Questions and Answers
What are the two major compartments of body fluids?
What accounts for 50% to 70% of body weight?
Total body water
Males generally have a higher percentage of body fat than females.
False
What is the larger of the two extracellular fluid subcompartments?
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What is the main characteristic of interstitial fluid?
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What must each body fluid compartment obey?
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One osmole is the number of particles into which a solute __________.
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What is the pH level of extracellular fluid?
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What ions have a concentration of 140 mEq/L in extracellular fluid and 14 mEq/L in intracellular fluid?
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What property makes phospholipid molecules amphipathic?
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Study Notes
Body Fluid Compartments
- Water is a fundamental component of the body, occupying two main compartments: Intracellular Fluid (ICF) and Extracellular Fluid (ECF) in a ratio of approximately 2:1.
- ECF is divided into plasma (small compartment) and interstitial fluid (larger compartment).
- Differences in ICF and ECF composition are maintained by transport proteins in cell membranes.
Total Body Water
- Total body water constitutes 50% to 70% of body weight, inversely related to body fat percentage.
- Males typically exhibit a higher percentage of total body water and lower body fat compared to females.
Extracellular Fluid
- Plasma acts as the circulating fluid within blood vessels and forms one of the ECF subcompartments.
- Interstitial fluid bathes cells and is derived from plasma through filtration across capillary walls, containing minimal proteins due to the impermeability of large molecules.
Osmoles
- An osmole is defined as the number of particles into which a solute dissociates in solution.
Fluid Compartments and Electrolyte Balance
- Each fluid compartment must maintain macroscopic electroneutrality, ensuring equal concentrations of cations and anions.
- Total solute concentration (osmolarity) remains consistent between ICF and ECF, facilitated by the free flow of water across cell membranes.
| Substance and Units | Extracellular Fluid | Intracellular Fluid |
|---|---|---|
| Na+ (mEq/L) | 140 | 14 |
| K+ (mEq/L) | 4 | 120 |
| Ca2+, ionized (mEq/L) | 2.5 | 1 x 10⁻⁴ |
| Cl- (mEq/L) | 105 | 10 |
| HCO3- (mEq/L) | 24 | 10 |
| pH | 7.4 | 7.1 |
| Osmolarity (mOsm/L) | 290 | 290 |
- Major intracellular anions include proteins and organic phosphates.
- The total [Ca²⁺] in extracellular fluid is approximately 5 mEq/L or 10 mg/dL.
- pH is calculated as -log of the [H+]; a pH of 7.4 indicates a [H+] of 40 x 10⁻⁹ Eq/L.
Na⁺-K⁺ ATPase (Na⁺-K⁺ Pump)
- Phospholipid molecules in membranes are amphipathic, possessing both hydrophilic and hydrophobic characteristics.
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Description
Explore the major components and distribution of body fluids, including intracellular and extracellular compartments. Understand the significance of transport proteins in maintaining the composition of these fluids. This quiz covers the fundamentals of total body water and its relation to body weight.
