Membrane Dynamics (Chapter 5) - Biol 3513 Human Physiology

Vocabulary flashcards covering key concepts from Membrane Dynamics. Each card defines a term relevant to diffusion, osmosis, membrane transport, and insulin secretion.

Mass balance

The balance of a substance in the body, including clearance and mass flow; used to analyze excretion, metabolism, and homeostasis.

Clearance

Rate at which a molecule disappears from the body; a key measure in pharmacokinetics and mass balance.

Mass flow

The product of concentration and volume flow; used to describe how a substance moves through compartments.

Homeostasis

Maintenance of a stable internal environment, including chemical, electrical, and osmotic balances.

Equilibrium

A state where opposing forces are balanced, resulting in no net change.

Osmotic equilibrium

Balance of osmotic pressures across a semipermeable membrane, resulting in no net water movement.

Chemical disequilibrium

Unequal chemical composition across compartments despite other balances.

Electrical disequilibrium

Unequal distribution of electrical charges across the cell membrane.

Plasma

The liquid component of blood in the extracellular fluid compartment.

Interstitial fluid

Fluid in the extracellular space surrounding cells.

Intracellular fluid (ICF)

Fluid contained within cells.

Extracellular fluid (ECF)

All fluid outside cells, including plasma and interstitial fluid.

Resting membrane potential (RMP)

Voltage difference across the cell membrane at rest, typically around -70 mV, mainly due to K+ gradients and leak channels.

Equilibrium potential (Eion)

Membrane potential at which there is no net flux of a particular ion across the membrane (Nernst potential).

Potassium equilibrium potential (E_K)

Equilibrium potential for K+; about -90 mV in the provided notes.

Sodium equilibrium potential (E_Na)

Equilibrium potential for Na+; about +60 mV in the provided notes.

Chloride equilibrium potential (E_Cl)

Equilibrium potential for Cl−; about -63 mV in the provided notes.

Calcium equilibrium potential (E_Ca)

Equilibrium potential for Ca2+; determined by the Ca2+ gradient across the membrane.

Osmosis

Movement of water across a semipermeable membrane toward higher solute concentration.

Osmotic pressure

Pressure that must be applied to a solution to oppose osmosis.

Osmolarity

Total solute concentration per liter of solution (OsM).

Hyperosmotic

A solution with higher osmolarity than another solution.

Hyposmotic

A solution with lower osmolarity than another solution.

Tonicity

Describes the volume change of a cell placed in a solution; depends on penetrating vs non-penetrating solutes.

Hypotonic

A solution that causes cells to swell by drawing water in (lower tonicity than the cell).

Isotonic

A solution with the same tonicity as the cell; no net water movement.

Hypertonic

A solution that causes cells to shrink by water leaving the cell.

Diffusion

Passive movement of molecules from high to low concentration down a gradient.

Fick's Law of Diffusion

Rate of diffusion = (surface area × concentration gradient × membrane permeability) / membrane thickness.

Simple diffusion

Diffusion of molecules directly through the lipid bilayer without transport proteins.

Facilitated diffusion

Diffusion via membrane transport proteins (channels or carriers) that is still passive.

Membrane permeability

Ability of the membrane to allow passage of a substance; influenced by lipid solubility, size, and membrane structure.

Lipid solubility

The tendency of a molecule to dissolve in the lipid portion of the membrane, increasing diffusion rate.

Channel proteins

Membrane-spanning proteins that form pores for specific ions or water; can be open or gated.

Aquaporins

Water channel proteins that facilitate rapid water movement across membranes.

Ion channel

Channel protein selective for ions (e.g., K+, Na+).

Carrier proteins

Proteins that bind substrates and undergo conformational changes to shuttle them across the membrane.

Uniport

Carrier that transports one substrate at a time.

Symport

Carrier that moves two or more substrates in the same direction across the membrane.

Antiport

Carrier that moves substrates in opposite directions across the membrane.

Cotransport

Transport by carriers that move two or more substrates together (includes symport and antiport).

Saturation

Maximum rate of transport when all carriers are occupied.

Transport maximum (Tm)

Maximum rate of transport when transporters are saturated.

Endocytosis

Process of taking material into the cell via vesicle formation.

Exocytosis

Process of releasing material from the cell via vesicle fusion with the membrane.

Phagocytosis

Endocytosis of large particles or microorganisms.

Pinocytosis

Endocytosis of extracellular fluid and dissolved solutes (cellular drinking).

Receptor-mediated endocytosis

Endocytosis initiated by ligand binding to a cell-surface receptor, often via clathrin-coated pits.

Clathrin-coated pits

Membrane regions that invaginate to form vesicles during receptor-mediated endocytosis.

Caveolae

Flask-shaped membrane invaginations involved in certain endocytic pathways.

Vesicular transport

Bulk transport of substances using membrane-bound vesicles.

Transcytosis

Transport of materials across an epithelial cell by vesicles from one membrane to the opposite one.

Transepithelial transport

Directed movement of substances across an epithelium from lumen to interstitial fluid or vice versa.

Apical membrane

Membrane facing the lumen of an epithelium or tubule.

Basolateral membrane

Membrane facing the external environment/ECF on the opposite side of the epithelium.

Tight junctions

Cellular junctions that prevent paracellular passage and help establish polarity.

Polarized epithelia

Epithelial cells with distinct apical and basolateral transport protein distributions.

Absorption

Transport from lumen into the extracellular fluid.

Secretion

Transport from the extracellular fluid into the lumen.

GLUT transporter

Glucose transporter that mediates facilitated diffusion of glucose.

SGLT transporter

Sodium-glucose cotransporter that uses the Na+ gradient to bring glucose into the cell (secondary active transport).

Na+/K+-ATPase

Primary active transporter that pumps 3 Na+ out and 2 K+ in per ATP consumed; maintains gradients.

Primary active transport

Direct use of ATP to move substances against their gradient.

Secondary active transport

Movement of one substance against its gradient powered by the gradient of another (e.g., Na+).

Na+ gradient

Chemical and electrical Na+ gradient maintained by Na+/K+-ATPase that powers secondary transport.

Insulin secretion

Release of insulin from pancreatic beta cells in response to high blood glucose, initiated by closing KATP channels, depolarization, Ca2+ influx, and vesicle exocytosis.

Beta cell

Pancreatic cell that secretes insulin.

KATP channel

ATP-sensitive potassium channel; closes when ATP rises, causing cell depolarization.

Voltage-gated Ca2+ channel

Calcium channel opened by depolarization; triggers insulin vesicle exocytosis in beta cells.

Insulin vesicles

Secretory vesicles containing insulin that release it via exocytosis in response to Ca2+.