What physiological mechanism leads to an increase in cardiac output?
Slowest blood flow is seen in?
P wave is due to:
Lowest pH is seen in which of the gastrointestinal secretions?
Which receptor is primarily stimulated in response to moderate cold temperatures?
Which hormone is secreted by the "Delta cells" of the stomach?
What is the primary solute responsible for the hyperosmolarity of the renal medulla?
Normal renal threshold for glucose is at plasma glucose level ?
Which of the following is the most accurate measure of Glomerular Filtration Rate (GFR)?
Which type of muscle fibers has fewer mitochondria?
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 21: What physiological mechanism leads to an increase in cardiac output?
- A. Inhalation
- B. Increased myocardial contractility (Correct Answer)
- C. Increased parasympathetic activity
- D. Transitioning from a supine to a standing position
Explanation: ***Increased myocardial contractility*** - **Increased myocardial contractility** directly leads to a greater **stroke volume** (the amount of blood pumped with each beat), thus increasing cardiac output (Cardiac Output = Stroke Volume × Heart Rate). - This can be stimulated by factors such as **sympathetic nervous system activation** or positive inotropic agents. *Inhalation* - While inhalation can temporarily affect venous return and intrathoracic pressure, it does not directly or consistently lead to a sustained increase in **cardiac output**. - Its primary effect is on **respiration**, not cardiac performance. *Increased parasympathetic activity* - Increased parasympathetic activity, primarily via the **vagus nerve**, acts to **decrease heart rate** and myocardial contractility. - This effect would typically **reduce cardiac output**, not increase it. *Transitioning from a supine to a standing position* - Transitioning to a standing position usually causes a **temporary decrease in venous return** and a brief drop in cardiac output as blood pools in the lower extremities. - The body then compensates by increasing heart rate and peripheral vascular resistance to maintain blood pressure, but the initial effect on cardiac output is generally a transient decrease.
Question 22: Slowest blood flow is seen in?
- A. Arteriole
- B. Veins
- C. Capillaries (Correct Answer)
- D. Venules
Explanation: ***Capillaries*** - Blood flow is slowest in capillaries due to their **large total cross-sectional area**, allowing sufficient time for efficient **exchange of nutrients, gases, and waste products** between blood and tissues. - Despite their individual small diameter, the combined area of millions of capillaries significantly reduces the overall velocity of blood flow. *Arteriole* - **Arterioles** are designed to **regulate blood flow** into capillary beds by constricting and dilating, but blood velocity is still relatively high compared to capillaries. - While smaller than arteries, the **cross-sectional area** of individual arterioles does not collectively exceed that of the major arteries enough to cause the slowest flow rate in the circulatory system. *Veins* - Blood flow in **veins** is generally faster than in capillaries, and is aided by muscle pumps and valves, as they collect blood from the capillary beds. - Although veins have a larger total capacity than arteries, the **velocity of blood flow increases** as blood returns to the heart through progressively larger vessels. *Venules* - **Venules** collect blood from capillaries and begin the return journey to the heart, with blood flow velocity starting to increase as they merge into larger veins. - While slightly faster than in capillaries, the flow in venules is still relatively slow compared to larger veins and arteries, but not the slowest in the system due to their **collecting function and relatively small combined cross-sectional area compared to the entire capillary network**.
Question 23: P wave is due to:
- A. Atrial depolarization (Correct Answer)
- B. Atrial repolarization
- C. Ventricular depolarization
- D. Ventricular repolarization
Explanation: **Atrial depolarization** - The **P wave** on an electrocardiogram (ECG) represents the electrical activity associated with the **depolarization of the atria**. - This depolarization leads to **atrial contraction**, pushing blood into the ventricles. *Atrial repolarization* - **Atrial repolarization** also occurs but is usually hidden within the **QRS complex** and thus not separately visible as a distinct wave on a standard ECG. - While it's an electrical event, it does not produce the P wave. *Ventricular depolarization* - **Ventricular depolarization** is represented by the **QRS complex** on an ECG. - This electrical activity leads to **ventricular contraction**, pumping blood out of the heart. *Ventricular repolarization* - **Ventricular repolarization** is represented by the **T wave** on an ECG. - This process allows the ventricles to relax and refill with blood.
Question 24: Lowest pH is seen in which of the gastrointestinal secretions?
- A. Gastric juice (Correct Answer)
- B. Bile juice
- C. Saliva
- D. Pancreatic juice
Explanation: ***Gastric juice*** - Gastric juice contains **hydrochloric acid (HCl)**, secreted by parietal cells, which gives it a very **low pH (1.5-3.5)**. - This acidic environment is crucial for protein digestion by **pepsin** and for killing ingested microorganisms. *Bile juice* - Bile juice is typically **alkaline**, with a pH ranging from **7.6 to 8.6**. - Its primary role is to **emulsify fats** in the small intestine, and it does not contain significant acidic components. *Saliva* - Saliva has a relatively neutral pH, typically ranging from **6.2 to 7.6**. - It contains enzymes like **amylase** and **lipase** for initial carbohydrate and lipid digestion, but no strong acids. *Pancreatic juice* - Pancreatic juice is highly **alkaline**, with a pH usually between **8.0 and 8.3**, due to its high concentration of bicarbonate. - This alkalinity neutralizes the acidic chyme entering the duodenum from the stomach, creating an optimal environment for pancreatic enzymes.
Question 25: Which receptor is primarily stimulated in response to moderate cold temperatures?
- A. Vanilloid Receptor 1 (VR1)
- B. Vanilloid Receptor 2 (VR2)
- C. Vanilloid Receptor-Like 1 (VRL-1)
- D. TRPM8 Receptor (Menthol Receptor) (Correct Answer)
Explanation: ***TRPM8 Receptor (Menthol Receptor)*** - The **TRPM8 receptor** is a **cold-sensitive ion channel** that is primarily activated by moderate cold temperatures (around 8–28°C) and by cooling compounds like **menthol** and **eucalyptol**. - Its activation leads to an influx of cations, primarily **calcium**, causing depolarization and generation of action potentials. *Vanilloid Receptor 1 (VR1)* - Vanilloid Receptor 1, also known as **TRPV1**, is primarily activated by noxious heat (temperatures above 43°C), low pH, and capsaicin. - It plays a significant role in **pain sensation** and inflammation, not moderate cold detection. *Vanilloid Receptor 2 (VR2)* - Vanilloid Receptor 2, or **TRPV2**, is activated by even higher temperatures than TRPV1, typically above 52°C, and is also involved in the detection of **intense heat** and mechanical stimuli. - It does not respond to cold temperatures at all. *Vanilloid Receptor-Like 1 (VRL-1)* - **VRL-1**, or **TRPV3**, is a heat-sensitive channel activated by warm temperatures (above 31°C) and plays a role in the sensation of warmth and heat hyperalgesia. - It is not involved in the detection of cold stimuli.
Question 26: Which hormone is secreted by the "Delta cells" of the stomach?
- A. Cholecystokinin
- B. Gastrin-releasing peptide
- C. Somatostatin (Correct Answer)
- D. Secretin
Explanation: ***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.
Question 27: What is the primary solute responsible for the hyperosmolarity of the renal medulla?
- A. urea
- B. K
- C. Na (Correct Answer)
- D. Cl
Explanation: ***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 28: Normal renal threshold for glucose is at plasma glucose level ?
- A. 100 mg/dl
- B. 200 mg/dl (Correct Answer)
- C. 300 mg/dl
- D. 400 mg/dl
Explanation: ** _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**.
Question 29: Which of the following is the most accurate measure of Glomerular Filtration Rate (GFR)?
- A. Cystatin C
- B. Serum creatinine
- C. Creatinine Clearance
- D. Iothalamate Clearance (Correct Answer)
Explanation: ***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.
Question 30: Which type of muscle fibers has fewer mitochondria?
- A. Type I fibers (Red fibers)
- B. Type IIb fibers (Fast-twitch fibers) (Correct Answer)
- C. Type IIa fibers
- D. Type IIx fibers (Intermediate fibers)
Explanation: ***Type IIb fibers (Fast-twitch fibers)*** - These fibers rely primarily on **anaerobic glycolysis** for ATP production, which is a less efficient process than aerobic respiration and therefore requires fewer mitochondria. - Their primary function is rapid, powerful contractions over short durations, leading to quick fatigue. *Type IIa fibers* - These fibers are **fast-twitch oxidative-glycolytic** fibers, meaning they have a moderate number of mitochondria to support both aerobic and anaerobic metabolism. - They are capable of generating strong contractions and are more fatigue-resistant than Type IIb fibers but less so than Type I fibers. *Type I fibers (Red fibers)* - Known as **slow-twitch oxidative fibers**, they have a high density of mitochondria to support continuous **aerobic respiration** for sustained, low-intensity contractions. - Their rich blood supply and high myoglobin content give them their characteristic red color and make them highly fatigue-resistant. *Type IIx fibers (Intermediate fibers)* - These fibers are very similar to Type IIb fibers in their metabolic profile, often considered an intermediate or even functionally equivalent type depending on the species. - They also primarily utilize **anaerobic glycolysis** and have a relatively low mitochondrial content, making them prone to fatigue.