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Questions and Answers
What is the primary reason for the difference in body water composition between men and women?
How does age affect body water content?
What percentage of body weight does the total fluid volume approximately represent in a 70 kg individual?
Which fluid compartment is NOT classified as part of the extracellular fluid?
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Which condition is NOT typically associated with chronic or repeated dehydration?
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What is the osmolality threshold indicating hypertonicity of serum?
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What specialized fluid compartment includes cerebrospinal fluid and synovial fluid?
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What common cause contributes to dehydration among older adults?
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What role does the Na-K pump primarily play in maintaining cellular homeostasis?
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In using the Nernst equation, what is primarily calculated?
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What is a significant characteristic of intracellular fluid compared to extracellular fluid?
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How does gender typically influence body water composition?
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What correlation exists between age and body water content?
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Which of the following statements about solutes in the body's fluid compartments is correct?
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Why is the lipid bilayer considered semi-permeable?
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What aspect of osmosis is critical to maintaining homeostasis within fluid compartments?
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What is the primary function of the Na-K pump in maintaining cellular homeostasis?
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How would you apply the Nernst equation to determine the equilibrium potential for potassium ($K^+$) in muscle cells?
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What distinguishes intracellular fluid from extracellular fluid in terms of sodium concentration?
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Which of the following statements correctly describes gender differences in body water composition?
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How does age correlate with body water composition?
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What is the primary electrolyte difference between muscle cells and plasma?
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Which factor does NOT contribute to the osmolarity of a fluid compartment?
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Which electrolyte is predominantly higher in plasma than in intracellular fluid?
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Study Notes
Fluid Compartments in the Body
- The adult human body consists of approximately 60% water.
- This water is found in various compartments:
- Interstitial fluid: The fluid between cells, including lymph. It accounts for 36% or 15L of body water.
- Blood plasma: Makes up 7% or 3L of body water.
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Transcellular fluid: Specialized fluid compartments, such as:
- Cerebrospinal fluid (CSF) in the spinal cord, choroid plexus, and brain ventricles.
- Aqueous and vitreous humor in the eyeball.
- Synovial fluid in joints, representing 2% or 1L of body fluid.
- Saliva, gastric juice, and urine.
- Total body fluid: The sum of all fluid compartments is approximately 42L, representing around 60% of total body weight.
- Fluid differences between genders: Women have slightly less body water than men due to their higher adipose tissue content.
- Fluid changes with age: Water content decreases with age, particularly noticeable in the skin. Older individuals may experience dehydration because they drink less.
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Dehydration: Can be assessed by:
- Measuring the osmolality of blood.
- Assessing the specific gravity or osmolality of urine.
- Hypertonicity of serum: Sodium levels greater than 145 mmol/L.
- Sport medicine: Urine osmolality above 700 mOsmol/kg H2O or urine specific gravity greater than 1.02. However, urine measurements are less reliable as they depend on factors like exercise timing and fluid intake.
Consequences of Dehydration
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Chronic or repeated dehydration can lead to:
- Urinary tract infections.
- Lung infections.
- Kidney stones.
- Kidney failure.
- Seizures.
- Dehydration is particularly dangerous for babies, children, and older adults.
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Causes of dehydration:
- Diarrhea and vomiting, often due to infections or fevers.
- Intensive exercise in hot weather, leading to excessive sweating.
- Medication use.
- Diabetes.
- Insufficient fluid intake.
Fluid Compartment Composition
- The extracellular compartments (plasma, lymph, and interstitial fluids) have similar composition, but plasma contains more protein than interstitial fluid.
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Intracellular fluid differs significantly:
- Sodium (Na+): Lower concentration in intracellular fluid (10 mMol/L) compared to plasma (140 mMol/L).
- Potassium (K+): Higher concentration in intracellular fluid (150 mMol/L) compared to plasma (5 mMol/L).
- Calcium (Ca2+): Significantly lower concentration in intracellular fluid (10-4 mMol/L) compared to plasma (2 mMol/L).
- Chloride (Cl-): Higher concentration in plasma (105 mMol/L) compared to intracellular fluid (5 mMol/L).
- Organic phosphates: Higher concentration in intracellular fluid (100 mMol/L) compared to plasma (10 mMol/L).
- Proteins: Higher concentration in plasma (1 mMol/L) compared to intracellular fluid (2 mMol/L).
- pH: Slightly more acidic in intracellular fluid (7.1) compared to plasma (7.4).
- Osmolarity: Similar in both compartments (approximately 263 mOsmol/L in plasma and 267 mOsmol/L in muscle cells).
Biological Membranes
- Lipid bilayer: The main component of biological membranes.
- Phosphatidylcholine: A glycerophospholipid found in the bilayer.
- Glycolipids and sterols: Also present in the lipid bilayer.
- Thickness: The lipid bilayer is approximately 5nm thick.
- Signaling proteins: These proteins span the entire thickness of the membrane, facilitating communication across the membrane.
Key Concepts
- Permeability of membranes: Lipid membranes are semi-permeable, allowing some molecules to pass through easily while restricting others.
- Diffusion: Movement of molecules from a high concentration area to a low concentration area.
- Brownian motion: Random movement of particles in a fluid.
- Osmosis: Movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration.
- Osmolarity: The concentration of solute particles in a solution.
- Osmolality: The concentration of solute particles per unit mass of solvent.
- Tonicity: The relative concentration of solutes in two solutions separated by a semi-permeable membrane.
- Transport across membranes: How substances move across the membrane.
- Exchange across capillary walls: The movement of substances between blood and interstitial fluid through capillary walls.
- pH: A measure of the acidity or alkalinity of a solution.
- Electrical charge: The charge carried by ions and other charged particles.
- Electrolytes: Ions in biological systems.
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Description
Explore the various fluid compartments within the adult human body, including interstitial fluid, blood plasma, and transcellular fluid. Understand the importance of these compartments and how fluid distribution varies with gender and age. Test your knowledge on body water percentages and their physiological significance.
