Test: Homeostasis of Body Fluids- 2 - NEET PG MCQ

The volume of plasma constitutes 5% of an individual's overall body weight. In the case of a person weighing 70 kg:

• Plasma volume amounts to 3.5 L
• Total body water is 42 L (representing 60% of body weight)

Thus, plasma accounts for 8.3% of total body water, calculated as [(3.5/42) × 100].

ECF constitutes 20% of the overall body weight. Therefore, the nearest answer is 25% among the given choices.

Extracellular fluid (ECF) makes up 20% of the overall body weight. Plasma comprises 5% of body weight.

I¹²⁵ albumin is utilised for measuring plasma volume rather than blood volume.

Inulin is the most suitable option for measuring the extracellular fluid (ECF).

Predominant ECF: Na⁺, Cl⁻, HCO₃⁻ and Ca²⁺

• Predominant ICF: K⁺
• Mg²⁺
• phosphate
• and protein.

The composition of ions in the body can vary significantly between different environments. Here are some key points:

• Intracellular and extracellular ion compositions are not the same.
• Phosphorus and magnesium are major ions found inside cells.
• Sodium and chloride are the principal ions present in the extracellular fluid.
• The kidneys play a crucial role in regulating the levels of sodium, potassium, and chloride.

The primary reservoir of Na⁺ is found in bones rather than in muscle.

The variation is not noticeable until the onset of puberty.

At 37°C, a concentration of 1 osmole per litre will result in an osmotic pressure of 19,300 mm Hg in the solution. Similarly, a concentration of 1 mOsmol per litre is equal to an osmotic pressure of 19.3 mm Hg.

Highly permeable substances, like urea, can lead to temporary changes in fluid volume between the intracellular fluid (ICF) and extracellular fluid (ECF). However, with sufficient time, the concentrations of these substances ultimately equalise in both compartments and exert minimal influence on intracellular osmolality and volume when in a steady state. This is why urea is considered an ineffective osmole.

The baroreceptor reflex is an example of a negative feedback system. This means it works to maintain stability in the body by counteracting changes. Here's how it functions:

• Baroreceptors are sensors located in blood vessels that detect changes in blood pressure.
• When blood pressure rises, these receptors send signals to the brain.
• The brain then responds by lowering the heart rate and dilating blood vessels, which reduces blood pressure.
• If blood pressure drops, the process reverses: the heart rate increases and blood vessels constrict to raise blood pressure.

This feedback mechanism helps keep blood pressure within a normal range, ensuring that the body's organs receive adequate blood flow.

A feed forward control system is used to regulate various bodily functions by anticipating changes. In the context of temperature regulation, this system helps maintain a stable internal environment by adjusting responses before changes occur.

• When body temperature rises, mechanisms are activated to cool the body down.
• If body temperature drops, the system prompts warming actions.

This proactive approach is essential for maintaining optimal body function and overall health.

The normal plasma volume in an adult is approximately:

• 3.8 L is the correct answer.
• 55% of its total volume.
• The plasma volume can vary based on factors such as body size and hydration levels.
• Understanding normal plasma volume is important for assessing health conditions and fluid balance.

Water is a hypotonic solution, therefore it will be evenly distributed between the extracellular fluid (ECF) and intracellular fluid (ICF) based on their respective volumes. Thus:

• 2/3 of 1500 mL will be allocated to the ICF, which equals 1000 mL.
• 1/3 of 1500 mL will be allocated to the ECF, equating to 500 mL.
• The interstitial fluid (ISF) constitutes 3/4 of the ECF, which is 3/4 of 500 mL, resulting in 375 mL.

• Blood volume = Plasma volume / (1 – Hct)
• Substituting the values gives: Blood volume = 3 / (1 – 0.4) = 5 L.

• NaCl and KCl each dissociate into two particles.
• CaCl₂ breaks down into three particles.

• 12 mmol of NaCl results in an osmolality of 24 mOsmol.
• 4 mmol of KCl equals 8 mOsmol.
• 2 mmol of CaCl₂ corresponds to 6 mOsmol.

The 1 mM CaCl₂ solution (osmolarity = 3 mOsm/L) is hyperosmotic compared to the 1 mM NaCl solution (osmolarity = 2 mOsm/L). The solutions of 1 mM glucose, 1.5 mM glucose, and 1 mM sucrose are hyposmotic in relation to the 1 mM NaCl.

The RBC was equilibrated in 150 mM NaCl (which corresponds to 300 mOsmol NaCl), making it an isotonic saline solution.

• A 300 mOsm CaCl₂ solution is likewise an isotonic solution with a non-penetrating solute.
• As a result, there will be no alteration in the volume of the RBC.

200 mOsm NaCl is non-penetrating, whereas 200 mOsm glycerol penetrates gradually.

• At first, the effective osmolarity of the solution is 400 mOsm (200 NaCl + 200 glycerol), leading to cell shrinkage.
• Over time, glycerol penetrates, resulting in a final effective osmolarity of only 200 mOsm due to the NaCl.
• As glycerol continues to penetrate, water moves into the red blood cell, causing the final volume to exceed that at the initial moment.

Curve B, which illustrates initial shrinkage followed by overall swelling, represents the most accurate response.