NEET-PG 2013 Practice Questions

Q: What is the approximate number of cones in the human retina?

Approximately 3-5 million cones. Approximately 3-5 million cones - The human retina contains roughly **4.5 million cones**, concentrated in the **fovea**, which is responsible for **high-acuity vision** and color perception [1]. - Cones are light-sensitive cells that detect **fine details** and are essential for vision in **bright light conditions** [1]. *Approximately 10-20 million cones* - This range is significantly higher than the actual number of cones found in the human retina. - While there are millions of photoreceptors, the *majority are rods*, not cones [1]. *Approximately 25-50 million cones* - This figure vastly *overestimates* the number of cones in the human eye. - The total number of photoreceptor cells (rods and cones combined) in the retina typically ranges from **100-125 million** [1]. *Approximately 50-100 million cones* - This range is incorrect as it refers more closely to the *total number of rods* in the human retina, which is about **90-120 million** [1]. - Cones constitute a much smaller proportion of the total photoreceptor population [1].

Q: Which of the following plant components is not fermented by gastrointestinal microorganisms?

Lignin. ***Lignin*** - **Lignin** is a complex polymer found in plant cell walls that is highly resistant to degradation by digestive enzymes and microbial fermentation in the gastrointestinal tract. - Its complex, cross-linked structure makes it **non-fermentable** by the microorganisms typically present in the human gut. *Cellulose* - **Cellulose** is a major component of plant cell walls and is a type of dietary fiber that can be fermented by certain gut bacteria. - While humans lack the enzymes to digest cellulose, colonic microorganisms possess cellulases that break it down into **short-chain fatty acids (SCFAs)**. *Hemicellulose* - **Hemicellulose** is a diverse group of plant polysaccharides that are a significant source of fermentable fiber for gut microbiota. - It is readily broken down by gastrointestinal bacteria into **SCFAs** and gases, contributing to colonic health. *Pectin* - **Pectin** is a soluble dietary fiber found in fruits and vegetables, known for its gel-forming properties. - It is highly fermentable by gut microorganisms, leading to the production of **SCFAs** like butyrate, propionate, and acetate.

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: 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: 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 most important extracellular buffer?

Bicarbonates. ***Bicarbonates*** - The **bicarbonate buffer system** is the most important extracellular buffer because its components (carbonic acid and bicarbonate) are present in high concentrations and their levels can be regulated by both the lungs (CO2 excretion) and the kidneys (bicarbonate reabsorption/secretion). - Its pKa (6.1) makes it an effective buffer against metabolically produced acids, which frequently challenge blood pH. *Phosphate buffer* - The **phosphate buffer system** is more important as an intracellular buffer and in renal tubular fluid due to its higher concentration in these compartments. - Its concentration in the extracellular fluid is relatively low compared to bicarbonate, limiting its capacity as the primary extracellular buffer. *Plasma protein buffer* - **Plasma proteins**, particularly albumin, have numerous ionizable groups and contribute to buffering in the extracellular fluid. - However, their overall buffering capacity is less significant than that of the bicarbonate system due to lower concentration compared to bicarbonate and less dynamic regulation. *Ammonium buffer* - The **ammonium buffer system** (ammonia/ammonium) is primarily important for acid-base regulation by the kidneys, where it plays a critical role in excreting excess acid, particularly in chronic acidosis. - It is not a major extracellular fluid buffer in the systemic circulation under normal physiological conditions.

Q: Which hormone is secreted by the "Delta cells" of the stomach?

Somatostatin. ***Somatostatin*** - **Delta cells (D cells)** in the stomach and pancreas secrete **somatostatin**, a potent inhibitory hormone. - Somatostatin **inhibits the release of gastrin**, histamine, secretin, cholecystokinin, and gastric acid secretion, acting as a "universal off switch." *Cholecystokinin* - **Cholecystokinin (CCK)** is primarily secreted by **I cells** in the duodenum and jejunum. - Its main functions include stimulating gallbladder contraction and pancreatic enzyme secretion. *Gastrin-releasing peptide* - **Gastrin-releasing peptide (GRP)**, also known as **bombesin**, is a neuropeptide released from **enteric neurons**. - It stimulates the release of **gastrin** from G cells. *Secretin* - **Secretin** is secreted by **S cells** in the duodenum in response to acidic chyme entering the small intestine. - Its primary role is to stimulate the pancreas to release **bicarbonate-rich fluid** to neutralize gastric acid.

Q: What is the term for the salivation of a dog in response to a bell after it has been conditioned with food?

Conditioned reflex. ***Conditioned reflex (Conditioned Response)*** - A **conditioned reflex** is a learned response developed through **classical conditioning**, where a previously neutral stimulus becomes associated with an unconditioned stimulus. - In Pavlov's experiment: The **bell (Conditioned Stimulus)** is paired with **food (Unconditioned Stimulus)**, leading the dog to eventually salivate to the bell alone. - The **salivation to the bell** is the **Conditioned Response (CR)** - a learned behavior, not an innate one. *Reinforcement* - **Reinforcement** is a concept from **operant conditioning** (Skinner), not classical conditioning. - It involves strengthening a behavior by providing a consequence (reward or punishment) after the behavior occurs. - This describes a process that increases behavior frequency, not the learned response itself. *Habituation* - **Habituation** is a decrease in response to a repeatedly presented stimulus that proves to be irrelevant. - The organism learns to **ignore** the stimulus over time (e.g., getting used to background noise). - This is the opposite of developing a new learned response. *Innate reflex* - An **innate reflex** is an **unlearned, inborn** automatic response (e.g., salivation directly to food, pupillary reflex, sucking reflex). - The dog's salivation **to food** is innate, but salivation **to the bell** is learned through conditioning.

Question 1

What is the approximate number of cones in the human retina?

Accepted Answer

Approximately 3-5 million cones

Answer

Approximately 25-50 million cones

Answer

Approximately 50-100 million cones

Answer

Approximately 10-20 million cones

Question 2

Which of the following plant components is not fermented by gastrointestinal microorganisms?

Accepted Answer

Lignin

Answer

Cellulose

Answer

Hemicellulose

Answer

Pectin

Question 3

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 4

Cushing reflex is associated with all except?

Accepted Answer

Hypotension

Answer

Irregular respiration

Answer

Increased intracranial pressure

Answer

Bradycardia

Question 5

Which of the following does not have sympathetic noradrenergic fibers?

Accepted Answer

Sweat gland

Answer

Heart

Answer

Eye

Answer

Blood vessels

Question 6

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 7

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 8

What is the most important extracellular buffer?

Accepted Answer

Bicarbonates

Answer

Phosphate buffer

Answer

Plasma protein buffer

Answer

Ammonium buffer

Question 9

Which hormone is secreted by the "Delta cells" of the stomach?

Accepted Answer

Somatostatin

Answer

Cholecystokinin

Answer

Gastrin-releasing peptide

Answer

Secretin

Question 10

What is the term for the salivation of a dog in response to a bell after it has been conditioned with food?

Accepted Answer

Conditioned reflex

Answer

Reinforcement

Answer

Habituation

Answer

Innate reflex

NEET-PG 2013

Anatomy

Biochemistry

Physiology

Psychiatry