Physiology 1

Question 1

Define what osmolarity is

Answer 1

It is the concentration of osmotically active particles in a solution

Question 2

What is the difference between osmolarity and osmolality ?

Answer 2

The units:

• Osmolality has units of osmol/kg water
• Osmolarity has units of osmol/l

Question 3

How is osmolarity calculated ?

Answer 3

Osomlarity = number of osmotically active particles x molar concentration of the solution

Question 4

Define what is meant by tonicty ?

Answer 4

It is the effect a solution has on a cell

Question 5

What are the 3 main different toncities a solution can be ?

Answer 5

• Hypertonic
• Hypotonic
• Isotonic

Question 6

What happens to a cell when placed in each of the 3 different toncities ?

Answer 6

• When a cell is placed in a hypertonic solution is will shrink
• When cell is placed in hypotonic solution it will become bigger and protentially burst
• When cell is placed in isotonic solution it will stay the same

Question 7

Appreciate that the cell membrane can be very permeable to some substances and not very permeable to others

Answer 7

.

Question 8

What are the body fluid compartments?

Answer 8

• Total body water (TBW) = ECF + ICF
• ECF = Plasma + Interstitial fluid

Question 9

How are the sizes of fluid compartments measured?

Answer 9

Using tracers:

• TBW - measured by measuring H2O
• ECF - measured by measured inulin
• Plasma volume measured by measuring labelled albumin
• ICF can therefore be calculated if we know the ECF and TBW

Question 10

What is required for water homeostasis in the body ?

Answer 10

The water input = the water output of the body

Question 11

What is the ionic composition of the major fluid compartments (ECF and ICF) in the body ?

Answer 11

Useful way to think about it is that we used to live in the sea but now our body has internalised this environment (salty) so the salt is high around our cells

ECF:

• High Na, Cl and HCO3
• Low K+

ICF:

• High K+
• Low Na+, Cl- and HCO3-

Question 12

What allows cells to maintain there internal environments?

Answer 12

Cell membrane and membrane transport mechanisms

Question 13

Describe what is meant by fluid shift

Answer 13

The movement of water between the ICF and ECF

Question 14

How do you increase the osmotic concentration of a solution?

Answer 14

Loose water or increase the number of osmotically active particles in the solution (e.g. NaCl)

Question 15

What happens is there is gain or loss of isotonic fluid from a solution?

Answer 15

There will be no change in osmolarity only a change in the volume

Question 16

What is the regulation of ECF key for ?

Answer 16

Maintaining BP

Question 17

Which 2 ions are the main contributors to the osmolarity of ICF and ECF?

Answer 17

Na+ and K+

• Specifically Na+ the main determinate of ECF osmolarity
• K+ the main determinate of ICF osmolarity

Question 18

What follows the movement of Na+?

Answer 18

Water - as a rule of thumb water always follows sodium

Question 19

Na+ and K+ balance is vital

Answer 19

• Na+ inbalance can affect BP
• and K+ inbalance caause arrhythmias, muscle weakness etc