Week 2

Question 1

ICF vs ECF

Answer 1

ICF - is 2/3 of the total body water volume

ECF is 1/3 total volume
It contains interstitial fluid which lies between. Circulatory system and the cells
Also contains blood plasma is the liquid matrix of the blood

Question 2

Body is in osmotic equilibrium

Answer 2

[particles] ICF = [particles]ECF

Plasma membrane is impermeable to solutes to achieve equilibrium we have to add water

Normal cell has 300mOsm/L
Extra cellular fluid also has 300mOsm/L

Water moves into higher concentration

Question 3

Body is in Osmotic equilibrium but in chemical disequilibrium

Answer 3

Concentration of solutes is equal in the ECF and ICF

But….

The nature of the solutes is strikingly different between the ICF and ECF

In a cell K+ is high in the cell low on the outside

In a cell Na+ is low on the inside and high on the outside

Question 4

Water moves via osmosis

Answer 4

Passive movement of water across a membrane in response to a solute concentration gradient

Passive movement does not require ATP

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

Greater the osmotic pressure =Greater H2O movement

Question 5

Calculating Osmolarity

Answer 5

300m Osm/L
Osmolarity(mOsm/L): Calculates the concentration of particles in a solution

Molarity (mmol/L):calculates the concentration of molecules in a solution

Glucose contains covalent bonds - it does not dissociate in water
1molecule of glucose = 1 particle
10mmol/L =1x10 =10 mmOs/L

NaCl contains ionic bonds - it dissociates in water
1 Molecule of NaCl = 2 particles

Ex 10mmol/L NaCl =10x2 =20 mOsm/L

mOsm/L: calculate the # of particles in a solution
=molarity x #of particle it dissolves into

For this course ionic compounds will be written as chemical formula and covalent bonds will be written as their name

KCl 2 particles and ionic
CaCl2 3 particles and ionic
HCl 2 particle

Question 6

What is the Osmolarity of the solution below

Answer 6

100mM of NaCl =2 particles
100x2=200 mOsm/L

50mM CaCl2
50x3 = 150mOsm/L

10 mM glucose (remains as 1)
10x1= 10 mOsm/L

To find Osmolarity of solution add all Osmolarity 200+150+10= 360

Higher Osmolarity compared for the normal 300 mOsm/L

Hyper osmotic to regular body fluid because it will pull the concentration inwards to the higher gradient

Question 7

Tonicity describes the volume change of a cell

Answer 7

Tonicity is different from Osmolarity because it only takes into account non penetrating solutes

Solutes cannot cross plasma membrane most solutes in humans are non penetrating.

Penetrating solutes: solutes that can freely move across a membrane

Question 8

Osmolarity and Tonicity example

Answer 8

75 mM NaCl
30 mM KCl
50 mM glucose
20 mM urea (penetrating solute)

Osmolarity = 280msOmL
2x75
30x2
50x1
20x1
Hypoosmotic

Tonicity =non penetrating -penetrating = 260msOm/L
Hypotonic

We always use Tonicity

260 to 300

So we would say solution is hypotonic and the cell swells volume increases