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Primary Physiology > Body Fluids > Flashcards

Body Fluids Flashcards

1
Q

Proportion of body water by weight in young adult male and female
Neonate?

What causes large variation in adults?

A

60%
50%
80%

Increasing adipose tissue means less water

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2
Q

Proportion of ECF to ICF of Total water and weight

A

34% vs 66% of total body water
(20% vs 40% of total body weight)

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3
Q

Proportions of ECF in different compartments

A

Interstitial 75% of ECF (approx 15% body weight)
Plasma 25% of ECF (approx 5% body weight)
Transcellular (approx 1% body weight)

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4
Q

What is the implication of the impermiability of the capillary membrane to proteins

A

Higher concentration of proteins in plasma so higher concentration of chloride in ISF to maintain electrical neutrality

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5
Q

What is Transcellular fluid

A

Fluid separated from plasma by epithelial layer e.g. csf, interocular fluid, bile, gi secretions, sweat, pleural fluid

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6
Q

Method of working out total blood volume?

A

Measure plasma volume using radioisotope dilution with a isotope that remains in plasma such as radioactive albumin then derive using haematocrit.

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7
Q

How to measure fluid compartment volumes? Issues that cause under or over estimates?

A

Inject a known volume of a radioactive isotope which stays in the compartment to be measured directly into the compartment. Measure its concentration and derive volume (volume = mass of indicator/concentration)
Issues if it doesn’t fully distribute - underestimates size
Issues if leaves compartment - overestimates size

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8
Q

What isotopes can be used to measure by dilution
Total body water
ECF
Plasma

A

TBW - antipyrine D2O
ECF - radioisotopes eg of Na or Br (though enters cells so overestimates) or saccharides such as insulin or mannitol (though incompletely distribute so underestimate)
Plasma volume - albumin

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9
Q

How can we calculate ICF volume

A

TBW - ECF

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10
Q

How can we calculate interstitial fluid volume

A

ECF-plasma volume

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11
Q

Why do we use moles instead of just mass

A

Chemical reactivity is proportional to number of molecules not weight

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12
Q

What is one mole of a substance

A

6.022 x 10^23 molecules

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13
Q

Define avogadros constant

A

The number of atoms in 12g of carbon12
6.022 x 10^23

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14
Q

Distinguish molarity from molality

A

Molarity - number of moles of solute per litre of solution (solute + water) (mol/L)
Molality - number of moles of solute per kg of solvent (just water) (mol/kg H2O)

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15
Q

What is the gram equivalent weight of an element?

A

The weight of an element that reacts with 8.000g O2

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16
Q

What is a normal solution in chemistry

A

1g equivalent solute per litre of solution

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17
Q

What is an electrical equivalent weight?

A

The atomic weight of an ion divided by its valency (eg Ca2+ = 40/2 = 20)

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18
Q

What is osmosis

A

Movement of water across a semipermeable membrane by diffusion to equalise solution concentrations

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19
Q

What is osmotic pressure

A

The pressure required to prevent osmosis when the solution is separated from pure solvent by a semipermeable membrane

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20
Q

What is the universal gas constant

A

8.32 J/K/mol

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21
Q

What is the equation for osmotic pressure? Name and formula

A

Van hoff’s

Pie = RTC
Osmotic pressure (pascals) = universal gas constant (J/K/mol) x absolute temp (K) x osmolality (mOsm/kgH2O)

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22
Q

What is an Osmole

A

Amount of solute that exerts an osmotic pressure of 1atm when placed in 22.4 litres of solution at 0 degrees Celsius

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23
Q

What is a rule of thumb for calculating number of osmoles

A

For a substance that does not associate or dissociate 1 osmole = 1 mole
For a solution that fully dissociates in 2 osmotically active particles (eg NaCl) 1 osmole = 1 mole/2

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24
Q

Define osmolarity and osmolality
Why is it Important?

A

Osmolarity - number of osmoles of solute per litre of solution (solute + water)
Osmolality - number of osmoles of solute per kg of solvent (water alone)

Osmolality is independent of temperature and independent of the volume taken up by the solute.

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25
Q

Which would be higher in a human, osmolality or osmolarity
When is it more significant

A

Osmolality usually higher as protein and lipid content ‘dilute’ osmolarity
More significant in gross hyperproteinaemia or hyperlipidaemia

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26
Q

Typical range for plasma osmolality
Significance for rest of body?

A

280-295mOsm/KgH2O steady at 290
Rest of body same - water moves freely equalising all

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27
Q

Given water moves freely between compartments and osmolality is kept equal across the body what determines compartment volume

A

Number of osmoles

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28
Q

How is body fluid osmolality regulated?

A

Secretion of ADH in response to increase in osmolality or decreased total body water detected in the hypothalamus

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29
Q

How is osmolality measured

A

Depression of freezing point of solution compared to pure solvent
Estimated by molality of major solutes:
Plasma osmolality = 2 x [Na] + [glucose] + [urea]

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30
Q

When estimating plasma osmolality why is Na concentration doubled

A

To account for anions eg Cl and bicarb

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31
Q

What is tonicity
What contributes to it in the ECF with relevance to ICF

A

The relative osmolality between two fluid compartments
All solutes in ECF contribute to osmolality but only those which do not cross cell membrane contribute to tonicity

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32
Q

What is the characteristic of an isotonic solution with regards to cell size

A

No change in size when a cell suspended in an isotonic solution

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33
Q

What is oncotic pressure
What other name can it have

A

The osmotic pressure exerted by the plasma proteins which are unable to leave the vessels.
Plasma colloid osmotic pressure

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34
Q

What is the most important determinant of oncotic pressure,
how much is oncotic pressure in mmHg

A

Albumin, around 75% of the total 25mmHg

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35
Q

What are the three main mechanisms of transport across the capillary endothelium

A

Filtration - hydrostatic pressure forcing fluid out of the capillaries
Diffusion - passive movement of substances down concentration gradient through fenestrations and intercellular junctions. Main barrier is basement membrane
Transcytosis - active transfer of substances by endo and exocytosis across endothelial cells

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36
Q

What is the Gibbs-Donnan effect

A

The presence of a non-diffusible solute such as a protein on one side of a membrane affects the distribution of the diffusible ions. The negative charge on the protein holds +ve ions (Na) back to preserve electroneutrality

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37
Q

What is the implication of the Gibbs Donnan effect at the capillary membrane?

A

Higher Na concentration in plasma vs ISF and higher Cl concentration in the ISF vs plasma
Gives a small electrical potential gradient

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38
Q

How does the Gibbs donnan effect balance mathematically

A

Cation x anion on one side of membrane = cation x anion on the other
Eg 9x4 = 6x6

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39
Q

What is the Nernst equation?

A

E = 60/z.log10(Ci/Ce)
(mV) (mmol/L)

Equilibrium potential = constant (at 37o)/valence . Log10(internal concentration of ion/external concentration of ion)

Constant derived by 2.3RT/F
2.3.universal gas constant.temp(K)/faridarys constant

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40
Q

What causes the small difference in ion concentration between plasma and ISF

A

Gibbs donnan effect

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41
Q

Rough weight of protein in plasma?

A

7g per 100ml

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42
Q

Plasma vs ICF concentration of Na. Mmol/L

A

153
10

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43
Q

Plasma vs ICF concentration of K Mmol/L

A

4.3
159

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44
Q

Plasma vs ICF concentration of Ca Mmol/L

A

2.7
<1

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45
Q

Plasma vs ICF concentration of Mg Mmol/L

A

1.1
40

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46
Q

Plasma vs ICF concentration of Cl Mmol/L

A

112
3

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47
Q

Plasma vs ICF concentration of HCO3 Mmol/L

A

25.8
7

48
Q

Plasma vs ICF concentration of Proteins Mmol/L

A

15.1
45

49
Q

Functions of albumin in plasma

A

Transport of free fatty acids and bilirubin
Oncotic pressure

50
Q

Intravascular half life of albumin

A

19 days

51
Q

Which is the heaviest immunoglobulin, why?
Implication of this to its distribution

A

IgM
It’s a pentameter in contrast to dimer IgA and monomers of IgG,IgM and IgD
Confined to intravascular space

52
Q

Rough weight in daltons of a Ig monomer? Implication for IgA and M

A

150,000 to 190,000
Multiply it up by number of groups x2 for IgA (400,000) and x5 for IgM (900,000)

53
Q

Rough pH, Na, K, Cl and HCO3 of gastric juices

A

pH3
Na 60
K 9
Cl 84
HCO3 0

54
Q

Rough pH, Na, K, Cl and HCO3 of bile

A

pH 8
Na 149
K 5
Cl 101
HCO3 45

55
Q

Electrolyte concentrations in Hartman’s
Osmolality

A

Na 131
K 5
Ca 4
Cl 112
HCO3 29

Osmolality 281

56
Q

Electrolyte concentration normal saline
Osmolality

A

Na and Cl 154
308

57
Q

Osmolality of 5% glucose

A

278

58
Q

Electrolyte composition of 4% glucose 0.18% NaCl
Osmolality

A

Na and Cl 31
Osmolality 284

59
Q

Daily water and key electrolyte requirements for an adult

A

Water 35ml/kg
Na/K 1 mmol/kg

60
Q

Why does Hyperchloraemic acidosis occur on excessive fluid resus with normal saline

A

Excess Cl leads to renal HCO3 secretion

61
Q

Causes of hypovolaemia hypernatraemia
Treatment

A

Loss of free water eg
Diabetes insipidus
Osmotic diuresis
Vomiting

Replace free water - orally if possible, slow correction of volume deficits with normal saline then further water deficit with hypotonic fluids.

62
Q

How can urine measurements be used to classify hypernatraemia?

A

High urine osmolality and low urine output indicates normal ADH function suggesting hypernatraemia from external loss or inadequate intake
Huigh urine osmolality with high urine output suggests osmotic diuresis

63
Q

Cause of hypervolaemic hypernatraemia

A

Iatrogenic fluid replacement

64
Q

How can you estimate water deficit in a hypernatraemic patient

A

Water deficit = ([Na] / 140xTBW) - TBW

65
Q

Signs and symptoms of hypernatraemia

A

Thirst lethargy weakness confusion coma seizures

66
Q

Signs and symptoms of hyponatraemia

A

Malaise, nausea, headache, irritability, confusion, weakness, coma, seizures

67
Q

Causes of spurious hyponatraemia

A

Sample from drip arm
High serum lipid or protein causing dilutional
Marked hyperglycaemia causing dilutional (add about 4 to Na for every 10 of BM above 20)

68
Q

Causes of hypervolaemic hyponatraemia
Expected urinary sodium

A

Heart failure, renal failure, hepatic failure, iatrogenic
Urinary sodium <20mmol/L

69
Q

Causes of euvolaemic hyponatraemia
Tests to differentiate?

A

Urinary osmolality >100 and Na >20 - SIADH
Urine osmolality <100 - water overload, severe hypothyroid, low glucocorticoids

70
Q

Causes of siadh

A

Tumour (lung - small cell, pancreas, prostate, thymus, lymphoma)
Cerebral abscess, stroke, haemorrhage, sle
Tb, pneumonia, lung abscess
Opiates, ssris, cytotoxic, psychotropics
Trauma, hiv, abdominal surgery

71
Q

Causes of hypovolaemia hyponatraemia and differentiating factor between them

A

Urinary Na >20 - loss from kidneys - addisons, renal failure, diuretics, osmolarity diuresis (e.g. high glucose or urea)
Urinary Na <20 - loss elsewhere - d+v, fistula, burns, SBO, trauma, cystic fibrosis, heat exposure

72
Q

Treatment of symptomatic hyponatraemia

A

Cautious rehydration with normal saline, max rise 15mmol/L per day if chronic or 1mmol/hr if acute
In emergency hypertonic saline

73
Q

Treatment of asymptomatic hyponatraemia

A

Fluid restriction
Consider demeclocycline (ADH antagonist)
Treatment of underlying disorder

74
Q

How to calculate amount of Na needed to raise serum Na in hyponatraemia

A

Na required (mmol/L) = (desired Na - measured Na) x TBW

75
Q

Features of hyperkalaemia
Causes

A

Arrhythmia, weakness, numbness, confusion
Renal failure, addisons, iatrogenic

76
Q

Features of hypokalaemia
Causes

A

Tachycardia, pvcs, weakness, hypotonia, muscle paralysis, alkalosis
Insulin, diet insufficiency, malbsorption, Cushing, hyperaldosteronism, diarrhoea, vomiting,

77
Q

Max rate of k administration
Why

A

0.5 mmol/kg/hr
To allow equilibrium between intra and extracellular compartments.

78
Q

Roughly what deficit of total body potassium is present with a 1 mmol decrease in plasma value?

A

100mmol

79
Q

Where is most calcium stored in the body?

A

Bone 99%

80
Q

Features and causes of hypocalcaemia

A

Tetany, convulsions, ectopic calcification if CNS
Hypoparathyroidism, thyridecomy, Vit D deficiency, renal failure, hyperventilation

81
Q

Features and causes of hyperkalaemia

A

Stones, moans and psychic groans (renal stone, personality change, weakness, atrophy, abdominal pain)
Hyperparathyroidism, malignancy, sarcoidosis, multiple myeloma, vit d toxicity,

82
Q

Where is most body magnesium

A

Bones and teeth >50%

83
Q

Body role of mg

A

Cofactor in many reactions (all kinases)

84
Q

Features and causes of hypomagnesaemia

A

Tetany, weakness, depression, irritability, convulsions
Diarrhoea, malabsorption hyperaldosteronism

85
Q

Features and causes of hypermagnaesemia

A

Prolonged AV and IV conduction
Iatrogenic, renal failure

86
Q

What is the anion gap
Normal value

A

Difference between measured cations and anions in plasma
12-18mmol/L

87
Q

Causes of metabolic acidosis with normal anion gap

A

Loss of bicarb replaced with chloride p

88
Q

Causes of metabolic acidosis with raised anion gap

A

Overproduction or injection of acid e.g. salicylates, dka

89
Q

How permiable is the lymphatic system. Why? Q

A

A series of blind ended tubules with endothelium similar to capillaries but no basement membrane or intracellular gaps. Pinocytosis makes it very permiable to proteins

90
Q

Function of lymph nodes

A

Encapsulated collections of phagocytic cells that engulf bacteria keeping distal lymph sterile normally.

91
Q

Where does lymph drain to? Through what?

A

Right lymphatic duct and thoracic duct drain into subclavian veins.

92
Q

24 hr volume of production of lymph

A

2-4 litres

93
Q

What promotes flow of lymph

A

Low resistance valves vessels
High resistance of returning interstitial space
Adjacent arteriolar pulsetations
Thoracic pressure driving forward flow

94
Q

Functions of lymph

A

Immunological
Drainage of fluid
Transport of nutrients

95
Q

How does lymph protein and electrolyte content compare to plasma, what does it contain

A

Lower than plasma
Contains coagulation factors, antibodies, lymphocytes
Electrolyte content similar

96
Q

How much csf exists at any one time

A

150ml

97
Q

How much csf is produced in 24 hrs

A

600ml

98
Q

Where is csf produced

A

Choroid plexuses and endothelium of cerebral capillaries (30%)

99
Q

Where are choroid plexuses located

A

3rd and lateral ventricles

100
Q

Route of flow of csf

A

Lateral ventricles
Third ventricle
Fourth ventricle
Foramen of luschka and magendie
Circulates around brain stem, brain and spinal cord
Re absorbed by subarachnoid villi in Venous sinus

101
Q

What is normal csf outflow pressure
What happens if it drops low to help

A

11.2 mmgh
Reabsorption stops

102
Q

Composition of csf

A

Ultrafiltrate
Low protein 0.3 g/L
Bicarb and na slightly low
K and glucose around half plasma
Ph 7.32
Osmolality 290
PCo2 slightly higher than plasma

103
Q

What is the function of the blood brain barrier

A

Provides tight control over CNS ions
Protects brain from transient changes in glucose
Protects brain from toxins
Prevents neurotransmitters entering systemic circulation

104
Q

Relationship between csf and brain interstitial fluid

A

They equilibriate but slowly

105
Q

Where are the chemoreceptors responsible for resp control located
What do they sense

A

Ventral surface of medulla and floor of fourth ventricle
H+

106
Q

What is the bbb permeability to co2 and h / HCO3
Implication for resp control

A

Permiable to co2 but much less so to others
Co2 diffuses into csf and brain interstitial fluid equilibriating with arterial pO2

107
Q

What is the implication of the low protein state of the csf on co2

A

Less buffering activity so pH changes for a given Co2 are greater

108
Q

Features of aqueous humour

A

Plasma dialysate with hourly turnover
Produced by ciliary body
Drains by canal of schlemm
Metabolic and respiratory substrate for anterior chamber

109
Q

Normal interocular pressure

A

15-18mmhg

110
Q

What is the composition of vitreous humour

A

Gelatin like protein vitrein

111
Q

How is pleural fluid created?
Why is there so little?

A

Ultrafiltration of plasma in capilaries on parietal and visceral pleura
These capillaries have low hydrostatic pressure and high colloid pressure so most is reabsorbed

112
Q

What might happen to UO on administration of NaCl to a hypovolaemic hyponatraemic
Why
Risk
Solution?

A

Sudden increase
Hypovolaemia resolved so brain ceases release of ADH and rebound UO
Sudden over correction due to concentration
Administration of 2mcg IV desmopressin (DDAVP)

113
Q

Which hyponatraemics is desmopressin to control UO contraindicated

A

Hypervolaemic (eg heart failure)
Uncontrolled free water intake (eg psychogenic polydipsia)

114
Q

How much should Na be corrected in hyponatraemia

A

Max 0.5mmol/hr 12mmol/day

115
Q

Equation for predicting change in serum Na concentration with administration of 1L of infusate
Name and formulae
Issue

A

Adrogue-Madias formulae

Change in Na = ([na in infusate] - [serum Na]) / TBW + 1

Can underestimate increase as doesn’t account for renal handling of Na

116
Q

What drugs aim to increase water excretion to manage hyponatraemia
Example
Function
Why not used

A

Vaptans (tolvaptan)
Antagonist at V2 vasopressin receptor
Not used as rapidly can overcorrect

Primary Physiology (15 decks)

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