Electrolytes and Body Fluids Practice Questions

Q: Extracellular fluid volume most commonly increases in which of the following conditions?

All of these. ### Explanation The correct answer is **D. All of these**. The expansion of Extracellular Fluid (ECF) volume, clinically manifesting as **edema**, occurs when there is a disturbance in Starling forces (capillary hydrostatic or oncotic pressure) or a primary failure in sodium and water excretion. **1. Cardiac Disorders (e.g., Congestive Heart Failure):** In heart failure, decreased cardiac output leads to reduced effective arterial blood volume. This activates the **Renin-Angiotensin-Aldosterone System (RAAS)** and stimulates the release of ADH. The resulting sodium and water retention by the kidneys increases the ECF volume to compensate for low output, leading to systemic congestion and peripheral edema. **2. Hepatic Disorders (e.g., Liver Cirrhosis):** Liver failure causes ECF expansion via two mechanisms: * **Decreased Oncotic Pressure:** Reduced synthesis of albumin (hypoalbuminemia) allows fluid to leak from capillaries into the interstitium. * **Splanchnic Vasodilation:** This triggers RAAS, leading to massive sodium and water retention (Ascites). **3. Renal Diseases (e.g., Nephrotic Syndrome, Acute Renal Failure):** * In **Nephrotic Syndrome**, heavy proteinuria causes hypoalbuminemia, leading to edema. * In **Renal Failure**, the kidneys lose the ability to filter and excrete sodium and water, causing direct primary ECF volume expansion. --- ### High-Yield Clinical Pearls for NEET-PG: * **Starling’s Law:** Edema occurs when Hydrostatic pressure increases (Heart failure) or Plasma Oncotic pressure decreases (Liver/Renal failure). * **Most common cause of generalized edema:** Congestive Heart Failure. * **Marker for ECF Volume:** Inulin is the gold standard for measuring ECF volume, while Mannitol and Sucrose are also used. * **Sodium is the primary determinant** of ECF volume; "Where sodium goes, water follows."

Q: Which of the following ECG changes is characteristic of hypokalemia?

Depressed ST segment. **Explanation:** Hypokalemia (serum potassium <3.5 mEq/L) affects the repolarization phase of the cardiac action potential. As potassium levels drop, the resting membrane potential becomes more negative, and the duration of the action potential increases. **Why the correct answer is right:** **ST segment depression** is a classic sign of hypokalemia. It occurs due to altered repolarization gradients across the ventricular wall. As hypokalemia worsens, you typically see a progressive "flattening" of the T wave and the appearance of prominent **U waves** (the most characteristic sign). In severe cases, the T wave and U wave may fuse, mimicking a prolonged QT interval (often called a "QU" interval). **Analysis of incorrect options:** * **A. Tall T wave:** This is a hallmark of **Hyperkalemia** (specifically "peaked" or "tented" T waves). In hypokalemia, T waves are flat or inverted. * **B. Short QRS interval:** Hypokalemia actually causes a **prolonged QRS duration** (widening) in severe cases, not shortening. * **C. Absent P wave:** Loss of P waves is a feature of **severe Hyperkalemia**, where the atria become non-excitable (sinoventricular rhythm). In hypokalemia, P waves may actually become peaked or increased in amplitude. **NEET-PG High-Yield Pearls:** * **Sequence of Hypokalemia ECG changes:** T-wave flattening → ST depression → Prominent U waves → Apparent QT prolongation. * **Sequence of Hyperkalemia ECG changes:** Tall peaked T waves → Prolonged PR interval → Loss of P wave → Widened QRS (Sine wave pattern) → Asystole. * **U wave:** Best seen in precordial leads **V2–V4**. * Hypokalemia increases the risk of **Digoxin toxicity** and arrhythmias like **Torsades de Pointes**.

Q: What is the normal glucose level in Cerebrospinal Fluid (CSF)?

40-70 mg/dL. **Explanation:** The normal glucose level in Cerebrospinal Fluid (CSF) is typically **40–70 mg/dL**. The underlying physiological principle is that CSF glucose is directly dependent on plasma glucose levels. Glucose enters the CSF from the blood via **facilitated diffusion** using **GLUT-1 transporters** located in the blood-brain barrier. Under normal physiological conditions, the CSF glucose concentration is approximately **60% (two-thirds)** of the simultaneous plasma glucose concentration. **Analysis of Options:** * **Option A:** Incorrect. Glucose is a vital metabolic substrate for the brain and is always present in the CSF. * **Option C:** Incorrect. This range (80–120 mg/dL) represents normal fasting or post-prandial **blood** glucose levels, not CSF levels. * **Option D:** Incorrect. This represents a hyperglycemic state in the blood. **Clinical Pearls for NEET-PG:** 1. **Hypoglycorrhachia:** This refers to low CSF glucose. It is a hallmark of **Bacterial, Fungal, and Tubercular meningitis** because the bacteria and infiltrating white blood cells (neutrophils) consume glucose for metabolism. 2. **Viral Meningitis:** A high-yield distinction is that CSF glucose remains **normal** in viral meningitis, as viruses do not utilize glucose for energy. 3. **Diagnostic Ratio:** For an accurate diagnosis, CSF glucose must always be compared to a simultaneous blood glucose sample. A CSF/Serum glucose ratio **< 0.4** is highly suggestive of bacterial meningitis. 4. **Appearance:** Normal CSF is clear and colorless ("crystal clear"). Turbidity often indicates high protein or cell count (pleocytosis).

Q: When capillary hydrostatic pressure is 30 mm of Hg and interstitial hydrostatic pressure is 5 mm of Hg, and the colloid oncotic pressure of capillaries is 25 mm of Hg and the interstitium is 5 mm of Hg, what is the net filtration pressure?

5 mm Hg. ### Explanation The net movement of fluid across a capillary membrane is determined by **Starling’s Forces**. The Net Filtration Pressure (NFP) is calculated using the Starling equation: **NFP = (Forces favoring filtration) – (Forces opposing filtration)** **NFP = [ (Pc + πi) – (Pi + πc) ]** Where: * **Pc** (Capillary Hydrostatic Pressure) = 30 mm Hg (Favors filtration) * **πi** (Interstitial Oncotic Pressure) = 5 mm Hg (Favors filtration) * **Pi** (Interstitial Hydrostatic Pressure) = 5 mm Hg (Opposes filtration) * **πc** (Capillary Oncotic Pressure) = 25 mm Hg (Opposes filtration) **Calculation:** NFP = (30 + 5) – (5 + 25) NFP = 35 – 30 = **5 mm Hg** Since the result is positive, there is a net movement of fluid out of the capillary into the interstitial space. #### Analysis of Incorrect Options: * **B (10 mm Hg):** This error usually occurs if one forgets to subtract the interstitial hydrostatic pressure or incorrectly adds the oncotic pressures. * **C (15 mm Hg):** This result occurs if the interstitial oncotic pressure is ignored or if the hydrostatic pressures are subtracted incorrectly (30 - 15). * **D (20 mm Hg):** This value is obtained if only the difference between the two hydrostatic pressures (30 - 10) or two oncotic pressures is considered in isolation. #### High-Yield Clinical Pearls for NEET-PG: 1. **Edema Formation:** Edema occurs when NFP increases significantly, often due to increased $P_c$ (e.g., Heart Failure), decreased $\pi_c$ (e.g., Nephrotic Syndrome, Cirrhosis), or lymphatic obstruction. 2. **The "Safety Factor":** The lymphatic system can increase its flow up to 20-fold to compensate for increased filtration before clinical edema becomes apparent. 3. **Negative Interstitial Pressure:** In most loose subcutaneous tissues, the interstitial hydrostatic pressure ($P_i$) is actually slightly **sub-atmospheric (negative)**, which helps hold the tissues together.

Q: Which of the following concentrations of IV fluid is hypertonic in nature?

3% normal saline. **Explanation:** The tonicity of an intravenous fluid is determined by its **effective osmolality** relative to human plasma (normal range: 275–295 mOsm/L). A hypertonic solution has a higher concentration of solutes than plasma, causing water to move out of cells via osmosis. **Why 3% Normal Saline is Correct:** * **3% Normal Saline (NaCl):** This is a concentrated salt solution containing 513 mEq/L of Sodium and Chloride each, resulting in a total osmolarity of **1026 mOsm/L**. Since this is significantly higher than plasma osmolarity, it is classified as a **hypertonic** crystalloid. It is clinically used in emergencies to treat severe symptomatic hyponatremia or cerebral edema. **Analysis of Incorrect Options:** * **0.9% Normal Saline (Option C):** Known as "Isotonic Saline," it has an osmolarity of **308 mOsm/L**. Although slightly higher than plasma, it is physiologically considered **isotonic** as it does not cause significant fluid shifts between compartments. * **5% Dextrose (Option A):** In the bag, it is **isotonic** (252 mOsm/L). However, once infused, the dextrose is rapidly metabolized by cells, leaving behind free water. Therefore, it acts as a **hypotonic** solution physiologically. * **0.45% Normal Saline (Option B):** Often called "half-normal saline," it has an osmolarity of **154 mOsm/L**. Since this is lower than plasma, it is a **hypotonic** solution. **High-Yield Clinical Pearls for NEET-PG:** * **Ringer’s Lactate (RL):** The most physiological fluid; it is **isotonic** (273 mOsm/L). * **Colloids:** (e.g., Albumin, Dextran) exert high oncotic pressure and are used for rapid volume expansion. * **Caution:** Rapid correction of hyponatremia with hypertonic (3%) saline can lead to **Osmotic Demyelination Syndrome** (Central Pontine Myelinolysis).

Q: What is the average insensible water loss from the body per day?

800 ml per day. ### Explanation **1. Understanding Insensible Water Loss (IWL)** Insensible water loss refers to the continuous, unconscious loss of water from the body that cannot be easily measured. It occurs via two primary routes: * **Skin (Transepidermal):** Diffusion through the skin layers (distinct from active sweating). * **Lungs:** Evaporation into expired air during respiration. In a healthy adult under normal sedentary conditions, the total IWL is approximately **700–800 ml/day**. Specifically, about 300–400 ml is lost through the lungs and 300–400 ml through the skin. Therefore, **Option C (800 ml)** is the most accurate average value cited in standard physiological texts like Guyton and Hall. **2. Analysis of Incorrect Options** * **Option A (400 ml):** This represents the loss from only one component (either skin or lungs) or the "obligatory urine volume" required to excrete metabolic waste. * **Option B (600 ml):** While closer, this underestimates the combined loss from both the respiratory tract and skin in an average adult. * **Option D (1500 ml):** This is the typical daily **urine output** for an adult, not insensible loss. **3. High-Yield Clinical Pearls for NEET-PG** * **Solute-Free Water:** IWL consists of pure water, not electrolytes. This is a key distinction from sweat, which contains sodium. * **Fever:** For every 1°C rise in body temperature, IWL increases by approximately 100–150 ml/day. * **Burns:** Extensive skin burns can increase IWL dramatically (up to 3–5 L/day) due to the loss of the cornified layer of the skin which acts as a vapor barrier. * **Tachypnea:** Increased respiratory rate significantly elevates IWL via the lungs.

Q: Which among the following is the main cation of intracellular fluid?

Magnesium. **Explanation:** The distribution of electrolytes across cell membranes is highly asymmetrical, maintained primarily by the Na⁺-K⁺ ATPase pump and selective membrane permeability. **Why Magnesium is the correct answer:** Intracellular fluid (ICF) is characterized by high concentrations of Potassium (K⁺), Magnesium (Mg²⁺), and organic phosphates. While **Potassium is the most abundant cation** in the ICF (~140-150 mEq/L), **Magnesium is the second most abundant intracellular cation** (~20-30 mEq/L). In the context of the given options, where Potassium is absent, Magnesium is the correct choice as the "main" cation listed. It serves as a vital cofactor for over 300 enzymatic reactions, including ATP-dependent processes. **Analysis of Incorrect Options:** * **A. Sodium (Na⁺):** This is the **principal cation of the Extracellular Fluid (ECF)**. Its concentration is high outside (~142 mEq/L) and low inside (~10-14 mEq/L). * **B. Chloride (Cl⁻):** This is the **principal anion of the ECF**. It follows sodium to maintain electrical neutrality in the extracellular space. * **D. Bicarbonate (HCO₃⁻):** This is a major **extracellular anion** involved in the blood buffering system. Its concentration is significantly higher in the ECF (~24-28 mEq/L) than in the ICF (~8-10 mEq/L). **High-Yield NEET-PG Pearls:** * **Most abundant intracellular cation:** Potassium (K⁺). * **Most abundant intracellular anion:** Proteins and Organic Phosphates. * **Most abundant extracellular cation:** Sodium (Na⁺). * **Most abundant extracellular anion:** Chloride (Cl⁻). * **Magnesium Fact:** Hypomagnesemia often coexists with hypokalemia and hypocalcemia; you cannot correct potassium levels effectively until magnesium deficiency is addressed.

Question 1

Neurological manifestations of water intoxication are all of the following except?

Accepted Answer

Increased risk of intracerebral hemorrhage

Answer

Headache

Answer

Confusion

Answer

Convulsions

Question 2

Extracellular fluid volume most commonly increases in which of the following conditions?

Accepted Answer

All of these

Answer

Cardiac disorders

Answer

Hepatic disorders

Answer

Renal diseases

Question 3

Which of the following are the predominant extracellular ions?

Accepted Answer

HCO3-

Answer

Na+

Answer

K+

Answer

Cl-

Question 4

Which of the following ECG changes is characteristic of hypokalemia?

Accepted Answer

Depressed ST segment

Answer

Tall T wave

Answer

Short QRS interval

Answer

Absent P wave

Question 5

What is the normal glucose level in Cerebrospinal Fluid (CSF)?

Accepted Answer

40-70 mg/dL

Answer

Glucose is not present in CSF

Answer

80-120 mg/dL

Answer

120-180 mg/dL

Question 6

Which of the following statements regarding potassium balance is FALSE?

Accepted Answer

Acidosis leads to movement of potassium from the extracellular to the intracellular fluid.

Answer

Most of the body's potassium is intracellular.

Answer

Three-quarters of the total body potassium is found in skeletal muscle.

Answer

Intracellular potassium is released into the extracellular space in response to severe injury.

Question 7

When capillary hydrostatic pressure is 30 mm of Hg and interstitial hydrostatic pressure is 5 mm of Hg, and the colloid oncotic pressure of capillaries is 25 mm of Hg and the interstitium is 5 mm of Hg, what is the net filtration pressure?

Accepted Answer

5 mm Hg

Answer

10 mm Hg

Answer

15 mm Hg

Answer

20 mm Hg

Question 8

Which of the following concentrations of IV fluid is hypertonic in nature?

Accepted Answer

3% normal saline

Answer

5% dextrose

Answer

0.45% normal saline

Answer

0.9% normal saline

Question 9

What is the average insensible water loss from the body per day?

Accepted Answer

800 ml per day

Answer

400 ml per day

Answer

600 ml per day

Answer

1500 ml per day

Question 10

Which among the following is the main cation of intracellular fluid?

Accepted Answer

Magnesium

Answer

Sodium

Answer

Chloride

Answer

Bicarbonate

Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids — MCQs

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