General Physiology Practice Questions

Q: Of the total oxygen consumed by the body per minute, which organ consumes the greatest fraction?

Liver. **Explanation:** The correct answer is **Liver (Option A)**. Oxygen consumption ($VO_2$) is determined by the metabolic activity of an organ. At rest, the liver is the most metabolically active organ in the body, accounting for approximately **20–27%** of total oxygen consumption. This high demand is due to its continuous role in protein synthesis, gluconeogenesis, urea formation, and detoxification processes. **Why other options are incorrect:** * **Brain (Option B):** The brain is highly aerobic and accounts for about **18–20%** of total $VO_2$. While it has a high metabolic rate per gram of tissue, its total consumption is slightly less than that of the liver. * **Muscle (Option C):** At rest, skeletal muscle accounts for about **15–20%** of $VO_2$. However, during heavy exercise, muscle becomes the dominant consumer, potentially accounting for over 90% of total body oxygen use. * **Kidney (Option D):** The kidneys consume about **6–7%** of total $VO_2$. Most of this energy is dedicated to the active transport of sodium ($Na^+$) in the renal tubules. **High-Yield Facts for NEET-PG:** 1. **Oxygen Consumption ($VO_2$) at Rest:** Liver (27%) > Brain (20%) > Muscle (18%) > Kidney (7%) > Heart (4%). 2. **Oxygen Extraction Ratio:** The **Heart** has the highest oxygen extraction ratio (70–80%), meaning it removes the most oxygen per unit of blood delivered. 3. **Blood Flow per 100g:** The **Carotid Body** has the highest blood flow per unit mass, while the **Kidney** receives the highest percentage of total Cardiac Output (20–25%).

Q: Which of the following statements about synovial fluid is false?

Secreted primarily by type A synovial cells. ### Explanation The synovial membrane consists of two distinct types of synoviocytes, and understanding their specific functions is crucial for NEET-PG. **1. Why Option A is False (The Correct Answer):** Synovial fluid is primarily a **dialysate of plasma** supplemented with **Hyaluronic acid**, which is secreted by **Type B synoviocytes** (fibroblast-like cells). **Type A synoviocytes** are macrophage-like cells primarily responsible for phagocytosis and removing debris from the joint space. Therefore, stating that Type A cells secrete the fluid is incorrect. **2. Analysis of Other Options:** * **Option B (Non-Newtonian fluid kinetics):** This is true. Synovial fluid does not have a constant viscosity. Its flow properties change under pressure; it becomes less viscous as the shear rate increases (thinning during rapid joint movement), which is a hallmark of non-Newtonian fluids. * **Option C (Contains Hyaluronic acid):** This is true. Hyaluronic acid (hyaluronan) provides the fluid with its characteristic viscosity and serves as a primary lubricant for the articular cartilage. * **Option D (Viscosity is variable):** This is true. Viscosity varies based on the concentration of hyaluronic acid and the rate of joint movement (shear rate). In inflammatory conditions like Rheumatoid Arthritis, viscosity decreases significantly. **Clinical Pearls for NEET-PG:** * **Type A cells:** Phagocytic (Think **A** for **A**ating/Phagocytosis). * **Type B cells:** Secretory (Think **B** for **B**uilding/Secretory). * **Normal Synovial Fluid:** Clear, straw-colored, high viscosity, and forms a long "string" (String test) when dropped from a syringe. * **Rice Bodies:** Small, white free-floating bodies seen in synovial fluid, classically associated with **Rheumatoid Arthritis** and Tuberculosis.

Q: Which of the following statements about serotonin is true?

It causes vasoconstriction.. **Explanation:** **Serotonin (5-Hydroxytryptamine or 5-HT)** is a monoamine neurotransmitter synthesized from the amino acid **L-tryptophan**. It plays a diverse role in the central nervous system and peripheral tissues. **1. Why Option C is Correct:** Serotonin is a potent **vasoconstrictor** of large arteries and veins (acting via 5-HT₂ receptors). Its name, "serotonin," is derived from its discovery as a "serum tonic" factor that promotes hemostasis. When platelets aggregate at a site of injury, they release serotonin to cause local vasoconstriction, which helps reduce blood loss. **2. Why Other Options are Incorrect:** * **Option A:** Serotonin is actually a **sleep inducer**, not a suppressant. It is a precursor to **melatonin** in the pineal gland, which regulates the sleep-wake cycle. * **Option B:** Serotonin acts as an **anorexigenic** agent (it **decreases appetite**). Drugs that increase serotonin levels (like SSRIs or fenfluramine) are often associated with weight loss or reduced food intake. * **Option C:** In the lungs, serotonin acts as a **bronchoconstrictor** and an irritant, rather than a bronchodilator. **NEET-PG High-Yield Pearls:** * **Synthesis:** Rate-limiting enzyme is **Tryptophan hydroxylase**. * **Degradation:** Metabolized by MAO-A to **5-HIAA**. Elevated urinary 5-HIAA is a diagnostic marker for **Carcinoid Syndrome**. * **Location:** 90% of the body's serotonin is found in the **Enterochromaffin (EC) cells** of the GI tract, where it regulates intestinal motility. * **Receptors:** All 5-HT receptors are G-protein coupled except **5-HT₃**, which is a **ligand-gated ion channel** (target for anti-emetics like Ondansetron).

Q: What is the approximate volume of intracellular fluid (ICF) in the body, expressed as a fraction of body weight?

0.4 * body weight. ### Explanation The distribution of body water is a fundamental concept in physiology, often governed by the **"60-40-20 Rule."** **1. Why Option B is Correct:** In an average healthy adult (70 kg), **Total Body Water (TBW)** accounts for approximately **60% (0.6)** of the total body weight. This water is distributed into two main compartments: * **Intracellular Fluid (ICF):** This is the fluid contained within the cells. It constitutes **two-thirds (2/3)** of the TBW, which equates to approximately **40% (0.4) of the total body weight.** * **Extracellular Fluid (ECF):** This is the fluid outside the cells, constituting the remaining **one-third (1/3)** of TBW, or **20% (0.2) of the body weight.** **2. Analysis of Incorrect Options:** * **Option A (0.2):** This represents the **Extracellular Fluid (ECF)** volume, not the intracellular volume. * **Option C (0.6):** This represents the **Total Body Water (TBW)** in a standard adult male. * **Option D (0.8):** This value is too high for an adult; however, TBW can reach up to 75-80% in **neonates**, making them highly susceptible to dehydration. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Gender Variation:** Women have a lower percentage of TBW (~50%) compared to men (~60%) because they generally have a higher proportion of **adipose tissue** (fat is hydrophobic and contains very little water). * **Indicator Dilution Method:** To measure these volumes clinically: * **TBW** is measured using Tritiated water or Deuterium oxide ($D_2O$). * **ECF** is measured using Inulin, Mannitol, or Sucrose. * **Plasma Volume** is measured using Evans Blue dye or Radio-iodinated Albumin. * **ICF** cannot be measured directly; it is calculated as **TBW minus ECF.**

Q: Osmotic pressure can be calculated by using which law?

Van't Hoff law. **Explanation:** **Correct Answer: B. Van't Hoff law** Osmotic pressure ($\pi$) is the pressure required to stop the net movement of water across a semipermeable membrane. According to **Van't Hoff’s Law**, osmotic pressure is directly proportional to the molar concentration of solutes and the absolute temperature. The formula is expressed as: **$\pi = nCRT$** *(Where $n$ = number of particles, $C$ = molar concentration, $R$ = gas constant, and $T$ = absolute temperature).* In physiology, this law helps determine the tonicity of body fluids and how solutes like albumin maintain oncotic pressure in the plasma. **Why other options are incorrect:** * **Bernoulli’s Law:** Relates to fluid dynamics, stating that as the speed of a moving fluid increases, the pressure within the fluid decreases. It explains phenomena like the *Venturi effect* in narrowed heart valves. * **Ohm’s Law:** Describes the relationship between voltage, current, and resistance ($V=IR$). In physiology, it is applied to blood flow: **Flow = Pressure Gradient / Resistance**. * **Poiseuille’s Law:** Determines the resistance to laminar flow in a vessel. It states that resistance is inversely proportional to the **fourth power of the radius** ($R \propto 1/r^4$), making vessel diameter the most significant factor in determining peripheral resistance. **High-Yield Clinical Pearls for NEET-PG:** 1. **Reflection Coefficient ($\sigma$):** A value between 0 and 1 that describes how easily a solute crosses a membrane. If $\sigma = 1$ (e.g., albumin), the solute is "impermeant" and exerts full osmotic pressure. 2. **Plasma Osmolality:** Normal range is **280–295 mOsm/kg**. It is primarily determined by Sodium ($Na^+$), Glucose, and BUN. 3. **Formula for Plasma Osmolality:** $2[Na^+] + \text{Glucose}/18 + \text{BUN}/2.8$.

Q: The equilibrium potential for an ion is calculated using which equation?

Nernst equation. The **Nernst Equation** is the fundamental formula used to calculate the **equilibrium potential** (also known as the Nernst potential) for a single, specific ion. It determines the electrical potential difference across a cell membrane that exactly balances the concentration gradient of that ion, resulting in no net movement. ### Why the Nernst Equation is Correct: The equation is expressed as: **$E = \frac{RT}{zF} \ln \frac{[Ion]_{out}}{[Ion]_{in}}$** (Simplified at body temperature: $E = \frac{61}{z} \log_{10} \frac{[Ion]_{out}}{[Ion]_{in}}$) It accounts for the valence ($z$) and the concentration gradient of a **single ion** to find the voltage at which that ion is in electrochemical equilibrium. ### Explanation of Incorrect Options: * **Goldman-Hodgkin-Katz (GHK) Equation:** Unlike Nernst, this calculates the **Resting Membrane Potential (RMP)** by considering the concentrations and **permeabilities** of multiple ions (Na⁺, K⁺, and Cl⁻) simultaneously. * **Gibbs-Donnan Equation:** Describes the behavior of charged particles near a semi-permeable membrane when one ion is non-diffusible (e.g., intracellular proteins). It explains the resulting unequal distribution of permeant ions. * **Fick’s Law:** Describes the **rate of diffusion** of a gas or solute across a membrane. It states that the flux is proportional to the concentration gradient, surface area, and membrane permeability. ### High-Yield Clinical Pearls for NEET-PG: * **K⁺ Equilibrium Potential:** Approximately **-94 mV**. Since the RMP of a typical neuron is -70 to -90 mV, K⁺ is the primary determinant of RMP. * **Na⁺ Equilibrium Potential:** Approximately **+61 mV**. * **Key Concept:** If the membrane permeability to an ion increases, the membrane potential moves **toward** the equilibrium potential of that specific ion (e.g., during the upstroke of an action potential, the potential moves toward +61 mV due to Na⁺ influx).

Question 1

Of the total oxygen consumed by the body per minute, which organ consumes the greatest fraction?

Accepted Answer

Liver

Answer

Brain

Answer

Muscle

Answer

Kidney

Question 2

Which of the following statements about synovial fluid is false?

Accepted Answer

Secreted primarily by type A synovial cells

Answer

Follows Non-Newtonian fluid kinetics

Answer

Contains hyaluronic acid

Answer

Viscosity is variable

Question 3

Which of the following statements about serotonin is true?

Accepted Answer

It causes vasoconstriction.

Answer

It is a sleep suppressant.

Answer

It increases appetite.

Answer

It causes bronchodilation.

Question 4

Fick's law describes the rate of transport in which of the following types of diffusion?

Accepted Answer

Simple diffusion

Answer

Facilitated diffusion

Answer

Non-ionic diffusion

Answer

Secondary active transport

Question 5

What is the approximate volume of intracellular fluid (ICF) in the body, expressed as a fraction of body weight?

Accepted Answer

0.4 * body weight

Answer

0.2 * body weight

Answer

0.6 * body weight

Answer

0.8 * body weight

Question 6

Across the cell membrane of a skeletal muscle cell in the resting state with a non-electrogenic pump, what is the relationship between the rates of ion movement?

Accepted Answer

The rate of sodium influx is equal to the rate of potassium efflux.

Answer

Both sodium and potassium are in electrochemical equilibrium.

Answer

The rate of sodium influx is much less than the rate of potassium efflux.

Answer

The rate of sodium influx is much greater than the rate of potassium efflux.

Question 7

All of the following are true regarding the Donnan effect EXCEPT?

Accepted Answer

A non-diffusible ion on one side of a membrane affects the distribution of other diffusible ions.

Answer

The Donnan effect helps prevent cell rupture.

Answer

There is no Donnan effect on diffusible ion movement across the capillary wall.

Answer

The Donnan effect causes a decrease in both the concentrations of cations and the colloid osmotic pressure in the capillary lumen.

Question 8

Osmotic pressure can be calculated by using which law?

Accepted Answer

Van't Hoff law

Answer

Bernoulli's law

Answer

Ohm's law

Answer

Poiseuille's law

Question 9

If a region or compartment is in a steady state with respect to a particular substance, then:

Accepted Answer

The amount of the substance in the compartment does not change with respect to time

Answer

The amount of the substance in the compartment is increasing

Answer

The amount of the substance in the compartment is decreasing

Answer

There is no movement into or out of the compartment

Question 10

The equilibrium potential for an ion is calculated using which equation?

Accepted Answer

Nernst equation

Answer

Gibbs-Donnan equation

Answer

Goldman equation

Answer

Fick's law

General Physiology — MCQs

General Physiology — MCQs

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