true; volume receptors are indeed **low-pressure receptors** found in the atria and great veins. - They primarily monitor **extracellular fluid volume** and central venous pressure. *They provide afferents for thirst control* - This statement is true; when blood volume decreases, the firing rate of these receptors decreases, signaling the **central nervous system** to stimulate thirst. - This is an important mechanism for regulating **fluid intake** and maintaining hydration. *They mediate vasopressin release* - This statement is true; a decrease in blood volume reduces the afferent signaling from volume receptors, which consequently stimulates the release of **vasopressin (ADH)**. - Vasopressin then increases **water reabsorption** in the kidneys to conserve fluid.

Q: Gas exchange in tissues takes place at?

Capillary. ***Capillary*** - **Capillaries** are the smallest and most numerous blood vessels, with very thin walls (only one cell thick), which facilitates the efficient exchange of gases, nutrients, and waste products between blood and tissues. - Their extensive network ensures close proximity to nearly every cell in the body, maximizing the surface area and minimizing the diffusion distance for **gas exchange**. *Artery* - Arteries carry **oxygenated blood** away from the heart to the tissues but have thick, muscular walls designed for high pressure and transport, not for direct exchange with tissues. - They branch into smaller arterioles, which then lead to capillaries, making them a conduit rather than an exchange site. *Vein* - Veins carry **deoxygenated blood** back to the heart from the tissues and have relatively thin walls compared to arteries but are still too thick for efficient gas exchange. - They primarily serve as blood return vessels and reservoirs. *Venules* - Venules are small blood vessels that merge from capillaries and eventually combine to form veins; they primarily function in collecting blood from capillary beds. - While slightly more permeable than larger veins, their main role is still collection and transport, not the extensive gas exchange facilitated by capillaries.

Q: Growth hormone level is highest during

Sleep. ***Sleep*** - Growth hormone (GH) secretion is **pulsatile**, with the largest and most consistent pulses occurring during **slow-wave sleep** (deep sleep). - This nocturnal surge contributes significantly to the overall daily GH output and is crucial for growth and metabolic regulation. *Hypoglycemia* - While **hypoglycemia** is a potent stimulus for GH release, it is an acute stress response rather than a state where GH levels are consistently highest. - The body's primary response to hypoglycemia is to raise blood glucose, and while GH helps, it is not the peak physiological secretion time. *Fasting* - **Prolonged fasting** can increase GH secretion as a mechanism to mobilize fat stores and conserve glucose. - However, the peak levels due to fasting are generally less pronounced than the dramatic surge observed during deep sleep. *Exercise* - **Vigorous exercise** can acutely stimulate GH release, particularly with sustained effort. - This increase is typically transient and not as high or consistently cyclical as the secretion during nocturnal sleep.

Q: Which part of the brain is responsible for setting posture before planned movement?

Supplementary motor cortex. ***Supplementary motor cortex*** - The **supplementary motor cortex (SMA)** is responsible for **anticipatory postural adjustments** that occur before voluntary movements - It plays a key role in **internal generation and planning of complex motor sequences** - SMA activation precedes movement, ensuring **postural stability and coordination** - Essential for **bilateral coordination** and **motor programming** *Premotor cortex* - The **premotor cortex** is primarily involved in **externally guided movements** and selection of movements based on sensory cues - While it participates in motor planning, it is more focused on **sensory-motor integration** rather than anticipatory postural control *Motor cortex* - The **primary motor cortex** executes voluntary movements by sending signals directly to spinal motor neurons - Responsible for **fine motor control** and determining the **force and direction** of muscle contractions - Functions in **movement execution** rather than preparatory postural adjustments *Frontal eye fields* - The **frontal eye fields** control **voluntary saccadic eye movements** and visual attention - Not involved in trunk or limb **postural preparation** for planned movements

Question 1

Which of the following hormones does not mediate its action through cAMP?

Accepted Answer

Estrogen

Answer

Glucagon

Answer

Follicle stimulating hormone

Answer

Luteinizing hormone

Question 2

In which condition is venous blood most commonly observed to have a high hematocrit in routine clinical practice?

Accepted Answer

Dehydration

Answer

Anemia

Answer

Hypervolemia

Answer

Acute blood loss

Question 3

Lesion of preoptic nucleus of hypothalamus is associated with which of the following conditions?

Accepted Answer

Hyperthermia

Answer

Impaired thermoregulation

Answer

Increased body temperature

Answer

Normal thermoregulation

Question 4

Tetanic contraction is due to accumulation of?

Accepted Answer

Ca<sup>2+</sup>

Answer

Na+

Answer

K+

Answer

Cl<sup>-</sup>

Question 5

Nonshivering thermogenesis in adults is due to:

Accepted Answer

Brown fat between the shoulders

Answer

Muscle metabolism

Answer

Thyroid hormone

Answer

Noradrenaline

Question 6

What is the primary physiological effect of increased 2,3-DPG on hemoglobin?

Accepted Answer

Decreased affinity of hemoglobin to oxygen

Answer

Increased affinity of hemoglobin to oxygen

Answer

Left shift of oxygen-hemoglobin dissociation curve

Answer

Right shift of oxygen-hemoglobin dissociation curve

Question 7

Which of the following statements about volume receptors is NOT true?

Accepted Answer

They are located in carotid sinus

Answer

They are low pressure receptors

Answer

They mediate vasopressin release

Answer

They provide afferents for thirst control

Question 8

Gas exchange in tissues takes place at?

Accepted Answer

Capillary

Answer

Artery

Answer

Vein

Answer

Venules

Question 9

Growth hormone level is highest during

Accepted Answer

Sleep

Answer

Hypoglycemia

Answer

Fasting

Answer

Exercise

Question 10

Which part of the brain is responsible for setting posture before planned movement?

Accepted Answer

Supplementary motor cortex

Answer

Motor cortex

Answer

Frontal eye fields

Answer

Premotor cortex

NEET-PG 2012 — Physiology