Chapter 5 — Membrane Dynamics: Osmosis, Transport, & Membrane Potential (Master Review)

What is osmotic equilibrium?

The state where water concentration is equal across ICF and ECF; does not imply equal solute composition.

What is chemical disequilibrium?

The unequal distribution of solutes between ECF and ICF (e.g., Na+ high outside, K+ high inside).

What is electrical disequilibrium?

Slight charge difference between ICF (negative) and ECF (positive) that creates membrane potential.

How does total body water vary with age and sex?

TBW decreases with age and is lower in women due to higher adipose content.

What is osmosis?

Movement of water across a membrane in response to solute concentration gradients via aquaporins.

What is osmotic pressure?

Pressure required to prevent osmosis; proportional to solute particle concentration.

What is osmolarity?

Number of osmotically active particles per liter of solution.

What is tonicity?

Effect of a solution on cell volume after equilibrium; depends only on nonpenetrating solutes.

What does isosmotic mean?

Two solutions having the same osmolarity.

What does hyperosmotic mean?

A solution with more osmoles per liter than another.

What does hyposmotic mean?

A solution with fewer osmoles per liter than another.

What does isotonic mean?

A solution that causes no net change in cell volume.

What does hypertonic mean?

A solution that causes cells to shrink; higher NP solute concentration.

What does hypotonic mean?

A solution that causes cells to swell; lower NP solute concentration.

What are penetrating solutes?

Solutes that freely cross membranes (e.g., urea, glucose before uptake).

What are nonpenetrating solutes?

Solutes that cannot cross membranes (e.g., NaCl); determine tonicity.

What does Fick's Law describe?

Diffusion rate increases with surface area, gradient, permeability; decreases with thickness.

What is simple diffusion?

Movement of lipophilic molecules directly through membrane lipids.

What is facilitated diffusion?

Passive carrier-mediated transport down concentration gradients.

What is primary active transport?

Transport using ATP directly (e.g., Na/K ATPase).

What is secondary active transport?

Transport using energy stored in ion gradients (e.g., SGLT).

What are channel proteins?

Membrane proteins forming water-filled pores; include gated and leak channels.

What are carrier proteins?

Transporters that undergo conformational change and never form open pores.

What is a uniport carrier?

A transporter that moves a single substance.

What is a symport carrier?

A transporter that moves two substances in the same direction.

What is an antiport carrier?

A transporter that moves substances in opposite directions.

What is transport specificity?

A transport protein's ability to bind only specific substrates.

What is transport competition?

When similar substrates compete for the same transporter binding site.

What is saturation in membrane transport?

When transport rate plateaus because all carriers are occupied.

What is phagocytosis?

Actin-driven engulfing of large particles into phagosomes.

What is endocytosis?

Internalization of small vesicles; can be receptor-mediated.

What is exocytosis?

Release of large molecules via vesicular fusion with the plasma membrane.

What is transcytosis?

Vesicular transport of intact substances across epithelial cells.

What is the apical membrane?

The lumen-facing membrane of epithelial cells.

What is the basolateral membrane?

The ECF-facing membrane of epithelial cells.

What is paracellular transport?

Movement between epithelial cells via tight junctions.

What is transcellular transport?

Movement through epithelial cells requiring crossing both membranes.

What is the resting membrane potential?

Difference in charge between ICF and ECF; inside is negative relative to outside.

What is an equilibrium potential?

The membrane potential that exactly opposes an ion's concentration gradient (Nernst equation).

What is membrane depolarization?

When the membrane becomes less negative due to increased Na+ or Ca2+ permeability.

What is membrane hyperpolarization?

When the membrane becomes more negative due to increased K+ or Cl- permeability.

What is repolarization?

Return of membrane potential toward resting level.

What does the Na+/K+ ATPase do?

Pumps 3 Na+ out and 2 K+ into the cell using ATP; maintains ion gradients.

What is the SGLT transporter?

A sodium-glucose symporter using Na+ gradient to move glucose into cells.

What is the GLUT transporter?

A facilitated diffusion transporter moving glucose down its concentration gradient.

How does insulin secretion work at the cellular level?

Glucose ↑ATP → closes KATP channels → depolarization → Ca2+ influx → insulin exocytosis.