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Physiology > Fluid Compartments > Flashcards

Fluid Compartments Flashcards

1
Q

What is total body water (TBW)?

A

Total amount of fluid or water

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2
Q

How much of body weight does total body water make up as a %?

A

50-70%

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3
Q

Why is total body water lower in females than males?

A

Females = higher % of adipose/fat tissue (than males)
-High fat = low water & low fat = high water
–> indirect relationship

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4
Q

What 2 major body fluid compartments is total body water in - & how much?

A

-ICF (in cells) - 2/3 of total body water
-ECF (outside cells) - 1/3 of total body water

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5
Q

What can ECF be divided into (smaller body fluid compartments)?

A

-Plasma
-Interstitial fluid

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6
Q

Which of 2 parts of ECF is largest & smallest - plasma or interstitial fluid?

A

-Plasma = smaller
-Interstitial fluid = larger

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7
Q

How much of total body water is in plasma & interstitial fluid (parts of ECF)?

A

-Plasma = 1/4 (of the 1/3 of TBW in ECF)
-Interstitial fluid = 3/4 (of the 1/3 of TBW in ECF)

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8
Q

What is plasma?

A

Fluid circulating in the blood vessels

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9
Q

What is interstitial fluid?

A

Fluid that bathes cells

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10
Q

How does age effect TBW?

A

TBW decreases w/ age (in men & women)

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11
Q

What is the 60-40-20 rule?

A

60% of body weight = TBW
40% of body weight = ICF
20% of body weight = ECF

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12
Q

Calculate - TBW, ICF, ECF (body fluid compartments) when body weight = 70kg.

A

TBW = (60/100) x 70 = 42L
ICF = 2/3 of 42L = 28L (or use 60-40-20 –> 70 x (40/100))
ECF = 1/3 of 42L = 14L (or use 60-40-20 –> 70 x (20/100))
Plasma = 1/4 of 14L = 3.5L
Interstitial fluid = 3/4 of 14L = 10.5L

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13
Q

Calculate body fluid compartments of 100kg adult female - assume TBW is 50%.

A

CAN’T USE 60-40-20 as TBW isn’t 60%!!!
TBW = 100 x 0.5 = 50L
ICF = 2/3 of 50L = 33.3L
ECF = 1/3 of 50L = 16.7L
Plasma = 1/4 of 16.7 = 4.2L
Interstitial fluid = 3/4 of 16.7 = 12.5L

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14
Q

What is ICF made up of?

A
  • Major cations: potassium (K+) & magnesium (Mg2+)
  • Major anions: proteins & organic phosphates (ATP, ADP, AMP)
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15
Q

What is ECF made up of?

A
  • Major cation: sodium (Na+)
  • Major anions: chloride (Cl-) & bicarbonate (HCO3-)
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16
Q

What is plasma made of?

A

*55% of blood volume of which:
93% water
7% proteins (3% = albumin)
(other 45% = RBS/erythrocytes)

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17
Q

What is the haematocrit?

A

% of blood vol occupied by RBCs (around 45%)
-Avg = 0.45 or 45% –> higher in males (0.48) than females (0.42)

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18
Q

What is interstitial fluid made of?

A

*Ultrafiltrate of plasma
*Has nearly the same composition as plasma
EXCEPT plasma proteins & blood cells

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19
Q

Ions present in ICF & ECF?

A
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20
Q

What is the barrier between the plasma & interstitial fluid?

A

Capillary wall

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21
Q

Features of capillary wall?

A

-1 cell layer
-Pores/fenestrations & junctions between cells
-Water = freely permeable
-Small molecules (ions, glu & some small proteins) = permeable
-Large molecules/proteins e.g., albumin: impermeable

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22
Q

What is the barrier between the ECF & ICF?

A

Cell memb

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23
Q

Features of cell memb?

A
  • Lipid bilayer
  • Repels water & anything dissolved in it
  • Channels & carriers
  • Membrane proteins that allow charged ions & water to cross
  • Ions: relatively impermeable
  • (Can cross via channels but very slowly & very small amounts)
  • Larger molecules (e.g. cytosolic proteins): relatively impermeable
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24
Q

How are amounts of solute measured?

A

-Moles
-Equivalents
-Osmoles

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25
Q

How are concentration of solute measured?

A

-Moles per litre (mol/L)
-Equivalents per litre (Eq/L) - mEq/L = milli
-Osmoles per litre (Osm/L)

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26
Q

What are moles & millimoles?

A

-1 mole = 6 × 10^23 molecules of a substance
-Millimoles =10^−3 moles
e.g.,1mmol/L = 1 × 10−3 moles of glu in 1L

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27
Q

What are equivalents?

A

-Way to measure amount of solute (above)
-Amount of ionised (charged) solute = no. solute molecules x valence (charge)

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28
Q

1mol of CaCl2 in solution (so = solute), dissociates into what equivalents?

A

2 equivalents of Ca2+ = 2mEq/L (1mmol/L) - as 1mol x charge of +2 = 2
2 equivalents of Cl- = 2mEq/L (1mmol/L) - as 2moles x charge of -1 = 2

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29
Q

What is an osmole?

A

No. particles a solute dissociates into, when in solution

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30
Q

What is osmolarity?

A

Conc. of particles in solution (expressed as
osmoles per litre - Osm/L)

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31
Q

When does osmolarity = molarity?

A

When solute doesn’t dissociate into solution

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32
Q

How is osmolarity calculated if solute dissociates into more than 1 particle?

A

Molarity x no. particles in solution

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33
Q

What is molarity?

A

No. of moles of solute in an amount of litres of the solution –> moles per litres of a solution
-aka = molar conc

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34
Q

What is 1mmol/L equal to in mOsm/L?

A

2Osm/L

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35
Q

What is the osmolarity of 1mmol/L CaCl2?

A

-Dissociates into 3 particles (Ca2+ & x2 Cl-) so:
= 3mOsm/L

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36
Q

What is osmolality?

A

Conc of osmotically active particles (osmoles/milliosmoles per kg of water)

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37
Q

Osmolarity vs osmolality?

A
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38
Q

What is the principle of macroscopic electroneutrality?

A

In each fluid compartment -> conc of cations = conc of anions (in mEq/L)

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39
Q

How are conc differences across cell membs created & maintained?

A

Na+/K+ ATPase pump
OR
Ca2+ ATPase
(i.e., by energy-consuming transport mechanisms in cell membs)

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40
Q

Why is it important to create conc grads across cell membs?

A

For ICF & ECF to control:
-Resting pot (nerves + muscles)
-Generating action pot (of exc cells)
-Excitation-coupling in musc cells
-Absorbing nutrients

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41
Q

Which has more Na+ - ICF or ECF?

A

ECF

42
Q

Which has more K+ - ICF or ECF?

A

ICF

43
Q

Which has more Cl- - ICF or ECF?

A

ECF

44
Q

Why do plasma & interstitial fluid have roughly same composition as plasma EXCEPT plasma proteins & blood cells?

A

Because capillary wall (barrier between plasma & interstitial fluid) has fenestrations = leaky
–> can cross
-However albumin (protein) CANNOT cross capillary wall (big)
-SO NO PROTEINS IN INTERSTITIAL FLUID (only plasma)

45
Q

Where is plasma?

A

Capillaries

46
Q

What are starling forces?

A

Pressures that control fluid movement across the capillary wall

47
Q

What are the 2 forces that make up starling forces?

A

-Oncotic forces
-Hydrostatic forces

48
Q

What are oncotic forces?

A

Force exerted by proteins

49
Q

What are hydrostatic forces?

A

Forces exerted by water/fluid

50
Q

What is filtration?

A

Net movement of water (nutrients) out capillaries

51
Q

What is absorption?

A

Net movement into capillaries (of waste products - CO2) - closer to venule end

52
Q

What is Pc?

A

= Capillary hydrostatic pressure
–> forces fluid out capillaries (pushes @ capillary walls)

53
Q

What is πc?

A

= Capillary oncotic pressure
–> fluid into capillaries

54
Q

What is Pi?

A

= Interstitial hydrostatic pressure
–> fluid into capillaries

55
Q

What is πi?

A

= Interstitial oncotic pressure
–> fluid out capillaries

56
Q

What is σ?

A

= Reflection coefficient (property of selective memb)
-How easy solute crosses memb 0-1
0 = No reflection (fully permeable)
0-1 = partial reflection
1 = All reflection

57
Q

What is Kf?

A

Filtration Coefficient

58
Q

What does a high filtration coefficient mean?

A

Highly leaky/permeable - lots of filtering

59
Q

What does a low filtration coefficient mean?

A

Not very permeable - little filtering

60
Q

How do proteins ‘suck’ fluid into capillary?

A

Are negatively charged

61
Q

How is net filtration calculated?
(No need to memorise!)

A

Net filtration= Kf[(Pc-Pi)-σ(πc- πi)]
Filtration coefficient x (diff in hydrostatic pressure) - reflection coefficient x (diff in oncotic pressure)
(must factor in any reflection)
-Filtration favoured or absorption favoured

62
Q

Describe why filtration occurs?

A

Capillary hydrostatic pressure = HIGHER near arteriole end than in interstitial fluid = so oxygen & nutrients forced out - diffuse into tissues

63
Q

Describe why absorption occurs?

A

-Proteins & blood cells remain in capillary = create high oncotic pressure in capillary (greater ‘sucking’ of capillary than interstitial fluid)
–> due to high protein conc (same no. proteins as @ arteriole end but fluid lower)

64
Q

Summarise the hydrostatic pressures & oncotic pressures?

A

Arteriole end
-Hydrostatic pressure - higher in capillary
-Oncotic pressure - lower in capillary

Venule end
-Hydrostatic pressure - lower in capillary
-Oncotic pressure - higher in capillary
–> hydrostatic pressure dropped below oncotic (due to fluid loss) - no change to oncotic - as is same all along - only conc of proteins changes

ONCOTIC IS RELATIVE TO HYDROSTATIC!

65
Q

What does net mean in terms of filtration & absorption?

A

You will mostly get either filtration or absorption - but both will be occurring

66
Q

What happens during high BP (hypertension) or heart failure?

A

-More filtration - hydrostatic pressure in capillary = higher
-> more fluid into interstitial fluid –> causes oedema

67
Q

What is Pc dependent on?

A

Both arterial & venous blood pressures (generated by the heart).

68
Q

What is πc dependent on?

A

-Protein conc in blood
-Proteins = only effective oncotic agent in caps - impermeable across vascular wall

69
Q

What does liver disease cause?

A

-Prot syn = decreases = less albumin
–> more filtration - as lowers capillary oncotic pressure (less protein in caps) - less sucking effect (RELATIVITY!)

70
Q

What happens during liver disease cause?

A

-Prot syn = decreases = less albumin
–> more filtration - as lowers capillary oncotic pressure (less protein in caps) - less sucking effect (RELATIVITY!)

71
Q

What happens during systemic inflammatory response?

A

-Increased Kf
–> so more filtration –> causes oedema

72
Q

Summarise filtration & absorption

A

-Pushing = high hydrostatic pressure fluid (O2, nutrients - glu) out into interstitial fluid
-Pulling starts & increases - as more fluid filtered = increasing oncotic pressure - absorb waste products - CO2

73
Q

What happens to excess fluid?

A

Removed by lymphatic system

74
Q

What to remember about oncotic pressure?

A

Sucks (in capillary - as is where proteins are)

75
Q

Summarise transport across cell membs.

A

Overview
-Simple diffusion
-Osmosis
-Facilitated diffusion
-Primary active transport
-Secondary active transport

76
Q

What is a term for down an electrical gradient?

A

Downhill

77
Q

How does downhill transport occur?

A

Diffusion (simple or facilitated) & requires NO metabolic energy

78
Q

What is a term for against an electrochemical gradient?

A

Uphill

79
Q

How does uphill transport occur?

A

Active transport (primary or secondary) & requires metabolic energy

80
Q

What is carrier-mediated transport?

A

ALL modes of transport EXCEPT simple diffusion!

81
Q

What does carrier-mediated transport involve?

A

-Prot carrier
-Saturation - carrier prots have a limited no. binding sites for solute
-Stereospecificity - of binding sites for solute on the transport prots
-Competition - binding sites for transported solutes can recognize, bind, & can transport chemically related solutes

82
Q

What is the Brownian motion?

A

= Random dispersion of molecules from high to low conc
-In compartments & across membs
-Will reach dynamic equ eventually

83
Q

What is osmosis?

A

= Flow of water across a semipermeable memb due to differences in solute conc

84
Q

What causes osmotic pressure differences (for osmosis to occur)?

A

-Conc differences of impermeant solutes
-Pressure generated from solute conc potential across a semipermeable memb

85
Q

How does osmotic pressure lead to hydrostatic pressure?

A

-2 compartments = 1 is pure water other has dissolved solute
-Prior to osmosis - vol is same
-Osmosis occurs = diff in height of 2 compartments (higher in solute one) = causes hydrostatic pressure
-Hydrostatic pressure = pushes water into prev pure water
-Hyd press will then stop water flow

86
Q
A
87
Q

What is facilitated diffusion?

A

-Downhill
-No energy needed
-Memb carrier (same 3 features as carrier-mediated)

88
Q

What is primary active transport?

A

-Uphill
-Energy needed
–> ATP energy source - coupled to transport process

89
Q

What is the Na+/K+ pump - outline?

A

-Na+/K+ pump - pumps 3 Na+ from ICF to ECF & 2 K+ from ECF to ICF
-Na+/K+ ATPase enzyme switches between 2 major configurational states, E1 and E2.
-Cycle starts w/ E1 enzy

90
Q

What are 4 steps of Na+/K+ ATPase pump?

A

-3 Na+ bind intracellularly
-ATP hydrolysed = ADP + P
-P transferred to enzy = E1-P
-Enzy switches from E1-P to E2-P
-3 Na+ released from enzy to ECF
-2 K+ potassium ions are bound, & P is released from E2
-Enzy binds intracellularly - switches to E1
-2K+ released into ICF
-Cycle continues
-Cardiac glycosides inhibit Na+/K+ ATPase by binding to E2-P form

91
Q

What is secondary active transport?

A

-Coupling movement of 2/more solutes
–> one solute moves downhill = provides energy - for other to move uphill - either in same or different directions (into or out of cell!)
-Indirect ATP usage - supplied generating Na+ conc grad (in first step)

92
Q

What are the 2 forms of secondary active transport?

A

-Cotransport = symport
-Counter transport = antiport/exchange

93
Q

What is cotransport?

A

-All solutes are transported in same direction
-Na+ moves into the cell on the carrier downhill - solutes cotransported w/ Na+ also move into the cell

94
Q

What is counter transport?

A

-Solutes move in opposite directions across the cell membrane
-Na+ moves into cell on carrier downhill the solutes that are counter transported or exchanged for Na+ move out cell

95
Q

What are isotonic solutions?

A

-Solutions has same osmotic pressure/water potential to cell
= No net movement

96
Q

What are hypertonic solutions?

A

-Solution has higher osmotic pressure/water potential than cell
-LOW IN SOLUTE
= Net movement of water into cell (cell expands)

97
Q

What are hypotonic solutions?

A

-Solution has lower osmotic pressure/water potential than cell
-HIGH IN SOLUTE
= Net movement of water out cell (cell shrinks)

98
Q

What happens when add isotonic solution to ECF?

A

No change to osmolarity of ECF (no movement of electrolytes)
–> BUT causes increase in ECF vol
(e.g., IV fluid)

99
Q

What happens when add hypertonic solution to ECF?

A

-Osmolarity of ECF increases (higher conc of particles/salts)
–> so osmosis out cells into ECF
-ECF fluid vol increases
-ICF fluid vol decreases
= osmotic equilibrium
–> osmolarity increases in both ICF & ECF

100
Q

What happens when add hypotonic solution to ECF?

A

-Osmolarity of ECF decreases (lower conc of particles/solute)
–> so osmosis into cells/ICF - until equal osmolarity reached
-ECF fluid vol increases
-ICF fluid vol increases (to greater extent)

Physiology (10 decks)

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