Bodily fluid compartments and challenges to homeostasis

Question 1

What is osmolarity?

Answer 1

Concentration of osmotically active particles in a solution

Question 2

What are the units of osmolarity?

Answer 2

(M)osmol/l

Question 3

Which two pieces of information are needed to calculate osmolarity?

Answer 3

Concentration of a solution

Number of osmotically active particles in a solution

Question 4

How is osmolarity calculated?

Answer 4

Multiplying to concentration of a solution by it’s number of osmotically active particles

Question 5

What is the difference between osmolality and osmolarity?

Answer 5

Units osmolality = osmol/kg and osmolarity = osmol/l (no difference when talking about weak salts)

Question 6

What is the rough osmolarity of most body fluids?

Answer 6

300 mosmol/l

Question 7

What is tonicity?

Answer 7

The effect a solution has on cell volume

Question 8

What are the three types of tonicity and how do they affect cell volume?

Answer 8

Hypotonic - increase cell volume
Isotonic - no effect
Hypertonic - decrease cell volume

Question 9

Is total body water high on average in men or woman? Why?

Answer 9

Men because they have less fat

Question 10

What two compartments can total body water be broken down into?

Answer 10

Intracellular volume

Extracellular volume

Question 11

What categories can extracellular fluid volume be broken down into?

Answer 11

Plasma
Interstitial (biggest proportion)
Transcellular
Lymph

Question 12

What separates the intracellular and extracellular fluid compartments?

Answer 12

Cell membrane

Question 13

How can the volume of body fluid compartments be measured?

Answer 13

Distribution volume of tracers

Question 14

Name three useful tracers and which compartment they measure

Answer 14

Tritiated water - total body water
Inulin - extracellular fluid volume
Labelled albumin - plasma

Question 15

How can intracellular fluid volume be measured?

Answer 15

If the volumes of the total body water and extracellular fluid are known intracellular fluid volume can be measured using the equation:
TBW = ECF + ICF

Question 16

How can the volume of water in a container be measured using the dilution principle?

Answer 16

Add a dose of tracer to the fluid volume in question (the body) and allow equilibrium to be reached. Sample the fluid and measure the tracer concentration (equilibrium volume). Use this equation:

Volume = dose of tracer (mol) / sample concentration (mol/l)

Question 17

In simple terms, what is homeostasis?

Answer 17

The maintenance of a variable within an acceptable range

Question 18

What are the inputs and outputs involved in water balance?

Answer 18

Input - fluids, food, metabolism

Output - faeces, sweat, skin, lungs, urine

Question 19

What is an insensible loss (in terms of water balance)? Give two examples

Answer 19

A loss of water which cannot be regulated by physiological means

Skin & lung water loss

Question 20

Water imbalance manifests as changes in fluid tonicity. T/F

Answer 20

False - changes in fluid osmolarity

Question 21

Can decreased excretion from the kidneys (i.e decreased urine output) maintain water balance alone?

Answer 21

No - physiological dysuria does not exist

Question 22

Describe the isotonic composition of the ICF and ECF repectively

Answer 22

ICF - high potassium, high magnesium and high negatively charged proteins
ECF - high sodium, high chlorine, high bicarbonate

Question 23

What allows the difference in environment between the ICF and ECF?

Answer 23

Proteins in the plasma membrane

Question 24

How do the osmotic concentrations differ between the ICF and ECF?

Answer 24

They don’t - both 300 mosmol/l

Question 25

Why is regulation of fluid balance and electrolyte concentration related?

Answer 25

Changes in solute concentrations cause changes in water distribution (osmotic gradient)

Question 26

Do kidneys regulate composition of ICF or ECF?

Answer 26

ECF

Question 27

What is fluid shift?

Answer 27

Movement of water between the ICF and ECF due to changes in the osmotic gradient

Question 28

What happens when the osmotic concentration of the ECF increases?

Answer 28

Concentration increase > hypertonicity > fluid loss from the ICF

Question 29

What happens when the osmotic concentration of the ECF decreases?

Answer 29

Concentration decreases > hypotonicity > fluid movement into the ICF

Question 30

List the three possible changes to fluid homeostasis

Answer 30

Gain/loss of water Gain/loss of NaCl (salt) Gain/loss of isotonic fluid

Question 31

What happens when there is a gain/loss of water?

Answer 31

Change in fluid osmolarity causes parallel changes in ICF and ECF volumes (both increase or decrease)

Question 32

What happens when there is a gain/loss of NaCl?

Answer 32

Change in fluid osmolarity causes opposite changes in fluid volumes in response to active transport of sodium into the ECF and osmotic gradient changes

Question 33

What happens when there is a gain of salt in the ECF?

Answer 33

ECF volume increases | ICF volume decreases

Question 34

What happens when there is a loss of salt in the ECF?

Answer 34

ECF volume decreases | ICF volume increases

Question 35

What happens when there is a gain/loss of isotonic fluid?

Answer 35

No change in fluid osmolarity but change in ECF volume

Question 36

Give an example of an isotonic fluid

Answer 36

0.9% saline

Question 37

Regulation of ICF volume is vital for long term blood pressure control. T/F

Answer 37

False - ECF volume

Question 38

Give two reasons why electrolyte balance is important?

Answer 38

Electrolyte concentrations affect water balance | Concentrations of individual electrolytes affect cell functioning

Question 39

What are the two most important electrolyte concentrations to maintain?

Answer 39

Sodium and potassium

Question 40

What is an electrolyte?

Answer 40

A substance which dissociates into free ions when put in solution

Question 41

What is sodium a major determinant of in terms of fluid balance?

Answer 41

ECF volume (water follows salt)

Question 42

Sodium is an accurate measure of the balance between input and output of water. T/F

Answer 42

True

Question 43

Minor fluctuations in plasma potassium can have serious affects. T/F

Answer 43

True

Question 44

Why must potassium concentration be so tightly regulated?

Answer 44

It is important for the membrane potential (K plasma)

Question 45

What are the two effects of deranged plasma potassium concentration?

Answer 45

Muscle weakness --> paralysis | Cardiac irregularities --> cardiac arrest

Question 46

What are the inputs and outputs of salt balance?

Answer 46

Input - diet | Output - sweat, faeces & urine

Question 47

How does salt imbalance manifest?

Answer 47

Changes in extracellular volume