Osmolarity and Osmotic Pressure

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Questions and Answers

What is the primary difference between osmolarity and osmolality?

Osmolarity is the concentration of solutes in a solution, while osmolality is the concentration of solutes per mass of solvent. (correct)

Osmolarity only accounts for non-dissociable solutes, whereas osmolality includes all solutes.

Osmolarity can be adjusted in response to temperature changes, while osmolality cannot.

Osmolarity is measured in Osm/L, while osmolality is measured in Osm/kg. (correct)

What role do aquaporins play in cell membranes?

They facilitate the movement of solutes across a cell membrane.

They block the passage of all solutes through the membrane.

They act as receptors for signaling molecules.

They enhance the diffusion of water through the lipid bilayer. (correct)

Which of the following statements is true regarding osmotic pressure?

Osmotic pressure is independent of the concentration of solute particles in a solution.

Osmotic pressure is the driving force for the net movement of water across a semi-permeable membrane. (correct)

Osmotic pressure is directly affected by the temperature of the solution.

Osmotic pressure decreases with increasing solute concentration.

How does a semi-permeable membrane function in osmosis?

It permits passage of water but restricts movement of certain solutes. Signup and view all the answers

Which of the following describes a hyperosmotic solution?

It has a higher concentration of solutes compared to the cell. Signup and view all the answers

What happens to a cell placed in a hyposmotic solution?

The cell will swell and may burst due to water influx. Signup and view all the answers

When comparing fluid compartments in the body, which statement is correct?

The movement of fluids between these compartments is regulated by osmolarity and tonicity. Signup and view all the answers

What can happen to a cell with a membrane permeable to both water and sucrose when placed in a solution with a higher sucrose concentration?

Water will flow out of the cell and sucrose will flow in. Signup and view all the answers

What is the primary difference between osmolarity and tonicity in a solution?

Osmolarity is affected by all solutes, tonicity is affected by solutes that cannot cross the membrane. Signup and view all the answers

Which of the following statements about a hypertonic solution is true?

It causes cells to shrink because water exits the cells. Signup and view all the answers

What condition may result from low levels of plasma proteins?

Fluid movement from the plasma to the interstitial fluid, causing oedema. Signup and view all the answers

What happens to a red blood cell (RBC) placed in a hypotonic solution?

The cell bursts if it swells more than 1.6 times its original size. Signup and view all the answers

How does the body maintain osmolarity between extracellular fluid (ECF) and intracellular fluid (ICF)?

By keeping ECF and ICF at approximately the same osmolarity of 270 - 300 mOsm/L. Signup and view all the answers

What is the role of aquaporins in cell membranes?

They allow selective permeability to water, facilitating osmosis. Signup and view all the answers

In the case of cerebral oedema, what might be a potential treatment method?

Administering a hypertonic solution such as mannitol. Signup and view all the answers

Which solution is used as isotonic with respect to red blood cells?

0.9% NaCl solution. Signup and view all the answers

What happens to a cell placed in a hyperosmotic solution compared to an isosmotic solution?

The cell shrinks due to water leaving the cell. Signup and view all the answers

Which term best describes a solution with a lower concentration of solutes compared to the intracellular fluid (ICF)?

Hypoosmotic Signup and view all the answers

How does osmotic pressure relate to solute concentration?

Osmotic pressure increases with greater solute concentration. Signup and view all the answers

When a cell is encased in a rigid box, what pressure is exerted onto the box due to the net movement of water?

Osmotic pressure Signup and view all the answers

What is the expected outcome when the concentration of the extracellular fluid (ECF) increases?

Water moves out of the cell, causing it to shrink. Signup and view all the answers

Which characteristic is true of an isosmotic solution?

It has no net water movement across the cell membrane. Signup and view all the answers

What effect would placing a cell in a solution with a solute concentration of 100 mmol/L compared to the cell's ICF concentration of 300 mOsm typically have?

The cell will swell due to water entering. Signup and view all the answers

Aquaporins are specialized proteins that facilitate what kind of movement across the cell membrane?

Water molecules primarily. Signup and view all the answers

Study Notes

Objectives

Define osmotic pressure
Calculate osmolarity and osmolality
Understand hyposmotic, hyperosmotic, and isosmotic
Understand the difference between osmolarity and tonicity
Understand osmosis at the cell membrane and capillary wall

Osmolarity (Osmotic Concentration)

Osmolarity is the concentration of all solutes in a solution
Units of osmolarity are Osm/L (Osmoles per Litre)
Osmolarity is similar to molar concentration (M)
Units of osmolality are Osm/kg
Osmolarity values are usually similar; the variation accounts for solutes that contribute to a solution's osmotic pressure
Some substances dissociate in solution
- 1 mol/L glucose = 1 Osm/L
- 1 mol/L NaCl = 2 Osm/L
- 1 mol/L CaCl₂ = 3 Osm/L

Cell Membranes

Cell membranes are selectively permeable barriers
Allow hydrophobic (lipid-soluble) substances to easily cross
Allow some small hydrophilic (polar) substances to cross easily
Prevent large polar substances (e.g., glucose, ions) from freely passing

Movement of Water Across the Cell Membrane

Water is a polar molecule (+/-)
Small amounts of water pass through the lipid bilayer via simple passive diffusion
Membrane permeability to water can increase with aquaporins (specialised water channels)

Osmosis

Osmosis is a passive transport mechanism
Water moves from an area of high water concentration (high water potential) to an area of low water concentration (low water potential) across a semi-permeable membrane
High solute concentration = low water concentration
Low solute concentration = high water concentration
Osmosis must occur across a semi-permeable membrane
Semi-permeable membrane is permeable to water but impermeable to at least one solute
Driving force for osmosis is osmotic pressure (i.e., dilute to concentrated)

Osmosis Example

A solution in a beaker contains 180 g/L sucrose.
A "cell" contains 360 g/L sucrose.
The cell membrane is permeable to water, but not sucrose.
Water moves into the cell, causing it to swell.
Water continues to move until the concentration of solutes is equal on both sides of the membrane

Osmosis Results in...

Higher water concentration in the beaker than in the cell.
Water moves into the cell.
Cell swells
Water continues to move until concentration is equal on both sides of the membrane

Osmotic Pressure

Osmotic pressure is the pressure required to prevent osmosis.
The larger the solute concentration, the greater the osmotic pressure

Body Fluid Compartments

In the body, all compartments are normally in osmotic equilibrium (~300 mOsm)
Changes in concentration of intracellular fluid (ICF) or extracellular fluid (ECF) result in fluid shift between compartments

Comparing Osmolarity

Use terms like isosmotic, hyposmotic, or hyperosmotic to compare osmolarity of different solutions.
A cell placed in an isosmotic sucrose solution has no net water movement and no volume change
Sucrose cannot cross the cell membrane

Comparing Osmolarity (Hypo/Hyperosmotic)

A hypoosmotic sucrose solution (100 mmol/L) causes water to move into the cell, leading to cell swelling.
A hyperosmotic sucrose solution (400 mmol/L) causes water to move out of the cell, leading to cell shrinkage

Tonicity

Describes how a solution affects cell volume
Osmolarity is affected by all solutes, tonicity is only affected by solutes that don't cross the membrane.
A hypotonic solution causes cells to swell
An isotonic solution causes no volume change
A hypertonic solution causes cells to shrink

Comparing Tonicity (Isosmotic Example)

A cell placed in a 300 mmol/L urea solution (isosmotic).
Urea can cross the cell membrane, followed by water.
Cell swells (oedema)

Osmotic Behaviour of Cells

RBCs in isotonic solution (e.g., 0.9% NaCl): No change in volume
RBCs in hypotonic solution (e.g., water): Swells, potentially bursts (haemolysis)
RBCs in hypertonic solution (e.g., 2% NaCl): Shrinks
Dehydration prevention: Don't give water intravenously to dehydrated patients

How Osmosis Relates to Cells in the Body

Cell membranes are permeable to water, which moves across membranes by osmosis
Movement depends on the solute concentration in ECF and ICF
Electrolytes contribute to body fluid osmolarity.
ECF and ICF must have similar osmolarity.
Osmosis occurs if water is lost from one compartment.
Body fluid osmolarity is approximately 270-300 mOsm/L

Oedema

Plasma proteins maintain osmotic pressure to keep fluid in blood vessels.
Low plasma proteins cause fluid to leave the plasma and enter tissues, leading to oedema.
Causes of oedema include hypoproteinaemia, liver or kidney disease, malabsorption, and nutritional lack

Cerebral Oedema

Fluid accumulation in the brain from stroke, tumours, trauma, etc. causing increased intracranial pressure.
Can lead to hypoxia, damage, and potentially death
Treatment may involve hypertonic fluids (e.g., mannitol) intravenously

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Description

This quiz covers key concepts related to osmotic pressure, including definitions, calculations of osmolarity and osmolality, and the distinctions between hyposmotic, hyperosmotic, and isosmotic solutions. Additionally, it explores the implications of osmolarity at the cell membrane and capillary wall.