Water and Ion Balance in Cellular Physiology

Na+

Sodium ion, crucial for cellular functions.

K+

Potassium ion, vital for nerve signaling.

ATP

Energy currency of the cell.

ADP

Adenosine diphosphate, lower energy molecule.

Pi

Inorganic phosphate, involved in energy transfer.

Osmolarity

Concentration of solute particles in solution.

Tonicity

Effect of solution on cell volume.

ICF

Intracellular fluid, high in potassium.

ECF

Extracellular fluid, high in sodium.

IF

Interstitial fluid, surrounds cells.

Plasma

Liquid component of blood, carries cells.

Homeostasis

Maintenance of stable internal environment.

Passive Transport

Movement across membrane without energy.

Active Transport

Movement against gradient, requires energy.

Simple Diffusion

Direct movement through membrane, no proteins.

Facilitated Diffusion

Transport via membrane proteins, no energy.

Primary Active Transport

Direct use of ATP to move substances.

Secondary Active Transport

Uses energy from primary transport indirectly.

Concentration Gradient

Difference in solute concentration across a membrane.

Diffusion

Movement from high to low concentration.

Driving Force

Force causing movement down concentration gradient.

Membrane Flux Equation

Describes solute movement across membranes.

Integral Membrane Proteins

Proteins that span the membrane, affecting permeability.

Random thermal motions

Movement of particles due to temperature effects.

Fick's law of diffusion

Describes solute movement based on concentration gradient.

Diffusion coefficient (Ds)

Measures solute mobility in a medium.

Concentration gradient (C2 - C1)

Difference in solute concentration driving diffusion.

Semi-permeable membrane

Allows selective passage of certain substances.

Permeable

Substances can pass through the membrane.

Impermeable

Substances cannot pass through the membrane.

Hydrophobic solutes

Substances that diffuse through lipid membranes easily.

Hydrophilic solutes

Substances that require pores to diffuse through membranes.

Membrane permeability

Defines ease of substance crossing the membrane.

Transmembrane proteins

Integral proteins spanning the lipid bilayer.

Ion channels

Proteins that regulate ion movement across membranes.

Open state of ion channels

Allows ions to pass through the membrane.

Closed state of ion channels

Prevents ion passage through the membrane.

Na+-K+ ATPase

Enzyme maintaining Na+ and K+ concentration gradients.

Osmosis

Movement of water across a semi-permeable membrane.

Colligative property

Depends on solute concentration, not solute type.

Boiling point elevation

Increase in boiling point due to solute presence.

Freezing point depression

Decrease in freezing point due to solute presence.

Vapor pressure elevation

Increase in vapor pressure due to solute presence.

Hydrophobic core

Barrier preventing hydrophilic substances from passing.

Concentration of pure H2O

55 M or 55,000 mM in 1 liter.

Osmotic Pressure

Hydrostatic pressure generated by osmosis.

1 Molar

1 mole of solute per 1 liter solution.

1 osmolar

1 mole of solute per 1 liter solution.

1000 milliosmolar

Equivalent to 1 osmolar.

Dissociation in H2O

Solutes like NaCl dissociate into ions.

Osmolarity Calculation

Total osmolarity adds independently from solutes.

Hypertonic Solution

Higher osmolarity than cell, causes water efflux.

Isotonic Solution

Equal osmolarity inside and outside cell.

Hypotonic Solution

Lower osmolarity than cell, causes water influx.

Osmoregulator

Maintains stable body fluid osmotic concentration.

Osmoconformer

Body fluid concentration matches environmental osmotic concentration.

Euryhaline

Survives wide range of osmotic concentrations.

Stenohaline

Tolerates limited osmotic concentration range.

Transcellular Transport

Movement through cell membranes.

Paracellular Transport

Movement between adjacent cells.

Transport Epithelia

Specialized cells for solute and water transport.

Channel Proteins

Membrane proteins facilitating passive transport.

Carrier Proteins

Membrane proteins facilitating active transport.

Water Budget

Balance of water intake and loss in organisms.

Body Fluid Osmotic Concentration

Osmotic concentration of body fluids, ~300 mOsm.

Environmental Osmotic Concentration

Osmotic concentration of surrounding environment.

Passive Regulation

Water movement without energy expenditure.

Regulated Gain/Loss

Active control of water and ion levels.

BFOC

Body fluid osmotic concentration, e.g., 300 mOsm.

Osmoregulators

Organisms that maintain constant internal osmotic pressure.

Aquatic Environment

Habitat with water as the primary medium.

Terrestrial Environment

Land habitat with varying water availability.

Cutaneous Evaporation

Water loss through the skin.

Chloride Cell

Cell type for ion transport in fish gills.

Pavement Cell

Cell type in fish gills for passive transport.

Loop of Henle

Kidney structure for water reabsorption.

Temporal Counter-Current Exchange

Mechanism to minimize respiratory water loss.

Hyperosmotic Urine

Urine with higher osmolarity than body fluids.

Hypoosmotic Urine

Urine with lower osmolarity than body fluids.

Dietary Influence

Food intake affecting water and ion balance.

Excretion Mechanisms

Processes for removing excess water and ions.

Metabolic Water

Water produced from metabolic processes.

Environmental Osmotic Concentration (Env OC)

Osmotic concentration of surrounding water.

Freshwater Fish Adaptation

Gain water osmotically, do not drink.

Saltwater Fish Adaptation

Drink seawater, excrete excess ions.

Behavioral Adaptation

Strategies to minimize water loss in animals.