ANSC 300 Water Balance

Ways to Express Mass of Solutes

• g (grams) / mw (molecular weight) = mols

• mols * mw = g

• osmol = mol * # of ions

• mol = osmol / # of ions

• eq (equivalent) / valence = mol

• mol * valence = eq

Ways to Express Concentration of Solutes

• osmolarity = osm / kg of fluid

• osmolarity = osm / L of fluid

• molarity = mol / L of fluid

• g / L

Solute Concentration Inside vs Outside the Cell

• more sodium, calcium, and chloride outside the cell

• 285-290 mOsm/kg both inside and outside the cell

• concentration gradients for individual ions are important for cell function

• concentration gradients maintain membrane electrical potential: difference in net charge between inside and outside the cell (action potential)

Diffusion

• molecules are in constant motion

• molecules bounce off each other and transfer energy

• random trajectory

• energy (heat) of molecules is directly related to the temperature

Net Diffusion Rate

• depends on concentration, charge, and pressure

• higher concentration outside means molecules cross the membrane to the inside than the other way

• more positive charge inside draws more negatively charged ions from the outside

• higher pressure (P1) drives more molecules to cross the membrane

Osmosis

• net movement of water across a semi-permeable membrane

• movement of water across the membrane equalizes solute concentration on both sides

• water moves towards the compartment with lower water concentration

• water moves towards the compartment with higher solute concentration

Osmotic Pressure

• is the force required to equalize volume on both sides of the membrane

• high water concentration on left side

• water diffuses through the membrane from compartment 1 to compartment 2

• water moves to the right until the opposing pressure gradient is equal to the force of the concentration gradient

Net Movement of Water can Change _____

cell shape

Hypotonic

lowest solute concentration causing water to move into the cells

Isotonic

water movement is in equilibrium

Hypertonic

highest solute concentration causing water to move outside the cell which leads to cell shrinkage

Cell Structure

• defines function

• interior of a cell is highly structured

• different compartments do different things

• cells specialize by altering their structure

• specialization is called differentiation

Membrane Physiology

• selective semi-permeable: water can freely diffuse across the membrane or through protein channels

• transporters and channel proteins alter membrane permeability when open

• carrier membrane proteins control transport of other molecules:

  • nutrients

  • ions

  • metabolites

• allows for separate internal compartments to contain different molecules: Mitochondria (H+), ER (Ca++), Lysosomes (H+)

• source of signaling molecules (IP3, DAG)

Lipid Bilayer

• hydrophobic tails orient away from the aqueous environment. Exclude water

• polar heads interact with water molecules

• phospholipids move around which makes membrane fluid and flexible

• composition of phospholipids alter membrane fluidity and stiffness

Simple diffusion

small molecules that are lipid soluble pass through the membrane, such as oxygen and carbon dioxide

Facilitated Diffusion

• molecules move down their energy gradients

• requires a carrier protein

• binds molecules with high specificity

• binding causes a change in shape (conformation) of the carrier protein

• no ATP required

Active Transport

molecules move against energy gradients, requires ATP

Energy Gradients

concentration or electrical

Rate of Diffusion

• rate of simple diffusion increases at a constant rate as concentration of the solute increases

• rate of diffusion increases more rapidly in facilitated diffusion

• facilitated diffusion has a maximum rate at which higher solute concentration will not longer increase the rate of diffusion (Vmax)

Primary Active Transport: Na-K Pump

• maintains concentration gradients of Na and K

• uses to generate electrochemical gradients for action potentials (neurons and muscle contractions)

• requires ATP

• important for maintaining isotonic environment of the cell

• other pumps move Ca, Cl, and H against concentration gradients

Sodium Electrochemical Gradient

• sodium and glucose co-transporter (SLGTs) are important for absorption in Gi and kidney

• sodium gradient is used to move calcium and hydrogen ions out of the cell

Heat Tolerance in Camelids

• body temp can increase during day ~40 C

• cooling at night to ~34 C

• tolerate losing up to 25% of body water

• can rehydrate without side effects