Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids Indian Medical PG Practice Questions and MCQs

Question 161: Major ions in ECF are:

A. Potassium and phosphate
B. Sodium and phosphate
C. Potassium and chloride
D. Sodium and chloride (Correct Answer)

Explanation: ***Sodium and chloride*** - **Sodium (Na+)** is the primary cation, and **chloride (Cl-)** is the primary anion in the extracellular fluid (ECF). - These ions play crucial roles in maintaining **osmotic pressure**, **fluid balance**, and **nerve impulse transmission**. *Potassium and phosphate* - **Potassium (K+)** is the major intracellular cation, while **phosphate (PO43-)** is a major intracellular anion. - While present in the ECF, their concentrations are significantly lower compared to sodium and chloride. *Sodium and phosphate* - **Sodium** is a major ECF cation, but **phosphate** is predominantly an intracellular anion. - Therefore, phosphate is not considered one of the major extracellular ions. *Potassium and chloride* - **Potassium** is primarily an intracellular ion, not a major ECF cation. - While **chloride** is a major ECF anion, its pairing with potassium does not represent the two major ions in the ECF.

Question 162: Concentration of Potassium in children's CSF is:

A. 10 mEq/L
B. 3 mEq/L (Correct Answer)
C. 5 mEq/L
D. 15 mEq/L

Explanation: ***3 mEq/L*** - The normal concentration of **potassium (K+)** in **cerebrospinal fluid (CSF)** in children is typically **2.5 to 3.5 mEq/L**, similar to adults. - This **lower concentration** compared to plasma (3.5-5.0 mEq/L) is maintained by the **blood-brain barrier** and **choroid plexus**, which actively regulate ion concentrations in the CSF to protect neuronal function. - In pediatric patients, this concentration remains relatively constant across age groups, though neonates may show minor variations during the early postnatal period. *10 mEq/L* - A potassium concentration of **10 mEq/L in CSF** is significantly higher than the normal physiological range in children. - Such an elevated level would be indicative of a **pathological condition**, potentially associated with **hemolysis**, **traumatic tap**, **cellular damage**, or severe CNS pathology. *5 mEq/L* - While closer to the normal range, **5 mEq/L** is still **higher than the typical physiological concentration** of potassium in pediatric CSF. - This level may suggest contamination with blood, compromise in blood-brain barrier integrity, or early pathological changes, though it is not as profoundly abnormal as 10 mEq/L. *15 mEq/L* - A potassium concentration of **15 mEq/L in CSF** would represent a **severely elevated and highly dangerous level** in children. - Such a high concentration is incompatible with normal brain function and would indicate **severe hemolysis**, **massive cellular breakdown**, or **critical CNS injury**.

Question 163: Which of the following is the approximate extracellular fluid volume of a normal individual?

A. 40% of body mass
B. 5% of body mass
C. 20% of body mass (Correct Answer)
D. 10% of body mass

Explanation: ***20% of body mass*** - Extracellular fluid (ECF) volume constitutes approximately **20% of total body mass**, or roughly one-third of the total body fluid. - This fluid compartment includes plasma, interstitial fluid, lymph, and transcellular fluid. *40% of body mass* - This percentage represents the approximate volume of **intracellular fluid (ICF)**, not extracellular fluid. - ICF accounts for about two-thirds of the total body fluid, residing within the cells. *5% of body mass* - This percentage is too low for the total extracellular fluid volume. - It more closely approximates the volume of **plasma**, which is a component of ECF, but not the entire ECF. *10% of body mass* - This value is lower than the typical extracellular fluid volume. - It does not accurately represent the combined volume of all fluid outside the cells.

Question 164: Which of the following is true about ICF?

A. 14 L
B. 33% of body weight
C. 20 % of body weight
D. 28 L (Correct Answer)

Explanation: ***28 L*** - The **intracellular fluid (ICF)** volume is approximately two-thirds of the total body water, which for a 70 kg individual is around **28 liters**. - This fluid is found within the cells and is crucial for various cellular functions and metabolic processes. *14 L* - This value typically represents the **extracellular fluid (ECF)** volume, which is divided into interstitial fluid and plasma, not the ICF. - The ECF is approximately one-third of the total body water, or about 14 liters. *33% of body weight* - This percentage is **inaccurate for both ICF and ECF**. - ICF accounts for approximately **40% of body weight**, while ECF accounts for about 20% of body weight. - This option does not correctly represent any major fluid compartment. *20% of body weight* - While **20% of body weight** more closely represents the **extracellular fluid (ECF)** volume, it is an underestimate for the intracellular fluid (ICF) volume. - ICF makes up approximately **40% of body weight** in an adult, which is double this value.

Question 165: Which of the following areas of the adrenal gland would you expect to increase in activity in a patient subjected to salt restriction?

A. Zona fasciculata of the adrenal cortex
B. Zona glomerulosa of the adrenal cortex (Correct Answer)
C. Zona reticularis of the adrenal cortex
D. Adrenal medulla

Explanation: ***Zona glomerulosa of the adrenal cortex*** - Salt restriction leads to a decrease in **extracellular fluid volume** and an increase in **potassium** levels, which are potent stimulators for **aldosterone** release. - The **zona glomerulosa** is responsible for synthesizing and secreting aldosterone, a **mineralocorticoid** that helps regulate sodium and potassium balance. *Zona fasciculata of the adrenal cortex* - This layer primarily secretes **glucocorticoids (e.g., cortisol)**, which are involved in stress response and metabolism. - Their activity increases in response to **ACTH**, not directly due to salt restriction. *Zona reticularis of the adrenal cortex* - This layer produces **adrenal androgens** (e.g., DHEA), which are precursors to sex hormones. - Its activity is stimulated by **ACTH**, and it does not play a significant role in salt and water balance. *Adrenal medulla* - The adrenal medulla secretes **catecholamines (epinephrine and norepinephrine)**, which are involved in the "fight or flight" response. - These hormones are released in response to sympathetic nervous system activation and are not directly involved in regulating salt balance.

Question 166: Daily loss of water from skin in absence of sweating is:

A. 200-300 ml (Correct Answer)
B. 1.5 litres
C. 1 litre
D. 500-700 ml

Explanation: ***200-300 ml*** - This range accurately represents the typical daily **insensible water loss** from the skin when **sweating** is not actively occurring. - Insensible water loss is a continuous, unregulated process of water evaporation from the skin and respiratory tract surfaces, essential for thermoregulation and hydration balance. *1.5 litres* - This volume is significantly higher than the insensible water loss from the skin alone and generally reflects the total daily water loss through all routes, including urine, feces, and respiration, in an adult. - Active **sweating**, especially during exercise or in hot environments, would be required to reach this level of total dermal water loss. *1 litre* - While a substantial amount, 1 liter is generally too high for the daily insensible water loss from the skin in the absence of active sweating. - This value might be closer to the total insensible volume when considering both skin and respiratory losses. *500-700 ml* - This range is usually considered the total daily insensible water loss through both the skin and the respiratory tract together. - The skin's contribution alone is typically less than this total amount.

Question 167: Why is carpopedal spasm seen in hyperventilation?

A. Increased excretion of calcium in urine
B. Increased plasma protein binding of Ca (Correct Answer)
C. Increased sequestration of Ca in SER
D. Ca utilized in bones

Explanation: ***Increased plasma protein binding of Ca*** - **Hyperventilation** leads to respiratory alkalosis due to excessive CO2 exhalation, increasing blood pH. - This elevated pH enhances the binding of **calcium to albumin**, decreasing the amount of free ionized calcium available. *Increased excretion of calcium in urine* - **Hyperventilation** itself does not directly lead to increased urinary calcium excretion; rather, it primarily affects the **distribution of calcium** within the bloodstream. - While prolonged alkalosis can affect renal handling of electrolytes, the immediate cause of carpopedal spasm is not urinary loss. *Increased sequestration of Ca in SER* - **Calcium sequestration** in the sarcoplasmic/endoplasmic reticulum (SER) is a process related to intracellular calcium handling and muscle contraction. - It is not the primary mechanism by which **hyperventilation-induced alkalosis** causes **hypocalcemia** and carpopedal spasm. *Ca utilized in bones* - Calcium is continuously exchanged between bone and the extracellular fluid, but **hyperventilation** does not immediately or significantly increase **bone utilization of calcium** to cause acute carpopedal spasm. - Bone serves as a reservoir, but the rapid onset of spasm points to changes in **circulating ionized calcium**.

Question 168: Calcium absorption is increased by

A. Hypercalcemia
B. Oxalates in the diet
C. Iron overload
D. 1.25 Dihydrocholecalciferol (Correct Answer)

Explanation: ***1.25 Dihydrocholecalciferol*** - **1,25-dihydroxycholecalciferol** (calcitriol), the active form of vitamin D, plays a crucial role in **calcium homeostasis** by enhancing calcium absorption from the intestine. - This hormone stimulates the synthesis of **calcium-binding proteins** in intestinal epithelial cells, facilitating the uptake and transport of dietary calcium. *Hypercalcemia* - **Hypercalcemia** (high blood calcium levels) **inhibits** the production of parathyroid hormone (PTH) and **reduces the activation of vitamin D**, thereby decreasing calcium absorption. - The body aims to maintain calcium balance, so excessive calcium in the blood would trigger mechanisms to reduce further absorption, not increase it. *Oxalates in the diet* - **Oxalates** (found in foods like spinach and rhubarb) bind to calcium in the gut to form **insoluble calcium oxalate**, which cannot be absorbed. - This binding effectively **reduces the bioavailability** of dietary calcium, making it less available for absorption. *Iron overload* - **Iron overload** primarily affects iron metabolism and storage, with limited direct impact on calcium absorption mechanisms. - While excessive iron can have systemic effects, it does not directly enhance the absorption of calcium from the intestine.

Question 169: Major contributor to plasma osmolarity is:

A. Sodium (Correct Answer)
B. Plasma proteins
C. Glucose
D. Urea

Explanation: ***Sodium*** - **Sodium (Na+)** is the most abundant extracellular cation and accounts for approximately 90-95% of the **effective plasma osmolarity**. - Its concentration is tightly regulated by hormones like **ADH** and **aldosterone**, making it the primary determinant of water movement between intracellular and extracellular compartments. *Plasma proteins* - While plasma proteins contribute significantly to **oncotic pressure** (colloid osmotic pressure), they have a relatively small direct contribution to the overall **plasma osmolarity** due to their lower molar concentration compared to sodium. - Their primary role is in fluid distribution between the vascular and interstitial spaces, not the total effective solute concentration. *Glucose* - **Glucose** contributes to plasma osmolarity, especially in conditions like **diabetes mellitus** where its levels are high. - However, under normal physiological conditions, the concentration of glucose is much lower than sodium, making its contribution to overall osmolarity less significant. *Urea* - **Urea** is a significant contributor to **total plasma osmolarity**, but it is generally considered an **ineffective osmole** because it can readily cross cell membranes. - While it contributes to the measured osmolarity, it does not exert a significant osmotic force that causes sustained water movement between compartments in the same way sodium does.

Question 170: Which of the following is hypertonic?

A. 5% dextrose
B. 0.45% normal saline
C. 0.9% normal saline (NaCl)
D. 3% normal saline (Correct Answer)

Explanation: ***3% normal saline*** - This solution contains a significantly **higher concentration of sodium chloride** (NaCl) than the body's normal plasma osmolality (approximately 154 mEq/L for 0.9% NS). - Its high solute concentration creates an **osmotic gradient**, causing water to move out of cells and into the extracellular space, classifying it as **hypertonic**. *5% dextrose* - While initially isotonic in the bag, dextrose is rapidly metabolized by the body, leaving behind free water. - This makes it functionally a **hypotonic solution** once administered intravenously, as it dilutes plasma and can cause fluid shifts into cells. *0.45% normal saline* - This is also known as **half-normal saline**, meaning it has half the sodium chloride concentration of 0.9% normal saline. - With a lower solute concentration than plasma, it is considered a **hypotonic solution**, causing fluid to shift into cells. *0.9% normal saline (NaCl)* - This solution has an osmolality of approximately 308 mOsm/L, which is **similar to that of human plasma**. - It is therefore considered an **isotonic solution**, meaning it does not cause significant fluid shifts between the intracellular and extracellular compartments.

Practice by Chapter

Body Fluid Compartments and Composition

Practice Questions

Osmolality and Tonicity

Practice Questions

Sodium and Water Balance

Practice Questions

Potassium Homeostasis

Practice Questions

Calcium and Phosphate Regulation

Practice Questions

Magnesium Metabolism

Practice Questions

Fluid Shifts Between Compartments

Practice Questions

Edema Formation Mechanisms

Practice Questions

Dehydration Physiology

Practice Questions

Disorders of Electrolyte Balance

Practice Questions

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