Physiology 1

Question 1

what is osmolarity

Answer 1

the concentration of osmotically active particles in a solution

Question 2

units of osmolarity

Answer 2

osmol/l or mosmol/l

Question 3

mosmol/l can be used

Answer 3

for weak salt solutions i.e. body fluids

Question 4

osmolarity can be calculated if what 2 factors are known

Answer 4

1. the molar concentration of solution

2. the number of osmotically active particles present in the solution

Question 5

e.g 150mM NaCl work out its osmolarity

Answer 5

• molar concentration= 150mM
• number of osmotically activity particles: Na+Cl= 2

osmolarity= 2x150= 300 mosmol/l

Question 6

osmolarity vs osmolality

Answer 6

osmolality is the concentration of osmotically active particles per kg

Question 7

units of osmolality

Answer 7

osmol/kg water

Question 8

for weak salt solution the terms osmolarity and osmolality are

Answer 8

interchangeable

Question 9

tonicity

Answer 9

is the effect a solution has on cell volume

Question 10

tonicity of solutions can either be

Answer 10

• hypertonic
• hypotonic
• isotonic

Question 11

isotonic

Answer 11

the solution has the same osmolarity as the osmolarity of the fluid inside the cell, there will be no net movement of water into or out of the cell

Question 12

hypotonic

Answer 12

the solution has a lower osmolarity than the osmolarity of the fluid inside the cell, there will be a net movement of water into the cell

Question 13

hypertonic

Answer 13

the solution has a higher osmolarity than the osmolarity of the fluid inside the cell, there will be a net movement of water out of the cell

Question 14

although related to osmolarity tonicity

Answer 14

also takes into consideration the ability of a solute to cross the cell membrane

Question 15

total body water

Answer 15

• 60% of body weight in males

- 50% of body weight in females

Question 16

total body water exists as 2 major compartments

Answer 16

intra-cellular fluid (67% of total body water) and extra-cellular fluid (33% of total body water)

Question 17

extra-cellular fluid includes

Answer 17

• interstitial fluid (80% of ECF) which is the fluid in spaces between tissue cells
• plasma fluid (20% of ECF) which is the fluid portion of the blood
• transcellular fluid and lymph fluid is negligible

Question 18

how do you measure the volume of body fluid compartments

Answer 18

using tracers

Question 19

how do tracers work

Answer 19

you can determine the volume of distribution of a tracer substance

Question 20

useful tracers

Answer 20

• total body water= 3H20
• extra-cellular fluid= Inulin
• Plasma= labelled albumin

Question 21

total body water equals

Answer 21

the extra-cellular fluid plus the intra-celualr fluid therefore, if you use tracers to work out the total body volume and ECF you can calculated the ICF

Question 22

worked example

Answer 22

• imagine adding a dose of tracer (D=42MG) to a container containing a large and unknown volume of water (V)
• you mix the tracer allowing it to equilibrate
• you then take a small sample volume from the container( (5ml) and measure the concentration of tracer (C) in this sample
• on analysis c= 0.005mg/5ml= 1mg/litre
• so the volume of water in the container= DOSE/ SAMPLE CONC
• VOLUMEN= 42/1= 42 LITRES

Question 23

Summary for working out volume of distribution

Answer 23

1. add a known quantity of tracer X into the body (Qx: mol or mg)
2. measure the equilibrium CONCENTRATION of X in the body (X)
3. Volume of distribution= Qx/ X

Question 24

for water balance

Answer 24

inputs have to equal outputs

Question 25

water input

Answer 25

- fluid intake= 1200ml/day - food intake= 1000 ml/day - metabolism= 300 ml/day

Question 26

water output

Answer 26

insensible loss: - skin= 350ml/day - lungs= 350ml/day sensible losses: sweat= 100ml/day faeces= 200ml/day urine= 1500ml/day

Question 27

total input and total fluid output

Answer 27

input is 2500ml per day and output is 2500ml per day

Question 28

water imbalance is manifested as

Answer 28

changes in body fluid osmolarity

Question 29

water loss in hot weather

Answer 29

- skin= 350ml - lungs= 250ml - sweat= 1400ml - faces= 200ml - urine= 1200ml

Question 30

water loss in prolonged heavy exercise

Answer 30

- skin= 350ml - lungs= 650ml - sweat= 5000ml - faeces= 200ml - urine =500ml

Question 31

in hot temperatures and during prolonged heavy exercise

Answer 31

water balance is maintained by increasing water ingestion, decreased water excretion is not sufficiency to maintain water balance

Question 32

ionic component of the intra-cellular fluid

Answer 32

10mM Na+ 140mM K+ 7mM Cl- 10mM HCO3-

Question 33

ionic components of the extra-cellular fluid

Answer 33

140mM Na+ 4.5mM K+ 115 mM Cl- 28 mM HCO3-

Question 34

ECF and the ICF are separated by

Answer 34

compartments

Question 35

the cell membrane and membrane transport mechanisms all

Answer 35

cell to maintain internal environments that are different to there surrounding

Question 36

main ions in the ICF

Answer 36

K+, Mg2+ and negatively charged proteins

Question 37

main ions in the ECF

Answer 37

Na+, Cl- and HCO3-

Question 38

Cell membranes

Answer 38

are selectively permeable but despite this the osmotic concentrations of both ECF and ICF and identical (300mosmol/litre)

Question 39

because changes in the solute concentration lead to

Answer 39

immediate changes in water distribution, the regulation of fluid balance and electrolyte balance are highly intertwined

Question 40

fluid shift

Answer 40

movement of water between the ICF and ECF in response to an osmotic gradient

Question 41

Challenges to fluid homeostasis

Answer 41

1. Gain or loss of water 2. Gain or loss of NaCl 3. Gain or loss of isotonic fluid

Question 42

gain or loss of water

Answer 42

change in fluid osmolarity causes similar changes in the ICF and ECF (both either increase or decrease)

Question 43

gain or loss of NaCl

Answer 43

Change in fluid osmolarity causes A) Na+ to be excluded from the ICF B) osmotic water movements both of these factors combine to produce opposite changes in ICF and ECF volumes

Question 44

ECF NaCl gain

Answer 44

increased extra-cellular fluid volume | reduced intra-cellular fluid volume

Question 45

ECF NaCl loss

Answer 45

reduced extra-cellular fluid volume | increased intra-cellular fluid volume

Question 46

gain or loss of isotonic fluid

Answer 46

(e.g 0.9% NaCL) causes no change in fluid osmolarity only the ECF volume falls

Question 47

the kidneys alter

Answer 47

the composition and volume of the ECF, regulation of ECF is vital for long term control of blood pressure

Question 48

electrolyte balance occurs when

Answer 48

rate of gain= rate of loss

Question 49

electrolyte balance is important for 2 reasons

Answer 49

1. Total electrolyte concentrates can directly alter water balance 2. the concentrations of individual electrolytes can affect cell function

Question 50

Na+ and K+ are particularly important because

Answer 50

1. they are major contributors to the osmotic concentration of ECF and ICF respectively 2. they directly affect the functioning of cells

Question 51

sodium balance

Answer 51

more than 90% of the osmotic concentration of the ECF results from the presence of sodium salts

Question 52

the total amount of sodium in the ECF represents

Answer 52

a balance between 2 factors (input and output)

Question 53

Na+ is mainly present

Answer 53

in the ECF therefore it is a major determinant of ECF volume (water follows sodium)

Question 54

Minor fluctuations

Answer 54

in plasma potassium (K+) can have detrimental consequences

Question 55

potassium plays a key role in

Answer 55

establishing membrane potential

Question 56

95% of the bodies potassium is

Answer 56

intra-cellular so small leakages or increased cellular uptake may severely affect K+ plasma concentrations leading to - muscle weakness causing paralysis - cardiac irregularities causing cardiac arrest

Question 57

salt balance

Answer 57

for balance to occur input has to equal output

Question 58

intake of salt

Answer 58

fluids and food= 10.5g/ day

Question 59

output of salt

Answer 59

- sweat and faeces= 0.5g/day | urine= 10g/day

Question 60

salt imbalance is manifested as

Answer 60

changes in the extra-cellular fluid volume, regulation of extra-cellular fluid volume is very important for the long term regulation of blood pressure