6: Physiology 1

Question 1

What is osmolarity?

Answer 1

Concentration of osmotically active particles (cause osmosis) in a solution

Question 2

What is the unit of osmolarity?

Answer 2

Osmol / L

Question 3

How do you calculate osmolarity?

Answer 3

You need:

molar concentration

no. of osmotically active particles
e. g 150mM NaCl

molar concentration = 150mM, 2 particles, 2x150 = 300 mosmol/l

or 100mM MgCl3 -> 100mM x 3 = 300 mosmol / l

Question 4

What is the osmolarity of body fluid?

Answer 4

300 mosmol / L

Question 5

What is the difference between osmolarity and osmolality?

Answer 5

Osmolarity measured in osmol/L

Osmolality measured in osmol/kg

pretty much the same

Question 6

What is tonicity?

Answer 6

Effect a solution has on cell volume

Question 7

What are

a) isotonic
b) hypotonic
c) hypertonic

solutions?

Answer 7

REFERS TO SOLUTE CONCENTRATION

a) If cell is ISOTONIC to solution, no change in cell volume

b) If cell is HYPOTONIC (i.e lower water content) to solution, INCREASE in cell volume > bursts

c) If cell is HYPERTONIC to solution, DECREASE in cell volume > shrinkage

Question 8

Can solutions with the same osmolarity have different tonicities?

Why?

Answer 8

Cell membranes have different permeabilities

e.g Urea and sucrose are both isotonic to cell

Cell is very permeable to urea, water then follows urea causing lysis

compared to sucrose, which cell membrane is impermeable to, so no change in volume

Question 9

Which sex has a greater body water content?

Why?

Answer 9

Males (60%)

Females have a greater fat content, which doesn’t contain water

Question 10

Which two compartments is body water held in?

Answer 10

Intracellular fluid (ICF)

Extracellular fluid (ECF):

ECF divided into plasma and interstitial fluid

Question 11

Which body compartment has a greater volume?

Answer 11

Intracellular fluid (ICF)

Question 12

Which compartment of the extracellular fluid has a greater volume?

Answer 12

Interstitial fluid

Question 13

How can the volume of body compartments be measured?

Answer 13

Tracers

Question 14

What is the equation for total body water content?

Answer 14

TBW = ECF + ICF

Question 15

To calculate volume of distribution:

add known mass of tracer to unknown volume of water

take known volume of water and calculate concentration of tracer

volume of distribution = mass / concentration

m

c v

Question 16

What is the main input of water to the body?

Answer 16

Food and drink

Question 17

What is the main output of water from the body?

Answer 17

Urine

Question 18

On average, how much water is input and output every day?

Answer 18

2500 ml

Question 19

What changes if there is a water imbalance in the body?

Answer 19

Osmolarity

Question 20

Why can urine production never be turned off?

Answer 20

Toxic metabolites need to leave the body in solution i.e water

Question 21

Which ions are found mainly

a) inside
b) outside the cell?

Answer 21

a) K+, Mg2+ negatively charged ions

b) Na+, Cl-

think cells swimming in salty water

Question 22

What structures separate the

a) plasma from the interstitial fluid
b) the interstitial fluid from the intracellular fluid?

Answer 22

a) Capillary wall

b) Plasma membrane

Question 23

What is fluid shift?

Answer 23

Movement of water between ICF and ECF by osmotic gradient

Question 24

Osmolarity ___ as water leaves a compartment.

Answer 24

Water leaves > More solute = INCREASED OSMOLARITY

Water enters > Less solute = DECREASED OSMOLARITY

Question 25

What happens if the osmotic concentration of the ECF decreases?

Answer 25

Concentration of solute decreases (i.e water has entered ECF)

So osmotic gradient between high (ECF) and low (ICF)

So fluid shift to ICF

Question 26

If osmotic concentration of the ECF increases, what happens?

Answer 26

Osmotic gradient from high (ICF) to low (ECF)

So fluid shift from ICF to ECF

Question 27

As osmolarity increases there is a fluid shift (to / from) that compartment.

Answer 27

fluid shift TO that compartment

Question 28

As osmolarity decreases there is a fluid shift (to / from) that compartment.

Answer 28

fluid shift FROM that compartment

Question 29

Which organs regulate the composition and volume of the ECF?

Answer 29

Kidneys

Question 30

How does the osmolarity of the ECF affect blood pressure?

Answer 30

If low, water moves to ICF, so plasma volume decreases, so BP decreases

If high, water moves to ECF, so plasma volume increases, so BP increases

Question 31

Why is electolyte imbalance important?

Answer 31

Electrolyte (ion) concentration affects osmolarity and therefore water balance

Electrolyte concentration affects cell function

Question 32

Which two ions are particularly important in fluid balance and cell function?

Answer 32

Na+ and K+

Question 33

Which ion sets up the osmotic gradients of cells?

Why?

Answer 33

Na+

There’s so much sodium (140mM) that it effectively decides what the osmolarity is (osmolarity = 2x[Na])

Osmolarity decides where water goes

So water basically follows sodium

Question 34

Which ion sets up the membrane potential of cells?

Why is this important?

Answer 34

K+

Affects function of muscle and all other cells

Question 35

What is the average daily intake of salt?

Is this higher or lower than recommended?

Answer 35

Around 10g

Recommended is 6g