Body Fluid Compartments and Transport Across Cell Membranes

Flashcards covering body fluid distribution, ion concentrations, and mechanisms of transport across cell membranes based on Dr. Beth Kitts-Morgan's lecture.

Total Body Water (TBW)

The total amount of water in the body, accounting for approximately $60\%$ of body weight ($BW$).

Intracellular Fluid (ICF)

The fluid found inside cells, representing approximately $40\%$ of body weight ($BW$).

Extracellular Fluid (ECF)

The fluid found outside cells, representing approximately $20\%$ of body weight ($BW$) and comprised of plasma ($~4\%$) and interstitial fluid ($~16\%$).

Electroneutrality

The principle that in each body fluid compartment, the total positive charges must equal the total negative charges.

Major ECF Ions

The major cation is $Na^+$ and the major anions are $Cl^-$ and $HCO_3^-$.

Major ICF Ions

The major cation is $K^+$ and the major anions are proteins and organic phosphates.

Osmolarity

The concentration of dissolved particles expressed as osmoles/L ($Osm/L$) or $mOsm/L$; it determines water movement between compartments.

Amphipathic

The characteristic of phospholipids containing both a hydrophilic (glycerol) head and hydrophobic fatty acid tails.

Integral Proteins

Proteins that span the membrane once or are transmembrane proteins, such as hormone receptors, pores, and ion channels.

Simple Diffusion

A form of passive transport that is not carrier-mediated, requires no energy, and occurs down an electrochemical gradient.

Fick's Law

The principle identifying five variables that determine diffusion rate: concentration gradient, partition coefficient, diffusion coefficient, thickness of membrane, and surface area.

Partition Coefficient

A variable in Fick's Law based on the lipid solubility of a solute.

Diffusion Coefficient

A variable in Fick's Law based on the size of the solute and the viscosity of the solution.

Facilitated Diffusion

A carrier-mediated transport mechanism that does not require energy and occurs down an electrochemical gradient, such as the $GLUT4$ transporter.

Saturation

A feature of carrier-mediated transport where the rate of transport levels off because carrier proteins have a limited number of binding sites.

Stereospecificity

The characteristic where binding sites for solutes on carrier proteins are specific to certain isomers, such as recognizing $D$-glucose but not $L$-glucose.

Competition

A feature of carrier-mediated transport where carriers bind chemically-related solutes, such as $D$-galactose competing with $D$-glucose.

Primary Active Transport

Transport where one or more solutes are moved against a concentration gradient using $ATP$ directly.

$Na^+/K^+$ ATPase Pump

A primary active transporter in all cell membranes that pumps $3\,Na^+$ to the ECF and $2\,K^+$ to the ICF; it is inhibited by cardiac glycosides like digoxin and ouabain.

Secondary Active Transport

Transport that indirectly uses energy by utilizing the $Na^+$ gradient established by primary active transport to move solutes against their concentration gradient.

Co-transport (Symport)

A type of secondary active transport where all solutes are transported in the same direction, such as the $Na^+/$glucose co-transporter ($SGLT\,1$).

Counter-transport (Antiport)

A type of secondary active transport where solutes move in opposite directions, such as the $Ca^{2+}/Na^+$ exchange or $Na^+/H^+$ exchange.