General Physiology Practice Questions

Q: Which one of the following receptors acts by decreasing cAMP concentration when stimulated by Norepinephrine?

Alpha-2. The correct answer is **Alpha-2 (A)**. ### **Mechanism of Action** Adrenergic receptors are G-protein coupled receptors (GPCRs). The **Alpha-2 ($\alpha_2$) receptor** is coupled to the **$G_i$ (inhibitory)** protein. When norepinephrine binds to $\alpha_2$, it inhibits the enzyme **adenylyl cyclase**, leading to a decrease in the conversion of ATP to **cyclic AMP (cAMP)**. This reduction in cAMP levels results in the inhibition of neurotransmitter release (presynaptic effect) and smooth muscle contraction in certain vascular beds. ### **Analysis of Incorrect Options** * **Beta-1 ($\beta_1$):** These receptors are coupled to **$G_s$ (stimulatory)** proteins. Stimulation by norepinephrine activates adenylyl cyclase, **increasing** cAMP levels, which leads to positive inotropy and chronotropy in the heart. * **Vasopressin-2 ($V_2$):** Located in the renal collecting ducts, $V_2$ receptors are also **$G_s$ coupled**. They increase cAMP to facilitate the insertion of Aquaporin-2 channels. * **GnRH:** Gonadotropin-releasing hormone receptors are coupled to the **$G_q$ pathway**, which activates Phospholipase C (PLC) to increase Inositol triphosphate ($IP_3$) and Diacylglycerol (DAG), rather than primarily affecting cAMP. ### **NEET-PG High-Yield Pearls** * **Mnemonic for Adrenergic Receptors:** * **$Q-I-S-S$**: $\alpha_1$ ($G_q$), $\alpha_2$ ($G_i$), $\beta_1$ ($G_s$), $\beta_2$ ($G_s$). * **Clinical Correlation:** **Clonidine** and **Methyldopa** are $\alpha_2$ agonists used to treat hypertension by decreasing sympathetic outflow from the CNS. * **$\alpha_2$ Locations:** Presynaptic nerve terminals (autoreceptors), pancreatic $\beta$-cells (decreases insulin), and platelets (increases aggregation).

Q: Na+-K+ ATPase is which type of pump?

Electrogenic. ### Explanation The **Na⁺-K⁺ ATPase** (Sodium-Potassium Pump) is a primary active transporter found in the plasma membrane of almost all animal cells. **Why "Electrogenic" is the Correct Answer:** The pump moves **3 Na⁺ ions out** of the cell and **2 K⁺ ions into** the cell for every molecule of ATP hydrolyzed. Because there is an unequal exchange of cations (3 positive charges out vs. 2 positive charges in), it creates a net deficit of positive charge inside the cell. This directly contributes to the negativity of the **Resting Membrane Potential (RMP)**, typically contributing about -5 to -10 mV. Any pump that creates a net charge imbalance across the membrane is termed **electrogenic**. **Analysis of Incorrect Options:** * **A. Secondary active:** The Na⁺-K⁺ ATPase is a **Primary Active Transporter** because it derives energy directly from the hydrolysis of ATP (it is a P-type ATPase). Secondary active transport (like SGLT) relies on the gradient created by primary active transport. * **C. Symport:** This pump is an **Antiport** (counter-transport) mechanism because it moves the two ions in opposite directions across the cell membrane. * **D. All of the above:** Incorrect, as options A and C are physiologically inaccurate descriptions of this specific pump. **High-Yield Clinical Pearls for NEET-PG:** * **Inhibitor:** The pump is specifically inhibited by **Cardiac Glycosides** (e.g., Digoxin and Ouabain), which bind to the extracellular side of the alpha subunit. * **Structure:** It is a heteromer composed of an **alpha subunit** (catalytic, contains binding sites for Na⁺, K⁺, and ATP) and a **beta subunit** (essential for membrane trafficking). * **Functions:** It maintains cell volume, provides the driving force for secondary active transport, and is crucial for maintaining the steep Na⁺ and K⁺ gradients necessary for excitable tissues.

Q: Along with acetylcholine, what is released from sweat gland secretions?

Vasoactive intestinal peptide. **Explanation:** The correct answer is **Vasoactive intestinal peptide (VIP)**. **1. Why VIP is correct:** Sweat glands are unique in the autonomic nervous system. While they are anatomically part of the **sympathetic nervous system**, their postganglionic fibers are **cholinergic** (releasing Acetylcholine). In these specific fibers, **Vasoactive Intestinal Peptide (VIP)** is co-released with Acetylcholine (ACh). * **Mechanism:** ACh acts on muscarinic receptors to stimulate sweat secretion. VIP acts as a potent vasodilator, increasing local blood flow to the sweat glands, which provides the necessary fluid for sweat production and aids in thermoregulation by facilitating heat loss. **2. Why other options are incorrect:** * **A. Neuropeptide Y (NPY):** This is typically co-released with **Norepinephrine** in sympathetic adrenergic neurons. It acts as a vasoconstrictor, the opposite of what is required for active sweating. * **B. Enkephalin:** These are endogenous opioids primarily involved in pain modulation and are found in the adrenal medulla and CNS, not typically associated with sweat gland innervation. * **C. Substance P:** While involved in neurogenic inflammation and pain transmission, it is not the primary co-transmitter for thermoregulatory sweat glands. **Clinical Pearls & High-Yield Facts:** * **Exception to the Rule:** Most sympathetic postganglionic neurons release Norepinephrine; sweat glands (and some blood vessels in skeletal muscle) are the major exceptions, releasing ACh. * **Cotransmission:** This concept describes a single nerve terminal releasing multiple transmitters. In the ANS, the ACh-VIP pair is the classic example for parasympathetic-like sympathetic fibers. * **Clinical Correlation:** In **Lambert-Eaton Syndrome** or **Botulism**, ACh release is impaired, leading to anhidrosis (lack of sweating) alongside muscle weakness.

Q: Fever increases the basal metabolic rate by approximately what percentage for each 1-degree Celsius rise in body temperature?

7%. **Explanation:** The correct answer is **7% (Option B)**. This relationship is based on the **Van’t Hoff’s Law**, which states that the velocity of chemical reactions increases as temperature rises. In human physiology, an increase in body temperature accelerates enzymatic activity and metabolic processes. For every **1°C rise** in body temperature, the Basal Metabolic Rate (BMR) increases by approximately **7%** (or roughly 13% for every 1°F rise). **Analysis of Options:** * **Option A (3%):** This value is too low. While some minor physiological fluctuations occur, a 1°C rise triggers a more significant metabolic demand than 3%. * **Option B (7%):** **Correct.** This is the standard physiological constant cited in major textbooks (like Guyton and Hall) regarding the thermogenic effect of fever on metabolism. * **Option C (10%):** While some older texts or specific clinical scenarios might approximate 10%, 7% is the precise "high-yield" figure required for competitive exams like NEET-PG. * **Option D (20%):** This is an overestimation. A 20% increase per degree would lead to rapid exhaustion of energy stores and severe metabolic acidosis during common febrile illnesses. **Clinical Pearls for NEET-PG:** * **Q10 Effect:** This refers to the temperature coefficient, representing the factor by which a biological process increases with a 10°C rise. * **Clinical Significance:** Fever-induced BMR increase explains why patients with infections experience rapid weight loss, increased heart rate (tachycardia), and increased respiratory rate (tachypnea). * **Thyroid Link:** BMR is primarily regulated by **Thyroxine (T4)**. While fever increases BMR acutely via temperature, T4 increases it by stimulating Na+-K+ ATPase activity across tissues.

Q: What is the primary function of the Golgi tendon organ?

Detecting reflex muscle tension. ### Explanation The **Golgi Tendon Organ (GTO)** is a specialized sensory receptor located at the junction of muscle fibers and tendons. It is arranged **in series** with the muscle fibers, making it exquisitely sensitive to changes in **muscle tension**. **1. Why Option B is Correct:** When a muscle undergoes forceful contraction, the GTO is stretched. It sends impulses via **Ib afferent nerve fibers** to the spinal cord. These fibers synapse on inhibitory interneurons, which then inhibit the alpha motor neurons of the same muscle. This mechanism, known as the **Inverse Stretch Reflex (Autogenic Inhibition)**, prevents muscle damage by causing the muscle to relax when tension becomes excessive. **2. Why Other Options are Incorrect:** * **Option A:** Detecting muscle length is the primary function of the **Muscle Spindle**. Muscle spindles are arranged **in parallel** with extrafusal fibers and mediate the stretch reflex (e.g., knee jerk). * **Option C & D:** Nutritional status and excretory functions are regulated by metabolic, endocrine, and autonomic systems (e.g., hypothalamus, kidneys), not by musculoskeletal mechanoreceptors. **3. High-Yield Clinical Pearls for NEET-PG:** * **Arrangement:** Muscle Spindle = Parallel; GTO = Series. * **Afferent Fibers:** Muscle Spindle = **Ia** (primary) and **II** (secondary); GTO = **Ib**. * **The "Clasp-Knife Response":** In upper motor neuron (UMN) lesions, exaggerated GTO activity contributes to the sudden "melting away" of resistance when a limb is passively stretched, a classic clinical sign of spasticity. * **Function:** While the muscle spindle is a feedback regulator of muscle **length**, the GTO is a feedback regulator of muscle **force/tension**.

Q: All of the following are examples of primary active transport, except:

Na+/ glucose symporter. ### Explanation **Concept Overview:** Transport across cell membranes is categorized based on energy requirements. **Primary Active Transport** directly utilizes energy from ATP hydrolysis to move solutes against their electrochemical gradient. **Secondary Active Transport** (like the Na+/glucose symporter) does not use ATP directly; instead, it hitches a ride on the energy stored in an electrochemical gradient (usually Na+) created by a primary active transporter. **Why Option C is Correct:** The **Na+/glucose symporter (SGLT)** is a classic example of **Secondary Active Transport**. It moves glucose against its concentration gradient by utilizing the downward sodium gradient established by the Na+/K+ ATPase. Since it does not hydrolyze ATP itself, it is not a primary active transporter. **Analysis of Incorrect Options:** * **Option A (Na+/K+ ATPase):** The most ubiquitous primary active transporter. It pumps 3 Na+ out and 2 K+ in per ATP hydrolyzed, maintaining resting membrane potential. * **Option B (H+/K+ ATPase):** Found in gastric parietal cells, this "proton pump" uses ATP to secrete H+ into the stomach lumen in exchange for K+. It is the target of Proton Pump Inhibitors (PPIs). * **Option D (SERCA):** The **S**arco/Endoplasmic **R**eticulum **C**a2+ **A**TPase is a primary active transporter that pumps calcium from the cytosol into the SR to allow for muscle relaxation. **High-Yield NEET-PG Pearls:** 1. **P-type ATPases:** Na+/K+ ATPase, H+/K+ ATPase, and SERCA are all "P-type" because they are phosphorylated during the transport cycle. 2. **SGLT Locations:** SGLT-1 is primarily in the small intestine, while SGLT-2 is in the proximal convoluted tubule (PCT) of the kidney (target of Gliflozins). 3. **Digitalis/Ouabain:** These drugs inhibit the Na+/K+ ATPase, leading to increased intracellular Na+, which indirectly slows the Na+/Ca2+ exchanger, increasing cardiac contractility.

Q: Which law states that the amount of a substance crossing a given area is directly proportional to the area available for diffusion, concentration gradient, and diffusion coefficient?

Fick's law. ### Explanation **Correct Answer: C. Fick’s Law** **Why it is correct:** Fick’s First Law of Diffusion describes the rate at which a substance moves across a membrane. Mathematically, it is expressed as: **J = -DA (ΔC/ΔX)** Where: * **J** = Rate of diffusion * **D** = Diffusion coefficient (depends on the nature of the substance and temperature) * **A** = Surface area available for diffusion * **ΔC/ΔX** = Concentration gradient In medical physiology, this law explains how gases (like $O_2$ and $CO_2$) exchange across the alveolar-capillary membrane. The rate of exchange increases if the surface area or concentration gradient increases, and decreases if the membrane thickness increases. **Why the other options are incorrect:** * **A. Universal Gas Law ($PV = nRT$):** Relates pressure, volume, and temperature of an ideal gas; it does not describe the movement of substances across membranes. * **B. Dalton’s Law:** States that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases. It explains how partial pressures are calculated but not the rate of diffusion. **High-Yield Clinical Pearls for NEET-PG:** * **Emphysema:** Reduces the surface area (**A**) for diffusion due to alveolar wall destruction, leading to hypoxemia (Fick’s Law). * **Pulmonary Edema/Fibrosis:** Increases the diffusion distance (membrane thickness), thereby reducing the rate of gas exchange. * **Graham’s Law:** Often confused with Fick’s; it states that the diffusion rate of a gas is inversely proportional to the square root of its molecular weight. This explains why $CO_2$ (heavier) diffuses slower than $O_2$ in air, even though $CO_2$ is more soluble in liquids.

Q: Which of the following is true regarding a system which has oscillatory responses?

Positive feedback system. ### Explanation **Correct Answer: D. Positive Feedback System** In physiology, **positive feedback systems** are characterized by a response that reinforces or amplifies the initial stimulus. This creates a "vicious cycle" or an **oscillatory response** where the output continues to increase or fluctuate until a specific climax or external intervention occurs. Unlike negative feedback, which seeks stability (homeostasis), positive feedback drives the system away from the steady state, leading to instability or rapid physiological changes. **Why other options are incorrect:** * **A & B (Lesser/Greater Gain):** "Gain" refers to the efficiency of a control system (calculated as Correction/Error). While negative feedback systems have a high gain to maintain stability, the term "gain" is primarily used to describe the effectiveness of homeostatic regulation. Oscillatory behavior is a functional characteristic of the feedback loop's direction, not merely the magnitude of its gain. * **C (Proportional Component):** This is a term used in control systems (PID controllers) where the output is proportional to the current error. While it helps in stabilizing negative feedback, it does not inherently define the oscillatory nature of positive feedback loops. **High-Yield Clinical Pearls for NEET-PG:** * **Physiological Positive Feedback:** Most feedback in the body is negative. Key exceptions (Positive) include: * **LH Surge:** Leading to ovulation. * **Oxytocin:** During childbirth (Ferguson reflex). * **Blood Clotting Cascade:** Activation of one factor leads to the activation of many. * **Nerve Action Potential:** Opening of Na+ channels causes more Na+ channels to open (Hodgkin cycle). * **Negative Feedback:** The most common regulatory mechanism (e.g., Thyroxine regulation, BP control via baroreceptors). It is characterized by **stability** rather than oscillation.

Question 1

Which one of the following receptors acts by decreasing cAMP concentration when stimulated by Norepinephrine?

Accepted Answer

Alpha-2

Answer

Beta-1

Answer

Vasopressin-2

Answer

GnRH

Question 2

Na+-K+ ATPase is which type of pump?

Accepted Answer

Electrogenic

Answer

Secondary active

Answer

Symport

Answer

All of the above

Question 3

Along with acetylcholine, what is released from sweat gland secretions?

Accepted Answer

Vasoactive intestinal peptide

Answer

Neuro peptide Y

Answer

Enkephalin

Answer

Substance P

Question 4

Fever increases the basal metabolic rate by approximately what percentage for each 1-degree Celsius rise in body temperature?

Accepted Answer

7%

Answer

3%

Answer

10%

Answer

20%

Question 5

Which of the following statements regarding the homeostatic mechanism of the body is NOT true?

Accepted Answer

The body's homeostatic systems are primarily stabilized by positive feedback mechanisms.

Answer

Normal cell function depends on the constancy of extracellular fluid (ECF).

Answer

The actual environment of the cells of the body is the interstitial component of the ECF.

Answer

Renal and respiratory adjustments are constantly occurring to maintain homeostasis.

Question 6

What is the primary function of the Golgi tendon organ?

Accepted Answer

Detecting reflex muscle tension

Answer

Detecting muscle length

Answer

Monitoring nutritional status

Answer

Regulating excretory function

Question 7

Which is the most potent oxygen free radical?

Accepted Answer

Hydroxyl radical

Answer

Hydrogen peroxide

Answer

Superoxide radical

Answer

Both Hydroxyl radical and Hydrogen peroxide

Question 8

All of the following are examples of primary active transport, except:

Accepted Answer

Na+/ glucose symporter

Answer

The Na+/K+ ATPase in the red cell membrane

Answer

The H+/K+ ATPase in the parietal cell of stomach

Answer

SERCA in the skeletal muscle

Question 9

Which law states that the amount of a substance crossing a given area is directly proportional to the area available for diffusion, concentration gradient, and diffusion coefficient?

Accepted Answer

Fick's law

Answer

Universal gas law

Answer

Dalton's law

Answer

All of the above

Question 10

Which of the following is true regarding a system which has oscillatory responses?

Accepted Answer

Positive feedback system

Answer

Has a lesser gain

Answer

Has a greater gain

Answer

Proportional component

General Physiology — MCQs

General Physiology — MCQs

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