6: Physiology 1 Flashcards

1
Q

What is osmolarity?

A

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

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2
Q

What is the unit of osmolarity?

A

Osmol / L

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3
Q

How do you calculate osmolarity?

A

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

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4
Q

What is the osmolarity of body fluid?

A

300 mosmol / L

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5
Q

What is the difference between osmolarity and osmolality?

A

Osmolarity measured in osmol/L

Osmolality measured in osmol/kg

pretty much the same

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6
Q

What is tonicity?

A

Effect a solution has on cell volume

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7
Q

What are

a) isotonic
b) hypotonic
c) hypertonic

solutions?

A

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

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8
Q

Can solutions with the same osmolarity have different tonicities?

Why?

A

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

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9
Q

Which sex has a greater body water content?

Why?

A

Males (60%)

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

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10
Q

Which two compartments is body water held in?

A

Intracellular fluid (ICF)

Extracellular fluid (ECF):

ECF divided into plasma and interstitial fluid

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11
Q

Which body compartment has a greater volume?

A

Intracellular fluid (ICF)

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12
Q

Which compartment of the extracellular fluid has a greater volume?

A

Interstitial fluid

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13
Q

How can the volume of body compartments be measured?

A

Tracers

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14
Q

What is the equation for total body water content?

A

TBW = ECF + ICF

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15
Q

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

A
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16
Q

What is the main input of water to the body?

A

Food and drink

17
Q

What is the main output of water from the body?

A

Urine

18
Q

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

A

2500 ml

19
Q

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

A

Osmolarity

20
Q

Why can urine production never be turned off?

A

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

21
Q

Which ions are found mainly

a) inside
b) outside the cell?

A

a) K+, Mg2+ negatively charged ions

b) Na+, Cl-

think cells swimming in salty water

22
Q

What structures separate the

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

A

a) Capillary wall

b) Plasma membrane

23
Q

What is fluid shift?

A

Movement of water between ICF and ECF by osmotic gradient

24
Q

Osmolarity ___ as water leaves a compartment.

A

Water leaves > More solute = INCREASED OSMOLARITY

Water enters > Less solute = DECREASED OSMOLARITY

25
Q

What happens if the osmotic concentration of the ECF decreases?

A

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

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

So fluid shift to ICF

26
Q

If osmotic concentration of the ECF increases, what happens?

A

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

So fluid shift from ICF to ECF

27
Q

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

A

fluid shift TO that compartment

28
Q

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

A

fluid shift FROM that compartment

29
Q

Which organs regulate the composition and volume of the ECF?

A

Kidneys

30
Q

How does the osmolarity of the ECF affect blood pressure?

A

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

31
Q

Why is electolyte imbalance important?

A

Electrolyte (ion) concentration affects osmolarity and therefore water balance

Electrolyte concentration affects cell function

32
Q

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

A

Na+ and K+

33
Q

Which ion sets up the osmotic gradients of cells?

Why?

A

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

34
Q

Which ion sets up the membrane potential of cells?

Why is this important?

A

K+

Affects function of muscle and all other cells

35
Q

What is the average daily intake of salt?

Is this higher or lower than recommended?

A

Around 10g

Recommended is 6g