Cell Plasma Membrane, Transport Mechanisms, and Resting Membrane Potential

Vocabulary practice flashcards covering cell plasma membrane structure, cell junctions, passive transport (osmosis, diffusion, facilitated diffusion), active transport mechanisms, transport kinetics, and resting membrane potential based on Human Physiology I lecture notes.

Hydrophobic

Nonpolar property characterized as being "scared of" water, typical of the fatty acid tails of phospholipids.

Hydrophilic

Polar property characterized as water-"loving", typical of the phosphate heads of membrane phospholipids.

Fluid Mosaic Model

Structural representation of the plasma membrane as a dynamic bilayer composed of phospholipids, embedded proteins, carbohydrates, and cholesterol.

Gap Junctions

Communicating cell junctions made of connexin proteins that allow direct and rapid cell-to-cell movement of chemical and electrical signals between cytoplasm of neighbouring cells.

Tight Junctions

Occluding cell junctions that restrict or block the movement of material between adjacent cells.

Desmosome

Strong cell-to-cell anchoring junction formed by cadherin proteins and plaque glycoproteins linked to intermediate filaments that holds neighbouring cells together within a tissue.

Intracellular Fluid (ICF)

Fluid located inside cells that accounts for $\frac{2}{3}$ of total body water volume.

Extracellular Fluid (ECF)

Fluid located outside cells that accounts for $\frac{1}{3}$ of total body water volume, serving as a buffer between cells and the outside world.

Interstitial Fluid

Subdivision of extracellular fluid that lies between the circulatory system and cells, representing $75\%$ of total ECF volume.

Blood Plasma

Liquid matrix of blood, constituting the subdivision of extracellular fluid that makes up $25\%$ of total ECF volume.

Osmotic Equilibrium

State where water concentration and total solute particle concentration are equal across fluid compartments ($300\,\text{mOsm/L}$).

Chemical Disequilibrium

State where the overall concentrations of specific individual solute species differ significantly between the ICF and ECF.

Osmosis

The passive movement of water across a membrane in response to a solute concentration gradient toward the area of higher solute concentration.

Osmotic Pressure

The exact pressure that must be applied to oppose and stop the movement of water across a membrane driven by osmosis.

Osmolarity

Expression of total concentration of particles in a solution, measured in $\text{mOsm/L}$ and calculated as $\text{molarity} \times \text{number of dissociated particles}$.

Non-Penetrating Solutes

Solutes that are unable to cross the plasma membrane on their own, thereby determining the tonicity of a solution.

Toxicity

Description of how a solution affects cell volume at equilibrium, determined solely by the relative concentration of non-penetrating solutes.

Hypertonic Solution

A solution containing a higher concentration of non-penetrating solutes than the cell cytoplasm, causing water to leave the ICF and the cell to shrink.

Hypotonic Solution

A solution containing a lower concentration of non-penetrating solutes than the cell cytoplasm, causing water to move into the ICF and the cell to swell.

Simple Diffusion

Passive transport of small or lipophilic molecules directly across the lipid bilayer down their concentration gradient without transport proteins.

Fick's Law of Diffusion

Law stating that rate of diffusion is directly proportional to surface area, concentration gradient, and membrane permeability.

Channel Proteins

Membrane transport proteins that form water-filled pores bridging ECF and ICF for rapid movement of small ions and water without requiring shape changes.

Carrier Proteins

Membrane transport proteins that bind specific substrates and undergo conformational changes to transport them across without forming an open pore.

Uniport Carrier

A carrier protein that moves only one specific substrate across the cell membrane (e.g., GLUT transporters).

Symport Carrier

A cotransporter protein that moves two or more different substrates in the same direction across the membrane.

Antiport Carrier

A cotransporter protein that moves two or more different substrates in opposite directions across the membrane.

Facilitated Diffusion

Passive transport of lipophobic molecules down their concentration gradient across a cell membrane using a carrier protein.

Primary Active Transport

Active transport mechanism where ATP is directly hydrolyzed by a protein carrier to move solutes against their concentration gradient.

Na+/K+ ATPase

Primary active antiport carrier that uses ATP to pump $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell per cycle.

Secondary Active Transport

Active transport mechanism that relies indirectly on ATP by using the potential energy stored in an ion concentration gradient to move another solute against its gradient.

SGLT

Sodium-glucose transporter; a secondary active symport carrier that uses the downward $\text{Na}^+$ gradient to transport glucose into the cell against its gradient.

Transport Saturation

Condition when all binding sites on transport proteins are fully occupied, causing the transport rate to plateau at its maximum capacity ($V_{\text{max}}$).

Endocytosis

Active vesicular transport process by which large molecules or particles are brought into the cell via membrane invagination.

Exocytosis

Active vesicular transport process where intracellular vesicles fuse with the plasma membrane to export materials out of the cell.

Electrical Disequilibrium

Condition where positive and negative charges are distributed unequally across the cell membrane, resulting in a net negative charge inside relative to outside.

Equilibrium Potential

The membrane potential at which the electrical gradient pushing an ion across the membrane is equal and opposite to its concentration gradient.

Resting Membrane Potential

The steady electrical potential difference across the plasma membrane of an unstimulated cell, typically $-70\,\text{mV}$ in human cells.

Depolarization

Change in membrane potential that makes the cell interior less negative (more positive) relative to the resting potential.

Hyperpolarization

Change in membrane potential that makes the cell interior more negative than the resting potential.

Repolarization

Return of the membrane potential toward the resting level following a depolarization shift.