PHYL 1001 MODULE 2 (OSMOLARITY + TONICITY )

Extracellular fluid

Fluid outside of the cells, ⅓ of the total body water volume.

Intracellular fluid

⅔ of the total body water volume, fluid inside of cell and is separated from the ECF by the plasma membrane.

Interstitial fluid

Fluid between the cells, lies between the circulatory system and the cells.

Plasma

Water part of the blood, is the liquid matrix of blood.

Osmotic equilibrium

The body always tries to remain at osmotic equilibrium → where the concentration of particles in ICF = concentration of particles in ECF.

Healthy osmolarity

In a healthy, normal cell and its environment the osmolarity is 300mOsm/L.

Water movement towards solutes

To reach and maintain osmotic equilibrium, water in the body will always move towards where solutes are (WATER ALWAYS FOLLOWS SOLUTES) or will move towards a more concentrated environment.

Chemical equilibrium vs. Osmotic equilibrium

The body is not at chemical equilibrium when at osmotic equilibrium, because of the types of solutes in the ICF and ECF (chemical disequilibrium).

Osmosis

The passive movement of water across a membrane in response to a solute concentration gradient (difference in concentration).

Osmotic Pressure

The pressure that the piston must exert to stop the movement of water.

Osmolarity

Calculates the concentration of particles in a solution (mOsm/L) → molarity x # of particles it dissociates into.

Molarity

Calculates the concentration of molecules in a solution.

Hyperosmotic

Greater osmolarity than a normal cell.

Hyposmotic

Lower osmolarity than a normal cell.

Isosmotic

Same osmolarity as a normal cell.

Tonicity

Different from osmolarity because it only takes into consideration non-penetrating solutes.

Non-penetrating solutes

Solutes that cannot cross the plasma membrane (most solutes in the body are non-penetrating).

Penetrating Solutes

Solutes that can freely cross the plasma membrane.

Hypotonic solution

280 mOsm/L < 300 mOsm/L normal cell, therefore the solution is hypotonic to the normal cell.

Tonicity calculation

75mM NaCl : 75 x 2 = 150; 30mM KCl : 30 x 2 = 60; 50mM glucose : 50 x 1 = 50; = 260 mOsm/L.

Water movement in hypotonic solution

Hypotonic so water moves inside the cell, therefore causing cell to swell.