Fluid balance Flashcards
In an average young adult
A Intracellular water is 40% of body weight
B Interstitial fluid component is 10% of body weight
C The plasma volume is 20% of body weight
D The protein content is 30% of body weight
A
Explanation
In the average young adult male,
The intracellular component of the body water accounts for 40% of body weight and the extracellular component (ECC) for about 20%. Approximately 25% of the ECC is in the vascular system (plasma=5% of body weight) and 75% outside the blood vessels (interstitial fluid=15% of body weight). The total blood volume is about 8% of body weight.
18% of the body weight is protein and related substances, 7% is mineral and 15% is fat.
Which of the following is equal to the molar mass of a substance divided by its valence?
A Equivalents
B Osmolality
C Daltons
D Molecular wieght
A
Explanation
Equivalents: The concept of electrical equivalents is important as many of the important solutes in the body are in the form of charged particles. One equivalent (eq) is 1 mol of an ionized substance divided by its valence. One mole of NACL dissociates into 1 eq of Na and 1 eq of Cl. One equivalent of Na =23grams but 1equivaent of Ca is 40g/2=20grams. Electrical equivalence is not the same as chemical equivalence.
To diagnose the syndorme of inappropriate ADH secretion (SIADH), you need the following?
A Urine osmolality <100mOsm/L
B Plasma sodium >135mmol/L
C Plasma osmolality >280mOsm/L
D Urine sodium >20mmol
D
Explanation
Euvolaemic hyponatraemia <135mmol/L
Plasma osmolality <280mOsm/L
Urine osmolality >100mOsm/L
Urine sodium >20mmol
Urine osmolality>serum osmolality
Causes of SIADH include malignancy, CNS, lung infections and granulomatous disease, drugs-psychoactive drugs-MAOI, SSRI, TCI, NSAIDS, chlorpromazine and chemotherapeutic drugs
How many mmol of Na are in 50ml of 8.4% NaHCO3?
A 50mmol
B 84mmol
C 5mmol
D 8.4mmol
A
Explanation
8.4% NaHCO3 contains 1mmol/ml of Na.
How many grams of glucose are in 10ml of 50% glucose solution?
A 10g
B 25g
C 1g
D 5g
D
Explanation
50% implies a weight per volume measurement of 0.5, which is equal to mass of solute (g) divded by volume of solution (ml). Thus 0.5 x 10 = mass of solute = 5g.
What makes up 20% of body weight?
A Plasma
B Blood
C Extracellular fluid
D Intracellular fluid
C
Explanation
The intracellular component of the body water accounts for about 40% of body weight and the extracellular component for about 20%. Approximately 25% of the extracellular component is in the vascular system (plasma=5% of body weight) and 75% outside the blood vessels (interstitial fluid=15% of body weight). The total blood volume is about 8% of body weight. Flow between these components is tightly regulated.
A woman presents with left leg swelling following a recent long flight. What is the mechanism for the swelling?
A Increased hydrostatic pressure
B Lymphatic obstruction
C Increased osmotic pressure
D Increased capillary permeability
A
Explanation
Oedema is the accumulation of interstitial fluid in abnormal amounts – caused by increased filtration pressure, decreased osmotic pressure, increased capillary permeability, and inadequate lymph flow. Causes of increased filtration pressure (hydrostatic) include venular constriction, and increased venous pressure (heart failure, incompetent valves, venous obstruction, increased total ECF volume, gravity). Causes of decreased osmotic pressure gradient is from decreased plasma protein level, or accumulation of osmotically active substances in interstitial space. Causes of increased capillary permeability include substance P, histamine (and related substances) and kinins.
Since the swelling is unilateral – presumably the stem is describing a DVT, but regardless the answer should be increased hydrostatic pressure (either from venous obstruction, or gravity)
Name the major anion in intracellular fluid (ICF)
A Chloride
B Proteins
C Phosphate
D Potassium
C
Explanation
ICF:
major cation: K
major anion: Ph, then proteins
ECF:
major cation: Na
major anion: Cl
