Human Physiology, Vander Ch.4

Front 1

Diffusion

Back 1

Movement of molecules from one location to another because of random thermal molecular motion; net diffusion always occurs from a region of higher concentration to a region of lower concentration

Front 2

Flux

Back 2

Amount of a substance crossing a surface in a unit of time.

Front 3

Net flux

Back 3

Difference between two one-way fluxes

Front 4

Diffusion equilibrium

Back 4

State during which diffusion fluxes in opposite directions are equal; that is, the net flux equals zero.

Front 5

Permeability constant, kp

Back 5

Number that defines the proportionality between a flux and a concentration gradient and depends on the properties of the membrane and the diffusing molecule

Front 6

Channels

Back 6

Small passage in plasma membrane formed by integral membrane proteins and through which certain small-diameter molecules and ions can diffuse

Front 7

Membrane potential

Back 7

Voltage difference between inside and outside of cell

Front 8

Electrochemical gradient

Back 8

The driving force across a plasma membrane that dictates whether an ion will move into or out of a cell; it is established by both the concentration difference and the electrical charge difference between the cytosolic and extracellular surfaces of the membrane.

Front 9

Channel gating

Back 9

Process of opening and closing ion channels

Front 10

Patch clamping

Back 10

A procedure for isolating individual ion channels on the surface of a living cell and recording current through the channel.

Front 11

Ligand-gated channels

Back 11

Membrane channel operated by the binding of specific molecules to channel proteins

Front 12

Voltage-gated channels

Back 12

Cell-membrane ion channel opened or closed by changes in membrane potential.

Front 13

Mechanically gated channels

Back 13

Membrane ion channel that is opened or closed by deformation or stretch of the plasma membrane.

Front 14

Transporters

Back 14

Integral membrane protein that mediates passage of molecule through membrane; also called carrier.

Front 15

Mediated-transport

Back 15

Movement of molecules across membrane by binding to protein transporter; characterized by specificity, competition, and saturation; includes facilitated diffusion and active transport.

Front 16

Facilitated diffusion

Back 16

System using a transporter to move molecules from high to low concentration across a membrane; energy not required.

Front 17

Active transport

Back 17

Energy-requiring system that uses transporters to move ions or molecules across a membrane against an electrochemical difference

Front 18

Primary active transport

Back 18

Active transport in which chemical energy is transferred directly from ATP to transporter protein.

Front 19

Secondary active transport

Back 19

Active transport in which energy released during transmembrane movement of one substance from higher to lower concentration is transferred to the simultaneous movement of another substance from lower to higher concentration.

Front 20

Cotransport

Back 20

Form of secondary active transport in which net movement of actively transported substance and “downhill” movement of molecule supplying the energy are in the same direction.

Front 21

Countertransport

Back 21

Form of secondary active transport in which net movement of actively transported molecule is in direction opposite “downhill” movement of molecule supplying the energy.

Front 22

Aquaporins

Back 22

Protein membrane channel through which water can diffuse.

Front 23

Osmosis

Back 23

Net diffusion of water across a selective barrier from region of higher water concentration (lower solute concentration) to region of lower water concentration (higher solute concentration).

Front 24

Osmolarity

Back 24

Total solute concentration of a solution; measure of water concentration in that the higher the solution osmolarity, the lower the water concentration.

Front 25

Osmol

Back 25

1 mole of solute ions and molecules

Front 26

Semipermeable membrane

Back 26

Membrane permeable to some substances (usually water) but not to others (some solutes)

Front 27

Osmotic pressure

Back 27

Pressure that must be applied to a solution on one side of a membrane to prevent osmotic flow of water across the membrane from a compartment of pure water; a measure of the solution’s osmolarity.

Front 28

Nonpenetrating solutes

Back 28

Dissolved substances that do not passively diffuse across a plasma membrane.

Front 29

Isotonic

Back 29

Containing the same number of effectively nonpenetrating solute particles as normal extracellular fluid.

Front 30

Hypotonic

Back 30

Solutions containing a lower concentration of effectively nonpenetrating solute particles than normal (isotonic) extracellular fluid.

Front 31

Hypertonic

Back 31

Solutions containing a higher concentration of effectively membrane-impermeable solute particles than normal (isotonic) extracellular fluid.

Front 32

Isosmotic

Back 32

Having the same total solute concentration as extracellular fluid.

Front 33

Hyperosmotic

Back 33

Having total solute concentration greater than normal extracellular fluid.

Front 34

Hypoosmotic

Back 34

Having total solute concentration less than that of normal extracellular fluid.

Front 35

Endocytosis

Back 35

Process in which plasma membrane folds into the cell, forming small pockets that pinch off to produce intracellular, membrane-bound vesicles

Front 36

Exocytosis

Back 36

Process in which intracellular vesicle fuses with plasma membrane, the vesicle opens, and its contents are liberated into the extracellular fluid.

Front 37

Fluid endocytosis

Back 37

Invagination of a plasma membrane by which a cell can engulf extracellular fluid.

Front 38

Adsorptive endocytosis

Back 38

Receptor-mediated invagination of plasma membranes by which both extracellular fluid and specific extracelluar molecules are moved into cytosol.

Front 39

Pinocytosis

Back 39

Endocytosis when the vesicle encloses extracellular fluid or specific molecules in the extracellular fluid that have bound to proteins on the extracellular surface of the plasma membrane.

Front 40

Phagocytosis

Back 40

Engulfment of particles by a cell.

Front 41

Endosomes

Back 41

Intracellular vesicles and tubular elements between Golgi apparatus and plasma membrane; sorts and distributes vesicles during endo- and exocytosis

Front 42

Luminal membrane

Back 42

Portion of plasma membrane facing the lumen; also called apical or mucosal membrane.

Front 43

Basolateral membrane

Back 43

Sides of epithelial cell other than luminal surface; also called serosal or blood side of cell

Front 44

Paracellular pathway

Back 44

The space between adjacent cells of an epithelium through which some molecules diffuse as they cross the epithelium

Front 45

Transcellular pathway

Back 45

Crossing an epithelium by movement into an epithelial cell, diffusion through the cytosol of that cell, and exit across the opposite membrane.

Front 46

Exocrine gland

Back 46

Cluster of epithelial cells specialized for secretion and having ducts that lead to an epithelial surface.

Front 47

Endocrine gland

Back 47

Group of epithelial cells that secrete into the extracellular space hormones that then diffuse into bloodstream; also called a ductless gland.

Front 48

Hormones

Back 48

Chemical messenger synthesized by specific endocrine cells in response to certain stimuli and secreted into the blood, which carries it to target cells.