Questions and Answers
What is an aquaporin?
Creates special water channels through which water can freely move into and out of nearly every cell in the body
Which of the following factors influence body water content? (Select all that apply)
What is the distribution of water among body compartments?
67% intracellular, 33% extracellular (75% interstitial, 25% plasma)
What is osmosis?
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What is osmotic pressure?
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What does osmolarity refer to?
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What is the formula for calculating osmolarity?
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What is the normal osmolarity of the human body?
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What is osmolality?
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What does isosmotic mean?
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What does hyperosmotic describe?
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What does hyposmotic mean?
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What is the definition of hypotonic?
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What does hypertonic mean?
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What is the difference between tonicity and osmolarity?
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What are penetrating solutes?
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What are nonpenetrating solutes?
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Tonicity depends on the concentration of ____.
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What is the most important nonpenetrating solute?
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How can you figure out the tonicity of a solution without actually putting a cell in it?
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Why can an isosmotic solution be isotonic or hypotonic, but not hypertonic?
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What are the rules for osmolarity and tonicity?
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Study Notes
Aquaporin
- Facilitates water movement across cell membranes by creating specific water channels.
Factors Influencing Body Water Content
- Body water content varies by gender: males generally have higher water content than females.
- Age affects water content, with infants having more body water than adults.
Distribution of Water Among Body Compartments
- Intracellular fluid makes up 67% of total body water.
- Extracellular fluid accounts for 33%, divided into:
- 75% interstitial fluid
- 25% plasma
Osmosis
- Defined as the movement of water through a membrane driven by differences in solute concentration.
Osmotic Pressure
- Refers to the pressure required to prevent osmosis, measured in atmospheres (atm) or millimeters of mercury (mm Hg).
Osmolarity
- Measures the concentration of osmotically active particles in a solution, usually expressed in osmoles per liter (osmol/L or OsM), distinct from molarity.
Calculation of Osmolarity
- Osmolarity can be calculated using the formula: osmolarity (osmol/L) = molarity (mol/L) x #particles/molecule (osmol/mol).
Dissociation Factor
- Indicates the extent of molecular dissociation in a solution, with sodium chloride (NaCl) having a dissociation factor of 1.8 at body temperature.
Normal Osmolarity of the Human Body
- Typical osmolarity is around 300 mOsM, slightly less than this value.
Osmolality
- Refers to the concentration of solute in osmoles per kilogram of water; the terms osmolarity and osmolality are often used interchangeably in biological contexts.
Isosmotic Solutions
- Two solutions are isosmotic if they have the same concentration of solute particles per unit volume.
Hyperosmotic Solutions
- Solutions with a higher number of solute particles per unit volume compared to another solution.
Hyposmotic Solutions
- Solutions that contain fewer solute particles per unit volume than another solution.
Tonicity
- Hypotonic solutions cause a cell to gain water, leading to cell swelling.
- Hypertonic solutions lead to water loss from a cell, causing it to shrink.
- Isotonic solutions maintain the cell's size, with no net water movement.
Differences Between Tonicity and Osmolarity
- Osmolarity quantifies solute particles in a solution, while tonicity is a comparative term that does not have units and specifically pertains to the effect on cell volume.
- Tonicity always relates a solution's effect on a cell, while osmolarity can compare any two solutions.
Solute Penetration
- Penetrating solutes can freely enter cells, while nonpenetrating solutes cannot.
Tonicity Dependence
- Tonicity is determined by the concentration of nonpenetrating solutes within the solution.
Most Important Nonpenetrating Solute
- Sodium chloride (NaCl) is the key nonpenetrating solute in physiological contexts.
Tonicity Assessment Without Cell Exposure
- Tonicity can be inferred by comparing the concentrations of nonpenetrating solutes in the cell versus those in the solution.
Isosmotic Solution Characteristics
- An isosmotic solution cannot be hypertonic as it can't have a higher concentration of nonpenetrating solutes than the cell.
- If all solutes are nonpenetrating, the isosmotic solution is isotonic; if penetrating solutes are present, it becomes hypotonic.
Rules for Analyzing Osmolarity and Tonicity
- Assume all intracellular solutes are nonpenetrating when evaluating tonicity.
- Assess osmolarities before exposing a cell to any solution, noting that equilibrium results in isosmotic conditions.
- Tonicity specifies how cell volume will change at equilibrium.
- Determine tonicity by comparing concentrations of nonpenetrating solutes, as water moves toward higher solute concentrations.
- Always remember that hyposmotic solutions are equivalently hypotonic.
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Test your understanding of osmosis and tonicity with these flashcards. Learn about essential terms like aquaporin, factors influencing body water content, and the distribution of water in body compartments. Perfect for biology students looking to reinforce their knowledge!