Osmosis, Diffusion, Filtration & IV Fluids – Comprehensive Review

What is diffusion?

The movement of molecules from high to low concentration until equilibrium is reached.

What is osmosis?

Movement of water across a semi‑permeable membrane toward the higher solute concentration.

What is filtration?

Movement of fluid driven by pressure differences.

What is dialysis?

Separation of small solutes from large solutes using a semi‑permeable membrane.

What is a true solution?

A homogeneous mixture where solute particles are extremely small and remain dissolved (such as glucose or NaCl).

What is a colloid?

A mixture containing medium-sized particles that remain suspended but do not pass through membranes easily (such as proteins).

What is a suspension?

Large particles that settle and do not pass through membranes (such as RBCs or starch).

What is an isotonic solution?

A solution with the same solute concentration as the cell; no net water movement; RBC remains normal.

What is a hypotonic solution?

A solution with lower solute concentration outside the cell; water moves in; RBC swells and may lyse.

What is a hypertonic solution?

A solution with higher solute concentration outside the cell; water moves out; RBC shrinks (crenation).

What is hemolysis?

RBC swelling and bursting due to a hypotonic environment.

What is crenation?

RBC shrinking due to a hypertonic environment.

Give an example of an isotonic IV solution.

0.9% NaCl (Normal Saline).

Give an example of a hypotonic IV solution.

0.45% NaCl (Half Normal Saline).

Give an example of a hypertonic IV solution.

10% dextrose (D10W).

What is D5W in the IV bag?

Isotonic at approximately 252 mOsm.

What is D5W inside the body?

Hypotonic because dextrose is rapidly metabolized, leaving free water.

What is the effect of D5W on cells?

Water moves into cells, causing increased cell swelling.

What is hydrostatic pressure?

The "push" pressure exerted by fluid, such as blood pressure pushing fluid out of capillaries.

What is osmotic pressure?

The "pull" force created by solutes drawing water toward them.

What is glomerular filtration?

Fluid pushed out of the capillary into the nephron by blood pressure.

What is capillary osmotic pressure?

Pulls water back into the blood due to plasma proteins.

Which molecules can pass through dialysis tubing?

Water, glucose, salt, and iodine.

Which molecules cannot pass through dialysis tubing?

Starch and protein.

Why did the dialysis bag gain weight?

Water moved into the bag via osmosis.

What is the effect of a hypertonic IV solution on tissues?

It pulls water out of cells and reduces edema.

What is the effect of a hypotonic IV solution on tissues?

It pushes water into cells and causes swelling.

What is the effect of an isotonic IV solution?

It causes no fluid shifts and maintains equilibrium.

Give examples of isotonic IV solutions.

Normal Saline, Ringer's, D5W initially.

What happens to RBCs placed in 3% NaCl?

Water leaves the cells; they shrink; hypertonic environment; crenation occurs.

What happens to RBCs in distilled water?

Water rushes in; cells swell and may lyse; hypotonic environment; hemolysis occurs.

What happens to RBCs in 0.9% NaCl?

No change; isotonic environment.

Which IV should be used for a patient with severe dehydration needing cell hydration?

A hypotonic IV such as 0.45% NaCl to move water into cells.

Which IV should be used for a patient with cerebral edema?

A hypertonic IV to pull water out of brain cells.

Which IV should be used for fluid expansion without causing shifts?

An isotonic IV such as Normal Saline or Ringer's.

Why might cells swell during a D5W infusion?

The dextrose is metabolized, leaving hypotonic free water.

What happens if blood pressure in the glomerulus drops?

Filtration decreases because hydrostatic pressure decreases.

What happens if plasma proteins are lost, such as in liver failure?

Less osmotic pull; more fluid stays in tissues, causing edema.

What happens if pressure inside the kidney tubule increases?

Filtration decreases because back-pressure opposes flow.

Why is glucose found in the beaker after dialysis?

Glucose is small enough to diffuse through the membrane.

Why is starch not found in the beaker after dialysis?

Starch molecules are too large to pass through the tubing.

Why does iodine turn starch blue-black inside the dialysis bag?

Iodine diffuses in while starch remains trapped.

Why does a hypertonic solution decrease swelling?

It draws water out of swollen cells and tissues.

Why can't pure water be given intravenously?

It is extremely hypotonic and would cause dangerous hemolysis.

Why does adding more solute increase osmotic pressure?

More solute creates a stronger pull on water.

What determines whether a solute can diffuse across a membrane?

Molecular size and permeability.

Why does hydrostatic pressure promote filtration?

It physically pushes fluid across a membrane.

Why does albumin help maintain blood volume?

Albumin creates osmotic pull that draws water into capillaries.