Solutions, Body Fluids and Electrolytes.

Objectives : 

• Define solutions, colloids and suspensions

• Describe solubility factor and osmotic pressure

• Explain tonicity and its clinical implications. 

Solution: a mixture where the parts are complete blended into one layer and can’t be separated by spinning or setting.

Solute: The substance that gets dissolved in solution (the “smaller part” that mixes into the solvent)

Solvent: The liquid that does the dissolving the larger part of a solution that the solute mixes into. 

Electrolytes solution:

• A liquid that contains charged particle ions

  • Cations have a positive charge

  • Anions have a negative charge

Body water= Universal solvent

Three ways the body holds chemical particles:

• Colloids (like gelatin or protoplasm

  • Medium size particles are evenly mixed and stay suspended 

    • They hold on to water tightly so there is very little free water to move around. 

• Suspensions (like red blood cells in plasma)

  • Large particles float in liquid

    • If you shake them, they stay mixed for a bit, but they will settle to the bottom over time.

    • You can separate them by spinning (centrifuge)

• Solutions (like salt water)

  • Small particles (molecules or ions) are completely dissolved in the water

    • They never settle out and cannot be spun apart

    • How easily something dissolve is called solubility. 

Dissolve:

• The solute spreads out evenly in the solvent so you can’t see separate particles

Dissociate:

• The solute breaks apart into ions (charged particles) as it dissolves.

Five things that control solubility:

• Substances being dissolved (solute)

  • Some substances break apart (dissociate) more easily than other.

  • Strong internal forces= harder to dissolve

• The liquid that does the dissolving

  • Like dissolves like

    • Polar + polar= mixes (salt and water)

    • Non-polar + non-polar= mixes (oil and gasoline)

    • Polar + non-polar= doesn’t mix (oil and water)

• Temperature:

  • Warmer liquid= more dissolving for most solids

  • Higher temperature give molecules more energy to mix.

• Pressure

  • Gases: higher pressure pushes more gas into the liquid (think soda)

    • When pressure above a liquid is increased it forces more gas molecules into the liquid so more gas dissolves.

  • Solids (baking soda) and liquids (water): pressure doesn’t matter much.

    • Changing outside pressure (like squeezing the bottle) doesn’t really affect how much of a solid or another liquid can dissolve.

    • Temp is far more important for solids and liquids.

• Concentration

  • If the liquid is already packed with solute, less will dissolve

    • Southern sweet tea

  • Lower concentration= more room for solute

    • Lightly sweetened tea.

• Dilute Solution:

  • Only a small amount of solute

• Saturated Solution:

  • The liquid is full, it has dissolved as much solute as it possibly can at that temperature.

• Supersaturated Solution:

  • More solute is dissolved than normally possible- this only happens if you heat it, dissolve extra, then cool rapidly.

• Osmosis Basics:

  • Semipermeable membrane:    

    • A barrier (like a cell wall) that lets water move through but not larger solute particles.

  • Goal of water movement

    • Water moves to balance the concentration of solutes on each side like trying to even out the saltiness.

• Osmotic pressure

  • As water moves toward the side with more solute (salt/sugar) the liquid level on that side rises

  • The weight of this rising column creates pressure

  • This pressure is osmotic pressure- the pulling force drawing water in.

• Osmolality :

  • Ratio of solute (particles) to solvent (water)

  • Higher solute= higher osmolality= higher osmotic pressure

• Starling forces:

  • Named after Ernst Starling, a scientist who studied how fluids move in and out of tiny blood vessels.

  • Two key pressures

    • Hydrostatic pressure: the push

      • Blood pressure inside the capillary pushes water out toward the tissue.

    • Oncotic (osmotic) pressure: the pull

      • Proteins (mainly albumin) in the blood pull water back into the capillary.

    • At the arterial end of a capillary: hydrostatic pressure is stronger so fluid moves out into the tissue.

    • Arterial end of the capillary

      • Beginning of the capillary, closest to the small artery (arteriole) bring blood from the heart.

        • Hydrostatic pressure (BP) is high because blood just arrived under strong pressure from the heart.

        • Oncotic pressure from plasma proteins is lower compared to that push.

      • Result the stronger push forces water, oxygen, and nutrients out of the capillary into the surrounding tissue fluid.

      • Delivers oxygen and nutrients to cell.

    • Middle of the capillary   

      • As blood travels along, hydrostatic pressure drops because fluid has left and resistance slows the flow

      • Oncotic pressure stays about the same because proteins don’t leave

      • Pressures start to balance.

    • Venous end of capillary    

      • The far end of the capillary, closet to the small vein (venule) that carries blood back to the heart.

        • Hydrostatic pressure, is now low because the push from the heart has weakened

        • Oncotic pressure: is now relatively stronger.

      • Result strong pull draws water and some waste products back into the capillary.

      • Returns fluid to the blood stream and carries carbon dioxide and water wastes away.

• Osmotic pressure

  • The pulling force that draws water (solvent) across a semipermeable membrane to balance the solute concentration on both side.

  • Goal: water moves until the concentration of dissolved particles (solute) is equal on both sides.

  • Water is the solvent and it moves in or out of cells and blood vessels by osmosis.

• Tonicity: describes how strong the osmotic pull is in a solution compared to body fluids (normal blood plasma)

  • .9 % sodium chloride (NaCl) also called normal saline.

• Isotonic: Same solute concentration as body fluids

  • No net water movement, cells stay the same size.

• Hypertonic: higher solute concentration than body fluids.

  • Water moves out of the cell, cell shrinks

  • 3% NaCl

• Hypotonic: Lower solute concentration than body fluids.

  • Water moves into the cell, cell swells (may burst).