Body Fluids & Osmolarity Flashcards
What is a 1M solution?
1 mole of a substance (MW in grams) per litre of solution
How much is a millimole compared to a mole?
10^-3 or 0.001 mole = 1 millimole
How much is a umol compared to a mole?
10^-6
How much is a nmol compared to a mole?
10^-9
How much is a pmol compared to a mole?
10^-12
How much is a fmol compared to a mole?
10^-15
What are pressures in medicine usually measured in?
mmHg
How many mmHg is 1kPa?
7.5
How many kPa is 1mmHg
0.133
How much of a typical person is water (%)?
60%
What are the three main fluid compartments?
Plasma
Intracellular
Interstitial
How much water is in the body of a typical person (L)?
42L
What is the water content of lean tissue?
0.71 L/kg (depends on fat)
What percentage of a typical person’s body weight is intracellular water?
40%
What percentage of a typical person’s body weight is interstitial water?
15%
What percentage of a typical person’s body weight is plasma water?
5%
What volume of water is found in intracellular space?
28L
What volume of water is found in interstitial space?
10.5L
What volume of water is found in plasma space?
3.5L
What fluid compartments make up the extracellular space?
Interstitial
Plasma
(Bone fluid)
What volume of water is found in extracellular space?
14L
What percentage of a typical person is blood volume?
8%
How do you calculate the amount of fluid in intracellular space?
Total body water - extracellular space
How do you calculate the amount of fluid in interstitial space?
Extracellular space - plasma space
What are the transcellular fluids?
Cerebrospinal fluid
Aqueous and vitreous humours of eye
Synovial fluid
Amniotic fluid
GI secretions
Lymph
How do you measure an unknown volume?
Dilution method
Add a known amount of substance (S) to an unknown volume (V)
Measure the concentration of a thoroughly mixed sample
V = S/C
What substances are used to measure plasma volume and why?
Evans Blue, labelled inulin, albumin
Large so it will not leave capillaries
What substances are used to measure extracellular space and why?
24Na, sucrose
Must not enter cells easily
What substance is used to measure total body water and why?
3H2O
Distributes with all water
What are the constituents of body fluid other than water?
Ions/electrolytes
Proteins
Dissolved gases, nutrients and metabolites
Cells
What are the major ions in body fluids?
Na+
K+
Cl-
What is the difference between osmolarity and osmolality?
Osmolarity = mOsm/L
Osmolality = mOsm/kg
What is osmolarity determined by?
Total number of freely diffusible entities in solution
What is an osmole?
A mole of a substance in solution
What is Avogadro’s number?
6.022 x 10^23
How many mOsm/L will 140mmol/L of NaCl produce?
280mOsm/L
How many mOsm/L will 10mmol/L of CaCl2 produce?
30mOsm/L
What is tonicity?
Osmolarity when fluids are separated by a semi-permeable membrane
How much pressure does 1 osmole exert in 1 litre of solution?
> 17,000 mmHg
What controls plasma volume?
Osmolarity of plasma
What is the osmolarity of physiological fluids?
~300mOsm/L (>5000 mmHg)
What controls cell volume?
Osmolarity of intracellular fluid
What is an isotonic saline solution?
0.9% w/v NaCl
Same tonicity as plasma
What creates crystalloid osmotic pressure?
Small diffusible ions
Explain how crystalloid osmotic pressure differences are created
Membrane is largely impermeable to ions
Intra and extracellular osmolarity must be equal
Freely diffusible water moves across membrane to reach equilibrium
Why is there no crystalloid osmotic pressure difference across capillary walls?
Ions can easily cross capillary walls
What creates oncotic osmotic pressure?
Proteins
What is another term for oncotic osmotic pressure?
Colloid osmotic pressure
How are oncotic osmotic pressure differences created?
Proteins too large to leave cells or cross capillary wall
So very little protein in interstitial space
Protein increases osmolarity so water moves into these compartments
How much oncotic osmotic pressure is exerted by proteins in capillaries?
25 mmHg
What usually balances oncotic osmotic pressure?
Hydrostatic pressure
What are the plasma and intracellular concentrations of sodium ions?
Plasma = 140mmol/L
Intracellular = 10mmol/L
What are the plasma and intracellular concentrations of potassium ions?
Plasma = 4mmol/L
Intracellular = (120-)140mmol/L
What are the plasma and intracellular concentrations of calcium ions?
Plasma = 2mmol/L
Intracellular = 100nmol/L
What is the plasma concentration of chloride ions?
110mmol/L
What is the plasma concentration of bicarbonate ions?
24mmol/L
What is the concentration of plasma proteins in the blood?
70g/L
What is the concentration of albumin in the blood?
48g/L
What is the concentration of alpha/beta/gamma globulins in the blood?
0.7-13g/L each
What is the concentration of fibrinogen in the blood?
3g/L
What is the function of albumin?
Capillary fluid transport
Buffering
What is the function of globulins?
Haemostasis
Immune system
Transport
What is the function of fibrinogen?
Haemostasis
What is the haemocrit/PCV in males and females?
Males = 0.47
Females = 0.42
What does PCV stand for?
Packed cell volume
What is haemocrit?
Red blood cell volume
What is the lifespan of a red blood cell in the blood?
120 days
What does haemoglobin do?
Carries oxygen
Buffers blood pH
What is the typical red blood cell count in males and females?
Males = 5.5 x 10^12 /L
Females = 4.8 x10^12 /L
What is the average value of the mean cell volume (rbc)?
85fl (femtolitres)
What does a higher mean cell volume tell you?
Larger red blood cells
Decreased plasma osmolarity
How many leukocytes are in the blood?
4-11 x 10^9 /L
What important substances do basophils release?
Histamine
Heparin
How many thrombocytes are in the blood?
150-400 x 10^9 /L
What percentage of most tissues is water?
70-80%
What percentage of plasma is water?
93% with 7% plasma solids
What percentage of fat is water?
10-15%
What percentage of bone is water?
20%
What condition is caused by plasma proteins reaching the tissue via damaged capillaries?
Oedema