NEET-PG 2013 - Physiology Practice Questions

Q: Which of the following substances has the same concentration in cerebrospinal fluid (CSF) and plasma?

Cl. ***Cl*** - **Chloride ions (Cl-)** have the **closest concentration** between CSF and plasma among the listed options, with a CSF-to-plasma ratio of approximately 1.1-1.15. - CSF chloride is **slightly higher** than plasma chloride (CSF: ~120-130 mEq/L; Plasma: ~100-110 mEq/L) because chloride ions freely cross the **blood-brain barrier** and help maintain **electroneutrality** in CSF due to the low protein content. - The elevated chloride compensates for the absence of negatively charged proteins in CSF, making it the **best answer** among the given options. *Glucose* - **Glucose** concentration in CSF is approximately **60-70%** of plasma glucose concentration (CSF: 50-80 mg/dL; Plasma: 70-110 mg/dL). - Transport across the **blood-brain barrier** occurs via **GLUT1 transporters**, which are tightly regulated to meet brain metabolic demands. *Ca* - **Calcium (Ca2+)** concentration in CSF is **significantly lower** than in plasma (CSF: ~2.1-2.5 mg/dL; Plasma: ~8.5-10.5 mg/dL). - Only the **ionized, unbound fraction** can cross the blood-brain barrier, as protein-bound calcium cannot pass through. *HCO3* - **Bicarbonate (HCO3-)** concentration in CSF is typically **slightly lower** than in plasma (CSF: ~20-25 mEq/L; Plasma: ~22-28 mEq/L). - Active regulation maintains **CSF pH** and CO2 buffering capacity independent of plasma bicarbonate levels.

Q: Cell bodies of orexigenic neurons are present in?

Lateral hypothalamic area. ***Lateral hypothalamic area*** - The **lateral hypothalamic area** (LHA) contains neurons that produce **orexin (hypocretin)**, a neuropeptide critical for promoting appetite and wakefulness. - Stimulation of the LHA leads to increased food seeking and consumption, earning it the moniker "**feeding center**." *Dorsal raphe* - The **dorsal raphe nucleus** is a key source of **serotonin** in the brain, involved in mood, sleep-wake cycles, and appetite regulation (often promoting satiety). - It does not primarily house orexigenic neurons that directly stimulate appetite. *Locus coerulus* - The **locus coeruleus** is the primary source of **norepinephrine** in the brain, playing a significant role in arousal, attention, and stress response. - While it modulates appetitive behaviors indirectly, its neurons are not the primary orexigenic cell bodies. *Hippocampus* - The **hippocampus** is crucial for **learning, memory formation**, and spatial navigation. - It is not directly involved in the primary neural circuits that control hunger and satiety through orexigenic neuropeptides.

Q: Cushing reflex is associated with all except?

Hypotension. ***Hypotension*** - The **Cushing reflex** is a compensatory response to increased intracranial pressure (ICP) aiming to maintain cerebral perfusion, which typically involves **hypertension**, not hypotension. - While prolonged or severe ICP can lead to decompensation and eventual hypotension, it is not a direct component of the reflex itself. *Increased intracranial pressure* - The **Cushing reflex** is triggered by an elevation in **intracranial pressure (ICP)**, as the body attempts to maintain blood flow to the brain. - This increased ICP reduces cerebral perfusion pressure, prompting a systemic response to raise mean arterial pressure. *Bradycardia* - **Bradycardia** is a classic component of the **Cushing reflex**, occurring as a compensatory response to the reflex hypertension. - The increased arterial blood pressure stimulates carotid and aortic baroreceptors, leading to a vagal response that slows the heart rate. *Irregular respiration* - **Irregular respiration** is another key component of the **Cushing reflex**, often manifesting as **Cheyne-Stokes breathing** or **ataxic breathing**. - This respiratory dysregulation is due to direct compression and dysfunction of the brainstem, specifically the medullary respiratory centers, caused by increased ICP.

Q: Which of the following does not have sympathetic noradrenergic fibers?

Sweat gland. ***Sweat gland*** - While sweat glands are innervated by the **sympathetic nervous system**, their postganglionic fibers are **cholinergic**, releasing **acetylcholine** rather than noradrenaline. - This is an important exception where sympathetic stimulation leads to acetylcholine release, causing sweating. *Blood vessels* - Most blood vessels, particularly resistance vessels such as **arterioles**, receive substantial **sympathetic noradrenergic innervation** that causes vasoconstriction. - This sympathetic tone is crucial for regulating **blood pressure** and distributing blood flow. *Heart* - The heart is richly innervated by **sympathetic noradrenergic fibers** that increase **heart rate**, **contractility**, and **conduction velocity** via beta-1 adrenergic receptors. - This makes noradrenaline a key neurotransmitter in the sympathetic regulation of cardiac function. *Eye* - The eye receives sympathetic noradrenergic innervation primarily to the **dilator pupillae muscle**, causing **mydriasis** (pupil dilation) upon activation. - These fibers also contribute to the sympathetic control of the **tarsal muscle** (Müller's muscle) in the eyelid.

Q: All should be features of a substance to measure GFR, except?

Freely reabsorbed. ***Freely reabsorbed*** - A substance used to measure GFR should **not be reabsorbed** by the kidney tubules. If it were reabsorbed, the amount excreted in the urine would be less than the amount filtered, leading to an **underestimation of GFR**. - The ideal GFR marker is **neither reabsorbed nor secreted**, ensuring that its excretion rate directly reflects the filtration rate. *Freely filtered across the glomerulus membrane* - For a substance to accurately measure GFR, it must be **freely filtered** from the blood into the Bowman's capsule, without any restriction due to its size or charge. - This ensures that its concentration in the glomerular filtrate is the same as in the plasma, allowing for a direct calculation of the filtration rate. *Not secreted by kidney* - An ideal GFR marker should **not be secreted** by the renal tubules, as active secretion would add to the amount excreted in the urine, leading to an **overestimation of GFR**. - This property, along with not being reabsorbed, ensures that the amount of the substance appearing in the urine solely reflects the amount filtered. *None of the options* - This option is incorrect because there is a definitive feature listed among the choices that is *not* a characteristic of an ideal GFR marker. The ability to be "freely reabsorbed" is a disqualifying trait.

Q: What is the normal range of renal blood flow in humans?

1 to 1.2 L/min. ***1 to 1.2 L/min*** - The **kidneys** receive a substantial portion of the **cardiac output**, typically around 20-25%, to perform their filtration and regulatory functions. - This translates to an absolute renal blood flow of approximately **1000 to 1200 mL/min**, or **1 to 1.2 liters per minute**. - This represents the normal physiological range for healthy adults at rest. *1.5 to 2 L/min* - This range is **higher than the normal physiological** renal blood flow. - While renal blood flow can be influenced by various factors, sustained flow in this range would typically be considered **above the average baseline** for healthy individuals. *2 to 2.5 L/min* - This range significantly **exceeds the typical** renal blood flow observed in healthy humans. - Such high flow rates would be **unusual** and are not representative of normal renal perfusion. *2.5 to 3 L/min* - This range represents an **extremely high** renal blood flow, far beyond what is considered normal. - Sustained perfusion at this level would be **pathological** or indicative of an experimental setting rather than a physiological state.

Q: Which of the following is the most accurate measure of Glomerular Filtration Rate (GFR)?

Iothalamate Clearance. ***Iothalamate Clearance*** - **Iothalamate clearance** is considered the **gold standard** for directly measuring GFR in clinical practice because it is a substance that is freely filtered by the glomerulus and is neither reabsorbed nor secreted by the renal tubules. - This method provides the most accurate and precise assessment of kidney function by quantifying the actual GFR, often used in research settings or for precise diagnosis. - **Note:** Inulin clearance is the traditional reference standard, but iothalamate is more practical and widely used clinically as it can be measured using radioactive or non-radioactive methods. *Serum creatinine* - **Serum creatinine** is a commonly used biomarker but is an **imperfect measure** of GFR because it can be influenced by factors like muscle mass, diet, and certain medications. - Its levels can remain within the normal range even when GFR has significantly decreased, especially in the early stages of kidney disease. *Cystatin C* - **Cystatin C** is a protein produced by most nucleated cells and is also freely filtered by the glomerulus, with less influence from muscle mass and diet compared to creatinine. - While considered a better marker than serum creatinine, it is still an **estimated measure** and is more expensive and less widely available than creatinine, and can be affected by inflammation or thyroid dysfunction. *Creatinine Clearance* - **Creatinine clearance** (often estimated using urine and serum creatinine levels over a timed collection) attempts to approximate GFR but can be **inaccurate** due to incomplete urine collection and tubular secretion of creatinine. - The **creatinine secretion** by the renal tubules leads to an overestimation of the true GFR, making it less accurate than direct measurement methods.

Q: Normal renal threshold for glucose is at plasma glucose level ?

200 mg/dl. ** _200 mg/dl_ ** - The **renal threshold for glucose** represents the plasma glucose concentration at which the kidneys begin to excrete glucose into the urine. - This typically occurs when the glucose level exceeds the reabsorptive capacity of the renal tubules, usually around **180-200 mg/dL**. * _100 mg/dl_ * - A plasma glucose level of **100 mg/dL** is within the normal fasting range and well below the renal threshold. - At this level, virtually all filtered glucose is reabsorbed by the renal tubules, and no glucose appears in the urine. * _300 mg/dl_ * - A plasma glucose level of **300 mg/dL** is significantly above the renal threshold for glucose. - At this concentration, the kidney's reabsorptive capacity is overwhelmed, leading to substantial **glucosuria** (glucose in the urine). * _400 mg/dl_ * - A plasma glucose level of **400 mg/dL** is severely elevated and far exceeds the renal threshold. - This level would result in significant glucose excretion in the urine and is indicative of uncontrolled hyperglycemia, as seen in **diabetes mellitus**.

Q: What is the primary solute responsible for the hyperosmolarity of the renal medulla?

Na. ***Na*** - **Sodium (Na+), along with chloride**, is the primary solute responsible for establishing the **corticomedullary osmotic gradient** in the renal medulla. - Actively reabsorbed in the **thick ascending limb of the loop of Henle** via the Na-K-2Cl cotransporter, creating hyperosmolarity in the outer medulla. - NaCl accounts for the majority of osmolality in the **outer medulla** and provides the foundation for the countercurrent multiplication system. - While **urea contributes significantly to inner medullary hyperosmolarity** (especially during antidiuresis), **sodium chloride** is considered the **primary driving force** for the overall medullary concentration gradient. *K* - **Potassium (K+)** is primarily involved in maintaining intracellular fluid balance and cellular membrane potentials. - While K+ is reabsorbed in the loop of Henle (via Na-K-2Cl cotransporter), it does not accumulate in the medullary interstitium to contribute significantly to hyperosmolarity. *urea* - **Urea** contributes substantially to hyperosmolarity, particularly in the **inner medulla** (accounting for ~40-50% of inner medullary osmolality). - Through **urea recycling** (collecting duct → medullary interstitium → thin limbs), it enhances urinary concentration, especially during water deprivation. - However, the **initial establishment** of the osmotic gradient depends on **NaCl reabsorption** in the ascending limb, making sodium the primary solute. *Cl* - **Chloride (Cl-)** is reabsorbed together with sodium via the Na-K-2Cl cotransporter in the thick ascending limb. - Functionally, **NaCl works as a unit** to create medullary hyperosmolarity, so chloride and sodium are inseparable in this process. - Among the listed options, **sodium** represents this NaCl contribution as the cation driving active transport.

Question 1

Which of the following substances has the same concentration in cerebrospinal fluid (CSF) and plasma?

Accepted Answer

Cl

Answer

Glucose

Answer

Ca

Answer

HCO3

Question 2

Cell bodies of orexigenic neurons are present in?

Accepted Answer

Lateral hypothalamic area

Answer

Dorsal raphe

Answer

Locus coeruleus

Answer

Hippocampus

Question 3

Cushing reflex is associated with all except?

Accepted Answer

Hypotension

Answer

Irregular respiration

Answer

Increased intracranial pressure

Answer

Bradycardia

Question 4

Which of the following does not have sympathetic noradrenergic fibers?

Accepted Answer

Sweat gland

Answer

Heart

Answer

Eye

Answer

Blood vessels

Question 5

All should be features of a substance to measure GFR, except?

Accepted Answer

Freely reabsorbed

Answer

Not secreted by kidney

Answer

Freely filtered across the glomerulus membrane

Answer

None of the options

Question 6

What is the normal range of renal blood flow in humans?

Accepted Answer

1 to 1.2 L/min

Answer

1.5 to 2 L/min

Answer

2 to 2.5 L/min

Answer

2.5 to 3 L/min

Question 7

Which of the following is the primary mechanism that drives sodium reabsorption in the proximal tubule?

Accepted Answer

Active sodium transport via the Na+-K+-ATPase pump at the basolateral membrane.

Answer

Sodium reabsorption through cotransport with amino acids at the luminal membrane.

Answer

Sodium reabsorption through cotransport with glucose at the luminal membrane.

Answer

Sodium reabsorption through countertransport with hydrogen ions at the luminal membrane.

Question 8

Which of the following is the most accurate measure of Glomerular Filtration Rate (GFR)?

Accepted Answer

Iothalamate Clearance

Answer

Cystatin C

Answer

Serum creatinine

Answer

Creatinine Clearance

Question 9

Normal renal threshold for glucose is at plasma glucose level ?

Accepted Answer

200 mg/dl

Answer

100 mg/dl

Answer

300 mg/dl

Answer

400 mg/dl

Question 10

What is the primary solute responsible for the hyperosmolarity of the renal medulla?

Accepted Answer

Na

Answer

urea

Answer

K

Answer

Cl

NEET-PG 2013 — Physiology