Water

Question 1

How many litres of water is found in the extracellular compartment of the body

Answer 1

13 to 16 litres

Question 2

How many litres of plasma is in the body

Answer 2

3 to 3.5 litres

Question 3

Lean tissues and fatty tissues
Which has a higher fluid content

Answer 3

Lean tissues

Question 4

What are some things which affect variations of water levels in the body

Answer 4

Tissue type: lean tissues have higher fluid content than fat tissues.
•Gender: males have more lean tissue and therefore more body fluid.
•Age: lean tissue is lost with age and body fluid is lost with it

Question 5

How can you calculate an estimate of body water for your weight

Answer 5

0.6 * body weight in kilograms
Since roughly 2/3 of the body is made up of water

Question 6

What is the name of the formula used to calculate body water more accurately

Answer 6

Watsons formulas

Question 7

How are compartment volumes measured

Answer 7

Determining the volume of distribution of a tracer substance

Question 8

What is osmolality

Answer 8

Osmolality of a fluid is a measure of the total number of particles (ions, molecules) present in a one kilogram of solution
•is a measure of the number of osmotically active particles in a solution.
•Solutes are mainly Na, urea and glucose per kilogram of water.
•Its unit is usually osmol/kg or mmol/kg
•The physiological normal osmolality is 285 to 295 mmol /kg

Question 9

What device is used to measure osmolality

Answer 9

Osmometer

This measures colligative properties such as freezing point depression or osmotic pressure.

•It gives the total osmolality of the solution

•Its also measures the osmotic effects exerted by all the ions and molecules present in the solution

Question 10

What are the primary solutes that is measured in the lab for osmolality

Answer 10

The primary solutes that are measured in the clinical lab that contribute to the plasma osmolality are sodium, potassium, glucose and urea.

Question 11

What is the formula for calculating osmolality

Answer 11

Osmolality= (2x[Na]) + [K] + [Glucose] + [Urea]

Question 12

Why is Na the primary determinant for calculating osmolality

Answer 12

Under normal conditions the osmolar contributions of glucose and urea are less than 10 mOsm/kg thus Na is the primary determinant of osmolality

Question 13

What is an osmolal gap

Answer 13

An osmolal gap occurs when there is a difference between the true osmolality and the calculated osmolality.
If substances other than Sodium, Urea and glucose are present, then the measured osmolality is much larger than the calculated value.
A large positive (>10) osmolality gap can help identify the presence in plasma of other toxic osmotically active substances.
This may include alcohols, sugars, lipids and proteins (Hyperproteinaemia and hyperlipidaemia)