General Physiology Practice Questions

Q: Which of the following statements regarding exocytosis is correct?

All of the above.. **Explanation:** Exocytosis is the process by which a cell transports secretory vesicles to the cell membrane to release their contents into the extracellular space. It is a fundamental mechanism for neurotransmitter release, hormone secretion, and membrane protein integration. **Why "All of the Above" is correct:** * **Calcium-dependence (Option A):** Regulated exocytosis (e.g., neurotransmitter release at the synapse) is triggered by a rise in intracellular $Ca^{2+}$. When an action potential reaches the terminal, voltage-gated calcium channels open; the influx of $Ca^{2+}$ acts as the signal for vesicle fusion. * **Constitutive vs. Non-constitutive (Option B):** * **Constitutive exocytosis** is continuous and occurs in all cells (e.g., secretion of extracellular matrix components). It does not require an external signal. * **Non-constitutive (Regulated) exocytosis** occurs in specialized cells (e.g., endocrine cells, neurons) and requires a specific stimulus or second messenger. * **SNARE Proteins (Option C):** Fusion requires the interaction between **v-SNAREs** (on the vesicle membrane, e.g., Synaptobrevin) and **t-SNAREs** (on the target/plasma membrane, e.g., Syntaxin and SNAP-25). These proteins form a complex that "zips" the membranes together. **High-Yield Clinical Pearls for NEET-PG:** 1. **Tetanus and Botulinum Toxins:** These act by proteolytically cleaving SNARE proteins, thereby inhibiting neurotransmitter release. * *Tetanus toxin* affects inhibitory interneurons (Renshaw cells), leading to spastic paralysis. * *Botulinum toxin* affects excitatory cholinergic neurons, leading to flaccid paralysis. 2. **Synaptotagmin:** This is the specific $Ca^{2+}$ sensor on the vesicle membrane that triggers the final fusion step. 3. **ATP Requirement:** Exocytosis is an active process requiring energy (ATP).

Q: Actin's active site is covered by?

Tropomyosin. ### Explanation **Correct Option: B. Tropomyosin** In a resting muscle fiber, the interaction between actin and myosin is physically prevented to allow for relaxation. The **active sites (myosin-binding sites)** on the filamentous (F) actin strands are covered by **tropomyosin**. Tropomyosin is a long, rod-shaped protein that wraps spirally around the actin filament, specifically masking the sites where myosin heads would otherwise attach to initiate contraction. **Analysis of Options:** * **A. Myosin:** This is the thick filament. It possesses "heads" that seek to bind to actin to form cross-bridges. It does not cover the site; it is the protein being blocked. * **C. Troponin:** This is a complex of three regulatory proteins (I, T, and C) attached to tropomyosin. While Troponin I helps inhibit the binding, it is the **tropomyosin molecule itself** that physically lies over and masks the active site. Troponin acts as the "lock" that moves the tropomyosin "bar" when calcium binds to Troponin C. * **D. Desmin:** This is an intermediate filament found near the Z-line. Its primary role is structural—linking myofibrils together and anchoring them to the sarcolemma—rather than regulating the actin-myosin interface. **High-Yield NEET-PG Pearls:** * **The Troponin Complex:** * **Troponin T:** Binds the complex to **T**ropomyosin. * **Troponin I:** **I**nhibits the actin-myosin interaction. * **Troponin C:** Binds **C**alcium ions (requires 4 $Ca^{2+}$ ions to trigger a conformational change). * **Mechanism of Contraction:** When $Ca^{2+}$ binds to Troponin C, it causes a conformational change that pulls tropomyosin deeper into the actin groove, uncovering the active sites. This is known as the **"Dual-control mechanism."** * **Relaxation:** Occurs when $Ca^{2+}$ is pumped back into the Sarcoplasmic Reticulum (via SERCA), causing tropomyosin to return to its original masking position.

Q: What is the equilibrium potential of K+?

-90mV. **Explanation:** The equilibrium potential of an ion is the membrane potential at which the electrical gradient exactly balances the chemical concentration gradient, resulting in no net movement of that ion across the membrane. This is calculated using the **Nernst Equation**. **1. Why -90mV is correct:** Potassium ($K^+$) is the primary intracellular cation (approx. 140 mEq/L inside vs. 4 mEq/L outside). Because the concentration is higher inside, $K^+$ tends to diffuse out of the cell through leak channels. As positive charges leave, the inside of the cell becomes electronegative. At **-90mV**, the internal negativity is strong enough to pull $K^+$ back in at the same rate it diffuses out. This value is the "Nernst Potential" for $K^+$. **2. Analysis of Incorrect Options:** * **-70mV:** This is the typical **Resting Membrane Potential (RMP)** of a neuron. The RMP is close to the $K^+$ equilibrium potential because the membrane is highly permeable to $K^+$ at rest, but it is slightly less negative due to a small inward leak of $Na^+$. * **+70mV / +90mV:** These are positive values. Equilibrium potentials for cations like $Na^+$ (+60 to +65mV) are positive because their concentration gradient drives them *into* the cell, requiring an internal positivity to repel them and reach equilibrium. **3. High-Yield Clinical Pearls for NEET-PG:** * **Goldman-Hodgkin-Katz Equation:** Unlike the Nernst equation (which looks at one ion), this calculates RMP by considering the permeability of all ions ($K^+$, $Na^+$, and $Cl^-$). * **Hypokalemia/Hyperkalemia:** Changes in extracellular $K^+$ levels directly shift the equilibrium potential, altering cardiac excitability and leading to ECG changes (e.g., Tall T-waves in hyperkalemia). * **Na+/K+ ATPase:** This pump maintains the concentration gradients but only contributes about -5mV directly to the RMP (electrogenic effect).

Q: Autoregulation is seen in:

All of the above. ### Explanation **Concept of Autoregulation** Autoregulation is the intrinsic ability of an organ or tissue to maintain a relatively constant blood flow despite fluctuations in systemic arterial blood pressure. This process occurs independently of neural or humoral control, primarily through **myogenic mechanisms** (Bayliss effect) and **metabolic factors**. **Why "All of the above" is correct:** 1. **Kidney:** Renal autoregulation is highly efficient, maintaining a constant Glomerular Filtration Rate (GFR) and Renal Blood Flow (RBF) between mean arterial pressures of **80–180 mmHg**. It utilizes the myogenic mechanism and **tubuloglomerular feedback (TGF)**. 2. **Brain:** Cerebral blood flow is strictly autoregulated to protect against ischemia or edema. It remains constant between mean pressures of **60–140 mmHg**. Carbon dioxide ($CO_2$) levels are the most potent metabolic regulators here. 3. **Muscles:** While less rigid than the brain or kidney, skeletal muscle exhibits autoregulation, especially during exercise. Local metabolic vasodilators (lactate, adenosine, $K^+$) adjust blood flow to meet the oxygen demand of the tissue. **Analysis of Options:** Since the kidney, brain, and heart (and to a lesser extent, skeletal muscle and liver) all possess intrinsic mechanisms to stabilize blood flow, "All of the above" is the most accurate choice. **High-Yield NEET-PG Pearls:** * **Best Autoregulation:** Seen in the **Kidney** and **Brain**. * **Most Important Mechanism:** The **Myogenic Theory** (stretch-induced contraction of vascular smooth muscle). * **Critical Limits:** If blood pressure falls below the lower limit (e.g., <60 mmHg in the brain), autoregulation fails, leading to syncope or organ ischemia. * **Organs with Poor Autoregulation:** The **Skin** (primarily regulated by the sympathetic nervous system for thermoregulation) and the **Lungs** (where flow is passive and determined by gravity/cardiac output).

Q: What is the primary function of stellate cells in the liver?

Storage of Vitamin A. **Explanation:** **1. Why Option B is Correct:** Hepatic Stellate Cells (also known as **Ito cells** or lipocytes) are perisinusoidal cells located in the **Space of Disse**. Their primary physiological function in a healthy liver is the **storage of Vitamin A** (retinyl esters) within lipid droplets. They contain approximately 80% of the body's total Vitamin A reserves. **2. Why Other Options are Incorrect:** * **Option A (Phagocytosis):** This is the primary function of **Kupffer cells**, which are specialized macrophages located within the hepatic sinusoids. * **Option C (Blood Perfusion):** While stellate cells have some contractile properties that can influence sinusoidal tone, they do not primarily "increase" perfusion. In fact, in pathology, their contraction increases portal resistance. * **Option D (Formation of Sinusoids):** Sinusoids are formed by specialized **fenestrated endothelial cells**, not stellate cells. **3. High-Yield Clinical Pearls for NEET-PG:** * **Fibrogenesis:** In response to liver injury (chronic inflammation/alcohol), stellate cells undergo "activation." They lose their Vitamin A droplets and transform into **myofibroblasts**, which secrete Type I and Type III collagen. This is the **key event in hepatic fibrosis and cirrhosis.** * **Location:** Always remember they reside in the **Space of Disse** (the area between hepatocytes and sinusoids). * **Marker:** Desmin is often used as a histological marker for these cells.

Q: Which of the following physiological changes occur within 1 minute of standing up from a recumbent position?

Volume of blood in leg veins increases. ### Explanation When a person moves from a recumbent (lying down) to a standing position, the primary physiological challenge is the effect of **gravity**. **Why the correct answer is right:** Upon standing, gravity causes blood to pool in the highly distensible peripheral veins below the level of the heart, particularly in the lower limbs. Approximately **500 to 1000 mL of blood** shifts to the legs within the first minute. This increases the volume and pressure within the leg veins (venous pooling). **Analysis of Incorrect Options:** * **A. Skin blood flow increases:** To compensate for the drop in blood pressure caused by venous pooling, the baroreceptor reflex triggers **sympathetic activation**. This leads to peripheral vasoconstriction, which actually *decreases* skin and splanchnic blood flow to redirect blood to vital organs. * **C. Cardiac preload increases:** Because blood is pooling in the legs, there is a **decrease in venous return** to the heart. This leads to a decrease in end-diastolic volume (preload) and a subsequent drop in stroke volume. * **D. Cardiac contractility decreases:** The baroreceptor reflex responds to the drop in mean arterial pressure by increasing sympathetic outflow. This results in **increased cardiac contractility** (positive inotropy) and increased heart rate (tachycardia) to maintain cardiac output. **High-Yield NEET-PG Pearls:** * **The Baroreceptor Reflex:** This is the rapid-response mechanism for postural changes. It involves the carotid sinus (CN IX) and aortic arch (CN X). * **Orthostatic Hypotension:** Defined as a drop in systolic BP >20 mmHg or diastolic BP >10 mmHg within 3 minutes of standing. * **Skeletal Muscle Pump:** Contraction of leg muscles during walking helps counteract venous pooling by compressing veins and forcing blood toward the heart via one-way valves.

Q: What is the typical blood flow to skeletal muscle?

800-900 ml/min. **Explanation:** The correct answer is **800-900 ml/min**. In a healthy adult at rest, skeletal muscle receives approximately **15-20% of the total cardiac output**. Given an average cardiac output of 5 L/min, this equates to roughly 750–900 ml/min. While the metabolic demand of resting muscle is relatively low (approx. 2-5 ml/100g/min), the sheer mass of skeletal muscle (about 40% of body weight) makes it one of the largest reservoirs of blood flow in the resting state. **Analysis of Options:** * **A (800-900 ml/min):** This aligns with the physiological distribution of 15-20% of cardiac output to the muscular system at rest. * **B (1000 ml/min):** This value is slightly too high for resting muscle; it more closely approximates the blood flow to the **Liver** (Hepatic portal + arterial flow is ~1350-1500 ml/min) or **Kidneys** (~1100 ml/min). * **C (500-600 ml/min):** This represents the typical blood flow to the **Brain** (approx. 750 ml/min or 15% of CO) or is slightly lower than the standard muscle flow. * **D (100-200 ml/min):** This is significantly too low for the entire skeletal muscle mass; it is more characteristic of coronary blood flow (~250 ml/min) or flow to smaller organs. **High-Yield NEET-PG Pearls:** 1. **Exercise Shift:** During strenuous exercise, skeletal muscle blood flow can increase up to **20-fold** (reaching 15-20 L/min), receiving up to **80-85%** of the total cardiac output. 2. **Regulation:** At rest, flow is maintained by **sympathetic tone** (alpha-1 receptors). During exercise, **local metabolic factors** (adenosine, K+, H+, lactate) cause potent vasodilation (Active Hyperemia). 3. **Organ Flow Ranking (Rest):** Liver (30%) > Kidneys (20%) > Muscle (15-20%) > Brain (15%).

Q: Plasma osmolarity is maximally affected by?

Na+. **Explanation:** The correct answer is **Na+ (Sodium)**. Plasma osmolarity is primarily determined by the concentration of solutes in the extracellular fluid (ECF). Sodium is the most abundant cation in the ECF, and along with its associated anions (chloride and bicarbonate), it accounts for approximately **90-95% of the total plasma osmolarity**. **Why Na+ is correct:** The formula for calculated plasma osmolarity is: $2 \times [Na^+] + \frac{[Glucose]}{18} + \frac{[BUN]}{2.8}$ Since the normal concentration of Sodium is high (~140 mEq/L), doubling it accounts for nearly 280 mOsm/L of the total normal plasma osmolarity (~285-295 mOsm/L). Therefore, changes in sodium concentration have the most significant impact on plasma tonicity and water movement. **Why other options are incorrect:** * **K+ (Potassium):** This is the primary intracellular cation. While it determines intracellular osmolarity, its plasma concentration is very low (3.5–5.0 mEq/L), making its contribution to plasma osmolarity negligible. * **Glucose:** Under normal physiological conditions, glucose contributes only about 5 mOsm/L. It becomes significant only in pathological states like Diabetes Mellitus (Hyperglycemic Crises). * **Urea:** Urea is an "ineffective osmole" because it freely crosses cell membranes. While it contributes to total osmolarity, it does not create an osmotic gradient to shift water across the cell membrane. **High-Yield Clinical Pearls for NEET-PG:** 1. **Normal Plasma Osmolarity:** 285–295 mOsm/L. 2. **Osmolar Gap:** The difference between measured and calculated osmolarity. A gap >10 mOsm/L suggests the presence of unmeasured osmoles (e.g., Ethanol, Methanol, Ethylene glycol). 3. **ADH Regulation:** The hypothalamus senses changes in osmolarity as small as 1% via osmoreceptors, triggering ADH release to maintain water balance.

Question 1

Aerobic capability is maximally increased by which type of exercise?

Accepted Answer

Regular 3-minute exercises

Answer

Prolonged exercises

Answer

Strenuous exercises

Answer

Sporadic exercises

Question 2

Which of the following statements regarding exocytosis is correct?

Accepted Answer

All of the above.

Answer

It is a calcium-dependent process.

Answer

It can be constitutive or non-constitutive.

Answer

It requires SNARE proteins.

Question 3

Actin's active site is covered by?

Accepted Answer

Tropomyosin

Answer

Myosin

Answer

Troponin

Answer

Desmin

Question 4

What is the equilibrium potential of K+?

Accepted Answer

-90mV

Answer

-70mV

Answer

+70mV

Answer

+90mV

Question 5

Autoregulation is seen in:

Accepted Answer

All of the above

Answer

Kidney

Answer

Brain

Answer

Muscles

Question 6

What is the primary function of stellate cells in the liver?

Accepted Answer

Storage of Vitamin A

Answer

Phagocytosis

Answer

Increases blood perfusion

Answer

Formation of sinusoids

Question 7

Which of the following physiological changes occur within 1 minute of standing up from a recumbent position?

Accepted Answer

Volume of blood in leg veins increases

Answer

Skin blood flow increases

Answer

Cardiac preload increases

Answer

Cardiac contractility decreases

Question 8

What is the typical blood flow to skeletal muscle?

Accepted Answer

800-900 ml/min

Answer

1000 ml/min

Answer

500-600 ml/min

Answer

100-200 ml/min

Question 9

Which factor favors transport across a cell membrane?

Accepted Answer

High concentration gradient

Answer

Thick membrane

Answer

Large particle size

Answer

Polar substance

Question 10

Plasma osmolarity is maximally affected by?

Accepted Answer

Na+

Answer

K+

Answer

Glucose

Answer

Urea

General Physiology — MCQs

General Physiology — MCQs

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