Homeostasis of Body Fluids (Rao) Flashcards
T or F: At steady state, body fluid volume and not necessarily its composition is stable.
F: both body fluid volume and its composition are stable
To maintain homeostasis of body fluid, fluid and salt intake must equal …
fluid and salt output
T or F: For everyone, there is a constant fluid output of 2.5 L/day.
F: fluid intake is highly variable. therefore output will also be highly variable (intake = output)
*2.5L/day is the avg fluid intake per day
Total body water but be maintained in order to maintain ______
a high metabolic rate
TBW is higher in (men or women). Why?
Men because women have higher fat content
T or F: TBW decreases with age
T: due to inc in fat
T or F: As total body fat increases, total body water decreases
T
Where is most of our body water distributed?
muscle (46%)
skeleton (16%)
fat (10%)
organs (6%)
What % of the tissue in out organs is water?
75% is water
What are the 3 ways that we take in fluid?
Drinking. Food we eat > oxidative metabolism
What is the avg amt of fluid taken in per day?
2.5 L
What are the 3 ways that we get rid of water?
Urine > insensible water > feces
What is the minimum amount of urine that a person must excrete in order to still get rid of the metabolic waste?
0.5 L/day
A burn victim will loose (more or less) fluid than a healthy individual.
more
T or F: we loose water during expiration.
T: water is used to moisten the air we breathe in order to avoid drying out our alveolar spaces
What does the kidney regulate? (that does not involve it secreting hormones)
water and inorganic ion balance
What 2 things does the kidney remove?
metabolic waste products(urea, creatinine, and uric acid)
foreign chemicals (pesticides and food additives)
What hormones does the kidney secrete?
EPO
1, 25 dihydroxy vitamin D3
Renin-Angiotensin II
What additional role does the kidney play during fasting?
gluconeogenesis (makes glc from aa to maintain blood glc levels)
What are the fluid compartments and how many L of water are there in each?
ICF: 25 L
ECF: 15 L
–> plasma: 3 L
–> ISF: 12 L
What % of body weight is the blood volume? How many L is blood volume?
8%
5L
What barrier separates plasma from ISF?
capillaries
What compartments does the cell membrane separate?
ECF and ICF
What % of body weight is total body water in a healthy 70 kg male?
60%
Describe the permeability of a cell membrane.
highly impermeable except for Cl-, urea, and lipophillic molecules
T or F: A capillary is very permeable
T
Describe the ion composition of plasma. (major and minor cation and anion)
Major cation: Na+
Major anion: Cl-
Minors: K+, HCO3-, Protein-
Describe the ion composition of ISF
Major cation: Na+
Major anion: Cl- and HCO3-
Minors: K+, (NO PROTEIN-)
Describe the ion concentration of ICF.
Major cation: K+
Major anion: phosphate, bicarbonate
Minors: Na+, HCO3-, Protein-, Cl-
Why is the composition of the ISF and plasma very similar?
bc they are separated by a capillary which is very permeable
Why are negatively charged proteins found in the plasma and not in the ISF?
bc capillary wall is impermeable to the negatively charged proteins
What is the Gibbs Donnan effect?
Na+ is 2% greater in plasma and Cl- is lower.
Because the capillary keeps negatively charged proteins out of the ISF, there is an inc in neg charge in the plasma. Therefore, Na+ is attracted to it and remains in the plasma while Cl- is repelled and remains in the ISF
Where is Mg2+ and PO4 high?
ICF
T or F: Ca2+ is high in the ICF
F: there is no Ca2+ in the ICF
Where is there a high protein conc?
ICF
What are the 5 criteria for a probe that will be used to measure body fluid?
- non-toxic at conc to be used
- neither synthesized or metabolized
- Disperses evenly in fluid
- disperses only in the compartment of interest
- does not influence the compartment volume
How would your measurement of body fluid be effected if the probe you used was metabolized?
you will underestimate the amount of fluid
How would your measurement of body fluid be effected if the probe you used was synthesized in the body?
you will overestimate the amt of fluid
What probes are used to measure plasma volume? How is this done?
131-I-albumin or Evans blue dye
*avidly binds to plasma proteins
IV injection of known amt
What is the formula calculating plasma volume (PV)?
PV= amt of probe injected/concentration
PV = Q / (Q/V)
What is the formula for calculating blood volume?
blood volume = PV / (1-Hct)
What probes are used to measure ECFV?
inulin, thiosulfate, Na+
What is the formula for calculating ECFV with a probe?
ECFV= amt of probe injected/concentration
ECFV= Q / (Q/V)
If ECF and PV is known, how can ISF be determined?
ISF = ECF = PV
If the probe used to measure fluid volume is lost in the urine, how can the correction be made in your calculations?
ECF = (Q -Qexcreted) / plasma conc
What probes are used to measure TBW?
2 H2O, 3 H2O, antipyrene
T or F: plasma osmolarity is a factor that determines the movement of fluid between the plasma and the ISF.
F: it is NOT because the capillary wall is freely permeable to H2O and solutes
What determines the movement of fluid between the plasma and the ISF?
starling forces: hydrostatic pressure and oncotic pressure
NOT osmolarity
What is the driving force for the movement of water between the ICF and ECF?
osmosis (osmotic pressure)
T or F: The conc of Na+ in the ECF and ICF alteres the movement of water between these 2 compartments
T: Na is impermeable to the barrier btwn these 2 compartments. A differing conc between the sides will induce osmotic pressure –> movement of water
What molecules are permeable to the barrier separating the ICF and ECF?
urea, water (glycerol is slowly permeable)
*these will not create osmotic pressure
What does a mole measure?
number of molecules
What does an osmole measure?
number of particles
How many osmoles are there in 1 mol NaCl in 1 L soln?
2
What does osmolarity measure?
the amount of solute in solution
1 osmolal glucose = 1 osmole glucose per ____
kg of water
1 osmolar glucose = 1 omole per ______
L of solution
For any given solution, the osmolarity is (greater than or less than) the osmolality
less than
*because the total solution weight (the divisor used for osmolality) excludes the weight of any solutes, whereas the total solution volume (used for osmolarity) includes solute content
Define osmotic pressure
the amt of pressure that must be applied to prevent the net diffusion of water through the membrane
*pressure created by change in solute conc in one of the compartments
T or F: One particle of albumin (70,000 daltons) creates greater osmotic pressure than one particle of glucose (180 daltons).
F: they have the same. osmotic pressure is dependent on the number of particles not their size
T or F: Body fluid in different compartments all have the same osmolarity.
T: (they have a different compostion) the osmolarity needs to be the same too keeo RBCs from shrinking and swelling as they travel thru the body
If you put an RBC in a hypotonic solution will the cell shrink or swell?
swell
If you put an RBC in a hypertonic solution will the cell shrink or swell?
shrink
What does it mean for compartments to be iso-osmotic?
they have the same total osmotic pressure or osmolality
If you place a RBC in an iso-osmotic soln, containing hypoosmotic NaCl but with added urea to make it up to isoosmotic, what will happen to the RBC volume?
It will swell
The urea is freely permeable to the membrane and will go into the RBC (ICF) to reach equilibrium. This will causes the ECF to be hypotonic –> water will leave and go into cell
If you place a RBC in hyperosmotic solution containing isoosmotic NaCl conc, but with added urea to make it hyperosmotic, what will happen to the RBC volume?
No change
The urea will enter the ICF and equilibrate with the ECF, bringing the soln back to an isoosmotic state
If you place a RBC in an iso-osmotic soln, containing hypoosmotic NaCl but with added glycerol to make it up to isoosmotic, what will happen to the RBC volume?
shrink then swell
Glycerol is slowly permeable, so initially the ECF is hyperosmotic causing water to leave the RBC (shrink). Eventually, the glycerol in the outside equlibrates inside, leaving a hypoosmotic ECF state. Water goes into the cell (swells)
What effect does dehydration have on the volume and osmolality of the ECF and ICF? Why?
ECF and ICF volume decreases
ECF and ICF osmolarity increases
Water is lost from ECF –> inc ECF osmolarity –> water drawn out of ICF
What is the formula to determine plasma osmolarity?
plasma osmolarity = 2(Na) + glc/18 + urea/2.8
Dehydration results in a (hypo or hyper) plasma osmolarity.
hyperosmolarity
What is the osmolarity gap?
Osmolar Gap = Measured Plasma osmolarity – Calculated Plasma osmolarity
An gap > 10 indicates that there is a an unaccounted for osmotic particle in the plasma (i.e. alcohol, methanol, etc)
The osmolar gap is increased in the presence of low molecular weight substances that are not included in the formula for calculating plasma osmolarity (ie. not Na, glc, or urea)
What method is used to measure the plasma osmolarity? Why is it used?
freezing point depression bc it will catch ethanol and methanol in the blood
Describe the effects on osmolarity and volume of the ECF and ICF when an infusion of saline (isotonic) is administered. and explain why this happens)
inc in ECF volume (everything else says the same because there is no fluid movement between ECF and ICF)
Describe the effects on osmolarity and volume of the ECF and ICF when a person drinks a large amount of water. (and explain why this happens)
ECF and ICF volume increases
ECF and ICF osmolarity decreases
EFC volume increases first –> decrease in ECF osmolarity –> water fluxes into ICF to equilibrate the osmolarities –> ICF osmolarity decreases and volume increases
Describe the effects on osmolarity and volume of the ECF and ICF when a person is infused with glucose solution. (and explain why this happens)
ECF and ICF volume increases
ECF and ICF osmolarity decreases
EFC volume increases first –> decrease in ECF osmolarity –> water fluxes into ICF to equilibrate the osmolarities –> ICF osmolarity decreases and volume increases
*glc is freely permeable thru the memb so it does not change to the osmolarity
Describe the effects on osmolarity and volume of the ECF and ICF when a person is takes in an excessive amount of salt. (and explain why this happens)
ECF increases in volume and osmolarity
ICF inc in osmolarity and decreases in volume
Na inc ECF osmolarity and draws in water from ICF -> ECF volume increases while ICF volume decreases and osmolarity increases in all compartments
*hypernatremia
Describe the effects on osmolarity and volume of the ECF and ICF when a person loses an excessive amount of salt. (and explain why this happens)
ECF decreases in volume and osmolarity
ICF increases in volume and decreases in osmolarity
loss of Na decreases ECF osmolarity which draws water into the ICF to equilibrate. Th ICF then decreases in osmolarity and increases in volume
Describe the effects on osmolarity and volume of the ECF and ICF when a person is infused with isotonic urea. (and explain why this happens)
ECF and ICF volume increases and osmolarity stays the same
initally there is an inc in ECF volume, but since the urea is freely permeable it will diffuse into the ICF which will bring water with it. Once the urea equilibrates, there will be an increase in volume in both ECF and ICF but the osmolarity will not change
