Week 1 - C - Physiology 1 - Body fluid compartments

Question 1

What is the concentration of the osmotically active particles in a solution and what is its unit of measurement?

Answer 1

This is the osmolarity Unit of measurement is mosmol/l

Question 2

What two things need to be known when calculating the osmolarity?

Answer 2

The number of osmotically active particles present and The molar concentration of the solution

Question 3

Once knowing the number of osmotically particles present and the molar concentration of the solution, how is the osmolarity calculated? Define osmolarity to help calculate this

Answer 3

Osmolarity is the concentration of osmotically active particles present in a solution Osmolarity = Number of omsotically active particles multiplied by the concentration of the solution

Question 4

The concentration is 150mM NaCl (150mM = 150mmol/l) Calculate the osmolarity of the solution

Answer 4

Concentration of the solution = 150mM Number of osmotically active particles = 2 Osmolarity = 150x2 = 300mosmol/l

Question 5

The concentration of the solution is 100mM MgCl2 Calculate the osmolarity?

Answer 5

Osmolarity = concentration of the solution x number of osmotically active particles = 100 x 3 =300mosmol/L

Question 6

What is the difference between the measurement of osmolarity and osmolality?

Answer 6

Osmolarity is the concentration of osmotically active particles in a solition (mosmol/l) Osmolality - concentration of osmotically active particles per kg (mosmol/kg) (For weak salt solutions (incl. body fluids) these 2 terms are interchangeable )

Question 7

Ina normal person if there is an increased AHD secretion, what will this do to the osmolality of the blood?

Answer 7

This will decrease the osmolality

Question 8

How does a water deprivation test show diabetes insipidus?

Answer 8

Patient is deprived of water In a normal person this would stimulate ADH production causing decreased blood osmolality and increased urine osmolality (increased water absorption) In a patient with diabetes insipidus , the urine osmolality will not increase as the body is not responding to/ or is not producing the ADH

Question 9

The vasopressin test to differentiate between cranial and nephrogenic diabetes insipidus desmopressin (vasopressin analogue) is given How do the results differentiate between the two?

Answer 9

Cranial - urine osmolality will increase Nephrogenic - urine osmolality will remain low

Question 10

A urine osmolality of what exlcudes diabetes insipdus?

Answer 10

Urine osmolality of >600mosmol/kg excludes diabetes inipidus

Question 11

the effect a solution has on cell volume is known as what?

Answer 11

Its tonicity

Question 12

What are the three types of tonicity?

Answer 12

Have an isotonic, hypotonic and hypertonic solution

Question 13

What does a hypertonic solution cause to the cell size?

Answer 13

Hypertonic is high in solutes so this cause the osmotic gradient of water from inside the cell to outside resulting in shrinkage of the cell

Question 14

What does a hypotonic solution cause?

Answer 14

Hypotonic soluton has more water than the cell which causes inflow of water which can cause cell lysis

Question 15

What does an isotonic solution cause?

Answer 15

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Question 16

Although related to osmolarity, tonicity also takes into consideration the ability of a solute to cross the cell membrane. What is an example of a substance to which cell membranes are very permeable to?

Answer 16

Urea - is very permeable to the cell membrane

Question 17

What approximate percentage of the male and female body weight is water? What accounts for the difference?

Answer 17

Male is approx 60% Female is approx 50% Female physiologically has more adipose taking up more space

Question 18

Total body water consists of two components Intracellular fluid (ICF) and Extracellular fluid (ECF) What are the 2main components of ECF?

Answer 18

Interstitial fluid - ~80% Plasma ~ 20%

Question 19

As the toal body water is split between the ICF and ECF Which between the two accounts for the majority?

Answer 19

ICF accounts for 2/3rds of the total body water ECF accounts for 1/3rd of the total body water

Question 20

There are specific tracers that can measure the the body fluid compartments What are the tracers for: Total body water? ECF? Plasma?

Answer 20

Total body water tracer - Tritiated water ECF - Inulin Plasma - labelled albumin

Question 21

What two tracers are required so we can get body fluid compartment volumes to measure the itracellular fluid?

Answer 21

Required tritiated water for the total body water Require Inulin for extracellular fluid Then can do the TBW minus the ECF volume

Question 22

To calculate the volume of the body fluid compartment You need to add a known quantity of tracer to the unkown volume, then allow time for the tracer to mix A small sample volume from the fluid is then taken and the concentration of the tracer is measured Then the concentration is converted to conc.per litre and from this the volume is calculated as it equals mass over concentration What are the five steps of the dilution principle to measure volume of distribution?

Answer 22

1. Add a known dose of tracer (eg 42mg) to an uknown volume of fluid 2. Allow the tracer to mix/equilibriate in the fluid 3. Take a sample volume of the fluid and measure the concetration of the tracer within 4. Convert the concentration of the tracer eg , C = 0.005mg/5ml = 0.001mg/ml = 1mg/litre 5. The volume of the fluid can now be calculated as you know the tracer volume in a small sample V = 42litres

Question 23

What is the process of maintaining the balance in the body where (water) out must equal (water) in?

Answer 23

Homeostasis

Question 24

What are the three main inputs of water in the body?

Answer 24

Food, Fluid and metabolism

Question 25

For water output, there are insensible losses and sensible losses Which is the one over which we have no control?

Answer 25

Insensible loss of water is loss of water from which we have no physiological control

Question 26

What is the main way in which water is lost? How much is produced per day roughly?

Answer 26

Main way is urine About 1.5litres of urine per day (roughly 1ml per minute)

Question 27

If the water expenditure increases, is decreased excretion of water by the kidneys alone insufficient to maintain water balance?

Answer 27

No - water balance is maintained by water ingestion

Question 28

Why does the kidney have to produce urine?

Answer 28

This is because some watse products can only be excreted in a fluid and therefore urine has to be produced

Question 29

Ionic composition of major fluid compartments include, Na, K, Cl, and HCO3 What are the predominate ion compositions inside and outisde the cell? (ie ICF and ECF)

Answer 29

Predominant ionic composition - ECF is Sodium and and Chlorine Predominant - ICF is Potassium

Question 30

What separates the interstitial fluid from the intracellular fluid?

What separates the intersitial fluid from the plasma?

Answer 30

• Intestitial from intracellular is the Plasma membrane
• Interstitial from the extracellular is the Capillary wall
• Can see the interstitial fluid is the connecting factor

Question 31

REMEMBER ECF and ICF are separate compartments How does their osmolarity differ?

Answer 31

Despite being separate compartments this the osmotic concentrations of both ECF and ICF are identical (~300 mosmol/l)

Question 32

If the ECF osmotoic concentration increases – ECF is becoming hypertonic to ICF, what would happen?

Answer 32

Water would move from inside the cells (ICF) to outside the cells (ECF) ICF volume would be decreased and ECF volume would increase

Question 33

If the ECF was to lose salt, what would happen to the ECF and ICF volumes?

Answer 33

The ECF would decrease in osmolarity and therefore be hypotonic This would cause water to flow from ECF to ICF decreasing the ECF volume and increasing the ICF volume ECF NaCl gain: ECF ↑ ICF ↓ ECF NaCl loss: ECF ↓ ICF ↑

Question 34

If an individual takes in an isotonic solution, there is no fluid shift so same osmolarity however change in volume of ECF What regulates the ECF volume?

Answer 34

The kidneys regulate the ECF volume

Question 35

1) Total electrolyte concentrations can directly affect water balance (via changes in osmolarity) 2) The concentrations of individual electrolytes can affect cell function What are they involved in that can affect cell function?

Answer 35

They are involved in the production of action potentials within the cell to elicit contraction

Question 36

> 90% of the osmotic concentration of the ECF results from the presence of sodium salts The total amount of sodium in the ECF represents a balance between two factors (input and output). It is therefore vital to regulate Na+ concentration. What regulates sodium concentration from the kidney?

Answer 36

Aldosterone

Question 37

Minor fluctuations in plasma [K+] can have detrimental consequences K+ plays a key role in establishing membrane potential >95% of body K+ is intracellular: small leakages or ↑ cellular uptake may severely affect [K+]plasma leading to: What can hyperkalaemia cause to the muscles and the heart?

Answer 37

Can cause muscle weakness leading to paralysis Can cause cardiac arrythmias

Question 38

What is the daily guideline amount of sodium?

Answer 38

GDA = 6g