General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 191: Which of the following special circulations has the widest range of blood flows as part of its contributions to both the regulation of systemic vascular resistance and the modification of resistance to suit the organ's metabolic needs?

A. Large intestine
B. Cerebral
C. Small intestine
D. Skeletal muscle (Correct Answer)

Explanation: **Explanation:** The correct answer is **Skeletal muscle**. This is because skeletal muscle constitutes approximately 40% of total body mass and exhibits the most dramatic range of blood flow variation in the human body. 1. **Why Skeletal Muscle is Correct:** * **Metabolic Range:** At rest, muscle blood flow is low (approx. 2–5 mL/min/100g). However, during maximal exercise, it can increase up to **20–50 fold** (reaching 100+ mL/min/100g) due to active hyperemia and local metabolic factors (lactate, adenosine, K+). * **Systemic Regulation:** Because of its massive total volume, skeletal muscle vasculature is a primary determinant of **Systemic Vascular Resistance (SVR)**. Under sympathetic stimulation (α1 receptors), vasoconstriction in muscles can significantly increase blood pressure and shunt blood to vital organs. 2. **Why Other Options are Incorrect:** * **Cerebral:** The brain requires a constant, stable blood flow (approx. 50 mL/min/100g). It has the tightest **autoregulation** and shows very little variation in total flow, regardless of activity levels. * **Small & Large Intestine:** While splanchnic blood flow increases after a meal (post-prandial hyperemia), the range of variation (approx. 8–10 fold) is significantly narrower than that of skeletal muscle. **High-Yield NEET-PG Pearls:** * **Resting Tone:** Skeletal muscle has high intrinsic sympathetic tone; its removal causes immediate vasodilation. * **Capillary Recruitment:** The massive increase in flow during exercise is achieved not just by vasodilation, but by "recruiting" previously closed capillaries. * **Key Regulator:** At rest, sympathetic nerves control flow; during exercise, **local metabolic factors** override sympathetic control (Functional Sympatholysis).

Question 192: Transcytosis occurs in which of the following cells?

A. Epithelial cells of the intestine (Correct Answer)
B. Neuroglia
C. Neuron
D. Axolemma

Explanation: **Explanation:** **Transcytosis** (also known as cytopempsis or vesicle transport) is a type of transcellular transport where various macromolecules are transported across the interior of a cell. It involves a combination of **endocytosis** on one side of the cell, movement through the cytoplasm via vesicular transport, and **exocytosis** on the opposite side. **Why Option A is Correct:** Transcytosis is a characteristic feature of polarized cells, most notably **epithelial cells of the intestine** and vascular endothelial cells. In the intestine, specialized cells called **M cells** (Microfold cells) use transcytosis to transport antigens from the intestinal lumen to the underlying lymphoid tissue (Peyer's patches). Additionally, it is the mechanism by which maternal antibodies (IgA) are transported across the intestinal epithelium in neonates to provide passive immunity. **Why Other Options are Incorrect:** * **B & C (Neuroglia and Neurons):** While neurons utilize endocytosis and exocytosis for neurotransmitter recycling and synaptic signaling, they do not typically perform transcytosis as a primary means of bulk macromolecular transport across the cell body. * **D (Axolemma):** This is the cell membrane of an axon. It is involved in the propagation of action potentials and ion exchange, not the vesicular transport of macromolecules across the cell. **High-Yield Facts for NEET-PG:** * **Key Examples:** Transcytosis is essential for the transport of **IgA** into secretions, **IgG** across the placenta, and **Insulin** across the blood-brain barrier. * **Mechanism:** It utilizes **clathrin-coated pits** or **caveolae** to form the transport vesicles. * **Clinical Relevance:** Certain pathogens, such as *Listeria monocytogenes* and *Vibrio cholerae*, hijack the transcytosis pathway to bypass epithelial barriers and enter the systemic circulation.

Question 193: Which of the following statements about smooth muscle is false?

A. Ca2+ is the excitation-contraction coupler.
B. The "latch" mechanism facilitates prolonged holding of contractions of smooth muscle.
C. Shows the property of plasticity.
D. The musculature of the uterus is made of multi-unit smooth muscle. (Correct Answer)

Explanation: **Explanation:** The correct answer is **D** because the musculature of the uterus (myometrium) is a classic example of **unitary (single-unit) smooth muscle**, not multi-unit smooth muscle. 1. **Why Option D is False:** Unitary smooth muscles are organized in sheets or bundles, and their cells are electrically coupled via **gap junctions**. This allows the muscle to contract as a single functional syncytium, which is essential for the coordinated, rhythmic contractions required during labor. In contrast, multi-unit smooth muscles (like the iris or piloerector muscles) act independently and lack gap junctions. 2. **Why Option A is True:** Calcium ($Ca^{2+}$) is the universal excitation-contraction coupler. In smooth muscle, $Ca^{2+}$ binds to **calmodulin**, which then activates Myosin Light Chain Kinase (MLCK) to initiate contraction. 3. **Why Option B is True:** The **"latch" mechanism** allows smooth muscle to maintain high tension for long periods with very little ATP consumption. It occurs when myosin dephosphorylation happens while it is still attached to actin, slowing the detachment rate. 4. **Why Option C is True:** **Plasticity** (or stress-relaxation) is the ability of a hollow organ (like the bladder or stomach) to be stretched and then adjust its tension to maintain a constant internal pressure, preventing premature emptying. **High-Yield NEET-PG Pearls:** * **Unitary Smooth Muscle:** Found in the GI tract, ureter, and uterus. Characterized by pacemaker activity and gap junctions. * **Multi-unit Smooth Muscle:** Found in the ciliary body, iris, and large arteries. Requires individual nerve innervation for each fiber. * **Troponin:** Smooth muscle **lacks troponin**; calmodulin is the functional analog. * **Caveolae:** These are the functional equivalents of T-tubules in smooth muscle.

Question 194: Which brainstem-derived descending tract produces actions similar to the lateral corticospinal tract?

A. Vestibulospinal
B. Reticulospinal
C. Spinocerebellar
D. Rubrospinal (Correct Answer)

Explanation: **Explanation:** The **Rubrospinal tract** is the correct answer because it is the only brainstem-derived descending pathway that functionally mimics the **Lateral Corticospinal Tract (LCST)**. Both tracts are part of the **lateral system** of motor control. 1. **Why Rubrospinal is correct:** Originating in the **Red Nucleus** of the midbrain, this tract decussates immediately and descends in the lateral column of the spinal cord, adjacent to the LCST. Its primary function is to facilitate **flexor muscle tone** and govern fine, distal limb movements. In humans, while the LCST is dominant, the rubrospinal tract acts as a "backup" or synergistic pathway for voluntary motor control of the upper limbs. 2. **Why other options are incorrect:** * **Vestibulospinal & Reticulospinal:** These belong to the **medial (ventromedial) system**. They primarily regulate posture, balance, and axial/proximal extensor muscles rather than distal limb movements. * **Spinocerebellar:** This is an **ascending (sensory)** tract carrying unconscious proprioception to the cerebellum; it is not a descending motor tract. **High-Yield NEET-PG Pearls:** * **Decorticate Posture:** Occurs with lesions *above* the red nucleus. The rubrospinal tract remains intact, leading to characteristic **flexion** of the upper limbs. * **Decerebrate Posture:** Occurs with lesions *below* the red nucleus (but above the vestibular nuclei). Loss of rubrospinal flexion leads to unopposed extension by the vestibulospinal tract, resulting in **extensor** posturing of all four limbs. * The Rubrospinal tract is vestigial in humans compared to other mammals but remains clinically significant in localizing brainstem injuries.

Question 195: Bradykinin causes which of the following effects?

A. Stimulation of the visceral smooth muscle (Correct Answer)
B. Stimulation of the vascular smooth muscle
C. Inhibition of the visceral smooth muscle
D. Inhibition of the vascular smooth muscle

Explanation: **Explanation:** Bradykinin is a potent pharmacologically active nonapeptide belonging to the kinin system. Its physiological effects are mediated primarily through B1 and B2 receptors, and its action on smooth muscle is **tissue-specific**, which is a high-yield distinction for competitive exams. **1. Why Option A is Correct:** Bradykinin acts as a potent **stimulant of visceral (non-vascular) smooth muscle**. It causes contraction of the smooth muscles in the gastrointestinal tract, bronchioles, and uterus. This is why bradykinin is associated with bronchoconstriction in asthma and increased intestinal motility. **2. Why Other Options are Incorrect:** * **Options B & D:** While bradykinin "stimulates" the endothelial cells to release nitric oxide (NO) and prostacyclin ($PGI_2$), the net effect on the **vascular smooth muscle** itself is **relaxation (vasodilation)**. Therefore, it does not stimulate vascular smooth muscle (which would cause vasoconstriction); rather, it inhibits its tone indirectly. * **Option C:** As established, bradykinin is an excitatory mediator for visceral organs, not an inhibitor. **High-Yield Clinical Pearls for NEET-PG:** * **The "Triple Response":** Bradykinin causes vasodilation, increased capillary permeability (edema), and pain (by stimulating nociceptors). * **ACE Inhibitor Link:** Angiotensin-Converting Enzyme (ACE) is responsible for breaking down bradykinin. ACE inhibitors prevent this breakdown, leading to increased bradykinin levels, which results in the classic side effect of a **dry cough** (due to bronchial irritation) and, rarely, **angioedema**. * **Receptor Type:** Most of the acute inflammatory effects of bradykinin are mediated by the **B2 receptor**.

Question 196: Lysozymes are found in which of the following?

A. Eukaryotes (Correct Answer)
B. Prokaryotes
C. Plants
D. Bacteriophage

Explanation: **Explanation:** **1. Why Eukaryotes is the correct answer:** Lysozymes are specialized membrane-bound organelles found in **eukaryotic cells** (both animal and plant cells, though more prominent in animals). They function as the "digestive system" of the cell, containing approximately 50 different hydrolytic enzymes (acid hydrolases) like proteases, nucleases, and glycosidases. These enzymes are active at an acidic pH (~5.0), maintained by a proton pump (V-type ATPase) in the lysosomal membrane. Their primary role is the degradation of macromolecules from endocytosis, autophagy, and phagocytosis. **2. Why other options are incorrect:** * **Prokaryotes:** Bacteria do not possess membrane-bound organelles like lysosomes. While they secrete enzymes into the periplasmic space to degrade nutrients, they lack the compartmentalized lysosomal system. * **Plants:** While plants have "vacuoles" that perform lysosome-like degradative functions, the classical lysosome as defined in medical physiology is a hallmark of eukaryotic animal cells. (Note: In some contexts, plant vacuoles are considered specialized lysosomes, but in a competitive exam setting, "Eukaryotes" is the most encompassing and standard biological classification). * **Bacteriophage:** These are viruses that infect bacteria. They are non-cellular entities and do not contain organelles. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Marker Enzyme:** Acid phosphatase is the characteristic marker enzyme for lysosomes. * **I-Cell Disease:** Caused by a deficiency in the phosphotransferase enzyme, leading to the failure of "tagging" enzymes with Mannose-6-Phosphate. This results in enzymes being secreted extracellularly rather than being transported to lysosomes. * **Lysosomal Storage Diseases (LSDs):** Important examples include Gaucher’s (Glucocerebrosidase deficiency), Tay-Sachs (Hexosaminidase A deficiency), and Pompe disease (Alpha-glucosidase deficiency). * **Primary vs. Secondary Lysosome:** A primary lysosome is newly formed from the Golgi; a secondary lysosome (phagolysosome) is formed by the fusion of a primary lysosome with a phagosome.

Question 197: At an ambient temperature of 21 degrees Celsius, through which mechanism does heat loss primarily occur?

A. Respiration
B. Radiation (Correct Answer)
C. Sweating
D. Urine and faeces

Explanation: ### Explanation The human body maintains thermal homeostasis by balancing heat production and heat loss. At a comfortable ambient temperature (around 21°C or 70°F), the body loses heat through four physical mechanisms: **Radiation, Conduction, Convection, and Evaporation.** **1. Why Radiation is Correct:** Radiation is the transfer of heat from the body to cooler objects in the environment via infrared electromagnetic waves. In a sedentary person at normal room temperature (21°C), **radiation accounts for approximately 60% of total heat loss**, making it the primary mechanism. This occurs because the body surface temperature is significantly higher than the surrounding walls and objects. **2. Analysis of Incorrect Options:** * **Sweating (Evaporation):** At 21°C, evaporation (via skin and lungs) accounts for only about 22-25% of heat loss. Sweating becomes the **dominant** mechanism only when the ambient temperature exceeds the body temperature or during heavy exercise. * **Respiration:** While heat is lost through warming inspired air and vaporizing water in the lungs, it is a minor component (part of the evaporative/convective loss) and not the primary source. * **Urine and Faeces:** These account for a negligible amount of heat loss (usually <1%). **3. High-Yield Clinical Pearls for NEET-PG:** * **The "Goldilocks" Rule:** If the environment is **hotter** than the body, radiation, conduction, and convection actually *gain* heat for the body; in this scenario, **evaporation** is the *only* mechanism for heat loss. * **Conduction to Air:** Usually accounts for only 15% of loss, but **conduction to water** is 25 times faster (relevant in hypothermia/drowning). * **Regulatory Center:** The **Anterior Hypothalamus** (Pre-optic area) is the "thermostat" that senses heat, while the **Posterior Hypothalamus** coordinates responses to cold.

Question 198: What is the primary form of cortisol in the plasma?

A. Bound to albumin
B. Bound to transthyretin
C. Free in solution
D. Bound to corticosteroid-binding globulin (CBG) (Correct Answer)

Explanation: **Explanation:** Cortisol is a lipophilic steroid hormone produced by the adrenal cortex. Because it is hydrophobic, it cannot travel freely in the aqueous environment of the plasma in large quantities and requires carrier proteins for transport. **1. Why Option D is Correct:** The vast majority of circulating cortisol (**approximately 75–80%**) is bound to **Corticosteroid-Binding Globulin (CBG)**, also known as **transcortin**. CBG is an alpha-globulin synthesized in the liver with a high affinity for cortisol. This binding serves as a reservoir, protecting the hormone from rapid metabolic degradation and renal filtration, thereby prolonging its half-life. **2. Why Other Options are Incorrect:** * **Option A (Albumin):** About **15%** of cortisol is bound to albumin. While albumin has a high capacity, it has a much lower affinity for cortisol compared to CBG. * **Option B (Transthyretin):** Transthyretin (prealbumin) is primarily involved in the transport of thyroxine (T4) and retinol-binding protein, not cortisol. * **Option C (Free in solution):** Only about **5–10%** of cortisol exists in the "free" or unbound state. This free fraction is the biologically active form capable of crossing cell membranes to bind to intracellular receptors. **NEET-PG High-Yield Pearls:** * **CBG Levels:** Estrogen (e.g., pregnancy, OCPs) **increases** CBG synthesis in the liver, leading to high total cortisol levels, though free cortisol remains normal. Conversely, liver disease or nephrotic syndrome **decreases** CBG. * **Diurnal Rhythm:** Cortisol levels peak in the early morning (approx. 8 AM) and are lowest at midnight. * **Metabolism:** Cortisol is conjugated with glucuronic acid in the liver to make it water-soluble for excretion in the urine (measured as 17-hydroxycorticosteroids).

Question 199: Chromatolysis is seen in which cellular component?

A. Nissl substance (Correct Answer)
B. Mitochondria
C. Microtubule
D. Golgi body

Explanation: **Explanation:** **Chromatolysis** is a reactive change observed in the cell body (soma) of a neuron following axonal injury (axotomy). It is a hallmark of **retrograde degeneration**. 1. **Why Nissl Substance is Correct:** Nissl bodies are large granules composed of **Rough Endoplasmic Reticulum (RER)** and free ribosomes, responsible for protein synthesis. When an axon is injured, the neuron must shift its metabolic focus from neurotransmission to structural repair. During chromatolysis, the Nissl bodies undergo **dissolution and dispersal** throughout the cytoplasm, causing the cell body to appear pale and swollen under a microscope. This process is essential for increasing protein synthesis to regenerate the damaged axon. 2. **Why Other Options are Incorrect:** * **Mitochondria:** While mitochondria may increase in number or migrate during cell stress to provide ATP for repair, they do not undergo "chromatolysis," which specifically refers to the loss of staining in granular bodies. * **Microtubules:** These are structural components of the cytoskeleton involved in axonal transport. While they may reorganize, they are not the primary site of chromatolysis. * **Golgi Body:** The Golgi apparatus may shift to the periphery of the cell during injury, but the term chromatolysis is histologically defined by the disappearance of the basophilic Nissl substance. **High-Yield NEET-PG Pearls:** * **Histological features of Chromatolysis:** Swelling of the cell body, **peripheral displacement of the nucleus**, and disappearance of Nissl substance. * **Wallerian Degeneration:** Refers to the degeneration of the axon *distal* to the site of injury. * **Nissl Staining:** Nissl substance is basophilic and stains intensely with dyes like **Cresyl Violet** or Methylene Blue. * **Location:** Nissl bodies are found in the soma and dendrites but are notably **absent in the Axon Hillock** and the Axon.

Question 200: Which of the following is regulated by a negative feedback system in the body?

A. Thyroid production
B. Ovulation
C. Blood pressure regulation
D. All the above (Correct Answer)

Explanation: **Explanation:** In physiology, **negative feedback** is the primary mechanism for maintaining homeostasis. It works by detecting a deviation from a set point and initiating responses that negate or reverse the original stimulus. 1. **Thyroid Production:** This is a classic example of the **Hypothalamic-Pituitary-Thyroid (HPT) axis**. High levels of circulating Thyroxine (T4) and Triiodothyronine (T3) inhibit the release of TRH from the hypothalamus and TSH from the anterior pituitary, thereby decreasing further thyroid hormone production. 2. **Ovulation:** While the mid-cycle LH surge is a famous example of *positive* feedback, the overall regulation of the menstrual cycle is predominantly negative feedback. For most of the follicular and luteal phases, Estrogen and Progesterone inhibit FSH and LH to prevent overstimulation of the ovaries. 3. **Blood Pressure Regulation:** The **Baroreceptor Reflex** is a rapid negative feedback loop. An increase in blood pressure stretches baroreceptors in the carotid sinus and aortic arch, leading to increased parasympathetic and decreased sympathetic outflow, which lowers heart rate and causes vasodilation to bring BP back to normal. **Why "All the Above" is Correct:** While students often associate ovulation strictly with positive feedback, it is important to recognize that the body utilizes negative feedback loops in almost every physiological system to ensure stability. **High-Yield NEET-PG Pearls:** * **Positive Feedback Examples:** LH surge (ovulation), Oxytocin in parturition (Ferguson reflex), Blood clotting cascade, and Nerve action potential (Hodgkin cycle). * **Negative Feedback** is the most common regulatory mechanism in the body. * **Feed-forward Control:** Anticipatory regulation (e.g., cephalic phase of gastric secretion or increased heart rate before a race).

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